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Greetings oh wise ones  😉

 

I have a 1992 and a 1995 Pathfinder, in California

 

The 92 had some issues so I did some basic engine work.  Most likely I messed something up...  but

 

I have the 1995 Nissan Workshop Manual - FSM.  I could not find the 1992 version.

 

The vehicle will not get out of closed loop - as indicated by no flashing of the green ECM light.  The 95 does fine.

 

Following the checking procedure for the O2 sensor connections between the O2 sensor harness and the ECM it has me check continuity between the sensor harness and pins 106 and 19 on the ECM harness. Neither has continuity. To me it would be reasonable if maybe one didn't have continuity, but both seems unlikely without any evidence of tampered or burnt wiring.
So before I rewire for continuity I would like to check that for the 1992 Pathfinder the same pins as the 1995 (106 and 19) are involved.

 

I did check that the ECM's are different V numbers so there's no point in me checking wire colors and pins for correspondence.


Does anyone know where I can get a pin out diagram for the 1992 Pathfinder or a wiring diagram showing O2 sensor to ECM connections?

 

Thanks!

 

John

 

 

 

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I don't have a '92 manual, but I've got a '90. The oxygen sensor circuit shown is different than the one in the '95 manual. The '95 grounds the oxygen sensor through a black/yellow wire to pin 106 of the ECM. The '90 grounds the oxygen sensor to the engine via a black wire (ground point 35M, via joint connector A). The black/white wire should still have +12v with the ignition switch on, and the white wire should still go to pin 19 of the ECM.

 

I checked the oxygen sensor plug in my '93 and found white/black, white, and black, same as '90. Assuming the wire color changed when the wiring did, this suggests that mine and yours are both wired like the '90, not the '95.

 

The test procedure says to check for power between the black/white wire and ground (ignition switch on), check continuity between the white wire and pin 19, and check continuity between the black wire and ground.

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Hi Startibartfast,

 

Thanks.  I'll need to figure out how the pin numbers are calculated, and I'll count them in the morning.  Thanks for confirming that the O2 black wire goes to ground.  That checks out with my 92.  And yes with ignition switch on, per the 95 manual, I have battery voltage on the black/white wire (again I'll check its color in the morning - today I was going by O2 harness (a) (b) (c)).  Definitely pin 19 is not in the same place on the connector on my 92 as it is on the 95, but if I figure out the numbering I'll see what pin it does have continuity with (I did check and it does indeed have continuity with one pin on the connector, just not the one shown as 19 in the 95 manual)

 

Much appreciate your most helpful response.  Definitely confirms at least I don't have to rewire the black to pin 106.

 

Best regards

 

john

 

 

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I pulled up the ECM pinouts for '90 and '95 and looked at them side by side, and the location of pin 19 is the same between them. Everything is the same with the exception of pin 106 being present in the '95 and crossed out in the '90.

 

Weird that it's lighting up a different pin. The wiring diagram shows a straight shot with no other connections, so if the oxygen sensor and computer are unplugged and you have no continuity between pin 19 at the ECM connector and B at the oxygen sensor connector, but continuity from B to somewhere else, there's something wrong with your harness. Which pin is lighting up? The diagram shows the wire in question having a grounded shield, which is wired to pin 48 of the ECM (and to joint connector A, which ties it to an engine ground). If the wire is crushed somewhere, I wouldn't be surprised if it shorted to its shield. The ECM has multiple ground pins, so you'll find multiple pins with continuity to pin 19 if this is the case.

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Hi Slartibartfast,

 

Again, thank you so much.  This is precisely why I joined this forum - to connect with someone with vastly more experience than me at dealing with these things.

 

I found a Nissan pin out numbering diagram so now I can at least identify the correct pin numbers on the ECM and the connector.

 

My mistake.  Exactly as you describe - B has continuity to 19 at the ECM connector as it should. B wire is white. (This continuity  - pin 19 lighting up - was exclusive, so no crushed wire to ground shield)

 

Also, exactly as you describe, the black wire from A grounds the O2 connector.

 

And C is black/white and has 12V with ignition on.

 

So, my wiring all checks out.  You saved me by identifying the A black to ground on '92 vs A black/yellow to 106 on '95.  This difference led me down the garden path!! (My '92 ECM connector has a black/yellow at pin 34 I mistook for 106 so that helped too.)  106 on my '92 connector is empty - just as your '90 manual shows it crossed out in the '90.  So both your '93 and my '92 as you say are more like the '90 manual than the '95 manual in this regard.

 

Next step per FSM is to replace the O2 sensor.  Funny, this was my initial inclination - to throw parts at the problem.  Now I understand it a little better, even though the next step is the same.

 

I really, really appreciate your help.

 

Have a great day

 

john

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New O2 sensor installed.

 

Vehicle starts right up and runs find.

 

However, still the same issue.  After warming up there is no flashing green light indicating closed loop operation on the ECM at any RPM.  But the light does flash when I "blip" the throttle, from 1500 to 3500 and release it.  But only flashes while the RPM is transitioning.  Any ideas?  I'm not sure how the TPS functions or whether this might be the issue.  Fortunately I have the fully operational '95 so I can try various parts from that.  And ideas and help welcome!

 

Thanks

 

john

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I'm no stranger to making wiring harder than it needs to be. I unwrapped a section of my harness once chasing what I thought was a weird high-resistance short to ground on one of my high beam wires that turned out to be the indicator bulb in the cluster. :doh:

 

Just checked mine, warm, and it flashes if held steady at 2k rpm. Is yours throwing any codes? Could be an issue unrelated to the oxygen sensor preventing the ECU from going into closed loop, though I don't think the TPS is essential for that.

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Thanks for sharing that.  Its called experience!!

 

No codes.

 

I'll search for essential items for closed loop operation.  I understand the coolant temp sensor is one.  I've got a new one in hand but maybe I'll get my hands on a 2k ohm resistance which is what the manual calls for as a check, since apparently the CTS resistance drops the that value once its warm.

 

From what I recall, open loop mode is for:

initial start up, cold ops

idle

hard acceleration

 

Sensors involved in conveying that info to the ECM include:

CTS

TPS

MAF

Accelerator position sensor

 

Anything else?

 

Of course after all this it will likely be a leaking vacuum line.  So of course I'll change out any that don't look 100%

 

I guess the ECM could be bad also?

 

Best regards

 

John

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EF&EC 17 and 18 of the '95 manual covers open and closed loop, but yeah, you've pretty much got it. Checking sensors, connectors and vac lines is a good place to start. Clean the MAF if you haven't (you can get special MAF cleaner, but I used alcohol and a rag very carefully and got away with it--just don't damage the filaments or use a cleaner that leaves a residue). Might as well just replace the vac lines if they're original. It probably won't solve the problem, but it's cheap and easy to do and lets you rule them out.

 

ECM failures in these aren't common, apart from people drowning them because they didn't think the puddle was that deep.

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Good morning

Yeah, I've pretty much done all that.  Vac lines all replaced,  CTS,  MAF, TPS wiring and sensors checked.  The MAF filament was good, and clean.  I have an ECM with the same part number coming from a junkyard, although my best guess is its not the problem.  My ECM does detect and indicate codes - when I ran the engine with the CTS disconnected it immediately lit up.  Plus on deceleration from 3000-3500 to idle I do get a green light briefly and quite consistently.  This problem has me puzzled..  Thanks again for your comments - its helpful to know I'm not missing something obvious.

 

My understanding is that the TPS switch does not use the connection on the sensor which would sense full throttle operation, only the one which senses idle ("soft idle")

 

Have a great day

 

john

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Hello again,

Well, that's a bust.  Replacement ECM indicates and works precisely like the original.

 

Do you know if Nissan service centers have any special diagnostic equipment they can plug into the ECM harness or anywhere else?  I'm reluctant to spend big $$ per hour to have a dealer's guy just to repeat all I've done, but I've run out of things to try.

 

Have a great day

 

john

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Not with the old OBD 1 units. Most of the dealerships have a hard time with anything built before 2000. 

 

Just wondering, have you tried running the emissions on your 92 to see if it is really not going into closed loop? Perhaps the 92 California ECM has to be in a different mode to indicate closed loop operation? Just tossing ideas out there. I don't know with that one, mine is a 93 federal with a 3.3 transplant, so a little different. Haven't bothered looking at the indicator LEDs in years. Still passing the emissions tests too (Davis and Weber counties here in Utah). 

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I would be surprised if they still had the equipment kicking around, much less a tech trained to use it. I've been told there's an adapter for the Snap-On Modis reader that will work with these, but of course it's ludicrously expensive. The smog test is an interesting idea. They probably won't know what to do with the computer either, but their smog sniffer on a stick could give you some idea of the mixture. I'm not sure what that would tell you at this point, though.

 

There are some California vs federal differences in ECUs, but AFAIK mode 1 is the same across the board. Are you sure it's in mode 1? Long shot, but if it somehow ended up in mode 5, the green light will flash in twos if the MAF is acting up or in fours if the ignition signal is malfunctioning (EF&EC-43 of the '95 manual).

 

I'm puzzled, too. Other than the light not flashing, does the truck show any obvious symptoms? Hard starts, black smoke, rough idle, anything like that?

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Hi Mr Reverse,

 

Thanks. This was my feeling exactly - that dealers would not have useful diagnostic equipment for old vehicles.  We might both be right, but a very helpful sounding guy at my local Nissan dealer - Mossy Nissan - said he has an amazing $25k computer that can be hooked up to an ODB1 vehicle and give a roadmap for finding problems.  I'll meet with him on Wed, detail all I've done so far and ask if he's willing to do whatever scan they can do, as long as its more than just reading ECM codes, and give me a print out.  If not, I'll keeping beating my head against the wall.  If he does I'll let you know and find out what equipment they used.

 

My best guess is the problem is something I've messed up in working on the Pathfinder, but I still need to find the problem!  The guy at the scrapyard who sold me the replacement ECM suggested I double check all grounds.  So I'll do that.

 

The first thing I did was run an emissions test.  It failed as a gross polluter - meaning ALL readings are above max!  The history is that the truck had passed emissions tests for years, then it just sat in my driveway aside from occasional starts.  Then last year it failed emissions.  I did the simple things - change plugs, plug wires, air filter.  Then I checked the resistance of the injectors and found 4 out of six bad.  So I replaced all 6 injectors with new.  I felt like a hero when it started right up.  Headed to the smog place and it failed as noted above.  So I started to look for codes.  No codes.  Then I checked to see if the truck was going into closed loop.  No.  So I started trying to learn all the reasons it might not and either checked relevant components and their wiring/continuity to ground/ECM connector or replaced them.  This is where I am today.

 

Glad you're still passing emissions, happy for you its just Federal.  From all I have learned, and from comparing my 95 Pathfinder which is fine, and passes, closed loop is required for normal ops, is indicated by flashing green ECM lights, and the ECM defaults to Mode 1 on switch off.  This is pretty much confirmed by the replacement ECM, and by disconnecting the battery about 20 times so far  😉

 

All ideas appreciated.  Thanks.  Please also see my reply to Slartibartfast below. 

 

 

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Hi Slartibartfast,

 

Thanks again.

 

Please see my reply above to Mr Reverse also.

 

Yeah, my smog guy doesn't even look at the ECM on these older vehicles.  I think all he cares about is that the CEL (check engine light) is not on.  And it hasn't been on other than once when I drove back from the smog guy!  Not since after maybe 20 starts, and battery disconnects.

 

No two or four flashes, and since the replacement ECM indicates precisely the same as the original, I'd guess that rules out being stuck in other than Mode 1, the default mode.

 

No other symptoms at all!  No black smoke, easy to start, smooth idle.

 

I'm going to again go over all the O2 sensor (which was replaced with new) and CTS (which I verified has a resistance drop very close to that of a new one when exposed to normal engine operating temps) component and wiring checks - since this is what is called for in the WSM if the green - closed loop - light does not flash correctly.

 

Thanks again

 

john

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.

.My Snap-On Verus Pro is old, I bought it about 10 years ago, but I do have the many OBD1 adapters for domestic, 1asian, and euros. I have both of the Nissan adapters and when I was at the dealership, I tended to use my scanner more than the consult that they had. It was old and temperamental. From what I understand, the yellow brick finally kicked off shortly after I left. 

 

With the emissions programs here, 68 to 95 get a sniffer test, and visual inspection. MIL is ignored. Technically, my Pathfinder is in violation since it has an engine that was not a factory option and by the letter of the law, should have received an inspection and paperwork allowing the swap. In reality, the emissions it puts out are below the limits and the fact that all the emissions control hardware and systems are there and operational, they don't care. 

 

Trying to recall the various modes in the ECU(I quit thinking about them years ago because of my scanner) and isn't mode 2 for O2 monitor? Just what were the readings for your truck? Here we measure HC, CO, and CO2. My numbers have been going up on the HC and CO over the last few years, I believe the 17 year old aftermarket catalyst is showing its age. The original one died when 50° water filled the exhaust and hit the 800°+ catalyst ceramic. I learned that day not to shut off the engine when in 3' of water and the exhaust is submerged. 

Wasn't a big deal for a couple years because it still passed on the readings. Then the government in all their scientific wisdom decided that our fuel had to be diluted with ethanol. My mom who was a chemical engineer said it made no sense in scientific terms, but made plenty when you follow the money on that policy. A couple years later, those of us in the profession of working on autos noticed we went from a couple of bad cats per year to a few per month. Made sense when we got looking into it deeper. The ECU's were mapped for gasoline and are not properly programmed for E10, let alone E15 or higher. The O2 sensors are reading higher O2 levels, so they are running richer. That is leading to the cats working harder to convert the HC and CO to CO2 and water. It also tended to run them hotter, both leads to shorter life spans. If you have an IR thermometer you can check the condition of the cat easily enough. Run the engine up to operating temp, hold 2000-2500 rpm for a couple of minutes then measure the temperature of the inlet of the cat and the outlet of the cat. The outlet should be at a minimum of 100°f higher than the inlet. If it is the same or the inlet is hotter, then the cat is dead and needs replacing. If the outlet is hotter but not a minimum of 100°f higher, the cat is failing. If it is 2-300 hotter, cat is working well and the engine is a bit rich. 

 

Finally, double check the O2 sensor. I found with my 93, Nissan made a running change on the O2 sensor types in 93 and they are not interchangeable. It is possible to get the wrong one and the ECU can't use it. 

 

Good luck on your project.

 

 

 

 

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Posted (edited)

^Good point on the different O2 sensors. I don't remember if the bung size is the same but IIRC the wrench size isn't (the oxygen sensor socket I got for my '95 doesn't fit my '93).

 

Hopefully the scanner helps narrow things down. I'd be interested in whether the temp sensor and the oxygen sensor readings match reality. Sometimes when an oxygen sensor fails, it reads lean all the time, causing the engine to run pig rich as the computer tries to fix a lean condition that doesn't exist, but I'd expect it to run like poo whenever it tried to go into closed loop if that was the case. There is a code the computer can throw if it thinks there's an injector leak, but the '90 manual says only California-spec models check for that, so yours might not notice or report if that's the case. New injectors suggest it's not that. If you haven't, check that the vac line from the fuel pressure regulator to the intake doesn't have fuel in it. And +1 on cleaning and checking ground points! I've had weak grounds show up as good with a meter but fail to power a load.

 

Mode 1 is the oxygen sensor monitor (green light flashes as the oxygen sensor cycles in closed loop). Mode 2 does the same thing, but the red light flashes with the green one if the mixture is between 5% rich and 5% lean, and stays on or off if the mixture is outside of that range. (Worth noting, modes 1 and 2 only tell you anything when the ECU is in closed loop--either light staying on or off when the green light is not flashing does not indicate a rich or lean condition.) Mode 3 spits up trouble codes. Mode 4 lets you test the speed sensor, starter switch, and soft closed throttle position switch. Mode 5 watches the MAF, ignition signal, and camshaft position sensor (for tracking down intermittent issues).

 

Edit: one other idea. Old gas can get pretty nasty. Have you filled it up with fresh fuel since you un-mothballed it? It's a long shot (especially if it wasn't parked for that long,) but my dad's old Ford ran (and smelled) a whole lot better on fresh gas than it did on the seven-year-old varnished garbage it had in it when we dragged it out of a field.

Edited by Slartibartfast

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Posted (edited)

Hi Guys,

 

Thanks again.  Brainstorming this last night after rechecking O2 sensor and its connections and continuity of these, I'm curious whether I'm looking at this "not getting into closed loop" backwards.  Could the mixture be too rich, from some as yet undiscovered cause, to permit closed loop operation?  From what I understand closed loop operates in a pretty narrow range, going back and forth from being too rich to too lean but not by huge amounts.  What if the mixture is far too rich, the O2 sensor tries to make it leaner, but gets to its limit of control so never crosses into the too lean area so never cycles, so there are never flashing green lights?  Could the mixture be that far too rich without throwing any codes?  Please correct me if my thinking is off base.  The manual does call for checking various components if the Mode 1 blinking light test continues to be NG.  Today I'll recheck for any codes, and do a road test also.

 

9 hours ago, Slartibartfast said:

Edit: one other idea. Old gas can get pretty nasty. Have you filled it up with fresh fuel since you un-mothballed it? It's a long shot (especially if it wasn't parked for that long,) but my dad's old Ford ran (and smelled) a whole lot better on fresh gas than it did on the seven-year-old varnished garbage it had in it when we dragged it out of a field.

 

I'll try anything, so long shots are welcome.  Some of the gas has been in the truck a while - maybe 2 years - but I've topped off with fresh whenever possible.  I'll work on this too.

 

As a side note, I theorized that the throttle position switch was stuck at "wide open throttle", which supposedly causes open loop operation.  The 94 and 95 manuals both show tests for this but the wiring diagrams show this TPS wire as "not used".  The 92 TPS connector has no female connection in the plug wire going to this sensor so getting stuck in "TPS switch wide open throttle" isn't possible.  My 95 however, contrary to both manuals, does have a connection (and tests fine according to the manual tests - throttle released, no continuity; throttle fully depressed, continuity).

9 hours ago, Slartibartfast said:

If you haven't, check that the vac line from the fuel pressure regulator to the intake doesn't have fuel in it.

 

Yes, I checked that line yesterday.  No fuel in it.

 

9 hours ago, Slartibartfast said:

Hopefully the scanner helps narrow things down. I'd be interested in whether the temp sensor and the oxygen sensor readings match reality. Sometimes when an oxygen sensor fails, it reads lean all the time, causing the engine to run pig rich as the computer tries to fix a lean condition that doesn't exist, but I'd expect it to run like poo whenever it tried to go into closed loop if that was the case. There is a code the computer can throw if it thinks there's an injector leak, but the '90 manual says only California-spec models check for that, so yours might not notice or report if that's the case.

 

So the scanner will be able to see these reading?  That's hopeful and a good reason to try to get Mossy Nissan to give me a read out.  I wasn't hopeful they would, but now I'll try harder  😉

 

Yes, mine is a CA spec truck.  And of course since I changed the injectors (a real bear of a job for a non-mechanic!) that was the first thing I suspected.  And it still might be the case.  But no codes so far.

 

9 hours ago, Slartibartfast said:

Good point on the different O2 sensors. I don't remember if the bung size is the same but IIRC the wrench size isn't (the oxygen sensor socket I got for my '95 doesn't fit my '93).

 

The new O2 sensor looked identical to the old one, same appearance, same size of everything visible.  I now suspect the old one wasn't bad.

 

10 hours ago, Mr_Reverse said:

If you have an IR thermometer you can check the condition of the cat easily enough. Run the engine up to operating temp, hold 2000-2500 rpm for a couple of minutes then measure the temperature of the inlet of the cat and the outlet of the cat. The outlet should be at a minimum of 100°f higher than the inlet. If it is the same or the inlet is hotter, then the cat is dead and needs replacing. If the outlet is hotter but not a minimum of 100°f higher, the cat is failing. If it is 2-300 hotter, cat is working well and the engine is a bit rich. 

 

Thanks for this.  My cat may well be bad and even after I fix the open/closed loop issue I might still fail emissions because of the cat, but that's a step down the road.  Getting to closed loop ops is my first priority, even if that doesn't make the truck pass emissions  😉

 

10 hours ago, Mr_Reverse said:

Just what were the readings for your truck?

 Attached is the smog readout - I'd give you the whole thing but I'm limited in file upload size permitted  😉

 

Snap On Verus Pro looks like a great tool.  A little pricey on eBay right now - more than this Pathfinder is worth.  Fortunately for my sanity I don't count the hours I put in at any hourly rate!!

 

Again, thank you both so much.  I'm in awe of your knowledge and experience and your willingness to assist.  Long, long ago when my junk old vehicles had either a broken steering link (bought from an auction) or I took the engine apart to change the timing belt and got in waaay over my head, I just got rid of them.  This one I'll sort out.  But I'm not taking the intake manifold off again unless I know for sure something - like an injector or the fuel pressure regulator - is bad!

 

Have a great day

 

john

 

Smog basics1.pdf

Edited by paathfinderr
The 92 TPS connector has NO female connection in..

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Greetings friends,

 

After working on some grounds and checking all the diagnostics modes and still showing no closed loop operation, and no codes, I took the truck for a test drive.  Sure enough I got green closed loop flashing (sometimes) and a check engine light.  The stored code was the one I did not want to see - 45 - leaking injector. Ha!  So its back to the 137 step process I did to change the injectors!  I'll take a break from this project for a few weeks, and do something else easier - like fix old lawnmowers for my property.  I had a nasty suspicion that all the injectors did not seat as firmly as the others, so...

 

Thanks again for all your support and help.  I'm not done yet and I'll post the next steps as I encounter them.

 

Have a great day

 

John

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Ok, I lied.  I'm still working on it.

 

I retightened the ground near the ECM, and after reading about MAFS shield grounds I jumpered an additional ground to the MAFS connector (its a Mickey Mouse arrangement but I wanted to see if it made a difference).

 

Did a couple of road tests including a bunch of hills and some 65-70mph freeway.  I get normal closed loop operation in normal driving not in idle!  This is a big plus.  I do not however get closed loop (flashing lights) at any RPM when I'm stopped.  The 45 leaking injectors came up once on one drive, and the CEL flashes on occasion.  I cleared the 45  again and it did not recur.  On shutdown I checked codes and the only one is 55.

 

I think I'll still go see Mossy Nissan and see if they'll do a scan because that might help me narrow things down.  But I don't at this point think its critical.  My truck might even pass smog now because they run it on the treadmill, so its not stopped.

 

Obviously its not perfect yet.  What are your thoughts about the extra ground Nissan MAFS connector?  If I can find one its not big bucks.  Otherwise I'll solder a new ground onto the MAFS connector ground wire.  I'd like to solder it onto the female connector but I don't know how to remove the female connector from the connector assembly.

 

Thanks again guys.  Without your help I'd be lost!

 

Have a great day

 

John

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Sounds like you nailed it with your theory that a mixture issue was preventing it from cycling in closed loop. Makes sense that a small leak (or whatever's causing the rich condition) would cause more trouble when free-revving (no load) than when you're actually driving around (when there's enough air/fuel going through the engine to dilute the effect of the unwanted extra fuel).

 

Nissan put out a service bulletin (NTB95-021, pretty sure I found it in the '93 Pathfinder section on Nicoclub--I'd link it but I can't get their site to load right now) saying that the ECM throws an injector leak code any time there's a rich condition that it can't do anything about. They suggest checking the MAF, checking the fuel pressure (34 engine running, 43 engine off), watching the fuel pressure with the key off to see how quickly pressure drops (should take around four hours to hit zero if all is well, or ten minutes if it's leaking), then check the temp and oxygen sensors if everything else checks out. (Sounds like you've run through most of this already!) Once you've got it figured out, change the oil. The bulletin also suggests tightening up the pins in the MAF harness, which was enough to resolve an intermittent stalling issue with mine (though I did the MAF, TPS, and one of the idle plugs at the same time, because they all felt loose... and I didn't do it quite as professionally as what the bulletin shows, because I did it on the side of the road with a pocketknife). The additional ground shouldn't be necessary, but shouldn't hurt anything, either.

 

The bulletin doesn't specifically mention the WD21, though this is probably because it has you verify the repair using CONSULT, Nissan's super-special OBD1 checker box that these aren't set up for. It does list fuel pressures for the D21, though, so I assume the rest of it still applies.

It's been a while since I had my intake off but IIRC the only thing you'd get from the injectors not seating right would be a vacuum leak (at the manifold) or an external fuel leak (at the rail). An injector leak would come from the injector itself. If it fails the leakdown test, I'd pull the spark plugs and check them to see if one of them is darker or wetter than the rest, or smells like gas, to track down which injector is incontinent.

 

IIRC the plug for the TPS open/closed switch in mine has a third pin in it, too, though I don't know that it goes to anything. Strangely enough, there's a wide open throttle switch on the gas pedal, inside the cab, which tells the auto trans to kick down. I'm not sure why Nissan added another switch for that rather than tying into the existing one. Easier to adjust, maybe? In any case, mine drops out of closed loop long before it reaches wide open throttle. IIRC the turbo cars used the wide open switch for something, but don't quote me on that.

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Awesome, thanks.  I found and downloaded NTB95-021.  Too bad Consult can't be used on this truck.  Looks like its pretty amazing.  If my Mossy Nissan guy has something similar it doesn't look like just a simple one time scan will tell all.  Consult seems pretty specific to issues suspected.  But I'll see.  It will help to establish a rapport with them if possible, or even to learn that they won't help me  😉

 

Great analysis on the extra air when driving.  Implies that I'd still fail the smog test.  No worries, you saved me the $30 they would charge me for a failed recheck.  Gotta sort it our first.  I'll check the air intake plumbing, filter box, etc.  When I first started on this some rodents had found a good home there.  Maybe I left something further upstream when I cleaned out the filter box and replaced the filter.

 

I tightened most of the connectors to the pins on any of the many connectors I opened so far  😉 

021 also shows how to take the female connector out of the connector.

 

Thanks again my friend

 

john

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No worries man, good luck with it! Hopefully the dealership guy can at least get into live data or something.

 

Funny story, mine had a rat's nest in the air filter box when I got it. PO had no idea why it was down on power, and apparently his mechanic hadn't checked the computer, because it was coding for the MAF. All the nest material from the filter box was piled up against the screen in front of the MAF. After finding the remains of the rat in the resonator box in the fender (where's that smell coming from?), I screened off the intake (also behind the fender) to prevent a repeat performance.

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If I recall correctly, the ECU is in open loop at idle and WOT. The rest of the time it is closed loop when warmed up. 

 

I was looking at the emission numbers you have and sorry, but CA does things much different. I don't know what GP means. I figure the meas is what was measured and Max is Maximum, though the numbers there seem low. If I am reading it right, the O2 was at 0 and CO2 was 12.7% with elevated HC, CO, and I assume NOx. Those are indicating a rich condition, not enough air to completely burn the fuel. It is likely your MAF giving high readings from everything else I read in your posts. Your work on the connector probably fixed it. A gentle cleaning of the sensor and screen might help too. 

With the O2 sensors, they all use the same bung, and 99% use the same 22mm(7/8") wrench/socket. They also tend to look alike as well. It is inside where they are different. I don't remember off hand, is it a 3 wire sensor? If so, running a ground to the exhaust might help as well, since the sensor is grounded by the pipe. Originally, there was ground straps on both manifolds and a couple of other points on the pipe. Those tend to break over time. 

 

Here we do the sniffer test quite differently. It is done unloaded, no Dyno. First stage is 30 seconds at 2500 rpm(2250-2750) followed by 30 seconds at idle (600-1100 rpm). For autos and light trucks GVRW less than 8000 lbs in the 80s and 90s maximum HC is 210 ppm, CO is 1.2%, and NOx is not measured.  Just for the record, it is counter intuitive, but the emissions tend to be higher when the engine is unloaded than when under load. 

 

Most of the Snap-On scan tools that can do OBD1, can read data from your Nissan Consult port if you have the correct adapter. My first one many years ago was a first gen Ethos, and it did well on my 93, main reason I don't recall the nuances of playing with the switch on the ECU and it's lights. Only times had to deal with that in the last 15 years was with the 85 300ZX that I took to the junkyard 9 years ago. 

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12 hours ago, Slartibartfast said:

No worries man, good luck with it! Hopefully the dealership guy can at least get into live data or something.

 

Funny story, mine had a rat's nest in the air filter box when I got it. PO had no idea why it was down on power, and apparently his mechanic hadn't checked the computer, because it was coding for the MAF. All the nest material from the filter box was piled up against the screen in front of the MAF. After finding the remains of the rat in the resonator box in the fender (where's that smell coming from?), I screened off the intake (also behind the fender) to prevent a repeat performance.

 

To no-one here's surprise I'm sure, I got nowhere with the dealer.  The nice guy I was talking with was an order writer so his job is to get my keys and signature.  He did say that all his guys could get would be the same data I has getting by reading the flashing lights, plus a little more detail.  How much more detail?  He called his master tech and asked how much more info CONSULT could get from my computer.  When I mentioned that my truck is apparently not set up for CONSULT (nor does it have an ODB1 port, right?  Just what is that 12 pin connector near the hood release.  Its just a flashing light repeater, or is it more than that.  I'm curious and would love to know - I did not have this discussion in parentheses with him), he said CONSULT would connect wirelessly with my ECM.   Now that would be very cool.  I don't know that much about computers but I'd bet a solid 25c that no ECM built around 1990 had wireless connectivity capability.  So do they plug into the the 12 pin connector?  Do they have a connector with wifi which goes between the ECM and the ECM connector?  Now that would be cool, but I can't see the demand being sufficient to warrant the expense of building one by the dealer or any component maker.  Any ideas?  He did finish by saying a scan of my truck would be $150.  Say $200 out the door.  I can throw a lot of parts at this truck for $200 so I declined since I don't need a readout that my computer has code 45 stored.  I know that already.

 

Its mildly amusing to me that a stock low price alert I had entered years ago for Nissan stock, came up as my first email this morning!

 

How did you access the behind the fender resonator box?  I've looked at your "other project car" site so I know you're not afraid to disassemble things  😉  Thanks for the funny story.

 

Since the consensus is focused on the MAFS I'm going to disassemble the filter box and clean out both resonators and if access makes it feasible also screen off the intake.  Great idea!!  I'd sure my 95 has the same problem.

 

Then I'll solder a new ground to the MAFS B terminal and ground it to the engine ground

 

If the problem continues I'll take the MAFS assembly off my 95 and install is it on my 92 (assuming it passes visual inspection that it is pretty much identical.

 

After that I'll follow all the instructions on NTB95-021 but I may ask you for recommendations for fuel pressure gauges and other tools I'll need

 

Have a great day.   I've noticed researching things that you've answered almost all my questions some other place, years ago.  I much appreciate your patience answering again.

 

john

 

 

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