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'95 Pathfinder misfiring over 2500 rpm--but only when warmed up


shaggy
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Check the coolant temperature sensor. It's not a clogged cat. You need to test all the sensors and injectors and compare to values in fsm. If it runs fine cold but bad warmed up, it means when the ecu goes to closed or open loop or whatever it is getting bad data. This was the o2 sensor on my rig. Never heard of a Borg Warner o2? These trucks run best with a Bosch or ntk. Was this a direct fit sensor? The universals are @!*% so don't even bother. As a test unplug the o2 cold and try driving. If it still does it plug it in and do the same with the coolant temperature sensor.

 

I'm not sure why people on here recommend throwing fuel pumps and catalytic converters at the truck...this isn't some domestic pos ford explorer.

 

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Coolant temp. sensor... ok, I will try and check it.

 

Should I try running it with the coolant temp. sensor disconnected from the get-go and see what happens? So far nothing seems to have changed the basic symptoms, they just get more severe as the temp. goes beyond a certain point--after the sensor/feedback system goes closed-loop (by the sound of it).

 

Hope it's not the O2 sensor. It was a direct fit 3-wire job, even the same wire color coding. (They stated the brand on ebay, but maybe they got it mixed up with a brake or clutch part, wouldn't be surprised LOL!) I hope it's OK-- that was a lot of damn work to put in; I've still got a sore neck(!)

 

What about the EGR system?

 

 

thanks

Dave

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Coolant temp. sensor... ok, I will try and check it.

 

Should I try running it with the coolant temp. sensor disconnected from the get-go and see what happens? So far nothing seems to have changed the basic symptoms, they just get more severe as the temp. goes beyond a certain point--after the sensor/feedback system goes closed-loop (by the sound of it).

 

Hope it's not the O2 sensor. It was a direct fit 3-wire job, even the same wire color coding. (They stated the brand on ebay, but maybe they got it mixed up with a brake or clutch part, wouldn't be surprised LOL!) I hope it's OK-- that was a lot of damn work to put in; I've still got a sore neck(!)

 

What about the EGR system?

 

 

thanks

Dave

 

If it's of any use, the second picture in post #10 on this page:

 

http://www.nissanpathfinders.net/forum/topic/36294-engine-pictures-for-information-and-comparison/

 

... shows exactly the setup I have in regard to the EGR/BPT valve system (i.e. CA -compliant vehicle).

 

I just checked mode III ECU codes and I now have a 12 (air flow meter circuit), a 21 (ignition signal missing primary coil), and the usual 34 (detonation sensor). First time I've seen a 12, but it might be to do with the electrical checks I just made.

 

Thanks for any further thoughts...

 

Dave

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Check the coolant temp sensor, resistance should be 2.1-2.9 ohms at 68 degrees Fahrenheit, .68-1.0 at 122F and .30-.33 at 176F. Check it with the vehicle hot and failing.

Forget the egr system. That is the least likely to cause what you say is happening.

Did you remove the distributor and check that the shaft turns freely? Any dust or soot should not make it inside, should be sealed.

Forget the knock sensor code, most likely is being set due to the problem your having.

Probably should look closer into the ignition code. Check the power transistor. Follow diagnosis procedure 27 in the Esmond page ec-90

 

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Check the coolant temp sensor, resistance should be 2.1-2.9 ohms at 68 degrees Fahrenheit, .68-1.0 at 122F and .30-.33 at 176F. Check it with the vehicle hot and failing.

Forget the egr system. That is the least likely to cause what you say is happening.

Did you remove the distributor and check that the shaft turns freely? Any dust or soot should not make it inside, should be sealed.

Forget the knock sensor code, most likely is being set due to the problem your having.

Probably should look closer into the ignition code. Check the power transistor. Follow diagnosis procedure 27 in the Esmond page ec-90

 

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If you're talking about the front-most unit (with the single spade connector) of the two devices screwed into in the coolant inlet manifold, it's resistance, from spade terminal to ground (engine warm) is way over your spec-- it's a bit over 155 Ohms--no kidding(!) --and I do I know my multimeter and Ohms Law.) 8>)

(The second unit with two terminals I think is a switch, and reads open circuit as it probably oughta.)

 

In kind of a new development, the engine will not even fire when warm (maybe not even cold now, either). And the ECU gives a consistent code 21 (no signal to coil primary) --so basically, zero spark as of now. (I switched to a spare ignition coil to no effect.)

 

So, I'm thinking 'bad power transistor'(?) Damn thing is 60-70 bucks for a new Bosch, though, so I wanna be sure. And I hope it isn't the Crank Pos. Indicator electronics, 'cause that's even more $$$.

 

Between no spark at all, and bad coolant readings, maybe we got something...?

 

BTW, I'm reluctant to heat up the engine because I know it won't start until it cools again for hours, but that may all be a moot point now, as it won't even fire (mis or not)... 8>/

 

thanks again

Dave

Edited by shaggy
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The two terminal sensor is or the ecm, if it's open it is bad. Double check to be sure. The Esm states that backfire through exhaust can be caused by a failed coolant temp sensor.

Possibly you have two separate problems. Follow the esm and check the power transistor.

If you know anyone else that's close or have a junkyard close you can simply swap it to check.

 

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The two terminal sensor is or the ecm, if it's open it is bad. Double check to be sure. The Esm states that backfire through exhaust can be caused by a failed coolant temp sensor.

Possibly you have two separate problems. Follow the esm and check the power transistor.

If you know anyone else that's close or have a junkyard close you can simply swap it to check.

 

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Sorry, are you saying the unit that's closer to the engine block (with two wires and the yellow block connector) is the coolant temp. sensor? That figures. It's just that I saw a pic of the single-terminal one somewhere labeled that. What is that one, then?

 

If it's open, I guess that could cause the problem I'm having (misbehaving only when warmed up)?

 

I'll check the price of a new one at the parts store, maybe it's not too much...

 

Can't get to a junkyard that easily right now. I should be able to do a stand-alone check on the transistor first....

 

Thanks

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The sensor with the single pin is for the temp gauge on the gauge cluster.

 

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Yes, I figured that out thanks.

 

BTW, where did you get the resistance figures for the 2-terminal one from? I checked mine against a new one at the parts store, and they're both in the range of 1.5k Ohms at room temperature. Sticking them in near boiling water, the resistance goes down to 700 Ohms or so, but nothing like as low as your specs. I bought the new one just to test mine properly, it was only $20.

 

I'm on to checking that transistor now, and looking for spark... wonder if it's back now the engine's cooled off... 8>/

 

Dave

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I work at the dealer, looked up in the esm while I was at work today.

If you bought one might as well put it in and check if it's helped.

 

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Well, thanks... esm (?) But I think it was wrong specs for my vehicle. The new one and my original both track temperature the same as far as I can tell. Anyway, it was good to check it.

 

The big problem now looks like no spark at all anymore. Maybe something's been on the way out all this time 8>/

 

Will be looking for electrical test procedures on the power transistor, and crank position sensor electronics. After that, I dunno...

 

Dave

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Esm=electronic service manual. Also called assist.

I could also have overlooked K ohm spec. Not at work right now to double check but I think I did.

As I understand it you can download the manual from NPORA. and verify that spec.

Did you remove the distributor and check that the shaft turns freely? Quick and simple test and you need to eliminate that as a possibility. I've seen a lot of problems with the shaft bearings.

And one last though, pull off the cap and have a friend crank it over to make sure the rotor is turning ( referring to no spark).

 

 

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Esm=electronic service manual. Also called assist.

I could also have overlooked K ohm spec. Not at work right now to double check but I think I did.

As I understand it you can download the manual from NPORA. and verify that spec.

Did you remove the distributor and check that the shaft turns freely? Quick and simple test and you need to eliminate that as a possibility. I've seen a lot of problems with the shaft bearings.

And one last though, pull off the cap and have a friend crank it over to make sure the rotor is turning ( referring to no spark).

 

 

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Hi-- Yes, I removed the distributor cap yesterday to check the CPS disk. Everything in there looks good (the soot I mentioned was barely visible and nothing more than I'd expect), and I know the shaft and rotor turn because I cranked it a few times to get the screw to line up. I'll check it again, although I doubt anything's changed. I'm tempted to buy a power transistor unit, but it could as easily be the CPS block... or the ECU... or(?)

I've taken apart and cleaned all the +ve terminal blocks around the battery. I guess I'll start double-checking all the power and grounds again, including the transistor...

 

thanks!

Dave

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Wish I could be more helpful, a lot easier when you have it in front of you and can actually see what is happening.

There are a lot of good feedback on this post from the other members.

Best of luck.

 

 

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Hi -- I understand, and I appreciate your help anyway.

 

Maybe it'll turn out to be something simple--that's often the case, but you dare not hope too much. Still...

 

cheers

Dave

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Hi -- I understand, and I appreciate your help anyway.

 

Maybe it'll turn out to be something simple--that's often the case, but you dare not hope too much. Still...

 

cheers

Dave

 

Well guys, me and the Pathfinder had a horrible weekend. It was hot hot hot, and she'd barely do three miles from a cold start without starting to stutter and shut down, at which point nothing will get her going again short of sitting overnight wherever she happens to stall out. No more driving anywhere, unless it's to a garage or to the wrecking yard 8>/

 

Without throwing a few hundred dollars worth of parts at it that it maybe doesn't need or justify, I'm near the end of the road here.

 

Any ideas?

 

thanks!

 

Dave

Edited by shaggy
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PS--

 

Given the symptoms (starts and runs cold, sputters and dies after getting hot, no spark/no start when hot)...

 

Since I've replaced: plugs, plug wires, dist. cap and rotor, fuel filter, air filter, O2 sensor...

 

Checked/eliminated: Fuel pump, coolant temp sensor, CPS (disk)...

 

What do you think are the chances it's:

 

Crankshaft position sensor (electronics block)?

 

HT power transistor?

 

MAF?

 

One or more fuel injectors?

 

Bad CAT?

 

EGR/BPT valves?

 

ECU?

 

??

 

thanks

Dave

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PS--

 

Given the symptoms (starts and runs cold, sputters and dies after getting hot, no spark/no start when hot)...

 

Since I've replaced: plugs, plug wires, dist. cap and rotor, fuel filter, air filter, O2 sensor...

 

Checked/eliminated: Fuel pump, coolant temp sensor, CPS (disk)...

 

What do you think are the chances it's:

 

Crankshaft position sensor (electronics block)?

 

HT power transistor?

 

MAF?

 

One or more fuel injectors?

 

Bad CAT?

 

EGR/BPT valves?

 

ECU?

 

??

 

thanks

Dave

 

Another couple questions:

 

If the detonation/knock sensor is bad, could it be giving the ECU enough wrong data to be contributing to the problem (say retarding the ignition timing)?

 

I may have mentioned this, but along with the misfiring, there's some wheezing and flapping and undue noise around the left side manifolds (both intake and exhaust), and possibly the CATs and 'y' junction (which looks like a heap of rust, BTW). Thinking this could be an additional problem, on top of the no-spark when hot symptom.

 

I'm tempted to buy some used ignition parts (CPS, power transistor, and ECU)to throw at this. I could do it for under $150 and it might solve the problem. (Yeah, I know, used parts--but I can't afford 3x for new ones.)

 

Any more ideas?

 

thanks for your time guys

Dave

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I highly doubt the knock \ detonation sensor is your problem. If you look on eBay you can find inexpensive replacements that work just fine.

 

Have you checked your aac valve? This was bad on my 92 and was causing problems for me. If you can pull the harness connector at the front passenger side of the engine to test its easier. It should be 10 ohms.

 

Also rebound your maf. This is almost mandatory with any of these vehicles.

 

Have you confirmed your timing with a timing light?

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I highly doubt the knock \ detonation sensor is your problem. If you look on eBay you can find inexpensive replacements that work just fine.

 

Have you checked your aac valve? This was bad on my 92 and was causing problems for me. If you can pull the harness connector at the front passenger side of the engine to test its easier. It should be 10 ohms.

 

Also rebound your maf. This is almost mandatory with any of these vehicles.

 

Have you confirmed your timing with a timing light?

 

Hi and thanks for replying.

 

I thought it probably wasn't the knock/detonation sensor, I just wanted to make sure as I've read different opinions.

 

AAC? Will look it up and put it on the list.

 

Not sure what you mean by 'rebound' the MAF(?) I've cleaned it and checked it out electrically, with engine running--the voltage increase was smooth and within spec. But I didn't check it hot, just warm, so I'm not 100% sure.

 

No I haven't checked the timing yet. With the engine starting and running OK cold, I've been looking elsewhere. But yeah, it it could be going haywire when something heats up. I need to get another timing light (someone stole it awhile back). I wished I had it when the misfire started happening.

 

Thanks for your suggestions!

 

cheers

Dave

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Sorry I meant reground. Make sure that the actual ground lead is double grounded to a good ground position.

 

What's weird is the runs OK the bad when warming up/hot.

 

This makes me believe it's a coolant temp sensor, cylinder head temp sensor, or oxygen sensor or maybe egr. All other sensors are just reading a variation or variables. Nothing temp related.

 

Good luck but I would start with the 3 major. Fuel / compression / spark. You know you have good fuel pressure and spark, well check the timing to make sure its not doing anything wanky. Then verify fuel pressure when misfire studder and any issues. This means an inline gauge you can see while driving.

 

Does this happen only under load or also under idle no load conditions?

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Sorry I meant reground. Make sure that the actual ground lead is double grounded to a good ground position.

 

What's weird is the runs OK the bad when warming up/hot.

 

This makes me believe it's a coolant temp sensor, cylinder head temp sensor, or oxygen sensor or maybe egr. All other sensors are just reading a variation or variables. Nothing temp related.

 

Good luck but I would start with the 3 major. Fuel / compression / spark. You know you have good fuel pressure and spark, well check the timing to make sure its not doing anything wanky. Then verify fuel pressure when misfire studder and any issues. This means an inline gauge you can see while driving.

 

Does this happen only under load or also under idle no load conditions?

 

Will check grounds again, but I have a feeling it's not gonna be something that simple.

 

The coolant temp. sensor's resistace readings are OK, and I replaced the O2 sensor...

 

There was a period where she wouldn't start hot, and I was getting the no spark fault code... other times it seems like intermittent spark, or the timing going nuts.

 

Fuel is good as far as I can tell. Compression... I'm scared to check(!) --but it's been running fine. Gotta be something affecting the timing, or killing the spark...

 

I have tracked down an ECU (used), a CPS (new), and a MAF sensor (used), $150 worth. It might be worth the gamble...

 

Dave

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How much have you spent thus far trying to fix this ?

 

Hi BR... Not that much really, maybe $150. Why?

 

I haven't even spent this whole time on it--just spare moments and weekends-- because I've had to work. I'm trying to make the time and money I spend on it count.

 

BUT, right now I can actually afford to throw a couple hundred (parts mentioned in previous post) at it. I would do that in a heartbeat, if I believed that's all it would take.

 

Doubts about the catalytic converters and bad exhaust manifold are what's holding me back. As much as I love this vehicle, I can't see putting $1000 or more into it.

 

cheers

Dave

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You might try running it with the MAF unplugged. The computer should go to to stored values then. If the MAF is reading horrendously out from where it should be, the stored values would be an improvement. If not, I'd guess it's not the MAF. If pulling it does make it run better, it could be the MAF, or it could be going back to open loop and ignoring an erroneous input from another sensor.

 

I've only read about one ECU failure by natural causes (not counting submarine attempts as natural) and IIRC that one was an instant fatality.

 

My money's still on the dizzy.

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