Emissions Magician needed

[k9sar]

Ok... so here's the deal. My 95 pathy has failed emissions testing

 

Symptoms: The pathy seems to idle fine and run fine during accelleration but has a bit of a dead spot in the power band when cruising along steadily at 2000 to 2500 RPM. Almost like it's choked... hesitation, a bit of sputter, etc. Does not stall but does not respond immediately if I hit the gas. On occasion, after prolonged driving, the CEL pops on with a 33 code (O2 sensor). Once this occurs, she runs rougher and it seems like I have to try to keep it running although it never stalls. Obviously, the brain is trying to compensate for something and making it run worse. I can stop, clear the code and it runs fine for awhile.

I do not think I am getting good mileage but that is expected if running rough.

My temp reading stays barely above the bottom of the guage even when a 70 degree day running hard.

 

Test readings:

 

2007 test: CO% .62 (limit is 5.4) --- HC ppm 283 (limit 537) --- NO ppm 851 (limit 7380) --- 14.7% dilution at 1897 RPM

 

2008 test: CO% 20.55 --- HC ppm 882 --- NO ppm 234 --- 17.5% dilution at 1842 RPM ----> RESULT... FAILED

 

In addition, the O2 sensor threw a code during the test.

 

So... based on the FSM, I tested the O2 sensor circuit and got good voltage on the appropriate pins. When I tested the resistance across pins a and c (at temp) I read 4 ohms. Spec range is 3 to 1000 ohms. (anyone know what a new one reads? Is it on the low end or high end of range?) These readings lead me to believe that the O2 sensor is good and it truely is detecting something like it should.

 

I pulled my disty cap and preplaced it with my old one that had no issues passing inspection before I swapped the motor.

I replaced the rotor in the disty with my prior one as well. Again, the old motor never failed inspection.

I pulled the plugs and noticed the electrodes were burnt down so I replaced all 6 plugs with NGK's as recommended inthe FSM. side note, make sure you blow all the mud and crap out of the plug holes before removing your plugs. Mine sat in caked dirt halfway up the insulator.

I checked the resistance of each plug wire and they are well within spec.

I checked to see if I had good spark and found that it could easily jump a full inch from the plug to the intake manifold I was using as ground. With that much spark, I should be able to run with virtually no electrode or arm on my plugs. Replaced the plugs anyway.

I pulled my air filter and shook it. About a half cup of crud fell out. I blew out the intake and air box and replaced with a new filter.

 

She seemed to run better after that so I sent it back in for a retest

 

2008 test: CO% 21.54 --- HC ppm 699 --- NO ppm 684 --- 17.7% dilution at 2716 RPM ----> RESULT... FAILED

 

Obviously there is something that has failed that is causing increased CO and HC readings. I thought that running rich would only increase one of these but I forget which and could certainly be wrong.

 

I don't want to start replacing parts at a hundred bucks a shot and hope to happen upon the failed component so I am looking for real and knowledgeable information which would lead me to a solution. Who's the former nissan techie in here?

 

The mechanics of the O2 sensor are that it compares exhaust gas with outside air to make a determination of problem. Even though my test readings are good, could it be that the O2 sensor hasn't liked being submerged and caked in mud many times?

 

It was also suggested that my eng temp sensor could cause the ECU to run differently (change spark advance etc?) and may also explain the low temp reading.

 

again... I don't wanna just throw new parts in until it works.

 

If you have any knowledge of this type of situation and can steer me in the right direction for a solution, I'd certainly appreciate it.

 

Thanks

[Casey.T]

Stevens County does not require Emissions... but I do feel your pain, my 95 is having a similar issue with some sputtering but not giving me any codes. I have until the end of May to resolve mine, Spokane County does require Emissions... At first I thought it was going from Oxegenated Gas back to the summer mix, does this every year...

Edited April 16, 2008 by Casey.T

[GhostPath]

If the O2 sensor is more than 60,000 miles old, it's past it's spec life and needs to be replaced. It may still "work", but its readings will drift farther and farther away from accuracy. But that's not the key here. You have just encountered a classic VG30 problem.

 

"The pathy seems to idle fine and run fine during accelleration but has a bit of a dead spot in the power band when cruising along steadily at 2000 to 2500 RPM."

 

A dead spot, unwillingness to rev, or just not being able to go above the 2000-2500 rpm window *without* setting any codes (other than a possible O2 sensor code) is a classic sign of either a bad cylinder head temp sensor or bad wires going to it. The Z31 has the same issue - on it, though, the CHTS sensor has a replacable harness that you're supposed to replace at the same time you do the sensor. We aren't so lucky.

 

The CHTS is about $20-30 at the dealership.

Edited April 16, 2008 by GhostPath

[k9sar]

If the O2 sensor is more than 60,000 miles old, it's past it's spec life and needs to be replaced. It may still "work", but its readings will drift farther and farther away from accuracy. But that's not the key here. You have just encountered a classic VG30 problem.

 

"The pathy seems to idle fine and run fine during accelleration but has a bit of a dead spot in the power band when cruising along steadily at 2000 to 2500 RPM."

 

A dead spot, unwillingness to rev, or just not being able to go above the 2000-2500 rpm window *without* setting any codes (other than a possible O2 sensor code) is a classic sign of either a bad cylinder head temp sensor or bad wires going to it. The Z31 has the same issue - on it, though, the CHTS sensor has a replacable harness that you're supposed to replace at the same time you do the sensor. We aren't so lucky.

 

The CHTS is about $20-30 at the dealership.

 

I know the VG30i's have a CHTS under the timing cover but I don't recall ever seeing or hearing of one on the VG30E's. Not the same as the coolant temp sensor, I assume.

[msavides]

I know the VG30i's have a CHTS under the timing cover but I don't recall ever seeing or hearing of one on the VG30E's. Not the same as the coolant temp sensor, I assume.

 

 

 

I was in the same boat as you with my 1991 patrhfinder. All I did was replace the O2 sensor and the Cat, and cleaned my EGR passage and it brought both C0 and NOS numbers down to under 20. I would change those 2 things and clean the egr passage and send it in again. Never underestimate the power of a Brand New Cat.

 

 

 

Mark

[GhostPath]

I know the VG30i's have a CHTS under the timing cover but I don't recall ever seeing or hearing of one on the VG30E's. Not the same as the coolant temp sensor, I assume.

 

All fuel injected vehicles that use feedback systems have a coolant temp sensor for their fuel injection computer. Nissan calls theirs the Cylinder Head Temperature Sensor to distinguish it from the separate sensor that tells the gauge on the dashboard what to display for coolant temp.

 

It's not under the timing cover, either.

 

So, yes, both the I and E variants have a CHTS.

Edited April 16, 2008 by GhostPath

[k9sar]

All fuel injected vehicles that use feedback systems have a coolant temp sensor for their fuel injection computer. Nissan calls theirs the Cylinder Head Temperature Sensor to distinguish it from the separate sensor that tells the gauge on the dashboard what to display for coolant temp.

 

It's not under the timing cover, either.

 

So, yes, both the I and E variants have a CHTS.

 

under... behind... whatever

 

any guess where I would find it on my 30E? The item called the coolant temp sensor is on the housing by the thermostat. I couldn't find any online listing of parts for the 95 that had a seperate temp sensor for the heads.

 

update: found a reference to an egr temp sensor on one of the dealer sites. This what it looks like?

 

Edited April 16, 2008 by k9sar

[GhostPath]

The CHTS sensor is sold in the aftermarket as the "coolant temp sensor" - it's on top, right next to the outlet for the upper radiator hose.

 

This is what it looks like.

[systemf]

This won't fix your dead spot, but:

 

In my experience with pre OBDII vehicles that have failed with high CO it was probably due to a worn cat. I am not sure if the 95s had a 3 way cat, but if they did that should take care of CO and HCs. With my vehicles I just ran denatured alcohol in the tank, about 1 pint for 4 gallons, and passed every time with no other mods. I have actually had a busted ring landing on #3 in an old Honda blowing blue smoke out the back of the inspection shop and still passed with alcohol, the engine was replaced the next day, but I had to get an inspection. The emissions test pass stuff at AutoZone also does the same thing. Now this is just my experience with older Hondas that used speed/load based fuel injection systems, nothing as accurate as the speed/density based system on a 95 pathfinder.

[k9sar]

so.. as mentioned in the poho thread.... I have a new issue. On the way home from the junkyard, the pathy didn't have any oomf. Idled fine, rev'd fine in neutral or park but when placed in gear (didn't matter if it was 1, 2 or D), accelleration was sluggish like if you were dragging a boat or trailer. The engine would be retarded by what appeared to be a load on it. (sincker... sorry). Anyway, as I got up to speed, I noticed that ther tranny wasn't shifting. If I stomped on the gas, the engine just slowly climbed in RPM without downshifting. Turning on/off OD seemed to have an effect but only with the OD gear. What I determined was that I was starting in 2nd or 3rd gear and had lost the lower gear(s). Wondering ig the engine was powerless, I threw it into reverse and it took off, throwing gravel all over the place. back to Drive and it groaned as it accelelrated (and didn't shift).

 

Parked in front of the house when I got home and decided that the problem was with the forward gears in the tranny that had just been rebuilt. In the morning, I planned to take it to the tranny shop. So, at 7am this morning, I jumped in and put it into gear... damned thing took off like nothing was wrong (except running rough due to the emissions issue I'm trying to resolve) I called the tranny shop and they said to bring it in anyway and they'd look at it. I hoped it wopuld fail on their watch but it did not. I spoke with the mechanic and he says that there is nothing wrong internally to the tranny and that something is kicking it into effectively a safe mode or limp mode. I was not aware that an auto tranny had such a thing. He suggested perhaps a MLP switch or the TPS might be causing it.

What's an MLP switch?

Anyway... I'm picking it up so I can work on the emissions crap this weekend. Anyone have any insight into the AT limp mode (if it exists)? What might be common to the emissions problem or why would it resolve itself by just sitting. Temp dependent? I'm getting p[issed at this thing.

 

Gonna do some in-depth reading in my FSM this evening.

[GhostPath]

Hm, might be an ECU or wiring issue.

 

Nissan WD21 and later automatics are computer controlled; they go into a limp-home mode if they stop getting usable data from the ECU.

[k9sar]

Hm, might be an ECU or wiring issue.

 

Nissan WD21 and later automatics are computer controlled; they go into a limp-home mode if they stop getting usable data from the ECU.

 

good thing I snagged an ECU in the $7 haul the other day

[02silverpathy]

Past all the other emissions test prepare steps...use toluene! 1 gallon in 1/2 tank of 93 makes just about 95 oct....super clean burn. Isopropyl alchol never hurt either, but then go fill up after the alch. or you can start to fry sensors!

[02silverpathy]

After reading this again, the wife's old Saturn came to mind.

 

We replaced the EGR, ran high test (less than a 1/4 tank), and added about 2 quarts of isopropyl alcohol to the gas, it ran hot at idle, but otherwise great and passed with flying colors. The Saturns' problem was the oil ring was bad in piston #3...coated the spark plug all the time and ran rich! The EGR made the cars acceleration m-u-c-h smoother and probably helped with the exam also!

[k9sar]

well... she's going back in for the third time. (fingers crossed)

 

 

YAY! It passed. I'll see the numbers when I pick it up. Now, If I can figure out what piece of what I did actually fixed the problem....

 

the numbers...

 

2008 test: CO% 0 (limit 5.4%) --- HC ppm 63 (limit 537) --- NO ppm 60 (limit 7380) --- 14.5% dilution at 576 RPM

 

wonder what the numbers would be like if tested at over 1200RPM... oh well.. no matter now.

Edited April 28, 2008 by k9sar

[k9sar]

Since the last test, I cleaned the MAF (not very dirty), swapped the TPS with my old one, swapped both the temp sensor and the sending unit in the cooling system with junkyard finds, swapped the EGR temp sensor with my old one, swapped the coil with my old one, swapped the O2 sensor with one thought to be good but used, repaired a wire harness that ran to the speed sensor on the tranny (it was laying against and melted to the exhaust flange just down the pipe from the manifold), waved my chickenbone cross and sacrificed a virgin.

[Alkorahil]

under... behind... whatever

 

any guess where I would find it on my 30E? The item called the coolant temp sensor is on the housing by the thermostat. I couldn't find any online listing of parts for the 95 that had a seperate temp sensor for the heads.

 

update: found a reference to an egr temp sensor on one of the dealer sites. This what it looks like?

 

 

 

Only California emission WD21 had an EGR temp sensor

Edited September 16, 2008 by Alkorahil

[k9sar]

both my engines actually have one. I saw one on the junker at the u-pull-it too. That wasn't the problem btw. I ended up rplacing the TPS and the O2. Also found a wire harness against the downpipe on the passenger side. That was probably causing my tranny shift problems too.