Schump

I have a 1992 extra cab V6 4WD truck with "only" 187k/500k on the clock.
Last Friday, I failed my Virginia emissions inspection. I will disclose all the results below...
I know that a year or two ago, he BARELY passed the NOx ppm limit, it was ~997 out of a maximum 1000 ppm at 25mph on the chassis dyno. I have checked the EGR valve, it's only 2 years old and works fine. Planning on checking/retarding ignition advance as I have advanced it a bit several years ago. Combustion temps are too high which my old co-worker said could be caused by:
a) Too much advance
b) Not enough EGR
c) Mixture too lean
d) Thermostat allowing engine to run too hot
e) CAT not totally warmed up during test (guilty, he only idled for a while to bring it up to temp, I'll speed down the highway before the test to get the cat conv up to operating temp on Wednesday, re-test day.)

My Haynes manual mentions tons of hoses and part of the emissions being several valves w/ vacuum hoses, most of the system is mounted to the passenger fender near the charcoal filter.

Has anyone else had trouble passing emissions? If so, what was broken?
(I did replace the auxiliary temperature sensor, the one mounted in the back of the engine, screwed into a vertical hole. I think it controlled the cold start valve, and once replaced, fixed the problem. This was in 2006 I think.)

Here are my emissions results: (Only failed NOx limit @ 25mph)
@ 15 mph @25 mph
----------------------------------------------------------------
=====LIMIT- READING-- LIMIT- READING
HC ppm 162 28 157 19
CO% 1.32 0.12 1.64 0.10
NO ppm 1099 436 1000 1255
RPM 1752 "VALID" 2762 "VALID"
Dilution 14.5 "VALID" 14.5 "VALID"

I think it may be a combination of the cat not being hot enough, too much advance, and possibly a third problem.
Will go outside right now and check trouble codes, reply emminent.

Thanks a lot,
Schump

Schump

I put a paper clip in the two terminals on my engine, and there are no codes flashing. Could my ECU be wrong?

Also, I think I've seen some "guaranteed to pass emissions" stuff @ Advance Auto in cans. Is it worth anything?

Schump

I checked & adjusted my 3VZE's timing today. I had added a few more degrees a few yrs ago for more power, and that's what the plugs indicated from pix in back of haynes manual, the plugs said "combustion temps too high, we got burnt!" and "Damn it Dave, we're 4.5 yrs old and 40k or so used up, PLEASE put us in a retirement home & replace w/ our children!"

I did both. Replaced ND's w/ NGK's (don't remember the complete code, but part # 7090 spark plugs, say thieyre platinum but only $3 / piece @ advance, not the $12.50 the "100k warrantied plugs" are.

Didn't realize it, but truck was at +15 advance, not the +12 as someone else here reccomended for more power. can anything else change our advance besides the distributor position? Piece of cake, got it back to factory reccomended +10 the 1st time, idle went down from 800-550, added more air to turn it up.

Should I worry about any other component before my Wed 1/12/11 emissions retest? I ask as it's a LONG drive to get there n back.

Thanks,
Dave

ChzSoda

Did you jumper the terminal when you set that ignition timing?
If not, you need to get the paper clip back in so that you're setting the "base timing" or some business like that... I'm not really the expert on that, do a search on here. I believe it's the same thing you jumper for diagnostic mode.

Edit: And yes, the engine will itself adjust the advance, based on RPMs, temperature, alignment of the planets, etc. As far as I'm aware though, if you jumper the terminal, adjusting the distributor is the only thing that should change the timing, so you get a "true" set on it or something... Idk beyond that, a lot of magic and elves involved.

Other than that, yeah, sounds like you're covered... Although I've heard a lot of folks on here say that the factory Denso plugs and wires are the way to go. But that's just on a side note, probably not the difference between a pass/fail.
And I think I heard someone once tell me that a bad gasket on their gas cap caused them to fail. Idk what vehicle, type of test equip, so on so forth. You might do a search for that. Could be an inexpensive day-saver.

Schump

Yes, I did do the paper clip trick on the diagnostic terminals when I set the timing. And yes, it is the same two terminals used to get the CEL light to flash to tell you what sensor is sick. My gas cap has passed the test fine (twice.) Hopefully, -5 degree adjustment is all he needs to pass now. I'll find out tomorrow morning, but it doesn't smell as bad as it used to when running cold, so that's a good sign.

Thanks

scope103

While everything you have cited "can" cause high NOx, by far the most likely candidate is the EGR system. That's its purpose!

Start by do a systematic diagnosis http://personal.utulsa.edu/~nathan-b...77exhaustg.pdf Otherwise, you're just guessing.

One possibility is that your plenum (upper intake manifold) is so filled with "gunk" that there is no longer any flow through the EGR tube. I am told that the tube into the plenum should feel "warm." Or you can just pull out the tube and take a look (if you have trouble pulling it out .... there's your problem.)

Good luck!