New to GMT400 from Oregon

[PlayingWithTBI]

How old is your Cat? Maybe it's burned out giving you that rich odor.

 

[g00se]

How old is your Cat? Maybe it's burned out giving you that rich odor.

I hope not --is there a way to check it? I'm guessing it is original. There's 107k on the clock. I'll take a look at it --just to make sure it's there..!

 

[PlayingWithTBI]

I hope not --is there a way to check it?

I don't know if your 94 is the old pellet style or not. My 88 was and when I shook it, I could hear it rattling inside - I junked it and got a high flow cat. YMMV
https://www.amazon.com/Thunderbolt-...5396&sprefix=thunderbolt+3+cat,aps,782&sr=8-3

 

[g00se]

Hey Guys!
I haven't gotten back to working on my truck until this week. It seems to run good but was not passing emission testing. It originally failed for HC and CO -- I then replaced the coolant sensor and MAP sensor and it passed HC but still failed for CO. I then did a tune up, new plugs, wires, cap, rotor and air filter, oil change, etc. But when I took it in the third time it lit up the CEL so I turned back and found it had three codes IIRC:

DTC 15 (coolant sensor), DTC 32 (EGR) and DTC 54 (fuel pump relay?)

I wonder if that code 15 was in OBD1 memory and was displayed when I jumped the OBD1 A-B..?

So recently I have upgraded the 1 wire O2 sensor to a three wire -adding a heater. I haven't changed out anything else, same cat but it seems to be running well with the new O2 sensor so I drove it around for a while and decided to go in for the emissions test with fingers crossed. Just like before --I was almost there and got another CEL. This time it was just Code 32. Because of the CEL I did not have it checked for CO yet, but hoping the tune-up helped.

A bad EGR would not contribute to a CO fail would it? Is there a way to tell if the EGR is bad -or the EGR solenoid? I can move the EGR diaphram and it seems to hold vacuum with a finger on the port.

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[g00se]

I realize I made a mistake --it passed CO but failed for HC. sorry for the confusion!

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I picked up an ALDL cable and TunerPro ---could you take a look at the sample xdl recordings? I've just set it up and got it working. Not sure what if anything looks like it might be causing the high HC.

 

[NW4x4Chevy98]

I had a 91 that wouldn't pass when I lived in Portland, all I did was retard the timing and it passed with flying colors. After I left, pulled over and advanced it. This won't fix anything but it will get it to pass, if you can do that on your truck. Not sure if the 94 has the same distributor as my old truck or not.... welcome to the forum!

 

[steveed]

Welcome to the forum. Code says EGR so I would fix that first. If you go to the service manuals post look for the one named:

• X8936_1989_GMC_Light_Duty_Truck_Fuel_and_Emissions_Including_Driveability

On page 82. Section 3-52 it goes through all the steps to test and determine the issue for code 32.

Service Manuals: https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[steveed]

There is also the manual for the 1994, probably more up to date?

1994_NATP-9442_DRIVEABILITY_EMISSIONS_ELECTRICAL_DIAGNOSIS_MANUAL

The section for DTC 32 starts on page 115

 

[g00se]

Thanks Guys! I should have mentioned that I did a vacuum test on the EGR and it held okay. I took it out and cleaned it. I also pulled the EGR solenoid and the air-filter was pretty dusty. I cleaned that up and put it all back together --so far no EGR codes. I tried to upload the .xdl recording(s) but wasn't able to --I'll load up a screen shot..

I might try that timing trick --I did set it to zero with a timing light when I did the tune up.

 

[g00se]

This is what it looked like when it was warmed up (see below) when it was cold --it had 'rich and open loop' idled higher and the O2 sensor was in the 800ish range (see bottom). Does any of this look like a problem?

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when cold:

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