93 Olds 98 3.8 Digital EGR test

cliffw · #1 03-02-2008, 12:02 PM

Above failed emissions NOX. - about 40% over limit. Hydrocarbons & C0 well within limits. I understand most likely culprit is EGR. Can this be tested? I took it off. No plugged ports. Paint coat of carbon. Is there any way to check operation of solinoids? Does it have any connectors between it & ECM? Price of new about $360.00 floored me. Thanks.

maxwedge · #2 03-02-2008, 04:24 PM

Without a bidirectional scanner that can operate the egr to confirm it's operation, you will need a wiring diagram to see which wires at the egr connector must be grounded to activate the egr, then when the engine stalls or stumbles you can assume it works. Try autozone.com, repair guides for an under hood diagram.

cliffw · #3 03-03-2008, 08:54 AM

Thanks. I checked Autozone. Wow what a great site. I'll check resistance values tonight. A couple questions: First since solinoids are activated by grounding can I just ground appropriate pins to check? Also since EGR controlled by ECM & ECT, MAP, &TP feed ECM could problems in these circuits cause faulty operation?

cliffw · #4 03-03-2008, 08:56 AM

Sorry in rereading your reply I see you answered my first question.

BNaylor · #5 03-03-2008, 08:59 AM

This thread has been moved to the Olds 98 forum.

cliffw · #6 03-04-2008, 08:55 AM

I checked resistance on solinoids & all were within specs. Also grounded each & heard click & engine stumbled so assume egr is ok. I also pulled error codes got 12( test start) 37 (PNP sw), 56(not listed). I cleared codes & took for drive No codes on rechecking. When I checked egr ports were not clogged , but had some carbon. Could this cause failure NOX? ( about 240 ppm above limit) CO was 0 Hydrocarbons .07 limit .7. Any ideas? Does anybody have pinout for ECM? Thanks.

maxwedge · #7 03-04-2008, 04:50 PM

It is possible the cat is bad causing this also, again to see if the egr is being commanded you need a full scan. Lean mixtures can cause hi nox as well as high engine temps.

cliffw · #8 03-05-2008, 08:23 AM

Thanks. I'm thinking that since CO is not detectable & HC is very low the cat is probably ok. Also since no valid codes probably other factors ok. First I'd like to trace continuity back to ECM before going farther. Hence pinout for ecm. Really appreciate help.

cliffw · #9 03-20-2008, 01:51 PM

I rechecked codes & find 56 again. Autozone says " QDM "B" circuit"
can anyboby tell me what a QDM "B" circuit is Thanks

maxwedge · #10 03-20-2008, 04:19 PM

This is a driver in the pcm that controls high load relays and solenoids, the B circuit would have to be pinpointed t find which controls are involved using a comprehensive engine control wiring diagram.

cliffw · #11 03-20-2008, 09:51 PM

Thanks. Any idea where I can get that diagram, or even a pinout for pcm. I don't want to buy a new pcm if it's just a poor connector , broken lead etc. By the way love the pix of car.

maxwedge · #12 03-21-2008, 04:53 PM

Alldata.com has online repair manuals for a subscription price, usually good for a year.

peterjon1 · #13 03-21-2008, 07:58 PM

You can try here for repair manual. I have not drilled into it too far, but maybe------
http://www.automotiveforums.com/vbul...d.php?t=890937
Follow the instructions in the thread for access.

cliffw · #14 03-26-2008, 08:52 AM

Thanks. That's a great site. I found a wiring diagram, but it doesn't mention EGR. Still looking. Any other ideas?

cliffw · #15 04-04-2008, 08:41 AM

Just thought I'd let everybody know I finally got the old gal to pass. I never did get a good wiring diagram, but cleaned & checked all connectors at pCM. This fixed the error code, so assume I had a bad connection. On retest it went thro fine. Thanks again for your suggestions. I learned a lot about this system - probably more than I wanted to.

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