I recently bought a 1992 3.1L camaro and it seems to have a lot of ECM related issues.

No communication with ECM,

No Speedometer,

Cooling Fan stays on ( Relay grounded by ECM with key on)2 wire ECT sensor replaced 5v across the connector w/key on
Disconnected A/C High pressure switch with no change.

TCC does not seem to go into lock up

Low Idle when cold (500 RPM in park cold) (1000 in park when 180+ degrees)

I'm at the point I'm thinking it's time for a ECM however want to hear all inputs first..

Also could any of this be related to the PROM.. Thanks for all your help..

Doug,

 

sounds like the ecm the last update was a Broadcast code AZTY
could also be the vss or wires to the vss

http://www.austinthirdgen.org/mkport...F_and_vin8.jpg

 

if you end up needing an ecm i have a couple

 

Ok here is an update so far..$75 on an Reman ECM and still have the same concerns, however the car does seem to run and idle much smoother and don't get the sudden engine power surges I was getting before..

The TCC is still not locking up... reason is No Vehicle speed signal = no TCC lock up.. Checking into the VSS tomorrow and related circuits tomorrow.

Cooling fan still running all the times.. Turns out there is a third AC pressure (highside) switch that is normally closed (grounding a signal circuit to the ECM) when the switch opens the fans are commanded on in the ECM... Found connection issues at the switch once repaired I think the this issue will be corrected..

The no communication is still an issues however I think it's the cheap scanner I am using as from what I hear a GM Tech 1 is about the only tool that will communicate with this ECM. I have ground on pin A and 5v on pin B and M at the ALDL.

Will update more tomorrow as I managed to snap the old brittle brake switch off in the process of diag tonight.

 

What are you using to communicate with the ECM?

A Tech1 is not the only thing that will communicate with the ECM, there is laptop software that will also connect with it.

Is the MEMCAL installed in the ECM properly?

Many of the symptoms you describe are indicative of the ECM being in Limp Home Mode, which can happen if the MEMCAL is not seated properly or missing.

 

By MEMCAL I'm assuming you mean the PROM? If so yes the PROM is seated all the way, New ECM and same concerns..

I haven't tested the cold start low idle yet though, The throttle blade minimum stop screw has been adjusted previously by the previous owner for a fast idle concern..(vac leak)..... Ive been looking for info on how to reset this to the stock position however have been unsucessful so far.

I should have the VSS issue corrected tonight and wil update with my findings and outcome on the TCC operation with the VSS working.

 

after the engine warms up jumper a/b on the aldl and adjust idle speed.

 

Can you elaborate on this some more?

What is the result of jumping pins A and B at the ALDL?

I assume the AIC motor would then default and the idle speed should then be a ajusted to some # of set RPM?

If this is true I'm thinking it would be a good idea to clean the throttle body and AIC ports before doing so??

 

jumping the aldl a to b the ecm goes in to diagnostic and also causes the iac to close. At this point you can set the stop screw to set the idle speed.

 

the PROM is part of the MEMCAL.

The PROM is a 28 pin chip that is installed at one end of the MEMCAL, the other end has CALPAK resnets, and the knock Filter.

Have you verified that it is the correct MEMCAL?

What is the CEL doing while you can't connect, and have these issues?

 

you mean the cel, mil , ses or the yellow idiot light !!!

 

No I have not verified it is the correct MEMCAL for the vehicle. But starting to think the MEMCAL could be the problem..

VSS outputs less then 1v DC voltage when turned by hand and monitor across the 2 terminals with a DVOM. Circuits are good between the ECM and the VSS.

Jumped the Fan,A/C high side pressure switch (Dk blue and Blk/wht) and the cooling fan is still staying on. Verified there is ground present on the Blk/wht wire at all times.

Have no update on the Idle concern due to waiting on new Brake/cruise switch to come in.

 

I'd be more interested in the VSS signal while the car is moving under power than when turned by hand.

If the MEMCAL is the problem and the ECM is in LHM, the fan will be on a safety feature, so I would probably not worry about that too much at this point. I would check over the wiring though, to make sure a previous owner hasn't wired it to be on all the time, or installed a switch to turn it on, that may be in the on position.

 

What is a good way to test the VSS? What am I looking for at speed? Are you thinking the VSS could still be faulty?

How can I verify I have the correct MEMCAL?

 

Ok Just check the # on the MEMCAL it's a AZTY 1407

 

The info I have says that AZTY is for an '90 LHO 3.1, auto trans. The ECM should be a 1227730.

 

The only info I can find on AZTY is that its 90-92 3.1 auto trans SD. This is all from post on message boards.. how can I confirm?

Also I should mention currently the Knock sensor is disconnected and tied back.. any input on verifying the sensor is good or should I just replace it? Not sure why is was disconnected and the wiring tied back..

 

look on top of the eprom , on the chip looking through the blue window there is a silver tag with 3 to 4 letters yours should say azty. If you need this gmpartsdirect has it so will any major acdelco dealer p/n 16171406

having the knock sensor disconnected will not cause this problem !!!, when you get it going check your timing and plug it back on , you may have to repair the connector these get brittle.

 

It does say Delco AZTY 1407.

 

A disconnected KS can cause running issues.

Start by repairing all known problems first, then look for other reasons.

 

A scan tool has minimum value on an OBD I car. Simply placing a jumper between A & B at the ALDL, and turning the key to the run position will put the ECM into diagnostic mode. The Check Engine or Service Engine light will start flashing. Count the pulses and it gives you a list of everything the ECM is upset about. It will flash each code three times, starting with code 12... One flash, a short break, two flashes. After code 12, three times, it'll flash any other stored codes, before returning back to code 12 again and repeating. Start there and let us know what codes it has, or if it only flashes code 12 over and over again. If it doesn't flash code 12, then it's probably an ECM problem.

ECMs don't go bad THAT often. It's an easy scape goat for other problems, but really they're very durable. The chances are pretty slim that it's really an ECM problem.

The VSS issue and idle speed issues are really common too. All EFI thirdgens are subject to idle problems, but the 3.1L is particularly bad because the PCV system dumps blow-by in front of the throttlebody. That air carrying oil and contaminants deposits on the throttle blade, and in the IAC air passages. Get yourself a couple cans of the cheapest carburetor cleaner you can find (Walmart Supertech is fine) and clean the throttlebody, IAC, and it's passages. Open the throttle blade and clean the front and back side, scrub it with an old toothbrush to remove any stubborn deposits, etc. Remove the IAC and do the same treatment with the toothbrush and carb cleaner, while avoiding letting the cleaner into the electrical part of the solenoid. Once everything is cleaned out, you should be able to reset the idle speed if necessary. If the minimum air setting (throttle blade position) is set wrong, it can cause the IAC to fail.

I'd start there, the codes from the computer would be most important, and will probably lead to a solution.

 

Sounds like some great info thank you!

I will try to pull the codes tonight and post them up here.

When setting the minimun air/idle speed what RPM should it be set to?
I will be sure to fully clean the throttle body and IAC before doing so.

 

There is alot more information available on the diagnostic stream than just the codes (if any are stored).

Watching the actual values of sensors and commanded outputs can be very helpful.

Definitely worth while IMO.

this is the first that I've heard that third gens had common idle issues, with any engine.

Fix any and all known problems, even the ones that may seem unrelated first, then look deeper.

A disconnected KS can cause a 4* retard of spark advance to happen, with most code masks. I'll have to see if I have one for the RWD 3.1 and load it to my test bench to see what effect that has.

 

curious to hear the results

 

Yeah, but what good does it do if the computer won't even code 12 (self test)?
It's a lot harder to screw up a paper clip then a generic code scanner. Let's break this down to basics and work back up. OBD I is EASY. A DVOM, jumper wire, and test light can find all kinds of problems.

 

That's why I've said fix all known problems first, before searching for more.

 

Ok currently it does display Code 12 followed by Code 51, There may be more codes to come as I had the battery disconnected yesterday and have yet to drive it since do to waiting on a new brake switch (should be in tomorrow)

 

A code 51 is MEMCAL error.

So you may need to replace it or make absolutely sure it is installed correctly.

 

I gave you the part number previously !!! 16171406

 

From all the photo's I've looked at it appears to be installed correctly..... the tag (AZTY) is through the window on the left side of the MEMCAL this with the opening in the ECM at the bottom and the ECM wiring connectors at the top.

When I installed the MEMCAL in the new ECM I pressed on the 2 ends and the locking tabs flipped up and locked into the MEMCAL.

Any Ideas on a good place to get a good MEMCAL if needed?

 

im not sure you can buy those separate....im sure someone might chime in on that

however, i do have an ecm with mecemel i would sell...wouldve sold you the whole thing cheaper than the 75 you spent

pm me if you want

 

It sounds like you're on the right track. There isn't really a trouble shooting flow chart in the shop manual, for Code 51, it just says to try another memcal and reset the computer.

A V6 memcal shouldn't be hard to come by... Complete used ECMs with memcals usually sell for about $30-40. Before replacing it, I'd probably disconnect the battery, remove the memcal, wait 30 minutes and reinstall the memcal paying extra attention that none of the pins in the socket are bent, and that it's firmly latched in place. Then reconnect the battery and check the codes again.

 

If you do get another MEMCAL, make sure it's not from a FWD. The FWD DIS 3.1s have an additional 60* of timing built into the timing control circuit due to how they the DIS ICM works.

 

I'll take it.. Pm me some info on what you want for it and how you want payment.. if anything I'll have a spare.

 

I removed the MEMCAL Just now and verified it is installed correctly and that no pins are damaged.

Some other things I've found is the EGR circuits shorted (12v power to one of the Solenoid control circuits) under the connector cap, 2 out of 3 of the solenoids have 22 ohms resistance and 1 has 12.. Hmm..

I verified the powers and grounds to the ECM,

I also verified the speedometer will work if I pulse a ground to the circuit going to cluster from the ECM. (ECM disconnected of coarse)

Going to repair the EGR circuits and see if I can find out more info on the solenoid resistance values.

Thanks for all the replies.. back out to shop.

 

pm sent

 

That damn digital EGR is quite the piece of #$%@. I've actually seen them catch fire. I'd probably look for one in the junkyard. Used to be able to buy them new, maybe still, but they were expensive (had to replace the one that burst into flames).

 

i need to look around for my egr as it was fairly new when i deleted it...people are always looking for them

 

Can the EGR take out the ECM and cause a code 51 is what I'm looking to find out.. I can get an aftermarket for about $150 (ouch)

 

Forgot to update on the car,

Repaired the wiring to the EGR and no change. Not that I had much hope with that causing the other issues unless it took out the new ECM??

It still seems the only code I can get to set is the 12 and the 51...

 

why is it that the egr wiring is always jacked up on these cars(that i have had)

as far as i know the egr wont ruin the ecm itll just throw a code if its bad or disconnected.

i would say fix the code 51 then go from there if it still has problems.

 

Removed the throttle body tonight and cleaned, Installed a new thermostat while I was there.

Currently I think the IAC is doing nothing on this car.. I removed it and the TPS while cleaning the throttle body and everything looks good but the Idle is still way low on start up.. once warm it idle's right around 1000 rpms (original tach)

This is all I'm going to do to it for now till that ECM and MEMCAL come. Anything I should check/verify before installing the MEMCAL/ECM?

 

you should have it by Wednesday at the latest

 

when you check your codes the iac with close. have someone jump the terminals and listen to see if it moves at all under the hood if you havent already. could just be stuck.

 

Just wondering, how can you determine if you have a failed IAC? does the solenoid fail or visual mechanical failure?

 

I will try this tomorrow.. Also thought about jumping the terminals with the engine running to see if the engine RPM lowered or stalled

 

you will hear it reset when you check codes if it is working.

however read through this thread it may be of some use

https://www.thirdgen.org/forums/tbi/...imum-idle.html

 

if it is bad dont run out and buy one unless they are super cheap, i know i have one of those laying around as well that ill never need.

 

It could possibly throw a code, but your ECM problem might prevent that from happening. Obviously if the IAC has a broken spring, or the pintle has grooves worn in it, it's probably time for a replacement. If I was really concerned the IAC might be bad, I'd probably just try another one. But then when I was driving my 3.1L, there were at least 5 or 6 complete intakes in the scrap aluminum pile of my room mates shop, so it wasn't a big deal.

Keep in mind the idle should be set while the car is in D. In park/neutral it'll probably idle around 1k rpm.

Check out this post... but ignore anything about adjusting the TPS, it's fixed and auto-zeroing on the 3.1. https://www.thirdgen.org/forums/post...00-post19.html

If you're worried the EGR is shorting the ECM, just disconnect it. It should throw a code that the EGR is disconnected but if it's the EGR causing the Code 51 (highly unlikely), that would eliminate that possibility. On my 3.1, the injector wiring was screwed up which kept popping the INJ and ECM fuses.

 

Ok sounds good. I'm gonna hook up the new ECM (with the egr disconnected for safe measure) and see what codes I can pull off it and fix any code issues gefore going any further.. will update you guys in a few days when it gets here. Thanks again for everyones help..