changing ecm
Thread Starter
Racer
Joined: Jun 2001
Posts: 435
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From: How did I get here? AZ
changing ecm
Well, I ordered a new ecm and am going to install it tomorrow. I can't seem to get rid of '33' code no matter what I do. I have replaced several mafs to no avail....still getting the code. Checked the burn off module output to the maf. Seems to be working. My car will run, but it is really rich. I have ported the intake, but i don't think that would require a chip change-would it? It idles kind of low ~500, but the tps volts are adequate .53v. I have no afpr. Fans do not operate at all on thier own, I had to ground the fan relay to get the main fan to work, auxiliary does not come on. How can you tell if the prom may be bad? If some one has a suggestion, by all means, jump on in there! I would really like to see my car running correctly.
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: changing ecm (want2drivemy85)
Before I go in depth on the MAF burnoff module (found only on '85 models), what exactly do you mean you checked the signal to the MAF from the burnoff? I did a bunch of testing on my faulty one and learned a few interesting things.
I'll check through my stuff to see if I have my old 85 chips up here. If I do, I can send you one or 2 for testing. The PROM *could* be bad but usually it would act a little funkier than you are describing.
Ported intake shouldn't mess with the MAF readings really at all. You are still going to be bringing in the same amount of air at idle for the most part.
If you are running really rich, I would pay attention to O2 volts/crosscounts, MAT temp, and CTS, with the coolant temp sensor being what I feel is the most important of them all.
I'll check through my stuff to see if I have my old 85 chips up here. If I do, I can send you one or 2 for testing. The PROM *could* be bad but usually it would act a little funkier than you are describing.
Ported intake shouldn't mess with the MAF readings really at all. You are still going to be bringing in the same amount of air at idle for the most part.
If you are running really rich, I would pay attention to O2 volts/crosscounts, MAT temp, and CTS, with the coolant temp sensor being what I feel is the most important of them all.
Thread Starter
Racer
Joined: Jun 2001
Posts: 435
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From: How did I get here? AZ
Re: changing ecm (HighHopes85)
HighHopes..Thanks! I will be installing a new O2 when I put the new puter in tomorrow. The present one was in while I had the carb on, I'm not getting a signal for bad O2, just figured I'd change it just in case its too fouled. The coolant sensor(in front of intake the inboard one) I changed last week. After you shut off the motor, arent you supposed to get a short burst of voltage to the maf from the burnoff module? Miine reads about 5.3 or so for a few seconds after shutoff. Cant remember which pin. Should I also relocate the MAT as i do this? What is the procedure for checking the O2? Also if you know how to check the burnoff module, please fill me in! All I know is that you are supposed to geta voltage 'surge' after shutdown in order to clean the filament. The fans aren't working, I get a perpetual code 33, and the fusible link for the ECM blew a while back(had it replaced) this is why I am suspecting the ECM.
Pro
Joined: Jul 1999
Posts: 741
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From: Eagle IDAHO
Cruise-In I Veteran
Cruise-In II Veteran
Re: changing ecm (want2drivemy85)
There is a procedure where you remove the plenum end of the MAF with it hooked up and you can see the sensor wire glow red for about one second after shutting the engine (key) off. Of course the engine is not running for this since the MAF has been pulled off at the plenum end. I remember running this test on my 85, and I think I found it in Tech Tips. Naw, I just checked, it's from my Helms.
Just an idea.
[Modified by NHVett, 8:29 PM 6/11/2002]
Just an idea.
[Modified by NHVett, 8:29 PM 6/11/2002]
Thread Starter
Racer
Joined: Jun 2001
Posts: 435
Likes: 0
From: How did I get here? AZ
Re: changing ecm (HighHopes85)
Well I changed the ecm today. This is what I got for my efforts-- the fans now operate..come on at 225. I am still getting a code 33. I reset the IAC, and tps. It now surges at IDLE. Installed a new O2. Drove the car for a few miles ..code still there. swapped in my old burn off module, and tried to test both of them. The test I used was turn ign switch to on, waited about 30 sec, switched it off and looked at the maf to see if the filament glows. well, I didn't see a glow with either module plugged in. Although one of them clicked about five seconds after I switched the ign off. I will try it again tonight when it is dark, so i will be able to see better. Anyone know of any way to trouble shoot a burn off module?
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: changing ecm (want2drivemy85)
I have been trying to find these posts of mine for the longest damn time. Well, I finally found them.
My idle problem was due to a bad poickup coil, but there is a lot of stuff about the burnoff module in them. A few of the pictures I had posted won't load anymore because I cleared them from my website. Grab a stiff drink and have a read.
http://forums.corvetteforum.com/zerothread?id=103935
http://forums.corvetteforum.com/zerothread?id=103722
http://forums.corvetteforum.com/zerothread?id=103626
Good luck. Notice that the burnoff *isn't* always supposed to burn off. :cheers:
My idle problem was due to a bad poickup coil, but there is a lot of stuff about the burnoff module in them. A few of the pictures I had posted won't load anymore because I cleared them from my website. Grab a stiff drink and have a read.
http://forums.corvetteforum.com/zerothread?id=103935
http://forums.corvetteforum.com/zerothread?id=103722
http://forums.corvetteforum.com/zerothread?id=103626
Good luck. Notice that the burnoff *isn't* always supposed to burn off. :cheers:
