eProm causing erroneous codes? (Page 1/1)
c4hammer JUN 08, 07:56 PM
A brief background:

I just purchased an '88 GT, with the 2.8L and 5 speed manual this past weekend. No moonroof or t-tops. The engine idles high, between 1.5k and 2k, so I'm assuming I need to deal with EGR valve/tube/solenoid.

In addition, when driving it home the first time, I turned on the A/C, and got a little smoke through the vents and heavy exhaust fumes/smell. Running A/C on Max helps, but I've been just leaving the windows down even though it's HOT right now in Texas.


So the real point of this post -- because I had a couple things going on, I picked up a scanner that could handle OBD1. I've got a whole slew of issues noted: EGR, MAP, voltage high for too long, EPROM incorrect, Oxygen senor, and a few more that are error derivations of the EPROM/ECM. My question is, if someone has already installed an aftermarket PROM, would it cause incorrect codes? Or do I really have that many issues to tackle?
Mickey_Moose JUN 08, 09:01 PM
Well for one thing, the EPROM code should be on the label on both the ECM case and on the EPROM itself. Generally it is a 4 letter code, AKYN for example, but there are also some 3 letter codes.
Patrick JUN 08, 10:05 PM

quote
Originally posted by c4hammer:

In addition, when driving it home the first time, I turned on the A/C, and got a little smoke through the vents and heavy exhaust fumes/smell. Running A/C on Max helps, but I've been just leaving the windows down even though it's HOT right now in Texas.



Read this thread before you burn up your Fiero!

Heat/AC box cleaning, again...

[This message has been edited by Patrick (edited 06-08-2023).]

Dennis LaGrua JUN 09, 11:04 AM
Erroneous codes could be the result of a bad ECM. They do go bad.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
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theogre JUN 09, 01:35 PM

quote
Originally posted by Patrick:
Read this thread before you burn up your Fiero!

Heat/AC box cleaning, again...


could be that... smoke and smell help saying that.
Also if heater core leaks coolant... could seem to smoke but different smell. Plus often leak coolant on P-side floor when core is bad.
theogre JUN 09, 02:34 PM
ECM w/ Bogus "Codes" is often bad "Grounds." Some labeled Grounds even by GM are not real ground but return wires for some functions like "1 wire" O2 sensors.

Find and fix all grounds in engine bay and use silicone or permatex green brake grease to "seal" them and won't "eat" plastic and rubber.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

armos JUN 09, 08:55 PM
Definitely check for buildup of old leaves in the ducting as mentioned above. My car was loaded with them and they can start to burn as described in that thread.

If you have any of the "5x" codes then I'd ignore the other codes until those are fixed, because they are messing with the sanity of the ECM.

If you have code 53 (system over voltage) then get a multimeter and check the voltage of the battery circuit while the car is running. This code is set if the ECM detects over 17.1V, which is excessive. I don't know how much input voltage the ECM components are specced to tolerate before they'd be damaged.
If your meter agrees that the car is running on over 17V, the other error codes might not be reliable. Fix the voltage first. Replace the whole alternator or test/troubleshoot it and at least replace the voltage regulator in it.
If you have code 51, this means the EPROM is failing the checksum, which means it is corrupt.
If so then you need to get into the ECM. Remove the shift knob, screws from underneath the ashtrays, get the shift console out. Then pull the top of the large center armrest piece towards the front of the car and it should tilt forward and come out, unless there's screws I've forgotten. ECM is behind where the map storage door thing is.

Open the rectangular door on the ECM. The EPROM is the wider (24 pin I think) chip, in a black plastic carrier on the driver's side of the ECM. Note the orientation of the EPROM - you have to plug it back in the same way. There's always a notch or a dimple on one end of the chip itself (not sure if it's visible inside the plastic carrier). Pull the plastic carrier to remove the chip and carrier as one piece. Look at what markings are on it. There should be a code on it as mentioned above.
If my info is correct than the factory chip for an 88 Federal 5spd V6 should be AKYN3442, and factory chip for California cars should be AKYP3447.
Assuming it's the correct chip then you don't need to remove it from the carrier. Doing so may lead to damaged pins, it's not easy to get out. I swapped to an older chip carrier from a 1984 ECM on my car because it was much easier to deal with for me.

Plug it back in, making sure the orientation is correct. If you plug it in backwards it will fry the chip. Try again, hopefully reseating it will have fixed the code 51. I've had this happen a couple times on my car and had to reseat the chip, but that might be because I've messed with it a lot.

When you first turn on the key, the "check engine" light should turn on, then blink off for an instant, then turn back on and stay solid. That blink tells you the ECM is functioning (but not necessarily happy).

[This message has been edited by armos (edited 06-09-2023).]

c4hammer JUN 10, 11:46 PM

quote
Originally posted by armos:

Definitely check for buildup of old leaves in the ducting as mentioned above. My car was loaded with them and they can start to burn as described in that thread.

If you have any of the "5x" codes then I'd ignore the other codes until those are fixed, because they are messing with the sanity of the ECM.

If you have code 53 (system over voltage) then get a multimeter and check the voltage of the battery circuit while the car is running. This code is set if the ECM detects over 17.1V, which is excessive. I don't know how much input voltage the ECM components are specced to tolerate before they'd be damaged.




Thanks everyone -- I did indeed have the buildup in the blower/heater element box. I've clean as much as I could without taking it apart, and I'll be doing that long before I need to use that heater element.

That doesn't seem to change the exhaust smell in the cabin, so I still need to track down potential a/c system leaks or exhaust leaks.

Thank you so much for the 5x codes info, armos -- that's where I'm starting on the code troubleshooting.

Patrick JUN 11, 12:30 AM

quote
Originally posted by c4hammer:

I've clean as much as I could without taking it apart, and I'll be doing that long before I need to use that heater element.

That doesn't seem to change the exhaust smell in the cabin, so I still need to track down potential a/c system leaks or exhaust leaks.



Keep in mind we're not talking about a "heater element" that gets hot. It's the resistors for the fan motor that get hot. If you run the A/C on anything other than the fastest speed, the resistors are being used by the fan motor... and getting hot.
c4hammer JUN 12, 12:33 AM

quote
Originally posted by Patrick:

Keep in mind we're not talking about a "heater element" that gets hot. It's the resistors for the fan motor that get hot. If you run the A/C on anything other than the fastest speed, the resistors are being used by the fan motor... and getting hot.



Gotcha Patrick, I was looking at the resistor coils and thinking heater elements. I'll be sure to take care of that buildup.