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cruffenach
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AUG 30, 02:55 AM
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Hey folks,
Recently became the owner of an '84 2m4, love this car to death and she's in great shape. Have been spending the last few months banging out problems here and there getting her in great condition, however one problem I have leaves me a little stumped.
CEL is on and I'm pulling codes 15 (Coolant Sensor - high voltage) and 21 (Throttle Position Sensor - high voltage). Both the coolant sensor and TPS have been replaced and the problem is persisting. I have checked the TPS and it's giving solid readings in its full range (both the new one and old one). While this has been frustrating, I do believe I have a lead. I remember reading in an older discussion someone mentioning having these codes and that the TPS and ECM Coolant Sensor both share a ground, and after reviewing the wiring diagrams for the car this is absolutely the case. I am hoping to get out there tomorrow and investigate the wiring, but if anyone here has had this problem and would like to add anything the help would be more than appreciated!
Thanks,
Cody
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fierofool
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AUG 30, 09:40 AM
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I'm asking a dumb question and has absolutely no reflection on you. Did you replace the correct coolant temperature sensor? The one with the oval head? Also, when measuring TPS voltage, did you check it at closed throttle? I don't know what the range is on the 84, but on the V6's, the closed throttle voltage should be 0.50 V with almost 5 V at wide open throttle. Seems like all Fieros should have the same range, but maybe not.
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theogre
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AUG 30, 04:19 PM
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If we assume you replace both of correct sensors and parts are working right...
First check/clean/fix all "grounds" bolted/screwed to everything. More so in the engine bay. Some "Grounds" are really return wires like ICM and O2. Check battery cables and other things for power. Why? Iffy power, ground, or both can cause weird problems.
May have same problem w/ Iffy ECM covered in https://www.fiero.nl/forum/...HTML/146363.html#p12
one part or section of ECM can cause multiple "codes" or never set a code or turn on CES and not set a code... Sometimes can do all three when you have an ECM scanner + ECM data stream can have problem too or seem to be perfect but have the other problems.
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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[This message has been edited by theogre (edited 08-30-2022).]
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cruffenach
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AUG 31, 02:09 AM
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| quote | Originally posted by fierofool:
I'm asking a dumb question and has absolutely no reflection on you. Did you replace the correct coolant temperature sensor? The one with the oval head? Also, when measuring TPS voltage, did you check it at closed throttle? I don't know what the range is on the 84, but on the V6's, the closed throttle voltage should be 0.50 V with almost 5 V at wide open throttle. Seems like all Fieros should have the same range, but maybe not. |
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Yes I did make sure it was the correct sensor, but I do appreciate you checking! If you were asking me that same question the day I got the car the answer might have been different haha. And I did check the TPS at closed throttle (both the original and new one, both are fine). Like I said, both sensors are fine, but the wiring on the Coolant Sensor had been cut and spliced at some point, so I am gonna double check that and make sure the connection is good. Otherwise I am gonna inspect that ground wire best I can without taking everything out of the car.
Might also see if I can get another ECM to run some tests per Ogre's suggestion!------------------
1984 Pontiac Fiero 2m4, Iron Duke 2.5L, Red
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cruffenach
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SEP 24, 01:44 PM
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Hey folks, have an update for you all and thankfully a good ending!
Per suggestions on this thread, I double checked that all my sensors were operating correctly and that all the grounds in my engine bay were good/clean. Still getting a CEL. However, upon inspecting my engine bay I noticed that the coolant sensor connector was not the original one and had been spliced on at some point, likely by the previous owner. After inspecting that... the wires were swapped! So I quickly cut and re-spliced the new connector that came with my new coolant sensor (double checking that the right wires were spliced together of course). And while this is definitely the correct wiring for the coolant sensor now, I was still getting a CEL.
So next step of business was removing all of the tape from the wiring that goes to the ECM and finding where the two ground wires (the one from the TPS and the one from the coolant sensor) splice together!
And for anyone in the future looking for this information: the splice is about 6-10 inches up the wiring from the ECM connector, so all you have to do is go behind your center console, remove some tape and track the wiring to the right number on the ECM connection (in my case it was number 11 on the black connector).
Unfortunately (or guess fortunately would suffice as well), the splice where the two wires meet was in perfect shape! Not touching any other bare grounds/wires and very good looking, so I made sure to clean it off and re-tape everything.
Now I was running out of leads here, as I was starting to exhaust basically anything I could think to check, which is when I unplugged the connectors and checked the ECM to see if the board contacts needed a good cleaning. And that's when I saw it! Once of the ECM contact points (specifically the number 11 contact point) didn't have any sort of conductor on it anymore!
You can see it pretty clear in this picture I took:
Now I probably could have fixed this myself and if any of you know how to this could simply be what your problem is, so be sure to check it! But because I knew my ECM was in rough shape already in other areas, I had new one on the way. Upon getting the new ECM, I plugged her in, reconnected the battery and started the car up.
Boom! No more CEL! Runs like a champ now too. And an unexpected side affect of this new ECM, my car now cold-starts almost immediately. Where as before, if it sat overnight I would have to sit there cranking for a couple minutes before it would start!
Should also note that when your transfer the PROM from your old ECM to the new one, make sure there isn't any foreign gunk on the pins of the PROM or it will create weird issues (in my case I could not use the ALDL to check codes or anything and my CEL light was flickering faintly nonstop). So just gently clean the pins off and be careful not to get anything else on them or bend them!
I appreciate all your help in suggestions and I hope my summary might help one of you with a the same or a similar problem.
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1984 Pontiac Fiero 2m4, Iron Duke 2.5L, Red
[This message has been edited by cruffenach (edited 09-24-2022).]
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Patrick
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SEP 24, 04:09 PM
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Great report on your troubleshooting efforts! I wish everyone would do this. Congrats on finding and fixing the issue!
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cruffenach
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SEP 24, 11:46 PM
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