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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #1
Hello Fellow Caddy Enthusiasts,

My '81 Coupe is quite temperamental. She is misfiring, but intermittently. I took her out this morning, and she was fine. Stopped and started her several time with no issue. However, after lunch, she was misfiring terribly, and I had to have her towed. My check engine light comes on and off from time to time; when I check to see what DTCs the computer has, I only get "70", which I believe means no DTC at that time. I'm stuck, and don't know where to start. If anybody could offer any suggestions, I'd be quite grateful.

Thanks.
 

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1980 FBC
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979 Posts
If it were my car I'd reseat the ECM connectors along with under hood connections of sensors.

Check the MAP sensor vacuum line for restrictions.

Other than that just treat it like any older car when troubleshooting.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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1,473 Posts
I think your problem is in the ECM.. I Had a power transistor that drives one injector go bad. there are two of them in there.. I was lucky enough to have someone point me in the right direction and I change the bad transistor and it fixed the problem..
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #4
ECM is on order. Thanks guys, I'll let you guys know if that remedies the situation. I appreciate you guys being so quick to reply!!
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #5
I installed the new ECM, and now she won't start. She cranks, and all of the lights work. I tried to check for any DTCs, but she only displayed "..", and nothing else. I'm not sure where to go from here, any suggestions?

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So, upon further research, i found that the ECMs are not interchangeable. I found several videos that said they were, however, I swapped the PROM chip from the 1225120 ECM, into the new 1224760 ECM. I'm worried I may have damaged the PROM now because of that. Would that be the case, and if so, where can I purchase a new one?
I appreciate all of your help, as I'm extremely desperate now.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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1,473 Posts
Can you try to put the old ecm back in and see if it starts? If it does start I would think to only replace the ecm with the same number.. Find someone that repairs your old one.. What ever you do don't get rid of your old one...
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #7
Autozone says they can rebuild my original one, I'm going to give that a go. Do you think I'll have to find a new PROM as well? I'm not having much luck finding one. If I were to locate a new PROM, I'd purchase it just to be safe, can you recommend where to purchase one?

Thank you!
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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1,473 Posts
Go to car-part.com and put in your car stuff and look for a engine computer. they will list them and the distance from you that it is.. These are used and I feel the best way to fix your problem. they will come with a prom , but I don't think its your problem.. I just did a quick search and most were less than $100.. Let us know how you make out...make sure it's the same number as yours..
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #9
I've found ECMs, less the PROM chips. I've spoke to Jerry over at Cadillacs Only, and he has the entire unit, chips and all. He wanted 250, which seems to be almost double the prices I've found of ECMs without the chips. I've been calling all over the country, and haven't had much luck locating a prom chip. Thanks for the car-part.com referral, I'm making calls now. I've decided, as a last resort, she will be getting big block. Hopefully it doesn't come to that, but I really want to get her back on the road. ASAP.
I'll keep you posted, and your guidance is greatly appreciated.

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drmenard- you're the man. I located a part, and was able to have the vendor provide me with pictures of the unit, with the PROMs included. Hopefully this resolves the crisis.

-thanks again
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #12
The ECM was only $93-- cadillacs only wanted $250, and wouldn't even process the order until, "the end of the week or so". I found Ajax, out in Coachela, CA, which is about 100 miles from me. They UPS'd the ECM the day I ordered, and I had it the next day. Car-part.com is the way to go, for sure.
 

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84 Coupe w/500
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5,665 Posts
I didn't like when I called Cadillacs only either. Seemed like they were too good to move fast. Just didn't seem interested.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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1,473 Posts
They were just hoping that you did not know where to go to get a ECM and you would beg them to send a ECM to you... Then they would get one from car-part.com and send it to you and make $150....
 

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1981 Coupe DeVille 8-6-4
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9 Posts
Discussion Starter #15
Yeah, Cadillacs only did not seem interested at all. I offered to pay extra, if he were willing to read me the broadcast codes from the PROM chips. I wouldn't doubt it one bit that he would order the part, mark-up the price, then ship it to me; that is why he could't give me the codes or a ship date. Car-part.com is the way to go, BY FAR!!
 
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