I recently purchased an '81 Eldorado with 39K original miles. It had been in storage since '92 but I was able to get uit running with just fresh fluids and a new battery. I've owned several '81 to '83 Cadillacs and haven't run across the problem I'm experiencing in the others. The car runs rough...like it's working hard to get up to speed. I've noticed that the fuel mileage is half what it should be so I assume it's running rich and that's causing the rough running scenario. I pulled the codes and got a 15 and 30, open coolant sensor and ICS circuit respectively. Indeed, the idle isn't what it should be...sometimes it's way too high.
I think the issue may actually lie in the MAP sensor, however, I cannot find it. I know it's supposed to be behind the glove box but I've yet to locate it.
Has anyone else experienced the same problems with their car? I don't think the issue is with the 8-6-4 equipment as the car runs rough at startup. Compression is good in all 8 cylinders and I'm not losing any coolant so I know that much is good.
Any ideas?

 

Did you check the TP sensor? I have the same car and its been in the shop for three months with an ECM glitch, but I know the TP sensors go bad frequent and cause the same issues you are experiencing. Its connected near your injectors. To see if it is bad, simply pull out the fuse and see if its running better. They are like 50 bucks. Hope this helps-Roy

 

The fuse is right next to the sensor, by the way

 

I have the same engine and spent one heck of a lot of time on getting mine to run nice. But long story short get your ECM rebuilt and all will be right as rain. There is a company in Nashville that does them for around $189 bucks. autoecu.com Mine is running like it came from the factory now and I am very impressed with their work. I have a backup computer that I would sell you so you can still drive it while your main ECU is awol.

 

OK, an update on the Eldorado. I was lucky enough to find an 81 Seville parts car that had everything I think I need to get things straightened out with mine. Included in the purchase was the hard to find MAP sensor relocation kit, which consists of a long jumper cable that plugs into the existing connector behind the glove box. That then runs out to under the hood where the MAP sensor moved to high on the firewall. I made that swap, along with a new idle control motor and together, the car seems to run better, but not quite what it should be yet.

What I've now noticed is that the heater control module will not shut off. Even though I pressed the OFF button, the blower fan kept running. Interestingly, all of the fan speeds work, except that it will not shut off. So, I pulled the ground wire from under the hood. Any ideas on that one?

And, I checked the ECM that was in the Seville and it's a 2 year old rebuilt unit. Mine is Service # 1224760 and the Seville has 1225120 in it. Are they interchangeable?

 

Yes they will both run the car. The 4760 is the first gen. and the 5120 is the second gen. ECM. You might have some function not present with the 4760, like the econo minder or the diagnostic function on the climate control. It will however run the engine,etc. They are both used for the 368 with DFI.

 

GMparts direct have rebuilt ECMs for around 140 and ahat includes the core charge. They are very good quality.

 

Update - I have a 4760 ECM on its way. Hopefully, this solves the problem. Stay tuned!

 

One thing you are not taking into consideration is the Prom and Calpac chips. You will most likely not get these chips in the new unit you ordered. You will have to pull them from your old unit and put them in the new unit. That is why the price point is where it is. You really do want a new Prom chip as that manages all the DFI functions . At any rate good luck with the new unit.

 

Yep, I thought of that and made sure that the new unit has the chips. Now I'm like a kid at Christmas...I can't wait for it to arrive!