OK, I think I'm getting closer to resolving the issue with the car. The new ECM arrived...have not installed it yet because I want to prove it's the problem before I disassemble half the dash to get to it. I ran the trouble codes and got a 15 (open coolant circuit) and a 30 (ISC motor). I also ran a diagnostic and for the coolant circuit, it's truly open if the reading is zero to 3. I got a reading of 48 which means the sensor is working.
I have to believe that what's happening is that the car is staying in "cold" mode and is dumping too much fuel into the engine. When the car is cold...first started and run down the road, for the first 2 or 3 minutes it runs great and then you can tell when it starts to run poorly. In the old days, the choke plate was to blame...but with this car, it has to be the ECM. It seems like it's not kicking out of "cold" mode (my words).
Thoughts anyone? Should I go ahead and try the ECM swap?

 

You shouldn't have to rip your dash apart at all. You can get at the ECM by laying on the floor on the passenger side and you can look up and get at all the screws, etc. For all it will cost I would replace the temp. sensor at the same time and set up the throttle position sensor to specs. If your EGR is good and all the Vac. lines have been checked then it should run pretty nice after. Set the timing after the new ECM is installed so it will learn the new values for that. Good luck...

 

Well, the "new" 4760 arrived and when installed, the car would not start. So, I had a 5120 that I removed from a running 81 Seville I parted out so I put it in and the car starts and seems to run alot better. Unfortunately, the weather kept me from driving more than around the block so we'll see what happens when I can run it for more than just a few minutes. Keep your fingers crossed!

By the way, if anyone has an ECC (climate control head) for an 81, I would be interested. Mine will not cooperate...fan runs on high at all times, even with the new ECM so I'm sure the heads no good.

 

Ok gang, the 5120 ECM seems to have helped but now for a new problem. The rear calipers were hanging up so I installed new since those on the car were OEM and the emergency arms were stuck partially engaged. Guess what...same problem...the rear calipers hang up after the car is driven a short distance. I also have a hard brake pedal with very little travel. That tells me that the proportioning valve must be sticking. If I park the car and let it sit for an hour or so, all is well and the process repeats itself.

My question is, is there a way to free up a sticking valve? Should I attempt to remove it and clean it in some way? My car is an 81 and I have not yet been able to find an 81 valve...lots of 82 and up...so I'd like to try to get this one working as intended.

Thoughts and ideas are welcome!

 

Another question...I've read where the 8-6-4 system can be disconnected by cutting a wire that leads to the transmission. Can anyone tell me what wire is to be cut and where it is. Thanks

 

Rather than cut any wires just unhook the MD solenoid connections (4) two on each valve cover. That will de-energize the solenoids and if you ever want to have it function again then just hook them back up again. Good to hear you are making some head way.

 

Ok, I have confirmed that the proportioning valve in the 81 is bad. Anyone have a new or good used one for sale?

 

Update - the 4760 arrived and was junk so I installed one from an 81 Seville and the car starts more easily and seems to run a little better. It still surges when running at about 35 mph but that's not my biggest concern right now.

I'm experiencing issues with the brakes that I hope someone can solve. I have replaced the following:
- Master cylinder (twice with new units)
- Proportioning valve (known good unit)
- All 4 calipers
- Rear hoses and almost every steel line
- Complete fluid flush

What's happening is after driving the car for about 5 miles, there is no brake pedal travel...it's firm...and all 4 calipers are fully engaged. It's as if I'm driving with my foot on the brake pedal. I cannot figure this one out. I've replaced everything that could be at fault, yet I still have an issue with the brakes hanging up.

If I let the car sit for a half an hour or so, all is well and I can restart the same process. Also, if I crack open any brake line for just a moment, all pressure is released and all is well.

Your thoughts and ideas are welcome. I am at my wits end!!

Update 7/4 - The brakes still drag after driving for about 4 or 5 miles so I've not solved the problem. But, I did try something else to see if I can narrow things down. I mentioned that cracking a brake line relieves pressure and the calipers no longer drag. I've also found that if I loosen the master cylinder from the booster...just one or two turns of each bolt...it also relieves the pressure on the calipers and everything is fine. One would then assume that the booster rod is either not returning to rest or that it's too long but I don't think either is the case because when I reattach the master cylinder, the pedal is OK and the calipers are released. I've experimented and loosened the master cylinder with the engine running...so there's vacuum in the booster...and with the engine off. Same results, the calipers release. Either things are not lining up between the booster and the master, or the master is no good. I put a little axle grease on the end of the booster rod...we'll see if that helps. By the way, the car has 30K original miles and the booster has never been replaced. In fact, I replaced the master only because it was 30 years old and I didn't trust it.
Again, your thoughts are welcome!

 

Or you can adjust the length of the rod to the pedal underdash. I've also seen misadjusted brake light switches cause enough pressure on this rod to not let the master bypass and release calipers.

 

I thought of the brake light switch too, however, simply loosening the master cylinder from the booster relieves pressure and releases the calipers so I know the problem is not with the switch, calipers or hoses. I stopped by a local garage where there are tenured mechanics and when I explained my problem, in unison, they all said 'brake booster'. This car sat for nearly 20 years and the plenum isn't releasing as it should and my pulling the master cylinder away from the booster allows the rod to reset. So, we'll put a booster on and see what happens...