76 Seville issues

[mechanic80]

     I just sent off the ECM from my 76 Seville for rebuilding after several no-start situations where the car was up to operating temp but the fuel pumps ceased working.  At first it would happen while running (hesitate, stumble then quit) but to another driver so I never actually experienced the problem.  Most recently, I personally experienced a no-start after a short shut off to pick up roadside mail delivery.  I could hear that the fuel pumps did not turn on for that second before cranking the engine.  Every time, it would start after cool down (30 or so minutes) as if it were vapor lock, but that's unlikely as the earlier failures happened on 70 degree days.  I have prepared the fuel pump circuit for relay operation as suggested in several threads on this site.  Is there anything else that might cause this no-start?  The original ECM had 109K.

      Are the two wire temp sensors a cold start function or a hot start function?  The engine does not overheat, in fact it only just reaches operating temp with the A/C on here in New Mexico.  Pumps have been replaced as well as hoses and fuel filter.  Any thoughts?  Something I may have overlooked?

      I'll be getting to the timing chain change soon.  Does the oil pan need to be dropped to do this?  Any tips on that operation?

[waterzap]

The two temp sensors are only used when the engine is cold. Once the car is warm, does not come into effect anymore.
Car cannot get vapor lock, that’s really only an issue with mechanical pumps. This car has two pumps, one internal to the tank, one external. I think your ecu probably still isn’t good. You can rewire the pumps to run off the fuse box. Be careful though. The pumps wont switch off if you don’t switch off the ignition.
I also have a few extra ECU’s if you are interested. On some of them the pump circuit works, on some they don’t. But its always a good idea to have an extra ECU for these cars. If for nothing else than troubleshooting.
My money is on the ECU.

[Gene Beaird]

    <SNIP>

      I'll be getting to the timing chain change soon.  Does the oil pan need to be dropped to do this?  Any tips on that operation?

Waldo did a wonderful WIP here:

http://forums.cadillaclasalleclub.org/index.php?topic=118488.0

[waterzap]

Also, Bruce has a circuit on his site to rewire the fuel pump relays away from the ecu to externally. Save your relays.

[waterzap]

Waldo did a wonderful WIP here:

http://forums.cadillaclasalleclub.org/index.php?topic=118488.0

Thanks Gene. The Seville is gone, but doing sort of the same with Toronado now.

[mechanic80]

This sounds like a broken record.  The weather is warming up and we took the 77 Seville out for it's first real trip of the year.  On the way home, once again, we felt that "stumble" which might be ignition or fuel.  Pumps have been replaced, the FI system is redone, new distributor in place as well as a rebuilt ECM.  Granted,  that "stumble" might have been because of a heightened awareness and fear of it happening again (read: imagined) but this is really getting to me.  I'll take her out again when I have the time to wait an hour for her to cool down and operate properly (although it never really gets hot) and see if it really does it. or if the distributor replacement actually did the trick.  I'll keep you all posted.  I'm at the end of my rope here.

[TMoore - NTCLC]

Mechanic80 -

If it is just a "stumble" while driving, you might want to try switching out the TPS switch.  I have one that must have a dead-spot on it, and once in while, I will get it in just the right spot that the engine will briefly cut-out.   Took me a lot of trial and error (different ECU, rebuilt distributor, new sensors, new pumps) to finally discover the issue, and when I did, it was actually by accident (I had switched the TPS to a different car trying to resolve a bit of rough idle, when that car suddenly developed the engine cut-out issue).

This will not likely resolve your hard warm start issue, but if you have a temporary stumble, it might be something to look into.

[bcroe]

The weather is warming up and we took the 77 Seville out for it's first real trip of the year.  On the way home, once again, we felt that "stumble" which might be ignition or fuel.  Pumps have been replaced, the FI system is redone, new distributor in place as well as a rebuilt ECM.  Granted,  that "stumble" might have been because of a heightened awareness and fear of it happening again (read: imagined) but this is really getting to me.  I'll take her out again when I have the time to wait an hour for her to cool down and operate properly (although it never really gets hot) and see if it really does it. or if the distributor replacement actually did the trick.  I'll keep you all posted.  I'm at the end of my rope here.

The Throttle Position Switch on 70s EFI is completely different from later years.  I have never seen
a 70s TPS fail.  You can check it with the "21 pulse" test.  Just turn on the key, and slowly open the
throttle.  You should hear the injectors click about 21 times.  Bruce Roe

[bcroe]

If that is the same ECU tested last year, you could send it here & I can swap a different
one.  Bruce Roe