77 Seville cuts out

[mechanic80]

Well, I had hoped that rebuilding the ECM would do the trick but the Seville is still stalling out when at full operating temperature. 
The  external fuel pump can actually be heard to falter (I always thought it was too audible) with accompanying stumble from the engine and progresses to full out failure.  Letting the unit rest for a while (30 minutes or so) allows the pump to operate again until it gets to temperature and then stumbles and quits.  It took two hours to get home from work yesterday; 25 minutes driving and 90 minutes of down time.  I did get a NOS Airtex pump on the cheap and thought that might be the issue.  Also thinking of wiring up a "tell" circuit/light to show if the signal from the ECM is present even as the pump fails.  That should indicate if it's the pump or the ECM signal.   I've added the relay to the pump circuit to ease the load on the ECM.  Any thoughts?  This is really getting frustrating.
mechanic80

[Dave Shepherd]

2 pumps on this car as you know, to pinpoint which or both is an issue get a test lite on the connector the the chassis unit see if it loses 12v when it quits, if not and the pump dies obviously the pump is failing, do the same for the in tank pump.

[mechanic80]

Having replaced both pumps, and the in-tank unit being a Carter, I'm betting on the frame rail pump being the culprit.  Like I mentioned, I'm going to devise a "tell" lamp to show power and if there's power but no pump activity, game over.  Since the pump is tucked within the rear wheel opening,  I thought a visual clue would be best.  Just a thought, is there any possibility of the pressure regulator being the issue?

[TJ Hopland]

Did part of your ECU rebuild include the modification to an external fuel pump relay?  I read that the fuel pump circuit in the ecu was a weak point but easily repaired and modified to use an external relay so it won't happen again.

[mechanic80]

Yes, that was part of the modification.  Now i try to get the Seville to act up again and with the telltale pilot light I can determine the cause of the stalling.

[TJ Hopland]

Maybe also if you have a tachometer rig that up so you can see it in the car.  That way you can confirm that you are likely getting spark when it cuts out.  The tach terminal on the distributor cap is the feed to the coil so if that still has a signal that eliminates the ignition module and pickup coil as possible problems.

[waterzap]

Stupid suggestion. But my Seville ran so much better when I replaced the ignition coil.

[mechanic80]

Not a stupid suggestion.  I've been concentrating on fuel delivery and the problem could be ignition.

[waterzap]

I also had an ecu that would only give me problems when the car is warmed up.
Do you have a spare you can plug in for daignostics?
Also, re route the pumps away from the ecu to the fuse box. All you need to do is plug a wire in the fuse box, take it to the back. The wires for the pumps come from the back, under the trunk. You will see a plug there.
The current basically runs from the inner pump, to the outer pump. Back to front.

[mechanic80]

Well, it's been several weeks since the Seville has been out.  I took it into town to work and no problems as usual.  On the way home, after reaching full operating temperature, it stalled out again and restarted after a 45 minute cool down allowing the rest of the trip home.  This is getting old.  New coil, ignition module, fuel cap, rebuilt ECM (fuel pump operating as designed) pump relay modification and hoses.  At this rate I think I might swap the engine for a '74 Pinto 4 banger.  I'm at a loss.

[TJ Hopland]

When its dead have you been able to verify you have the basics?  Fuel pressure, injector pulses, and spark?

[bcroe]

Well, it's been several weeks since the Seville has been out.  I took it into town to work and no problems as usual.  On the way home, after reaching full operating temperature, it stalled out again and restarted after a 45 minute cool down allowing the rest of the trip home.  This is getting old.  New coil, ignition module, fuel cap, rebuilt ECM (fuel pump operating as designed) pump relay modification and hoses.  At this rate I think I might swap the engine for a '74 Pinto 4 banger.  I'm at a loss.   

That certainly sounds like an ECU problem, have I tested it before?  Sometimes they have a weak MAP
sensor, delivering enough fuel with cold enrichment, but then going too lean after warm up.  Should be
easy to see on my tester.  A spare ECU swap would find out also; any 76-79 Seville ECU is close enough
for this.  I don't trust any "good" ones till I test them, though.  Bruce Roe   CLC # 14630

[mechanic80]

Bruce, I'm going to send my recently rebuilt ECM to you for testing.  It's worth a try.  I have your address and I'll send it parcel post.

[Driver8]

Hey mechanic...

You won't regret getting that unit over to Bruce Roe for the peace-of-mind of testing, and/or needed repairs. My '79 had constant rough idle and hesitation/bog from start or at cruising speeds.

I was lucky to live close enough by to drive out, meet him and see his setup. Bruce is a very smart & talented man. He did a fantastic job of pin-pointing the problem (failing MAP sensor), explaining everything and 100% resolving the issue. After he installed & adjusted his own designed modern MAP sensor, my Seville is running like a new car.

Tonight, I will complete his external fuel pump relay mod. Would have done it sooner, but only had solder around for residential water lines. Now have my electrical Rosin core tin/lead solder, so good to go.

Good luck with your Seville.    Mark~

[waterzap]

I am 99% sure this is the ECU. Try another ECU.

[mechanic80]

I just installed a reman distributor from PartsGeek as well as a NOS AC/DELCO external fuel pump.  The pump is much quieter than the "replacement" pump that was recently installed.  I drove the car to work yesterday and back home with no falter or cutting out as in the past.  To be fair, it is getting cooler here in New Mexico and the car may not have reached temperatures it had in the recent past when it did cut out. 

The timing pointer that I'd been looking for seems unobtainable, so I bought timing tapes from Mr Gasket to install when I can determine TDC and fabricate a needle to mark it.  If these fixes solve my issues, the last problem is getting the cruise control to function properly, but that's a luxury I can wait for.

[bcroe]

The timing pointer that I'd been looking for seems unobtainable, so I bought timing tapes from Mr Gasket to install when I can determine TDC and fabricate a needle to mark it.  If these fixes solve my issues, the last problem is getting the cruise control to function properly, but that's a luxury I can wait for.   

That timing pointer is used on all Olds V8s around those years in many brands.  Certainly
can be found in junk yards, I have a few. 

Does a 77 have the box on the speedo cable for cruise, or does it use the optical pickup
on the speedo like the 79?  Bruce Roe

[mechanic80]

I don't see a box type of transducer.  Actually, I can barely see the speedo cable!  I thought the FI pointers were different.  I was wrong.  I only managed to find one olds 350 in a you-pull yard here in Albuquerque lacking a water pump and timing set up (can't find a good deep dish pizza either.)  Let me know if you can part with a pointer, and how much.
mechanic80_2000@yahoo.com   

[TJ Hopland]

The only reason I could think of for the timing mark to be different is if the specs are different for the FI than carb's.  I know in the 77-80 era they were doing odd things trying to meet emissions.   Seems like a 78 425 they wanted you to time them to something like 20 at 1200 rpm or something like that so those had a longer gauge than the earlier ones that were set to something like 8 at idle. 

The tape works fine just be sure you are using the correct tape for the pulley or balancer diameter you are putting it on.  Seems like I got bit on that one time.  A 1/2" diameter difference makes a difference.

I think 77 was the change year for the cruise for Cadillac and the Seville seemed to be the first to get all the new electronic do dads.   They got rid of that gearbox that mechanically operated valves to control the actuator.   They put an optical pickup on the back of the speedometer head.  This sent a signal to a electronic control module under the dash.   The module operated either a vacuum solenoid or a vent solenoid to control the actuator.   I'm pretty sure the service manual had a decent step by step process to trouble shoot the systems.   As I recall the module and optical sensor parts were pretty reliable, issues were usually the same as earlier systems with vacuum leaks and switch problems.