77 Seville still stalling at temperature

[mechanic80]

This is getting more than annoying.  My 77 Seville STILL falters and quits sometimes as much as 30 minutes or so into full operating temperature.  Waiting 30 to 40 minutes, the car will start right up and run for several minutes before usually failing again.  I  had cheaped-out and bought a NOS Airtex external pump which I'll be replacing with a Delco unit when I get it next week.   The one constant thing I've noticed is significant noise from the external fuel pump.  I have spark, the pumps have power and there's pressure in the FI system when I check the bleed valve.  It wants to start but won't until it has cooled down,  Brand new coil and module has made no difference. I put this thought out once again: could the pressure regulator be the culprit?  Is there a sensor that would prevent the engine from running in these conditions?  ECM rebuilt and providing power through a relay as it should.

[TJ Hopland]

Have you had it do this with a fuel pressure gauge connected?   In cases like this I have gone for a test drive with it duct tapped to the windshield so I could watch it while driving just to confirm that its not a pressure issue.    Since you notice a change in the sound I am thinking it could be an issue with the pickup in the tank. 

[TMoore - NTCLC]

I agree with TJ - some pressure at the bleed valve does not necessarily mean you have the 40 psi that you need.

Are pumps still audible when the stall occurs?  You had mentioned that you were going to verify the fuel circuit was still functioning when the engine stalls,  so I would be curious to know if the circuit is functioning or not. I am wondering if you have a bad pump, or if there is some blockage in the system that is causing loss of fuel delivery.

In all of your posts, I have not seen you mention that you replaced the fuel filter element  (canister located just forward of chassis mounted fuel pump) - you would want to do that after disturbing all of the lines.

The sensors in this system would not cause a stall - they are primarily designed to aid with the cold start function.

Let us know if the pump circuit is good at stall -

[Gene Beaird]

Norbert,

The fuel pressure regulator will usually fail one way or the other, rarely working for a while, then quitting.  They'll either stick so you don't get the pressure increase with engine load, or rupture, causing fuel to leak into the engine via the vacuum hose.  Testing is easy to verify.  Connect a fuel pressure gauge to the bleeder port and start the engine.  With the engine running, pull the vacuum hose going to the FPR.  The pressure should immediately increase.  If this doesn't happen, the FPR is stuck.  If you pull the vacuum hose off the FPR and get raw fuel in your hand, the FPR has ruptured. 

I'll note that on one of our cars, a 95 Caprice with a V8, I've had the FPR rupture 2 times, so it's not a rare occurrence. 

And one of the first things to do when troubleshooting driveability issues with a FI-equipped car is to attach a fuel pressure gauge to it, taping the gauge to the windshield and take a little road trip.  That's after you attach the gauge and verify the fuel pressure is the proper start/run pressure, and that the pressure changes when you disconnect the vacuum hose to the FPR. 

[mechanic80]

Thanks for the suggestions.  I'll have to find a pressure gauge that will connect to the bleed valve.  Being that it will cool down and run well for sometimes more than an hour, I thought maybe pick up coil or distributor speed sensor  might be acting up.    The fuel filter was the last thing replaced after the hoses were changed including the pump as well as the hose and pick up sock in the tank. The pumps are audible when cranking.  Am I wrong to suspect the ignition system?

[TJ Hopland]

The fuel pressure gauge will verify the fuel pressure when it acts up.   

With a little creativity maybe you can figure out a way to hook up a timing light so you can see it or turn it on when it acts up to see if you have spark when it acts up.   A tachometer hooked to the tach terminal on the distributor cap will tell you if you if the module end if things is working but won't tell you if the coil is good. 

If both those check out then you have look deeper into things like monitor the signals to the injectors.  Maybe one of the reed switches in the distributor is sticking and causing the injectors to stick on (don't know if that is even possible) or not fire.  I know they are batch fired in 2 groups of 4 so you would have to pick one from each set to get a good idea if they are firing like they should.   

[bcroe]

This is getting more than annoying.  My 77 Seville STILL falters and quits sometimes as much as 30 minutes or so into full operating temperature.  Waiting 30 to 40 minutes, the car will start right up and run for several minutes before usually failing again.  I  had cheaped-out and bought a NOS Airtex external pump which I'll be replacing with a Delco unit when I get it next week.   The one constant thing I've noticed is significant noise from the external fuel pump.  I have spark, the pumps have power and there's pressure in the FI system when I check the bleed valve.  It wants to start but won't until it has cooled down,  Brand new coil and module has made no difference. I put this thought out once again: could the pressure regulator be the culprit?  Is there a sensor that would prevent the engine from running in these conditions?  ECM rebuilt and providing power through a relay as it should.

One cause for this, is a marginal MAP sensor inside the ECU.  These can be intermittent too.  At first the engine will be fine with cold enrichment.  Then as enrichment goes away, the low output MAP will give too little fuel.  Best check is swap in a spare ECU, good idea to have for these cars.  I don't trust any "rebuilt" till I check it myself (is that one of mine?); could tell you some stories including the "good" ECU I got yesterday.  Bruce Roe

[Glen]

   The one constant thing I've noticed is significant noise from the external fuel pump. 

I have noticed that the electric pumps get very noisy when they are dry.  Your statement tells me that pump is not getting fuel. 

Just a WAG, but try driving without the gas cap.  It is possible your tank is not properly vented and it the pumps pull a vacuum in the tank that the pumps can not over come.  After sitting a while the vacuum bleeds off and it works again. 

Just a WAG

[bcroe]

If a gauge shows declining fuel pressure, it may be time to clean up the tank and the rest of the fuel system. 
Bruce Roe

[Gene Beaird]

Just a WAG, but try driving without the gas cap.  It is possible your tank is not properly vented and it the pumps pull a vacuum in the tank that the pumps can not over come.  After sitting a while the vacuum bleeds off and it works again. 

OR, when the car quits after driving a while, go loosen the cap and see if you can hear a 'whoosh' of air going into the tank.  Then see if the car will start and run again.  It could also be a loose connection in the in-tank pick up.

[mechanic80]

It never crossed my mind that it could be a vacuum in the tank that the pumps couldn't overcome.  I'll try this simple test at the next failure.  Loosening the cap should allow the car to start immediately if that is indeed the cause.  That certainly would explain the excessive noise from the external pump when the problem surfaces.  I really hope it's that simple.  BTW what's a WAG?

[Jon S]

Surprised nobody has mentioned Vapor Lock with this Ethanol-rich gasoline.  Would explain the noisy fuel pump and all.  If it  happens on extremely hot/humid days, my vote is Vapor lock.  Adding Marvel Mystery Oil to your gas tank will increase the boiling point of the gas and help minimize Vapor Lock.

[TJ Hopland]

Good thought on the tank not venting properly.  This would likely have a fairly complex for the era purge valve and such on the charcoal canister that is supposed to let the tank breathe.   If that is the issue a temp fix is take the smallest drill bit you have (1/16"?) and drill a small hole on the inside of the cap.  Don't drill all the way through to the outside, just the inside layer. 

I don't think its vapor lock. 

Cars with carburetors are more prone to it because the fuel pumps are usually mounted to the side of the hot engine in the hot engine bay.  The fuel in the carb is not under pressure which is on top of the hot engine in the hot engine bay.   The fuel between the fuel tank and fuel pump is under vacuum which makes the boiling point even lower not to mention if you happened to be on hot blacktop you got that heat source much closer to the fuel lines.   Later in the carb era cars with AC got a return line on the fuel pump that would always return some fuel back to the tank.  The idea here was it would keep a constant flow through the lines and reduce fuel temps and chances of vapor lock.  I suppose they figured AC equipped cars would have higher underhood temps while idling. 

A typical EFI car including this one has the electric fuel pump in the tank so the fuel is only under vacuum for a few inches vs the several feet of a carb system.  In the case of this car after the fuel is lifted out of the tank by the first pump it then goes into another pump that boosts the pressure.  Just like in the cooling system the higher the pressure the higher the boiling point is.   Once the high pressure fuel gets up to one end of the fuel rail the other end has the fuel pressure regulator on it.  The regulator keeps the rail at a the required for the conditions pressure and lets any un needed fuel return back to the tank so under most conditions there is quite a bit of fuel flow.   If it did vapor lock while sitting since the pump is still in good fuel when the pump cycles it would just push more fuel through the system and push the air bubbles back to the tank before you even tried to start it. 

[waterzap]

I forgot about the charcoal canister. If that is blocked, the tank wont breathe properly. Easy test is just to disconnect the lines to the canister. That should let in enough air into the tank. The canister is there to catch the fumes coming from the tank and then release them again when the engine starts. For my car, I just put a T connector in the line that comes from the tank. Plugged up the T when I was not driving. Did it help? Dont know, but I was sure to get enough air in the tank.

[Glen]

BTW what's a WAG?

Wild A** Guess

[mechanic80]

I took off the tank cap and applied a vacuum to the "inside".  It allowed air into the tank area.  Even though, it might not allow venting in actual conditions.  I'll try loosening the cap next time it fails.  If that doesn't do it, I'll vent the canister.  Will keep y'all posted on results.  BTW failure occurs at highway speed.  I rarely drive much in the city but it has never failed in city driving.  Additionally, I replaced the rear shocks with Gabriels and disconnected/plugged the vacuum line from the canister that supplied vacuum for the air pump.