Porsche 914 1.7 - Stalls when hot... Help!

[rivs914]

I don't know if I already post this concern but still have it and do not know how to deal with!

I have this issue since a while and it is still not resolved. When I go for a ride, everything starts very nice and idles ok (with cold engine). When I drive it around the block, the car runs very great with correct performance. But after few miles, when the engine comes warmer (~30min), it begins to run very poorly and it begins to stall everytime I stop the car to a stop sign or red light. It is then very difficult to restart. It needs some "strategic" fuel pedal to get it starts again and a lot of luck to return back to home...

- The battery is almost new.
- The alternator is new
- The head temperature sensor has been replaced (twice).
- Fuel pump has been moved in the front

I did a complete restoration on the car in 2005 with a lot of major works and everything was in perfect condition and worked very well until this recent problem. I drove the car for couple of years without any problem.

Engine is still equiped with original fuel injection with Pertronix Ignitor Electronic Ingnition (which has been replaced recently too) and Bosch hot start relay kit.

I have checked the following:
- Aux air valve
- Vaccum hoses
- Pressure sensor
- Throttle switch
- All the wiring
- ....

I am a little bit lost now....

Do you have some hints to help me with my troubleshooting (vapor lock? clugged fuel filter? MPS, cold start valve, ECU... ?) Thank you very much guys!

[Dave at Pelican Parts]

What is the fuel pressure when it is in its failed state? Should be 29 PSI any time the engine is running. Lower than that would point to the fuel filter or debris in the tank/lines/etc.

Clean the grounds. Dirty connections can have higher resistance when warm.

It may also be that the head temp sensor resistance is staying too high when the engine warms up, leading to an overly-rich mixture.

A wide-band O2 meter would tell you if the mixture is behaving or going wonky. It should be on the order of 12:1 to 14:1 under most driving in our cars.

--DD

[rivs914]

Tks Dave.

I will check for fuel pressure during warm issue. In addition, I already have a gage permanently installed on left fuel rail. On a cold engine, I know that it shows ~28psi. However, if I would have low pressure due to fuel filter or restriction in the feed line, It would occuring even on cold engine no matter temperature?

The grounds you are referring is all aound (on the main harness) or specially on the battery and the ground strap?

Temp sensor has been replaced twice without any improve... I wondering if something can be wrong with ECU or ECU wiring. I have a "spare" ECU, should it be a nice try?

Tks!
Sebastien

[Dave at Pelican Parts]

It is possible for the pump to not work as well when it heats up, if it is marginal. It is more likely for debris in the fuel tank to plug the outlet after it has time to move around while you drive. It is also possible that something moves and kinks a fuel line, either supply (resulting in low pressure) or return (resulting in high pressure).

Grounds are the ones at the crankcase seam, under the relay board, at the battery, and between the transmission case and the rear trunk floor.

Your problem is unlikely to be the ECU, but swapping is a relatively easy test.

--DD

[Potomacmidget]

Originally Posted by rivs914

I don't know if I already post this concern but still have it and do not know how to deal with!

I have this issue since a while and it is still not resolved. When I go for a ride, everything starts very nice and idles ok (with cold engine). When I drive it around the block, the car runs very great with correct performance. But after few miles, when the engine comes warmer (~30min), it begins to run very poorly and it begins to stall everytime I stop the car to a stop sign or red light. It is then very difficult to restart. It needs some "strategic" fuel pedal to get it starts again and a lot of luck to return back to home...

- The battery is almost new.
- The alternator is new
- The head temperature sensor has been replaced (twice).
- Fuel pump has been moved in the front

I did a complete restoration on the car in 2005 with a lot of major works and everything was in perfect condition and worked very well until this recent problem. I drove the car for couple of years without any problem.

Engine is still equiped with original fuel injection with Pertronix Ignitor Electronic Ingnition (which has been replaced recently too) and Bosch hot start relay kit.

I have checked the following:
- Aux air valve
- Vaccum hoses
- Pressure sensor
- Throttle switch
- All the wiring
- ....

I am a little bit lost now....

Do you have some hints to help me with my troubleshooting (vapor lock? clugged fuel filter? MPS, cold start valve, ECU... ?) Thank you very much guys!

Are you still running points? I had similar problem. My points gap was too small. Car would start but once hot would stall. Also check timing. Good luck.