Hi all,

I've got an interesting new problem with my 86.5 5spd. A couple of days ago, the car started stalling. Here are the symptoms: the car starts fine and has no issues until I come to a stop sign or light. At that point, it stalls and it takes 5-6 attempts to get it started again. During the unsuccessful attempts, the engine does turn over and it actually sounds like its starts but it dies immediately. On the 5th or 6th try, it starts, drives away and then no issues until it's been parked again for awhile.

This has only happened twice but it was on consecutive trips and I'm afraid to drive the car now because of the trouble I had restarting it. It's been hot here lately (90-100) and I had left the car outside before this started which I typically never do. Before I start blindly replacing pumps and relays, I'd love some advice on how to isolate the problem. Any help is much appreciated.

 

If you give it a large amount of throttle when it is reluctant to start, does that help ?

 

My 86.5 has starting doing this recently too. I'll be following this thread closely.

 

It's only happened twice and I don't think I gave it any pedal when trying to start it. I'll have to see if I can reproduce the problem and try that. It's an interesting hypothesis though since it may simply take five or six attempts to get the fuel pressure up enough to keep the engine running.

If I am able to reproduce the problem and giving it pedal makes a difference, would that indicate a bad fuel pump, relay, LH? My fuel pump does hum on a hot day - and not in a good way

 

pressing the pedal to the floor while starting will assist in clearing a flooding event

 

Dumb question here but what is flooding and what might cause the engine to flood?

 

Flooding = to much fuel to ignite, generally caused by excess fuel delivery or ignition failure while introducing fuel. Typically this does not happen under the conditions you described unless the initial stall is caused by ignition failure, then the starting attempts result in minor flooding until the ignition turns back on, or the high intake vacuum related to decelleration coming to a stop pulls in excess fuel.

Intermitant ignition failure can be pain to diagnose so start with the easier one. Start the car and let it idle for a few minutes. Shut it down and then check all of the vacuum lines connected to the fuel pressure regulators, etc. for any indication of fuel.

 

What Stan said, my thinking was you might have some leaky fuel injectrors......... foot to the floor does not introduce more fuel (like a carburettor engine) but just more air which helps clear the cylinders of excess fuel...

 

Thanks John. Working on an EFI car is relatively new to me but I should have remembered what happens when you step on the pedal since I've had the throttle body off before. My fuel injectors are pretty much brand new. I drove the car today and it didn't stall once. Drove really well in fact.

I have a crazy theory on what may have been happening. I've been doing some work on the A/C system and, as a result, there is zero refrigerant in it. Because my garage door opener had broken, the car had sat outside for a couple of days in 100 degree heat. Since the fuel cooler is basically inoperable, I'm wondering if the car was simply getting flooded because it had been tuned for cool fuel and not the very hot fuel that was in the tank.

I'm probably off the way off the mark, but it's pretty much the only thing that had changed before the problem started. And after finally being able to park in the garage last night, it seems the problem is gone. Maybe the car is just trying to tell me something

 

Very high under hood temepratures might cause fuel evaporation in the lines and a vapour lock.

This could cause a reluctance to start. This tendency is reduced by the return valve in the nose of the fuell pump, and the fuel pressure regualtor effectively retaining pressure in the rails after engine switch off, and this is turn should stop fuel vapourisation.

You can purchase a fuel pressure gauge from Roger Tyson which is a permanent fitment on the end of the passenger side fuel rail. The fuel pressure in the rail should be retained for at least an hour after switch off.

 

Thanks John. That's great advice and I think I will go ahead and order one of those. Do you think the fuel cooler is at all effective at preventing vapor lock? After my last post, I did some searching and read that it's true intent was preventing vapor lock but that some are doing without it altogether. Here I always thought it was there to cool the fuel going into the engine. I also read manufacturers started using an in tank pump to prevent vapor lock. Did Porsche use an in tank pump in some model years?

 

Yes, the intention of the fuel cooler is to......err cool the fuel but it is placed after the FPReg so not directly helpful in cooling fuel in the lines between front and back of engine.

The usual scenario for vapour lock is when the car is shut off when hot, hood closed, and under hood temps brew up... lots of heat damage to those poor injector connector wires, temp 2 wires etc. Also lots of heat into the fuel rails. If the pressure stays up during the initial cool down time, then the risk of vapour lock is much reduced.

Yes, Porsche did use an in tank pump as well as the external pump "for hot climates", but I am not sure if your 32v 86.5 has one. My 86.5 Euro 16v does not.

If you look at the main fuel pump terminals, if there is just the external pump then only one wire per terminal, two wires per terminal if an in tank pump is fitted.

Having said all that, the intake pumps are giving lots of problems, thought to be due to the addition of Ethanol to fuels, lots of people have removed it and have had no problems.

 

y - those plastic bits don't stand a chance in there. Is the heat under the hood less of an issue with the later cars and their electric fans? On some newer cars, it seems that fan will occasionally continue to run even after shutting down the engine. Not sure if that's the case on the Porsche or if it would cool anything other than the radiator.

By the way, the car stalled again today. This time it initially started up and drove fine for about 20 minutes. Then I parked it in the sun and came back 20 minutes later. The car started but stalled after a few seconds. I then tried starting it with the pedal to the floor and it started right up. Does that indicate flooding instead of vapor lock?

 

The S4 and later have a temperature switch at trhe back of the intake plenum that will bring on the electric fans even when ignition is off, when the sensor gets to about 90degC IIRC.

The 86.5 Euro 16v also have a similar setup, which switches on the electric aircon rad fan.

I don't know about the US 32v as the Euro verson of the 5 litre 32v are very rare in Europe. I've never seen one....

Yes, I would say you may well have a leaky injector(s), causing the flooding/stalling.

 

Looks like my issue was a bad battery ground strap. I didnt notice any electrical issues the first few times it died but then the gauges start acting up and warning lights appeared and the engine lost power. I did some searching and it started to look like a ground issue. Replaced the original strap, which had some signs of corrosion under the black plastic, with a $6 Pepboys ground wire, and it hasnt acted up since (about 5 test drives)