Hot Starting Problem

[Charlie V]

82 911 SC Targa. I am having hot starting problem. Replaced fuel accumulator, but no change. Pressure test OK. The fuel pump relay is warm. When I give it a hit, it works. When I replace it, there is some improvement. Could it be the relay socket?? Wiring connections?? Or??

Tx.

[Early_S_Man]

Chaarlie,

Yes, it could be corrosion inside the socket ... examine very closely with bright light after pulling out the replacement relay!

If you want to clean ... use 9% pickling vinegar and Q-tips, followed by rinse with distilled water and compressed air to blow dry. After problem is resolved, for sure ... apply silicone grease such as Dow Corning 4, 111, or 112 to socket and relay pins.

[Paulporsche]

Make sure the segments of the pins on the relay are splayed out a little so there is good contact.

[jax]

There is a check valve in the fuel pump, which is a removable fitting on
the same end as electrical connections. About $20-25. Typical symptoms
as you describe if cold start is good. Warm FP relay no problem unless it is HOT. Regards, Jax

[Charlie V]

Pressure tested last week and it was OK.

Tonight I ...........cleaned all the relay sockets. Qtips and lacquer thinner. Had to trim off most of the cotton end so it would easily fit the socket opening without forcing it. Took a box cutter to "open" the male ends on the relays. Put on dielectric grease and plugged them in. Seems to be better. Tomorrow will be the test when everything is hot. I'll let you know how it goes.

Interesting aside.......the fuel pump relay has a Porsche part number and it is made in China. A replacement H3 bulb for the driving lamp was made in India.

Thanks for your input!!

[millhaus]

Charlie,

I have a similar problem. The car runs great but if I drive for a short time 5-20 minutes and stop. When I restart it the starter spins but no gas. If I switch around the relays, it starts. Sometimes this takes up to 15 mintues of switching around the right combo to fire it up. (relay cools down?)

What I notice is that some of the relays stop working and must be stuck open. I know this because I use the power window relay as the tester to see if the relay is working. All of my relays are old and I ordered new ones. I am suspicious that the fix will be this easy. I think something is causing the resistance to be higher than normal and temporarily heats up the relay causing it to stay open. When the relay cools it seems to work again. I have kept old "non-working" relays and used them later and it worked fine.

Pelican has a HOT START RELAY (bypass) which they says fixes this problem but the tech article attached wasn't very helpful. Can anyone explain or theorize why these relays are heating up?

Thanks

[Paulporsche]

Millhaus,
If your fuel pump is getting close to its life and/or if you have a clog in the fuel line somewhere, the pump will work harder, draw more current, and heat up. Check the pump and see that it is not drawing significantly more than 5 amps.

[millhaus]

Paul,

Thank you that is some of the best advice I have heard regarding this problem and it makes sense.

Check the line for blockage could be a big task. Any thoughts as to where to start? Front fuel pump?

What about the fuel pump check valve? Would that contribute or cause this problem?

Thanks

[Charlie V]

I just repalced my fuel pump and check valve. Car runs much better, but not perfect - needs to have mixture adjusted.

When I tested the amp draw on the old pump it was 5.71 amps. Spec is between 4 and 6 amps. Close enough to the upper limit that it was time to go.

The new pump is the same Bosch part number that came out of the car. I picked up from a local shop specializing in Euro cars. This is the kicker - the new pump is for a 1974 to 1979 VW Rabbit. Comes with a check valve. Price was almost 50% of what a local Porsche shop wanted.

[Paulporsche]

Millhaus,
There is a screen @ the bottom of the fuel tank. These can get clogged and also deteriorate w/ age. Also, your fuel filter may be old/clogged. I would check those 2 things first.

Start problems such as those mentioned are quite often caused by either the fuel accumulator or fuel pump check valve, as others have said.

[no substitute]

When the fuel pump check valve is bad the car will typically start after about 30 seconds of cranking. What brand of ignition box do you have?

[millhaus]

I tested the voltage to the fuel pump and checked the relays. They are all good but the car will not start now even at cold start. It just turns over.

I am getting 12 volts to the fuel pump but when I jump the relay and bring power right to th efuel pump it works sometimes and it doesn't other times I try.

It would be simple to guess that it is the fuel pump but when I tried to go from the battery directly to the fuel pump to make sure there is no wiring problem from the fuse box to the fuel pump, I got a BIG spark off the battery post. My thought was that it is a bad ground since I got the spark.

I did not disconnect the leads from the fuse box to the fuel pump when I did this. Is that the reason for the spark or would you guess that there is a bad wire?

I have two days before my DE event!!

Thanks

[Early_S_Man]

Per spec book ... the CIS fuel pumps are allowed to draw up to 8.0 Amps before replacement is necessary!

Some here have reported finding up to 16.0 Amps draw on a worn, whining pump ...