Warm/Hot Start problem

[ausgezeichnet]

I’ve read about a lot of hot start problems but can’t find my exact scenario.

It cold starts fine and runs fine even after it is warmed including idling, up as long as I don’t turn the ignition off. If I turn the car off and then try to start it again I have to give it a little gas to get it started and continue to give it a little gas to keep it idling. Then after hot starting and I drive it for about 1 or 2 minutes it starts idling fine again. In order for it for the hot start problem to go away it has to cool down significantly.

Could this be a bad WUR? I plan of having the fuel pressures checked after we can leave the house again and we are done with this Coronavirus.

[boyt911sc]

Mike,

Your problem is residual fuel pressure loss. I will give a good tip. Read UKinUSA’s recent post about exactly the same problem you are having. And send him a PM. He will be eager to help you.

If you don’t have a pressure gauge, you can test your fuel accumulator by performing a very simple test procedure found in Steve M. (UKINUSA)’s post.

Tony

[356911930]

You should check the fuel pressures your self. The fuel pressure gauge kit is about $100 and the test is straight forward. I'm guessing that when you test you will find that the, I think it is called, residual fuel pressure test. Where you monitor the closed system to record the bleed-down rate. It must meet reasonable pressure after so many minutes. If it does not hold pressure you probably have a leaking fuel accumulator, or a leaky check valve at the fuel pump.

You can test the fuel accumulator by removing the fuel line at the bottom of the fuel accumulator. Little or no fuel should come out. If a lot comes out the fuel accumulator should be replaced.

But I would check the fuel system pressures with your new gauges first ;-)

Tony really knows what he is doing so I would follow his advise before my shade tree approach.

Rahl

[ausgezeichnet]

Thanks guys. Very helpful. I bought a fuel pressure tester several years ago but never used it. Hopefully I have the right connector.

[boyt911sc]

Originally Posted by 356911930

You should check the fuel pressures your self. The fuel pressure gauge kit is about $100 and the test is straight forward. I'm guessing that when you test you will find that the, I think it is called, residual fuel pressure test. Where you monitor the closed system to record the bleed-down rate. It must meet reasonable pressure after so many minutes. If it does not hold pressure you probably have a leaking fuel accumulator, or a leaky check valve at the fuel pump.

You can test the fuel accumulator by removing the fuel line at the bottom of the fuel accumulator. Little or no fuel should come out. If a lot comes out the fuel accumulator should be replaced.

But I would check the fuel system pressures with your new gauges first ;-)

Tony really knows what he is doing so I would follow his advise before my shade tree approach.

Rahl

Rahl,

Just to add a little bit of information to your post. There will be fuel present in the bottom port fuel hose line of the fuel accumulator when you disconnect it. Why? This line is connected to the main fuel return line near intake runner #3.

People inadvertently interpret the presence of some fuel from the bottom port of the fuel accumulator as a sign of fuel leak or broken diaphragm. Not always. You need to test to confirm it. You don’t need a pressure gauge to test or evaluate a FA.

UKinUSA (Steve M.) had recently tested and confirmed a failed fuel accumulator by performing a simple test procedure without a pressure gauge. See his recent post.

Tony

[ausgezeichnet]

Thanks Tony. Do you know the size of the male fuel connector on the WUR and fuel distributor?

[boyt911sc]

Originally Posted by ausgezeichnet

Thanks Tony. Do you know the size of the male fuel connector on the WUR and fuel distributor?

FD outlet = 8-mm x 1.0
WUR inlet= 10-mm X 1.0

Pressure Gauge = 12-mm x 1.5

You will need these male/male adaptors to connect your CIS press. gauge that has 12-mm x 1.5 (typically):
8-mm x 1.0//12-mm x 1.5 for the FD.
10-m x 1.0//12-mm x 1.5 for the WUR.

Inspect your gauge accessories for these metric fittings.

Tony

[ssinparadise]

I had a seemingly similar situation. It turned out to be a check valve at the fuel pump in my 73.5

If you are going to work on a 911 CIS you must own a fuel pressure tester.