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1984 GTI Rabbit Fuel Pressure Problem

Hello

I have a 1984 GTi Rabbit.

For the past month or so the car is difficult to start after it sits an hour or more. What happens is that the car starts right away and then dies after

5 seconds or so. It will start right up again and then after a few seconds die. If I start it with my foot on the pedal and have it rev at 2000rpm and hold it there for 1 minute I can release the pedal and the car will run fine. I can start and stop it fine, if the car sits for more then about an hour I am back to the problem. Temperature doesn't seem to affect it.

I think I am losing fuel pressure. I went to change the fuel filter in the morning after the car sat overnight. When I went to loosen the banjo bolt on the output side of the fuel filter the fuel didn't spray as I loosened the banjo bolt. This tells me that the system was not under pressure. I noticed that the output side banjo bolt has a little spring in it is this a check valve?

Now I have to narrow down where am I losing pressure: fuel accumulator? Leaky injectors? Cold start valve?

Is there a way to narrow down and divide the system? If there was no pressure at the fuel filter does that mean that the leak could be before or after the fuel distributor?

About a week ago I pulled the car into the driveway, the car was cold but the fuel system was under pressure. I had a spare warm up pressure regulator so I decided to swap it. When I went to loosen the lines at the warm up pressure regulator the fuel was under pressure and gas sprayed out as expected. I did however notice when I put the spare fuel accumulator in that the car started up pretty much right away. I am just trying to use this in my troubleshooting logic, that the fuel pressure got back up pretty fast after losing pressure at the warm-up regulator.

This is what I think is going on:

My fuel accumulator is leaky. And after it sits for a while, fuel pressure drops as fuel goes back into the tank. However there is fuel pressure up on the fuel distributor side that is why the car starts right away, but then dies as the fuel pump has the bring the capacity of the system back up as pressure has dropped from the accumulator to the fuel filter / fuel distributor input.

sorry for the rambling.

Any ideas?

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Leaks can be anywhere and they can be multiple.

I think if the pressure accumulator was bad you would see fuel under the car. The accumulator is actually a surge device next to the fuel pump. It also does have bit of gas stored to prevent vapor lock. I have not had one fail but I only had 300,000 miles on one Rabbit and about the same on the second. Do the injectors drip when you do the drip test? Have you changed the fuel distributor? Not a part many have laying around in their spare parts pile. How do you know the cpr you swapped is good without a pressure guage?

My problems were related to a bad control pressure regulator one time. Bad fuel distributor another time. Bad fuel pump relay another time. Probably leaky injectors but I tended to replace those at regular intervals.

It costs lots of money to guess without a pressure guage and a fused jumper wire.. Of course a good repair manual helps you use the pressure guage.

Reply to
Jim Behning

Hard starting of a warm engine can be caused by a loss of residual fuel system pressure, which can be caused by a leaky fuel pump check valve, a leak in the frequency valve, a leaky cold start valve or from leaky injectors. Usually not from an fuel accumulator, unless the accumulator is leaking gas on the ground. The usual cause is a bad fuel pump check valve, that has a speck of rust from the fuel tank keeping it from closing fully. This is especially true on older VW's which have issues with rust and gunk in the fuel tank. A good sign of this is an audible surge or ping that one hears as the fuel goes back into the tank when one shuts off the engine. It can also be a leaking (or non-sealing) system pressure valve, allowing the fuel to return to the tank when you shut off the engine. One needs to do a residual pressure test on the system, unless its obvious that it is a bad check valve, or a clogged check valve.

Reply to
jfruniontown

I worked on restoring a "junkyard" scirocco (1979? IIRC). The last thing I changed was the fuel accumulator which finished repairing the FI. Owner wanted only to touch the key and have that engine start instantly at any time. I told him that he would still need to turn it some! lol Fuel pressure gauge was very much needed to solve the multiple problems.

Reply to
dave AKA vwdoc1

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