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As usual, Stan's questions are great.
I would suggest making a wire jumper cable about 6" long with a 1/4" male spade plug on each end. Find and remove the FP relay. Find the 30 and 87 sockets. Put one end of your homemade jumper cable into the 87 socket, and then insert the other end into the 30 socket. Any whizzing sound? This tests the fuel delivery system potential without any ignition source activated. There's plenty else to test, but first let's see if the FP works. Not need to open fuel rails, just listen for sound or have you wife do so. You can leave the jumper in place and walk back to the rear of the car, where the FP is located behind an access panel below the rear license plate, an listen yourself, too.
Good luck.
Dave
PS
The jumpered fuel pump relay is a very good way to test for fuel leaks for the reasons stated.
As usual, Stan's questions are great.
I would suggest making a wire jumper cable about 6" long with a 1/4" male spade plug on each end. Find and remove the FP relay. Find the 30 and 87 sockets. Put one end of your homemade jumper cable into the 87 socket, and then insert the other end into the 30 socket. Any whizzing sound? This tests the fuel delivery system potential without any ignition source activated. There's plenty else to test, but first let's see if the FP works. Not need to open fuel rails, just listen for sound or have you wife do so. You can leave the jumper in place and walk back to the rear of the car, where the FP is located behind an access panel below the rear license plate, an listen yourself, too.
Good luck.
Dave
PS
The jumpered fuel pump relay is a very good way to test for fuel leaks for the reasons stated.
Yes that's what I'll do next. Do I need to put key on start position 2?
Yes that's what I'll do next. Do I need to put key on start position 2?
No. Once the relay is jumped (bridged) the fuel pump will run, and it will not stop until you remove that jump wire or disconnect the ground strap so keep that in mind.
You said that you had been getting fuel to the rails prior to installing your second wire harness, its just not doing it now. With all of the work that you have done on the car you seem to have plenty of knowledge about the car so... You must have already had someone turn the key while you stand at the rear to listen for the fuel pump to run, correct? Does it spin, make noise, while someone is cranking the ignition? 1. If it is running but not pushing fuel to the rails then jumping the relay isn't going to tell you anything. Can you do as HuskerBoxter described (above)? Put a hose from the fuel pump or the fuel filter in a container then turn the ignition or jump the relay and see if your pump is actually pumping gas? 2. If its not running, then that is a different animal, and the best place to start is with your newest harness installation.
No. Once the relay is jumped (bridged) the fuel pump will run, and it will not stop until you remove that jump wire or disconnect the ground strap so keep that in mind.
You said that you had been getting fuel to the rails prior to installing your second wire harness, its just not doing it now. With all of the work that you have done on the car you seem to have plenty of knowledge about the car so... You must have already had someone turn the key while you stand at the rear to listen for the fuel pump to run, correct? Does it spin, make noise, while someone is cranking the ignition? 1. If it is running but not pushing fuel to the rails then jumping the relay isn't going to tell you anything. Can you do as HuskerBoxter described (above)? Put a hose from the fuel pump or the fuel filter in a container then turn the ignition or jump the relay and see if your pump is actually pumping gas? 2. If its not running, then that is a different animal, and the best place to start is with your newest harness installation.
Yes Ive tried it. Key in ON position - no sound from fuel pump. But when cranking, the cranking is too loud that I couldn't hear if the pump is running. So I think I should try jumping the relay but I am getting conflicting location of fuel pump relay. Is it in location XX or XXV?
I will try HuskerBoxter method next if the above fails. Thanks!
Yes Ive tried it. Key in ON position - no sound from fuel pump. But when cranking, the cranking is too loud that I couldn't hear if the pump is running. So I think I should try jumping the relay but I am getting conflicting location of fuel pump relay. Is it in location XX or XXV?
I will try HuskerBoxter method next if the above fails. Thanks!
XX slot, fourth from the right. Here is your fuse and relay diagram:
If you stand at the rear of the car and ask your wife to just turn the key to On the FP will run for a couple of seconds, or it won't. You will hear it, or not. She doesn't have to crank the car.
Fuel pump is XX.
LH is XXV AND THERE SHOULD BE A 53 RELAY IN THERE.
Yes there's a relay in there but I took it off thinking that was the fuel relay. So I checked online to be sure that's when I saw the conflicting locations. Ok it will be XX.
I got confused because when I got it back from the Porsche dealer, the mechanic left XXV jumpered on 30 n 87. 😀
If you stand at the rear of the car and ask your wife to just turn the key to On the FP will run for a couple of seconds, or it won't. You will hear it, or not. She doesn't have to crank the car.
Thanks. I tried that yesterday and no sound. I will try again to confirm.
Thanks for asking. I base that on after a few cranks and non-start, I unscrew the fuel rail bolt connector from pic and no fuel comes out which normally there would be. I continue to crank starter while it's still unscrewed
and still no fuel comes out.
Is there another way to check?
Opening up the fuel system as you did is a good reason to understand the system is not pumping fuel. However, trying to start the thing with the union undone is non too clever. If the pump for whatever did kick in and that union was open the engine bay and more will be covered in fuel in no time and I suspect you will well know what could happen next!
As for another way to check I get someone to crank the starter and whilst I listen to the fuel pump at the rear of the car. If the pump is spinning it is a pretty safe bet it will be delivering fuel- not 100% guaranteed but close.
Now it should be a simple matter to determine why the pump is not kicking in. First obvious thing to do is put a 12 volt signal across the pump terminals and ensure it spools up- pumps can and do jam if the internal pump [when fitted] has an internal rubber fuel transfer line that has disintegrated. If the secondary chip in the LH computer has failed the pump will not start. The rest is relays and wiring- easy to test and eliminate.
Opening up the fuel system as you did is a good reason to understand the system is not pumping fuel. However, trying to start the thing with the union undone is non too clever. If the pump for whatever did kick in and that union was open the engine bay and more will be covered in fuel in no time and I suspect you will well know what could happen next!
As for another way to check I get someone to crank the starter and whilst I listen to the fuel pump at the rear of the car. If the pump is spinning it is a pretty safe bet it will be delivering fuel- not 100% guaranteed but close.
Now it should be a simple matter to determine why the pump is not kicking in. First obvious thing to do is put a 12 volt signal across the pump terminals and ensure it spools up- pumps can and do jam if the internal pump [when fitted] has an internal rubber fuel transfer line that has disintegrated. If the secondary chip in the LH computer has failed the pump will not start. The rest is relays and wiring- easy to test and eliminate.
Thanks for the tip. Now that I know a better way...
Anyway, tried listening to fuel pump with stethoscope and I hear no sound - in ON position or when cranking. I guess I need to open it up and check the 12v.
Now just wondering and looking ahead, how do you check the secondary chip in the LH?
Regarding the LH. Where are you located? (USA, Europe, etc...). Most people send them to Louis Ott in the USA or John Speake in the UK to test, repair if needed. But you have a running S4 donor car so you could just swap the LH / EZK from that in to this car.
Its possible to track down some new cause for the fuel pump failing to energize, but since you confirmed that it was working just prior to installing the second harness it is likely something related to that, the harness or it’s installation.
Also, since the Porsche mechanic left a jumper wire in your CE panel, you have one of those already to test your fuel pump by jumping it (bridging it). Please don’t open the fuel hose in the engine bay while it’s bridged though. Just try it to confirm that the pump energizes.
No. I would use the FP relay jumper first. The fuel pump relay is a known failure point. Unless I misunderstood you. Then check continuity to FP . Then energize FP directly.
At least that's how I'd start.
Good luck,
Dave
You have fire ext, get a fan to remove any vapors, to avoid any spark carefully apply 12v to the pump terminals. Reverse terminals as stated above to unstick the impeller. If you can't hear anything, the pump is fried or stuck.
For future ref you can get fuse and relay diagrams at : 928gt.com. Find your model year, print, laminate.
pic of a homy, single pole FP relay jumper. Not pretty, but it works, put some heat shrink on the terminals and you are in like Flint. One spade goes into "30" and the other into "87". This is good to have at all times when driving.
04-11-2020, 02:54 PM
get a fan to remove any vapors, to avoid any spark carefully apply 12v to the pump terminals. Reverse terminals as stated above to unstick the impeller. If you can't hear anything, the pump is fried or stuck.
