Fuel Pump Mystery?
09-15-2003, 12:04 PM
#16
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Hi Glack,
Glad you sorted the problem out.............lots of help on Rennlist !
The early LH2.2 fuel ECU in your '85 are much more relaible than the S4 onwards variety (LH 2.3), you'll be pleased to hear !
The '84 - 86 Euros are sensitive to mixture, due to MAF ageing. The cars start to hesistate when the throttle is snapped open, and max power is down.
Glad you sorted the problem out.............lots of help on Rennlist !
The early LH2.2 fuel ECU in your '85 are much more relaible than the S4 onwards variety (LH 2.3), you'll be pleased to hear !
The '84 - 86 Euros are sensitive to mixture, due to MAF ageing. The cars start to hesistate when the throttle is snapped open, and max power is down.
12-05-2010, 09:29 PM
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Need more help fuel pump relay no start w/ pics
Sounds like we might need WallyP on this one. I think you will need a good printout of the wiring diagram to help you figyre this one out (I did and a couple of highlighter markers to trace things out!!).
On the fuse power issue, all the fuses on the '85 up to and including Fuse 29 are linked in common power busses. That is to say, groups of fuses draw their power supply from several common battery feeds. All the fuses from 30 onward are more or less independant...and most draw their power through relays (ie: they are not powered unless the relay supplying them is activated).
Using the fuel pump circuit as an example, if Relay XX was not activated (for some reason), then there would be no power on either side of Fuse 42. It appears on quick review that most of the remaining higher position fuses in the panel follow the same process (ie: are downstream fused circuits).
Back to the fuel system electrics: Relay XX draws direct battery power at relay terminal 30, then feeds this through relay terminal 87 on to Fuse #42 and then on to the fuels pumps. As Jim bailey mentioned earlier, Relay XX is activated by the LH fuel computer (terminal 17 on the LH brain) and draws battery power through central electrical panel buss "15". There are no fuses in the activation circuit that I can see.
So, here's what you can check:
1. Pop Relay XX and check for:
- battery power at terminal plug 30 (key position does not matter);
- battery power at terminal plug 85 (ignition "off")
- battery power at terminal plugs 85 & 86 (ignition "on")
- assuming this is OK, continue on....if not trace down the wiring to find out what's wrong.
2. Jumper relay XX terminals 30 and 87 and the fuel pump should work. If it does not, then I suggest you follow Jim Bailey's advice and try powering the fuel pump directly to determine if the fuel pump is toasted or if you have a wiring/computer issue.
3. If the pump does work when the relay is jumpered, but the car does not start, I think it is highly likely your LH fuel computer is toasted. John Speake on the board has a service to rebuild these or one of the Big 3 can provide you with replacement options.
4. You could try to temporarily ground terminal W15 on the central electrical panel...this simulates the switching on of the fuel pump relay by the LH fuel computer. If the pump runs and the car starts/runs, then you have some form of wiring/electric gremlin in this circuit. If no run, again it points to an LH failure.
Hope this helps...I'm not an expect here, just reading the diagrams and attempting to return some of the troubleshooting knowledge gained from others on the forum.
Regards,
SteveCo in St. John's
On the fuse power issue, all the fuses on the '85 up to and including Fuse 29 are linked in common power busses. That is to say, groups of fuses draw their power supply from several common battery feeds. All the fuses from 30 onward are more or less independant...and most draw their power through relays (ie: they are not powered unless the relay supplying them is activated).
Using the fuel pump circuit as an example, if Relay XX was not activated (for some reason), then there would be no power on either side of Fuse 42. It appears on quick review that most of the remaining higher position fuses in the panel follow the same process (ie: are downstream fused circuits).
Back to the fuel system electrics: Relay XX draws direct battery power at relay terminal 30, then feeds this through relay terminal 87 on to Fuse #42 and then on to the fuels pumps. As Jim bailey mentioned earlier, Relay XX is activated by the LH fuel computer (terminal 17 on the LH brain) and draws battery power through central electrical panel buss "15". There are no fuses in the activation circuit that I can see.
So, here's what you can check:
1. Pop Relay XX and check for:
- battery power at terminal plug 30 (key position does not matter);
- battery power at terminal plug 85 (ignition "off")
- battery power at terminal plugs 85 & 86 (ignition "on")
- assuming this is OK, continue on....if not trace down the wiring to find out what's wrong.
2. Jumper relay XX terminals 30 and 87 and the fuel pump should work. If it does not, then I suggest you follow Jim Bailey's advice and try powering the fuel pump directly to determine if the fuel pump is toasted or if you have a wiring/computer issue.
3. If the pump does work when the relay is jumpered, but the car does not start, I think it is highly likely your LH fuel computer is toasted. John Speake on the board has a service to rebuild these or one of the Big 3 can provide you with replacement options.
4. You could try to temporarily ground terminal W15 on the central electrical panel...this simulates the switching on of the fuel pump relay by the LH fuel computer. If the pump runs and the car starts/runs, then you have some form of wiring/electric gremlin in this circuit. If no run, again it points to an LH failure.
Hope this helps...I'm not an expect here, just reading the diagrams and attempting to return some of the troubleshooting knowledge gained from others on the forum.
Regards,
SteveCo in St. John's
Relay plug XX Fuel Pump
1.) Battery Power at terminal plug 30 (key position any) = YES
2.) Battery Power at terminal plug 85 (key off) = NO
3.) Battery Power at plugs 85 and 86 (Key on) 85 = NO 86 = YES
I've got an issue with no power to terminal plug 85 in any key position.. thats my 1st Problem. My 2nd Problem is that when i jumped the XX Relay terminals 30 and 87
All I can hear is a faint "Clunk" sound from the fuel pump when i make the jump, and i hear the same faint "clunk" sound again when i disconect the jumper. I was hoping to hear some type of "running noise" from the pump but only get the "clunk on" "clunk off" sound. Needless to say car still wont start.
Looking for your help / advice on where to go froward from here.
Thanks,
Jon
Last edited by jhc68164; 12-10-2010 at 04:14 AM. Reason: Fixing Pics / spelling
12-05-2010, 10:03 PM
#19
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Fuel pump has failed. More common now that we're using Ethanol laced fuel. Order one from Roger at 928sRUS.
Nice thread resurrection.
Nice thread resurrection.
12-06-2010, 09:37 AM
#20
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Sorry for the delayed reply...and I have only a few minutes to review the info you have provided (will try to apply the "large brain" a little later on this). Yes, it would seem you have a dying fuel pump...if not already dead. Looks like you will have to pull it to verify for sure, but at least you have done all the diagnosis to get you to that point.
Regards,
SteveCo in St. John's
Regards,
SteveCo in St. John's
12-06-2010, 10:55 AM
#21
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The "clunk" often indicates that the pump is jammed, but electrically OK. One possible cause is a disintegrating fuel line inside the tank. If that is the case, a proper fix requires pulling the screw-in plug from the tank, replacing the line and cleaning the tank. The biggest "gotcha" is that the ring holding the screw-in plug may turn in the tank...
12-07-2010, 03:49 AM
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Sorry for the delayed reply...and I have only a few minutes to review the info you have provided (will try to apply the "large brain" a little later on this). Yes, it would seem you have a dying fuel pump...if not already dead. Looks like you will have to pull it to verify for sure, but at least you have done all the diagnosis to get you to that point.
Regards,
SteveCo in St. John's
Regards,
SteveCo in St. John's
Thanks,
Jon
12-07-2010, 06:26 AM
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The "clunk" often indicates that the pump is jammed, but electrically OK. One possible cause is a disintegrating fuel line inside the tank. If that is the case, a proper fix requires pulling the screw-in plug from the tank, replacing the line and cleaning the tank. The biggest "gotcha" is that the ring holding the screw-in plug may turn in the tank...
I hope replaceing the fuel pump and the fuel filter will solve my problem. I will be ordering them from 928 Specialists. Received good parts and service the last time I ordered.
12-28 2010 Update:
Replaced the fuel pump, fuel filter and the fuel pump relay today. Its running great now. Thanks everyone for your help.
Jon
Last edited by jhc68164; 12-29-2010 at 07:03 AM. Reason: updated information
12-26-2013, 12:07 AM
#24
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The "clunk" often indicates that the pump is jammed, but electrically OK. One possible cause is a disintegrating fuel line inside the tank. If that is the case, a proper fix requires pulling the screw-in plug from the tank, replacing the line and cleaning the tank. The biggest "gotcha" is that the ring holding the screw-in plug may turn in the tank...
You were absolutely correct about my fuel pump problem and the cause. I didn't pull the tank to clean it and I didn't replace the in-tank fuel screen as you suggested so the new pump I bought only lasted a few months. Lesson learned I guess.
But thanks to your answer to my original pump problem question I knew what I needed to do to fix it. I finally removed the fuel tank last week with the help of Dwayne's great write-up with pictures. I cleaned the tank and replaced the in-tank fuel screen, and reinstalled the tank without breaking anything.
. Still saving up for a few more parts and she should be running again soon. Here's a couple of pictures of the tank and the screen that was killing my fuel pumps.
Thanks again for your advice. Should have followed it at the beginning instead of delaying the inevitable.
03-11-2014, 10:14 AM
#25
Team Owner
that sure is a worn out fuel filter
