cowdoc
08-22-2018, 01:08 PM
#1
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cowdoc
Hi Rennlisters
! Have a 1987 928 S4 with a starting problem.My mechanic is getting frustrated. He's getting an intermittent ground to the fuel pump. Sometimes starts and runs well (pressure ok), other times does not (low pressure) and easily floods. He's rigged up a pressure gauge to monitor the pressure, changed the fuel filter and check valve, new gas (old gas was ok. worked fine in my truck) and changed plugs and oil due to a wash down (caused by me). He thinks it may be due to a control module but can't find much info to diagnose the problem. Can anyone point us in the right direction ? Most common fixs ?
Bye the way, the post on removing the plug from the tow hook receptacle was VERY helpful, had to do that before I could have it towed from my garage.Nasty, frustrating job !.
THANKS
! Have a 1987 928 S4 with a starting problem.My mechanic is getting frustrated. He's getting an intermittent ground to the fuel pump. Sometimes starts and runs well (pressure ok), other times does not (low pressure) and easily floods. He's rigged up a pressure gauge to monitor the pressure, changed the fuel filter and check valve, new gas (old gas was ok. worked fine in my truck) and changed plugs and oil due to a wash down (caused by me). He thinks it may be due to a control module but can't find much info to diagnose the problem. Can anyone point us in the right direction ? Most common fixs ?
Bye the way, the post on removing the plug from the tow hook receptacle was VERY helpful, had to do that before I could have it towed from my garage.Nasty, frustrating job !.
THANKS
08-22-2018, 01:14 PM
#2
Rennlist Member
Cowdoc,
Are you paying this mechanic to learn how to work on your 928?
928 mechanics are Porsche mechanics, but Porsche mechanics may not be 928 mechanics.
Where are you located? The problem could be your LH computer. There might be someone close to you. Easiest test for an LH is to install it in a known car to see if the symptoms move with the computer.
Are you paying this mechanic to learn how to work on your 928?
928 mechanics are Porsche mechanics, but Porsche mechanics may not be 928 mechanics.
Where are you located? The problem could be your LH computer. There might be someone close to you. Easiest test for an LH is to install it in a known car to see if the symptoms move with the computer.
08-22-2018, 01:33 PM
#3
Rennlist Member
The obvious question: Has your mechanic replaced the fuel pressure relay?
08-22-2018, 01:39 PM
#4
Rennlist Member
And looked at the Fuse holder, if the connections get oxidized, they get hot and melt.
As said, the LH is a known issue on '87's, flooding is a good indication of that
Dave K
As said, the LH is a known issue on '87's, flooding is a good indication of that
Dave K
08-22-2018, 01:49 PM
#5
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Thanks.Am near Burlington, Vermont and while there are knowledgeable 911 techs around, haven't found a 928 guru yet. .And yes i understand the value of a tech knowing the vehicle, I haven't been anywhere that had two 928s at the same time. So can't switch parts for diagnosis.928 international said the fuel injector brain (LH ECU) failure is a common cause of fuel pump failure.But mine is intermittent.
Thanks for the reply..
Thanks for the reply..
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08-22-2018, 02:22 PM
#8
Rennlist Member
Start by swapping the horn and fuel pressure relay and see if that changes anything.
08-22-2018, 06:19 PM
#9
Chronic Tool Dropper
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To the mechanic's statements:
The fuel pump ground on your car is in the spare wheel well area, at the front and covered by a black plastic shield. The spare wheel is under a cover on the left side of the luggage boot. Once the spare wheel is out, the cover will be apparent. It's A Good Idea to carefully clean and snug ALL the ground wires there. On the battery itself, the fuel pump and the fans have dedicated feeders that attach to the positive battery post clamp. Same deal -- clean each of those conductors and snug the nut that holds secures them Clean the main battery clamp connections too, replace the corroded ground strap, and you'll start off with some basic housekeeping items that will affect fuel pump operation.
The pump is fed from the fuel pump relay in the CE panel, under your front passenger's feet. The fuel pump is engaged by a signal from the LH controller and the crank position sensor via the ignition box. The pump will only run if the controllers see the engine turning. If you are sure that the pump should be running, you can add a switched jumper to the fuel pump relay socket to run the pump on demand.
The LH controller is a known failure point on '87+ cars. They all fail. Some sooner than others, but they do all fail. A common symptom of LH failure is injectors running even before the engine is spinning. With hood open, turning the key to "engine run position" but not engaging the starter should not cause noises under the hood. If you hear injectors clicking, the controller needs to be rebuilt ($$) or replaced with new ($$$$$). Running the injectors like that with the pump running or with residual pressure in the system will wash the cylinder walls, a symptom you described.
If you don't have another '87+ 928 handy to test your controller, get in touch with Roger at 928srus (ROG100 here on Rennlist) and make an arrangement to send your LH box to him. He'll test it in another car, and tell you what happens. He has rebuilt boxes and can ship you one if you need it, or return yours. I'll be the first to tell you that the 928 has some interesting symptoms and diagnostics, usually experience not shared with Porsche experts who don't work on them a lot. Help your mechanic by referring him here, and we can work with him interactively if needed.
The fuel pump ground on your car is in the spare wheel well area, at the front and covered by a black plastic shield. The spare wheel is under a cover on the left side of the luggage boot. Once the spare wheel is out, the cover will be apparent. It's A Good Idea to carefully clean and snug ALL the ground wires there. On the battery itself, the fuel pump and the fans have dedicated feeders that attach to the positive battery post clamp. Same deal -- clean each of those conductors and snug the nut that holds secures them Clean the main battery clamp connections too, replace the corroded ground strap, and you'll start off with some basic housekeeping items that will affect fuel pump operation.
The pump is fed from the fuel pump relay in the CE panel, under your front passenger's feet. The fuel pump is engaged by a signal from the LH controller and the crank position sensor via the ignition box. The pump will only run if the controllers see the engine turning. If you are sure that the pump should be running, you can add a switched jumper to the fuel pump relay socket to run the pump on demand.
The LH controller is a known failure point on '87+ cars. They all fail. Some sooner than others, but they do all fail. A common symptom of LH failure is injectors running even before the engine is spinning. With hood open, turning the key to "engine run position" but not engaging the starter should not cause noises under the hood. If you hear injectors clicking, the controller needs to be rebuilt ($$) or replaced with new ($$$$$). Running the injectors like that with the pump running or with residual pressure in the system will wash the cylinder walls, a symptom you described.
If you don't have another '87+ 928 handy to test your controller, get in touch with Roger at 928srus (ROG100 here on Rennlist) and make an arrangement to send your LH box to him. He'll test it in another car, and tell you what happens. He has rebuilt boxes and can ship you one if you need it, or return yours. I'll be the first to tell you that the 928 has some interesting symptoms and diagnostics, usually experience not shared with Porsche experts who don't work on them a lot. Help your mechanic by referring him here, and we can work with him interactively if needed.