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Thank you Alan, James & John...I was busy at work and hadn't had anytime for homework. Well; took out the fuel pump relay and sure enough when I turned on the key the fuel pump came on...I was even able to turn on the car without the relay! Who knows where they got power from??
If you where going to bypass the relay...where would you get the power from??
Given that the car would NOT RUN and stopped for the prior owner....I suspect that they may have messed with the wiring to provide constant power to the fuel pump...maybe remove the relay and see if the pump still runs ???
James, the fuel pump came on without the relay...I was even able to turn on the car! The search begins....
Ah yes, it does looks though it stays on. The only rare ones I have seen just stay for about one second, rather like L-Jet do.
John thanks for posting...yes the fuel pump energizes as soon as I turn the key on...I even turned the car on. Where should I look for a bypass? Thank you.
i have a Porsche shop in Pompano Beach....if you want to, you could send me the LH unit and i could test it for you...I know John very well and have done plenty of business with him....if the unit is bad, then the problem is found, if not, we can test other components for you and get you going....Vinnie@gulfperformance.com
i have a Porsche shop in Pompano Beach....if you want to, you could send me the LH unit and i could test it for you...I know John very well and have done plenty of business with him....if the unit is bad, then the problem is found, if not, we can test other components for you and get you going....Vinnie@gulfperformance.com
Thank you Vincent....I might do just that, but I suspect my problem lies with the PO or PM (I don't know if this terminology is used here; Previous Mechanic). My car was left for dead in a Miami holding lot. I got the engine running; installed the LH when I found the injectors were ticking like crazy, installed a new MAF thinking that was the problem originally, new plugs, fresh oil and it started right up. Then found out the transmission was gone; swapped it with a working unit. Now I'm updating fuel lines; planning to bring the tank down to clean. Next TB & WP. I'm going to spend sometime working thru this fuel pump thing and see where it goes!
The fuel pump coil is driven (grounded) by pin 21 of the LH. So if someone put a permanent ground on there, that would explain the problem.
When people sometime damage that pin of the LH, it always defaults to no FP activation.
Does the car have an immobiliser ? They usually act of the fuel pump relay primary circuit, that is a possible area to look.
Thanks for the heads up John. Next time I have some time for the car I'll go thru your suggestions. I'm not sure if my car has an immobiliser, but I'll go to work on the research. Thank you so much!
Here is a diagram for your year, W is the right most plug.
John - it runs without the relay - so more than that was done. Probably there is either a new relay controlled just by ignition, or the pump runs directly from the ignition now.
Neither is really a good idea...
Given this new information I'd be looking for connections directly to U25 (top right pin). Does fuse 38 still disable the fuel pump?
Here is a diagram for your year, W is the right most plug.
John - it runs without the relay - so more than that was done. Probably there is either a new relay controlled just by ignition, or the pump runs directly from the ignition now.
Neither is really a good idea...
Given this new information I'd be looking for connections directly to U25 (top right pin). Does fuse 38 still disable the fuel pump?
Alan
Thank you Alan. I've not yet had the time to dissect the plug, but before I headed out to work this morning I popped into the garage pulled fuse 38 which did disabled the fuel pump.
I think you mean the fuel pump runs as soon as you turn on the ignition? Your description of "opening a switch" is a bit odd - you are actually closing a switch in this case. Better to stick to the more obvious
Alan
Alan, you and most of us know exactly what a closed switch means. But in the now expansive realm of non-engineering trained IT professionals, an open switch is like an open door; letting everything (electrons) through. Yeah I choke every time I have to express a switch position in the lingo that they understand. But equipment vendors are also adopting the new lingo and terminology.
Here is a diagram for your year, W is the right most plug.
John - it runs without the relay - so more than that was done. Probably there is either a new relay controlled just by ignition, or the pump runs directly from the ignition now.
Neither is really a good idea...
Given this new information I'd be looking for connections directly to U25 (top right pin). Does fuse 38 still disable the fuel pump?
Alan
Alan; I pull the U plug and the connection to PIN 25 looks OEM front and back....well all the connections to the U & W plugs. Everything is tidy...like no one ever touched it! And fuse 38 does kill the pump. Should I then trace back the power from the pump? That's going to be fun...
I also looked at the LH connectors as suggested by John and all pins look good...no sign of any problem or someone messing with it.
If you unplug the LH relay (which provides ignition switched 12v to the FP relay contacts) does the pump still run as soon as the ignition is switched on ?
That may give a clue as to what has been changed on your car.
Another idea would be to see if pin 85 of the FP relay is permanently grounded (unplug the LH ECU for this check).
If you unplug the LH relay (which provides ignition switched 12v to the FP relay contacts) does the pump still run as soon as the ignition is switched on ? That may give a clue as to what has been changed on your car. Another idea would be to see if pin 85 of the FP relay is permanently grounded (unplug the LH ECU for this check).
John; unplugged the LH relay and the pump came on...unplugged the LH ECU and the pump came in...unplugged both and the pump still comes on. Who knows where they hacked to power that pump every time you turn the key!
I've been reading Alan's document how to understand the Wiring Diagram...fun stuff! It's actually starting to make sense...thank you Alan. But I'm afraid I'm far from solving this situation.
08-23-2016, 12:52 PM
