Dead Shark In Kansas
#16
Can be the pump.
Can be the LH not turning the fuel pump relay on.
Testing for power on the 30 terminal in the relay socket, then jumpering from 30 to 87 would be my first suggestion.
There is a good reason for the recommendation that every 928 should have a relay jumper in the glove box...
Can be the LH not turning the fuel pump relay on.
Testing for power on the 30 terminal in the relay socket, then jumpering from 30 to 87 would be my first suggestion.
There is a good reason for the recommendation that every 928 should have a relay jumper in the glove box...
QUOTE: I was reluctant to swap LH brains, 'cuz Brent's has a custom map since it has a blower on it. And since it's got a custom map, I'm guessing it's no longer prone to the typical LH brain failure problem.
END QUOTE
Sorry, not true, changing the EPROM does not mean the LH cannot fail in the normal way.
In Brent's case, I agree that the problem is likely to be in the fuel pump area, but if the FPR is not being energised when cranking, it could be LH failure.
END QUOTE
Sorry, not true, changing the EPROM does not mean the LH cannot fail in the normal way.
In Brent's case, I agree that the problem is likely to be in the fuel pump area, but if the FPR is not being energised when cranking, it could be LH failure.
So... IIRC, it would be OK for me to temporarily try my LH in Brent's car and/or vice-versa, right? Even with the '90S4 / '91 custom map GT difference, they should be compatible enough to swap?
But, isn't the typical failure mode of the LH such that the observable symptoms are injectors going random (a "clickathon") or some such? We're not hearing that on Brent's car.
In summary... at this point it seems like a good idea to work backwards from the fuel pump, starting with what Wally suggested. Checking for power on terminal 30 and then bridging 30/87 at the relay socket is a really easy next step to further isolate the problem.
And trying a donor LH (which I'd be happy to provide, if it's advisable to try a '90 S4's LH on Brent's SCed GT) is another easy thing we could try later.
#17
I don't think it would be a good idea to try another LH in Brent's car. He has 30lb injectors and all the fuel maps are very different from stock. A stock LH would probably run extremely rich, if at all. The only brain that would be guaranteed to work in his car would be the one from my car
Fuel pump jumper, you know you need one. On friday, I towed the boat out of the back yard and parked it in front of the house ready for a weekend at the lake, woohoo. Tow vehicle ('91 SAAB 9000 auto) is idling while I go outside to close the gate and as I am walking back down, car dies. WTF? First thing I do is take my jumper wire and bridge the fuel pump, don't hear anything. On the SAAB it's best to jumper the right side contact of the fuel pump fuse socket to the right side contact of the hazard light fuse socket. Since the hazard lights are powered all the time, it bypasses pretty much everything (except the wiring to the pump itself) and is putting +12 directly to the fuel pump. This is the same thing as jumpering pin 30 to 87 on the fuel pump relay socket on a 928. Good thing I had a spare walbro pump; one hour later we are on our way.
Dan
'91 928GT S/C 475hp/460lb.ft
Fuel pump jumper, you know you need one. On friday, I towed the boat out of the back yard and parked it in front of the house ready for a weekend at the lake, woohoo. Tow vehicle ('91 SAAB 9000 auto) is idling while I go outside to close the gate and as I am walking back down, car dies. WTF? First thing I do is take my jumper wire and bridge the fuel pump, don't hear anything. On the SAAB it's best to jumper the right side contact of the fuel pump fuse socket to the right side contact of the hazard light fuse socket. Since the hazard lights are powered all the time, it bypasses pretty much everything (except the wiring to the pump itself) and is putting +12 directly to the fuel pump. This is the same thing as jumpering pin 30 to 87 on the fuel pump relay socket on a 928. Good thing I had a spare walbro pump; one hour later we are on our way.
Dan
'91 928GT S/C 475hp/460lb.ft
Last edited by dprantl; 06-29-2009 at 11:56 AM. Reason: Edited lean to rich because of fuel dyslexia
#18
Brent: note that John Speake has a nice, concise summary of good troubleshooting techniques for dealing with a no start condition.
See Troubleshooting Porsche 928 Starting Problems.
Thanks, John... I don't think I ever noticed that page before today.
See Troubleshooting Porsche 928 Starting Problems.
Thanks, John... I don't think I ever noticed that page before today.
#19
I don't think it would be a good idea to try another LH in Brent's car. He has 30lb injectors and all the fuel maps are very different from stock. A stock LH would probably run extremely lean, if at all. The only brain that would be guaranteed to work in his car would be the one from my car
Arggghhhh! And I had one along in my "spare relays and fuses (and jumper!)" bag. I could kick myself for not remembering to try it.
#21
Thanks guys. Well, I'll test for power on the 30 terminal in the relay socket, then jump from 30 to 87. If I need a known working LH for my car, sounds like a call to MidNight Auto down in Atlanta.
I did get the info on the Bosch 044 FP. I need to pull the cover and see what's on the car. I got a busy week and probably won't get to it until this weekend. I'll report later.
I did get the info on the Bosch 044 FP. I need to pull the cover and see what's on the car. I got a busy week and probably won't get to it until this weekend. I'll report later.
#22
Yes the hybrid is the reaso for most LH failures, but not all. Not all LH failures give the "death rattle" :-)
Trying another stock LH to help diagnose this no start would be valid, Mark Anderson used stock LH with 30# in his race car some years ago.
A good check for fuel pump issues is to measure the fuel returned to the tank (RHS of trunk, under the big rubber bung, lengthen retun pipe into a container, bridge FPR for 30 secs, you should get 1350cc in the can.
Trying another stock LH to help diagnose this no start would be valid, Mark Anderson used stock LH with 30# in his race car some years ago.
A good check for fuel pump issues is to measure the fuel returned to the tank (RHS of trunk, under the big rubber bung, lengthen retun pipe into a container, bridge FPR for 30 secs, you should get 1350cc in the can.
#23
Ahhh... another good idea I'll try to remember for this and future fuel-pump-related issues.
#26
#27
OK, finally got to check things out. Fuse is good, contact fine. 30 on the relay panel is hot. Jumper from 30 to 87- no FP noise, no start. Did not try Ed's LH because we both feel it has to be the FP at this point. I was going to try the reverse polarity trick but the FP is turned to where I can't get to one of the terminals without removing the lines first. What's the point in that?
Question: if I change to the Bosch 044 FP, will that change the mapping/tuning on the car. I still don't have a good handle on the SC thing. And would it be a good idea to delete the internal FP if I use the Bosch 044? Something Andrew Olson alluded to I believe.
Question: if I change to the Bosch 044 FP, will that change the mapping/tuning on the car. I still don't have a good handle on the SC thing. And would it be a good idea to delete the internal FP if I use the Bosch 044? Something Andrew Olson alluded to I believe.