928S4 '91 Will NOT Start...Help Please !!
04-04-2005 | 07:46 PM
#16
Thread Starter
8th Gear
Joined: Apr 2005
Posts: 8
Likes: 0
From: Scotland
Originally Posted by Jim bailey - 928 International
The motorized noise might be your PSD limited slip pump pumping left rear fender... The fuel pump only runs briefly while the starter motor is cranking but as a test you can open a 141 951 253 B relay like for the horn and wedge the contact points together then insert into the fuel pump relay spot (top row tenth from the left ) and with the key switch on the fuel pump will run all the time BUT DO NOT DO THIS FOR LONG you can FLOOD the engine with fuel. Being a 1991 you have the odd clear relay (ignition monitoring) on the outside of the LH brain box. This is what checks exhaust temperature on cylinder 3 and 7 and if there is a low reading assumes the ignition has failed and it shuts off the injection to the 4 cylinders which are fired by one coil (two on each bank). Since it has the ability to shut down 1/2 of the injection alternatively it can also shut down ALL the injection.
Thanks for your reply. The problem seems to be that the engine just isn't getting fuel, but when the tap tap from the injectors happens it gets a little so tries firing. I did remove plugs on both sides and they were totally dry( I'd expected them to be dripping with fuel from all the cranking. I check out the relay you've suggested. Also there's a relay in the rear of this car, by the spare wheel, and a few fuese, which I think are radio related, but what's that realy doing there. Another thing that maybe is odd or maybe not, is if I short the fuel pump relay it runs wheter the key is in the ignition or not !
Time to buy a bike !
04-04-2005 | 08:03 PM
#17
Rennlist Member
Joined: Feb 2002
Posts: 7,056
Likes: 38
From: Cambridge England
I concur with Jim... if you bridge the fuel pump relay you may be able to start the engine, but it will only run at about 3500rpm.
The ticking of the injectors is the sure sign of LH failure, plus the fact that the fuel pump does not run when the engine turns. Sometimes the injectors will click for a few seconds only, sometimes continuously.
The best way to check your battery is with a battery hydrometer, check each cell, and you may find the SG of one cell is much lower than the others. If so, the battery is due for replacement.
Regards
The ticking of the injectors is the sure sign of LH failure, plus the fact that the fuel pump does not run when the engine turns. Sometimes the injectors will click for a few seconds only, sometimes continuously.
The best way to check your battery is with a battery hydrometer, check each cell, and you may find the SG of one cell is much lower than the others. If so, the battery is due for replacement.
Regards
04-05-2005 | 09:20 AM
#18
Racer
Joined: Mar 2002
Posts: 302
Likes: 0
From: Netherlands
If the pump produces a insufficient or irregular flow of fuel, I think the injectors can tick on occasion. Not sure though. If so, I would be curious about the fuel pump. Also because the plugs are dry.
I had the same. The pump buzzed on the turn of the key, but still it was stuck. It turned over once or twice, so there was fuel at the rail, but it wasn’t nearly enough to start the car. It is pretty simple to check. Pull the cover on the right-rear of the car. Disconnect the secondary fuel line and have someone juice the pump the way Jim described. Let it run in a bucket or container, from which you can read the amount. I’m not sure of the amount of fuel the pump should produce. It is in the workshop manual.
By the way, I think it’s nice of Algie to offer a brain-swap to try.
I had the same. The pump buzzed on the turn of the key, but still it was stuck. It turned over once or twice, so there was fuel at the rail, but it wasn’t nearly enough to start the car. It is pretty simple to check. Pull the cover on the right-rear of the car. Disconnect the secondary fuel line and have someone juice the pump the way Jim described. Let it run in a bucket or container, from which you can read the amount. I’m not sure of the amount of fuel the pump should produce. It is in the workshop manual.
By the way, I think it’s nice of Algie to offer a brain-swap to try.
Last edited by Andre Roodnat; 04-06-2005 at 04:15 AM.
04-05-2005 | 09:56 PM
#19
Instructor
Joined: Jun 2004
Posts: 175
Likes: 1
From: Bonnie Scotland
Call me on 01383 842312 Wednesday, call as late as as midnight if you log on late evening, as I work nightshift normally but will be off and awake.
They call me Allan on sundays- if the misses answers leave a number.
I'm in Edinburgh every day, so swapping brains is no problem!!!!
They call me Allan on sundays- if the misses answers leave a number.
I'm in Edinburgh every day, so swapping brains is no problem!!!!
04-08-2005 | 06:36 PM
#20
Thread Starter
8th Gear
Joined: Apr 2005
Posts: 8
Likes: 0
From: Scotland
Update on a Brain Dead 928
Many Thanks to everyone who came in on this topic, your help was invaluable in diagnosing and sorting this apparently terminal problem. The diagnosis was entirely spot on. My car had suffer a terminal "stroke" and was in a coma, it was definately entirely brain dead! 
The most alarming thing was that the condition hit without warning at all. One minute it was fine, next dead, bit like real life I guess!! Thinking on it there may have been some symptoms but they were very mild and so not really noticable....the occassional cough on takeup, the occassional dip in idle speed, but little else. I had a third party imobiliser disarmed about 2 months back, as it frequently malfunctioned stopping me from using the car and I was sick of it. I suspect the Auto-Electrical person who did it, probably didn't bother to disconnect the battery before doing his worst. The imobiliser was disarmed and I bet the brain took a hit there. In fact looking at the wiring in my car, the original porsche stuff is neat and tidy, all the aftermarket stuff, is just a complete mess, as each auto-electrical person has added new bits without removing the old, maybe there's a moral in there. Don't let an autoelectrician loose on your car unsupervised ! For others whose brain hasn't gone yet, this is seriously scary, literally my car was fine when I parked it in my garge and dead a few days later, and it didn't turn a wheel in between times and nothing had happened to it in between ! Well weird!
JOhn Speake of JDSPorsche ( Brain Surgeons! ) repaired / remanufactured the "brain" on a 24 hour turnaround basis and gave extrememly helpful advice and guidance for the entire process. His diagnosis was entirely spot on ( along with that of several other posters here too ) The brain was returned , re-fitted today and the car started on the first turn of the key, like it used to. I was then able to drive it out my garage, finish the re-installation with a bit more space an dtake th ecar for a well deserved spin. If anything it's now running better than ever before. Well done Dr John !
I should add I can highly recomend the services of John Speake, from my excellent first hand experience.
Also many thanks to Algie for his kind offer of a brain swap.
Altogether a really brilliant result.
The most alarming thing was that the condition hit without warning at all. One minute it was fine, next dead, bit like real life I guess!! Thinking on it there may have been some symptoms but they were very mild and so not really noticable....the occassional cough on takeup, the occassional dip in idle speed, but little else. I had a third party imobiliser disarmed about 2 months back, as it frequently malfunctioned stopping me from using the car and I was sick of it. I suspect the Auto-Electrical person who did it, probably didn't bother to disconnect the battery before doing his worst. The imobiliser was disarmed and I bet the brain took a hit there. In fact looking at the wiring in my car, the original porsche stuff is neat and tidy, all the aftermarket stuff, is just a complete mess, as each auto-electrical person has added new bits without removing the old, maybe there's a moral in there. Don't let an autoelectrician loose on your car unsupervised ! For others whose brain hasn't gone yet, this is seriously scary, literally my car was fine when I parked it in my garge and dead a few days later, and it didn't turn a wheel in between times and nothing had happened to it in between ! Well weird!
JOhn Speake of JDSPorsche ( Brain Surgeons! ) repaired / remanufactured the "brain" on a 24 hour turnaround basis and gave extrememly helpful advice and guidance for the entire process. His diagnosis was entirely spot on ( along with that of several other posters here too ) The brain was returned , re-fitted today and the car started on the first turn of the key, like it used to. I was then able to drive it out my garage, finish the re-installation with a bit more space an dtake th ecar for a well deserved spin. If anything it's now running better than ever before. Well done Dr John !
I should add I can highly recomend the services of John Speake, from my excellent first hand experience.Also many thanks to Algie for his kind offer of a brain swap.
Altogether a really brilliant result.
