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930 Won't start!

Alan Woods

Alan Woods

New member
A mechanic friend of mine has a 930 in, 4spd 1988, bought 2 weeks ago, was running great then concked out. No spark, fuel pump is running constant when ignition is on. Called Strasse, they suggested sensor plate on the fuel metering unit. Any ideas here? Any suggestions appreciated.
 
Is the front fuel pump working?

May need new relays (one in rear, two at front)?

Or loose electric connection in fuse box?

Good luck. It will be something simple.
 
Thanks for that Tim, he wasn't aware of the additional relays, but still no luck. Called Strasse, can't look at it for 3 weeks! Anyone else have any ideas?
 
If there is no spark what does it have to do with the fuel metering plate? I'm no 930 expert but if you definitely have no spark that's the first place you should look. The fuel pump should 'hum' with the ignition on. Investigate the spark side of things first if you're sure you don't have one. Call your Reg' Sec.
 
Strasse definately going in correct direction. of course check you have a spark (fundamental). has he checked the cold start sytem parts ? sensor plate? Does he know how? To the best of my knowledge both the normally aspirated and the turbo engines used downdraught metering units and sensorplates. the sensor plate is a large flat plate attached to a cantelever which in turn is connected to a rod which is housed in the metering head this rod moves up and down in it's bore and buy it's action allows more or less fuel to flow to the injectors. The movement of the rod is controlled by the sensor plates movement. Air entering the sensor plate area is sucked (over simplyfied term) into the combustion chamber as the engine turns over, this forces the sensor plate down (hence down draught) this causes a coresponding movement of the rod in the metering head upwards flowing more fuel. What can happen is that the rod can gum up and stick inside the bore of the metering head or the sensor plate can become offset causing similar problems. To confim the sensor plate is functioning correctly you need to remove the rubber boot connecting it to the air intake (it may be differently done on the turbo) and check the action of the sensor plate. DO NOT USE FORCE or you will jam the rod make sure the fuel pumps have primed the metering head you should feel even resistance as you depress the plate. If there is no resistance verify you have primed the metering head and if there is still no resistance it is very likely your rod has stuck in the highest position and that why you cannot start the engine, as you are effectively flooding the engine.If this is the case please also check your oil for fuel contamination (not as likely on a flat engine, i would guess but a possibilty) I have very much oversimplyfied the operation and checks and would recommend if you are serious in finding the fault yourself that you purchase the excellent book by Probst ,Bosch fuel injection and engine mangement as minimum to understanding the system.
 
Bu**er all that typing and i did'nt see the no spark bit. confirm You have a spark FIRST or you will be wasting your time with anything else.
 
There is also another relay in the rear which controls the ignition box/amplifier (not sure if that is the correct term) which is just in front of the relays on left hand side of the engine bay. On my 930 you can hear the box 'buzz' as soon as the ignition is switched on. This relay failed on my car and resulted in no spark.
 
Whoa! Thanks everyone, that's about as comprehensive as suggestions can possibly get based on the very limited amount of info I posted. I'm going over there tomorrow take some pics of another 911T I have which will be for sale which is at his place, so I'll print this out and take it with me. Thanks again, I'll let you know how we go on!
Regards
Alan.
 
I had the same problem with my 82 930.It turned out to be two problems.Firstly the cdi ignition box had developed a fault (the box on the left hand side of the engine bay),and secondly the ht lead from the coil to the distributer was no good.Check the ht lead first as these are cheap(you can get this lead as a seperate item from porsche),the cdi box was £395 exchange from jz machtech.(The cdi box was making the right noise,whistling when the ignition was on,but when i removed the back of the box,components were burnt out) Hope this helps you out,as it took me a while to track down the fault(replacing relays etc) Regards, Andrew
 
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