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The banjo holes that Guy is referring to are the ones on top of the FD that go to each injector. Jump the fuel pump relay, and turn the adjustment screw from lean to rich until you just get fuel from those holes. I would also STRONGLY advise you to get a good book on Bosch CIS injection. The Porsche WSM only gives very limited info on the subject.
Mike
If the return line is blocked you will have higher fuel pressure. Probably system pressure and control pressure will be the same as you have no relief on return.
Have you put gauges on it?
If the return line is blocked you will have higher fuel pressure. Probably system pressure and control pressure will be the same as you have no relief on return.
Have you put gauges on it?
So higher fuel pressure then means more fuel flow per minute and
thus too much fuel?
No I do not have any gauges. Where can I get them, because here in
Belgium these type of gauges are hard to get?
And what pressure should I measure to have a correct pressure ?
Wow, thank you for that vital information. Before ordering a set, I will just try to disconnect the return line to make sure fuel is not blocked in the return line. If this doesn't solve my problem, I will start measuring pressures as indicated by the sheet you've sent me.
I indeed also believe I have a pressure issue. but often issues with pressure are caused by too low pressure, not too high...
You REALLY NEED vacuum gages to work on the CIS system. Without them you're like a blind man crossing the highway. There should be a fine mesh screen in the fuel feed fitting in the FD. If it's clogged you might not get enough fuel flow. The mixture screw is very sensitive, 1/4 turn can drastically change the a/f ratio. You can go from too lean to too rich easily. Also CIS systems like to be CLEAN. IRRC the bleed port for the WUR line is .004" dia. so it can easily get plugged.
You REALLY NEED vacuum gages to work on the CIS system. Without them you're like a blind man crossing the highway. There should be a fine mesh screen in the fuel feed fitting in the FD. If it's clogged you might not get enough fuel flow. The mixture screw is very sensitive, 1/4 turn can drastically change the a/f ratio. You can go from too lean to too rich easily. Also CIS systems like to be CLEAN. IRRC the bleed port for the WUR line is .004" dia. so it can easily get plugged.
I discovered another issue : when turning the mixture screw CW for richening the mixture and then wanted to turn back the mixture leaner by turning it CCW, mixture screw does not move! Only when detaching the mechanism with spring to push downwards, I could turn back the mixture screw . So apparantly the rod does not always grip in the actual mixture screw when pushing it downwards .
the fuel pressure regulator constantly regulates the fuel pressure between idle and WOT . Its achieved by the vacuum system. At idle there is greater vacuum which pulls the diaphram open in the regulator allowing more flow back to the tank (reduced fuel pressure ).
The greater the rpm the greater fuel delivery needed and therefore the higher fuel pressure required . The higher the rpm the less the vacuum allowing the FPR diaphram to close and decrease the return flow to the tank.
If you pull the vacuum lead off your FPR at idle you should see a distinct change in rpm as the FPR increases fuel pressure which produces more fuel flow to the engine briefly before the ECU compensates .
I do not have a separate FPR on my 928S euro . only the l-jet and later models have this.
nor do I have an ECU.
Everything on my Kjet is controlled by the WUR and FD .
Instead of getting a 'Factory' mixture screw tool, I made one by cutting a 3mm ball driver in half and using a piece of aluminium tubing to make it the right length. It's really light so I can 'feel' the screw engage when I push it down. I also made my own because 'I'm a cheap SOB' LOL
I do not have a separate FPR on my 928S euro . only the l-jet and later models have this.
nor do I have an ECU.
Everything on my Kjet is controlled by the WUR and FD .
kr
All fuel injection cars have a fuel pressure regulator of some sort .
Also your car does has a ECU (electronic control unit ) its a K-Jetronic ECU some folk incorrectly call it a DME but that can lead to confusion on cars that have a DME relay
Your car must be very early, a 78-79 model ?
In 1980 928S Euro model was fitted with a LH-Jetronic ECU
Your K-jetronic model has the fuel pressure regulator integral to the fuel distributor but it does the same job as the remotely fitted FPR fitted to the fuel rail on later cars and maintains an even fuel pressure and returns excess fuel pressure back to the tank but it does this with a spring diaphram and doesn't use inlet vacuum assistance as the later models do
When the ignition is switched off the FPR should shut off the fuel return to the tank and maintain fuel pressure in the fuel delivery system.
Your injectors function purely by fuel pressure so if you have no fuel from the injectors and the pump is ok and you have no leaks you presumably have insufficient fuel pressure to operate the innjectors .I would suggest you check your fuel pressure is to spec 3.5BAr or whatever and if it isn't check the FPR
I surely don't have a ECU. The only electronics I have, is the Bosch Hal sensor to my distributor.
But it is a Kjet not a Ljet , and my 928S of 1980 is model 1979. But it is the euro model. I believe that the S model in the US came later then the euro model.
indeed the pressure regulator is integrated in the FD.
I believe there are 4 possible issues :
- FD is not delivering correct pressure => overhaul necessary
- WUR is not delivering correct pressure => overhaul necessary
- return line of FD is blocked causing too much fuel
- mixture is completely off set => set from lean to rich
my apologies I have misunderstood you.
In your post #56 you mentioned your 'Kjet which I took to mean that your model had a KE-Jetronic ECU
I have re-read the entire thread which I should have done before my last post ....lazy me.
I think the main problem here is that instead of following a proper diagnostic sequence you have jumped about all over the place from fuel to electrics to ignition back to fuel . Also you adjusted your fuel mixture which is pointless as the mixture setting is unlikely to have adjusted itself and you still haven't found the source of the problem
From the symptoms that you describe I would guess that the problem is fuel related and possibly caused by fuel over-pressure causing a rich idle mixture.
Your first move before adjusting or replacing anything should be to fit a fuel pressure gauge and see exactly what fuel pressure you have. Otherwise its all speculation .
The accumulator should not be removed ,its function is to act as a fuel pressure reservoir maintaining some residual fuel pressure of around 2 Bar on switch off .
Your fuel pump delivery pressure should be around 5 Bar according to my Bosch bible but apparently the minimum fuel pressure to cause continuous injection of fuel is around 3 Bar+
You might also check that your fuel tank is being vented
02-25-2017, 08:27 PM
