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After a assembly of my rebuilt 78 928 engine, I am trying to diagnose why it's not starting. As for now, the obvious cause it that there is no fuel coming out of the fuel lines to the injectors. There is fuel coming in to the fuel distributor, but as far I can see there is nothing coming out.
Any idea what causes this ?
Are there any schematics that is avilable ?
There may be something obvious that I have not yet connected, so any help would be appreciated.
have you tried to adjust the air fuel mixture screw on the front of the fuel distributor?
Full counterclockwise is closed and you should not get fuel out of the FD. As you adjust CW with the fuel pump jumpered you should see fuel flow evenly form all 8 orifices on the top side of the FD if the top lines are disconnected.
When I tested mine it happened at about 9.5 turns CW from full closed.
Are you sure fuel is making it into the FD or just to the FD? THere is a union at the fuel input to the FD, it has a fine mesh screen that often gets clogged/occluded.
There are also small screens in the ports themselves, topside, though I don't recall reading of those getting blocked.
Do you have the pressures available? System 65-75psi, cold control ~ 15-25 depending on ambient temp. The injectors should not see fuel flow until they get ~50psi.
jp 83 Euro S AT 56k
When my fuel distributor went, and it was after it sat for a few years back in the 90's, I took the fuel injectors off and fuel did not flow out of the fuel distributor into the lines.
Pushing down the big round went, will get the fuel out to the injectors, but it's stop after a short while. Seems there is not nothing streaming it out.
The distributor went is the screw with a spring in the middle of the picture? How do one make the turns. Mine just go down with no possibility to turn it.
Pushing down the big round went, will get the fuel out to the injectors, but it's stop after a short while. Seems there is not nothing streaming it out.
It shouldn't stop with the air valve pressed down.
It shouldn't stop with the air valve pressed down.
If it stops, there is a problem.
Air fuel ratio adjustment shouldn't fix that.
Well, it do not stop when pushing down the air valve, its just that its shuts tight after a while and the engine stop. If I set a screwdriver in the went just enough that there is a small gap, the engine is running, not fine but ok.
What is making the valve open ?
the air fuel mixture screw, the one in front of the FD is spring loaded. Insert the allen head wrench and depress before turning. With the fuel pump jumpered you should be able to adjust the AF screw CW until you hear the injectors start a high pitched squeal, then back off CCW slightly. That should get the engine running enough to where you can make very small adjustments to refine.
There is a control plunger in the center of the FD that adjusts fuel flow based on air plate position. Best to adjust using an oxygen sensor.
You may have multiple issues going on. Correct fuel pressures are very important (measured at the WUR). Lots of great resources out there like the one below and at 928Classics website.
I did get to start after adjusting the fuel mixture screw in front of the FD, but the exhaust comming from the car is so dense and there is so much, that I have to turn it of after about 30-40 sec. I have to do intervals at this startup process. I beleive that if I continue, I surely will get complains from my neigbour. The exhaust is black/blue in color.
Is it possible that by adjusting this screw, the car is getting to much fuel and causes this exhaust overdose?
Finally got the -78 started, but I find the engine extremely difficult to tune. I may have the timing correct, but it's increasing and decreaseing in rpm and it's extremely easy to stal when trying to take off. Adjusting both fuel/air mix screw by the fuel distributor and the big adjuster screw in front.
I know this problem has been up on the board before, but I believe I have been in the to do list several times.
I must admit I am close to order time at local Porsche workshop, but Iam skeptical regarding their knowhow on the 78 928. Any advice?
the fuel/air mix screw is VERY sensitive - turn it VERY small amounts! The big screw at the front is only idle speed. If exhaust is black(rich), move mixture screw CCW in VERY small amounts and engine should run better and black smoke should reduce.
jp 83 Euro S AT 56k
09-28-2015, 12:54 PM
No fuel to the fuellines - K-Jetronic distributor
