munro

Hi can anyone help, I accidently put a small amount of alloy cleaner in with some petrol and killed my 928! it fires fuel from the could start injector but not the 8 main ones. I have replaced the fuel pump and filter to no avail Does anyone have any ideas what I may have done ?

jpitman2

All I can suggest is drain whatever is left in the tank, refill asap and flush it around, maybe with Berryman's as well. Flush by bridging pump relay and let it circulate, andmaybe change filter as well.
Whats the active ingredient of the alloy cleaner?
jp 83 EuroS AT 52k

GregBBRD

What was the chemical and what is a "small amount"? How much fuel did it mix with? It is possible that this is not an issue, at all, but something else.

Mrmerlin

what was the last thing you fixed??
Plus what Greg said

Glenn Evans

Either the system pressure is too low to open the injectors (4.0 bar opening pressure, from memory) or the sensor plate and plunger aren't moving; this could be mechanical jamming or because the control pressure is way too high. Since you have replaced your fuel pump, and the car presumably was running OK before, low fuel pressure is the less likely fault.

My guess is that whatever you put in the fuel has clogged the control pressure regulator's inlet screen, which will increase the control pressure (to as much as system pressure if it is completely blocked)..

I suggest that you remove the air cleaner when the engine has not been run for several hours (and won't have residual fuel pressure) and push down on the sensor plate to feel how easily it moves. (It should move very easily). Then remove the fuel pump relay, bridge relay sockets 30 and 87 to run the fuel pump, then gently push down on the sensor plate again. If it does not move easily, most likely your control pressure is too high. Do not hold the sensor plate down more than momentarily with the fuel pump running, as the injectors will be spraying.

You should systematically diagnose the problem by measuring the fuel delivery rate, then the fuel pressures, using a CIS fuel pressure gauge, in accordance with the troubleshooting procedures in the workshop manual.

munro

Hi folks thanks for your reply’s, I have flushed everything and I don’t know what the active ingredient was, However Glenn the paddle under the air filter is free and easy to push, but after fuel pump powering up it is hard to push down but still no fuel going through the injectors?

Glenn Evans

Were you pushing the sensor plate (the "paddle") down only enough to feel resistance? The sensor plate must deflect downward slightly before the injectors are opened. In normal operation (when you haven't bridged the relay contacts), this ensures that the engine is turning over as the air being drawn in will deflect the plate. The deflection required to initiate injection won't be much; you should be able to hear the injectors spraying. On what do you base your belief that the injectors aren't spraying?

It is possible that the metal cleaner has clogged all the injectors. I presume that the engine would have run for a while after you put the cleaner in the fuel?

Another possibility - which does not explain no fuel being injected at all - is that the cleaner has clogged the galleries in the fuel distributor. It may have affected any, or all, of the fuel distributor, control pressure regulator and injectors.

You already have gone to the expense of replacing your fuel pump, probably unnecessarily. I cannot recommend strongly enough that you diagnose the problem systematically to save probable unnecessary expense if you simply replace things on the basis of hope.

If you are going to work on the fuel injection, you need to do so safely. Be careful of fuel spills; avoid releasing fuel which is under pressure; don't open the system if the engine is hot or if anything electrical might ignite the fuel. Have your fire extinguisher at hand. Counterhold fuel unions (ie use a spanner on both "nuts") so you don't twist the fuel lines. Don't risk stripping threads by overtightening. Always pressurise the system after you've worked on it and check carefully for leaks before starting the engine.

IMHO, the first things you need to do are acquire a copy of the workshop manual and buy a CIS pressure gauge set. WSMs are available on CD-ROM and on the web to download, though these are unauthorised and Porsche in the past has forced such sources to desist. The CIS gauge set is only about $80 and I am pretty sure that Roger Tyson carries then at 928sRUs.

You can perform a fuel delivery rate check before these arrive (if you don't have them already). You need to open the fuel return line at the side of the engine bay, clamp a hose to the engine side and run that to a suitable container. I use a pair of heavy wires, about 6ft long, with spade connectors at one end and a switch at the other, to bridge the relay sockets. The wire and switch must be rated to a minimum of 16 amps. Using this, I can operate the fuel pump while holding the hose in the container beside the car, and can see any leaks and immediately stop the pump if necessary.

The required fuel delivery rate is 1150 ml in 30 seconds. If it is significantly less than this, either the fuel pump is dying (and probably will be noisy; should not be the case with your new one) or there is a blockage in the fuel distributor and it needs to be rebuilt. I have been told that it is difficult to ensure that the fuel distributor is properly sealed throughout and that a rebuild is best left to an authorised Bosch facility. I recall that some on the forum have done it themselves.

If the delivery rate is low, I suggest that you don't remove the fuel distributor until you have performed the pressure checks with the CIS gauge. This will indicate whether the control pressure regulator is working or not, even if the system and control pressures are not correct.

Both fuel distributor rebuilds and new control pressure regulators are expensive, so you don't want to do these unnecessarily.

If the control pressure regulator looks to be a problem, you can remove it and take it apart. You should be able to blow through the inlet screen. If you can't, you may be able to flush it clean to see whether this fixes it. Another failure mode is that the bimetallic strip fails and sticks in the operating temperature position, which leans the mixture far too much to start a cold engine.

You also need to test the injectors directly to see whether they are blocked. It probably isn't worth your while to build a rig to do this yourself. They need to be tested for operation, spray pattern, opening pressure, and not leaking below the specified opening pressure; and probably flushed with a suitable cleaner. They probably are old, if not original, and you may wish to replace them regardless.

I can't emphasis proper diagnosis enough. Guessing will waste your money.

munro

Ok thank you very much for taking the time to reply, I have arranged to borrow a pressure tester for the weekend and I already have the full 9 volume repair manuals so I will give you all an update after the weekend.

SimonC

I have just been through troubleshooting my K-Jetronic together with a local garage, and agree with Glenns comments. Get a pressure gauge and measure at the right spots according to the workshop manual. It will save you a lot of guessing and probably save you a lot of money.

From trawling the archives, its seems that most of the K-Jetronic parts can be repaired if you have the time and competence, but its important to find which bit is playing up.

michael j wright

So what did you find?

Jadz928

^^^^^
Glenn... fantastic post!

OP, report back. Curious to read the diagnosis. Good luck, be systematic.