dr bob

The earlier S4 is different from the '89, critical for the measurements because the protection relay isolates the harness from the power side when it's pulled. I need to spend more time on the earlier circuit to see where there might be a path to ground; the possibilites include the ISV, for instance, as well as the flappy solenoid. Lifting the W connector doesn't completely isolate those from the power side of the harness. The ISV may ground through one coil to the case, and could be thecause of the continuity to ground.

The "resistance beteen pins" you measured-- what were you measuring? Harness with injectors disconnected? Harness with injectors connected? Or the injectors themselves?

With the injectors disconnected, the harness should show infinite ohms between the two pins in any injector connector. With te injectors still plugged in, removing any single connector and checking between the connector pins should give you the same reading no matter which comnnector you lift, so long as all the others are connected. About 2.3 ohms if all the individual injectors are 16 ohm coils. Reading the individual injectors themselves with plugs pulled, each should be about 16 ohms.

Rod Underwood

Hmmm, Yes, harness with injectors disconnected. Disconnected the U, W LH, EZK and O2 Sensor and then checked the harness connectors at the injectors between the pins, unplugged from injectors. The resistances were as noted except for no. 8 which did not have continuity. At this point, assuming a break in no. 8 line somewhere, probably a partial short for 6 and 7 at that same point. Does this make sense?

dr bob

Rod--

With the LH unplugged and all the injectors unplugged, there should be no continuity between the pins in any of the connectors. With the readings you see, it's time to inspect that whole section on the injector rails. That's a task I haven't yet had the pleasure of doing; For the OP's '89, I can do almost all of it from the desk, and only went out to the garage with the meter a couple times to verify suspicions. The protection relay on the '89+ cars makes troubleshooting a lot easier with just a meter, since the injection power is separated by the relay and completely isolated from the car when that relay is pulled.

Take pictures as you get into the physical checking, showing what you are testing and looking at. This is an area that will see more and more failures as the cars age; a good troubleshooting guide will be really helpful as we move forward.

88porsche928

Just to give an update, I decided I was possible damaging more components in the process of troubleshooting. I towed it back to the mechanic. He is still working on it. He said a few times he got the car to start 1 out of a 100 times and it would run until you turn the engine off (Ran perfect while on). It sounds like some one from this forum is helping him out. Their was a turn signal not working problem I didn't tell him about I don't think that would help much with the car not starting. I'll keep you all posted on the end result of what was wrong with it.

88porsche928

update: the mechanic has narrowed it down the the LH ECU that was rebuilt. He said their was corrosion in it and some problem with the the inside chip. I am going to send the unit in and see if they find the same problem.

88porsche928

i shipped to ecu out today to get repaired or replaced. until i get it back or another one i cant really be certain this was the problem. however the mechanic did say the number on the outside cover did not match the bottom half, it seems like a simple mistake. two pins had corrosion on the lh ecu. i will post back next week when another ecu gets installed

88porsche928

I got the 928 back today from the mechanic, a hero named Jerry volunteered his time to troubleshoot the car. Just in time for me to move to NY (I am going to be stationed their). I am assuming what happen was the first time the car stopped running the fuel pump went bad. But I replace fuel pumps and ECU at the same time. Since I though the ECU was perfect every thing else was getting checked. I checked all the connnections even the one to the ECU but not the ECU pins itself.

John Speake

Please check that the drain on the heater box is not blocked. That's the usual reason for water to run down the LH cable and into the connector. I am sure the rebuilt LH didn't have corroded pins when it was supplied to you.

The LH pins are steel, with a plating. Once the plating is destroyed the steel is eaten away very quickly.

88porsche928

john, do you have a picture of where the drain on the heater box is?

John Speake

I think I have on my office computer, I'll look tommorrow..... do you see any signs of water getting inside the passenger footwell or central electric area ?

88porsche928

no, do you still sell the repair 928 cds?

John Speake

Best for you to buy from Roger Tyson at 928sRus.

John Speake

Sorry for the delay, here's a picture of drainage flap location...... you don't need to remove the engine first :-)

I can't remember who first posted this picture - thanks !