Chris Prack

Well I would start at the battery and make sure the terminals are clean and tight. The connections at the starter need to be clean and tight. Check the ground at the top of the bell housing at the rear of the engine. Check the white connector above the brake booster. It has two wires, one red and one blue with a black tracer (IIRC). This blue wire is the wire from the ignition switch in the car to the small terminall at the starter. If all these connections are good the engine will crank, given the battery, starter and ignition switch are all good.

951Porschiste

Chris,

I did check all of these items before finding the loose injector connector. First, I checked voltage at the battery. That was good. I then made sure the contacts on the battery pole were clean and tight. Still no crank. I checked the ground at the bellhousing. Clean and tight. Still no crank. I checked the white connector. Connection was fine. Still no crank. It's only when I repaired the loose injector connector that I got a crank.

In your previous post you said that one could pull the DME out of the car and still be able to crank the engine. But, if the DME is in the car and if it is getting a bad signal from one of the injectors, could that be enough to make the DME "overide" the starter?. Am I making sense? Or is what I am saying just not possible?

TIA,
Andre

Chris Prack

The DME does not get a signal from the injectors. There is no way for DME to "overide" the starter. They are completely seperate. Even if you had a factory alarm the starter would still crank the engine with the alarm going off.

951Porschiste

You are right. The DME does not get a signal from the injectors. It provides a signal to the injectors.

VWaddict

You know, I wondered if this might be a case of 'coincidence', in so far as fixing the harness merely coincided with disturbing something else that fixed it, which was why I suggested doing the test to prove or disprove the case. -I also mentioned that it would also require that the starter gets DME 'authorisation'...

In simple electrical terms, it is possible for a single wire to be used as a trigger and a continuous continuity/load present check without the requirement for a second wire, though from what Chris Prack says, it seems that the DMU doesn't actually employ this method.

In OBD-2, P0201 though P0208 are used for cylinder injector electrical fault reporting. P0261 -P0283 are for reporting shorts to ground and/or open circuit/shorts to B+. This is done by monitoring the *output* lines, so definately outputs to injectors can also be read as inputs for sensing, witout the need for a second wire.

Keith

Chris Prack

While that is true today it was not the case with the 951. The Motronic is not that sophisticated. Porsche didn't use the new OBD 2 system until 96.

VWaddict

Right. -I think it seems safe to say that there's some other fault at issue here, the injector connection was pure coincidence.

Keith

951Porschiste

Chris Prack and VWAddict:

I came to the same conclusion you guys did. Somehow correcting the faulty injector connector was just a coincidence. Some other problem was causing the no crank prob. However, I still can't figure out why I can now start the engine and I was unable to previously.

You gotta love Rennlist for these kinds of exchanges. It forces us to think more carefully about how our cars work.

Thanks a bunch to everyone who contributed!