Discussion
Posting this on PH (It's already on a 928 owners-club list, but I'm getting nowhere).
Basically I have an '81 928S with the K-Jet mechanical fuel injection. The car starts from cold, or from hot (if only stopped a short while). However if she's been allowed to cool (for an hour or two), she'll refuse to start (just cranks and cranks and cranks). Let her cool more (ie overnight) and she'll start fine.
I've been investigating this since she did this to me last tueday night (Mrs S and I had gone out for the evening and needed the car to get home!). Eventually after bump-starting the car, I was able to get her running well enough to go home. When I did the bump-start, she was very reluctant to spring to life.
I'd struggled to get this to happen when I take the car to/from work (it appear that the fifteen mile commute isn't long enough to trigger the symptoms), but today I took a longer route (and sitting in a queue because of a crash helped too!!).
So I've now been able to rule out a few things: She has got spark when she cranks. I've bypassed the fuel-pump relay and made it run all of the time (no joy), I pulled the connector plug off the cold-start injector (incase this was flodding her) but no change. Pulled the temperature sensor and left the connector open-circuit, no joy.
Only simple thing left to try is to short-circuit the temperature sensor to see if that will cause the car to think it needs the cold-start (not sure if open-cct or short-cct is "cold"
Any suggestions welcome.
Basically I have an '81 928S with the K-Jet mechanical fuel injection. The car starts from cold, or from hot (if only stopped a short while). However if she's been allowed to cool (for an hour or two), she'll refuse to start (just cranks and cranks and cranks). Let her cool more (ie overnight) and she'll start fine.
I've been investigating this since she did this to me last tueday night (Mrs S and I had gone out for the evening and needed the car to get home!). Eventually after bump-starting the car, I was able to get her running well enough to go home. When I did the bump-start, she was very reluctant to spring to life.
I'd struggled to get this to happen when I take the car to/from work (it appear that the fifteen mile commute isn't long enough to trigger the symptoms), but today I took a longer route (and sitting in a queue because of a crash helped too!!).
So I've now been able to rule out a few things: She has got spark when she cranks. I've bypassed the fuel-pump relay and made it run all of the time (no joy), I pulled the connector plug off the cold-start injector (incase this was flodding her) but no change. Pulled the temperature sensor and left the connector open-circuit, no joy.
Only simple thing left to try is to short-circuit the temperature sensor to see if that will cause the car to think it needs the cold-start (not sure if open-cct or short-cct is "cold"
Any suggestions welcome.
I've been pointed towards two possibilities: The air-flow sensor and a leak in the fuel system causing air to enter the pipe (eg a leaking injector).
The air-flow sensor in the K-jet for the 928 apparently can get jammed in a way that allows air in (so the engine cranks) but doesn't move the plate to allow fuel to be pumped through. hence it cranks and cranks etc.
Leak in the fuel system will only be detected by using a pressure gauge and looking for loss beyond spec.
The air-flow sensor in the K-jet for the 928 apparently can get jammed in a way that allows air in (so the engine cranks) but doesn't move the plate to allow fuel to be pumped through. hence it cranks and cranks etc.
Leak in the fuel system will only be detected by using a pressure gauge and looking for loss beyond spec.
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