shane_b

Evening all,

I am having a strange idle / starting problem when the engine is warm on my 1984 Porsche 928S and I wondered if anyone knew what it could be.

Basically it starts on the button when cold and runs like a dream initially….however, after it has been running for a while and is warm, the idle becomes lumpy or throbs, and if the engine stalls because I haven’t kept the revs up, or I turn it off, then it won’t restart (or even fire for that reason) until the engine has cooled down.

If I come back 20 minutes later, starts fine….. but if I literally turn off the engine after a short run and then turn the key immediately, it won’t start.

Thank you in advance.

Cheers

Shane

shane_b

Here she is by the way!

Cosmo Kramer

A bit more info on the car would help, but it looks like a 1984 Euro S correct? If so I would suspect the Temp II sensor is malfunctioning and making it run too rich when its warm.

Mrmerlin

also it may be time for a rebuilt MAF to find its way into the throttle body

Crumpler

Nice pic, like the twists with that color.

shane_b

The car is a UK car, 1984, 928S 4.7l, manual transmission.

Interesting, you are the second person that has said that today!

I decided to eliminate a couple of easy things first such as faulty relay etc.... a pal of mine came round tonight and had a quick fettle.... we noticed some intermittent voltage problems at the fuel pump. In fact during one of the periods of not starting, when I stopped cranking the fuel pump then made a whirring noise instead of initially when the key was first turned?!

Going to download a wiring diagram tonight (Are there any good ones that anyone can recommend?)

Cheers

Shane

shane_b

Thanks!

shane_b

Does anyone have a link to a wiring diagram that covers the fuel pump and related?

ltoolio

Check out Alan's site here.
Tons of things related to electronics. I *think* the full wiring diagrams are floating too. A quick Google should help uncover them.

You may want to consider picking up Jim Moorehouse's CD's from Roger. They are the full WSM and are a great reference for all things 928, beyond just the electronic system.

soontobered84

Sounds like the Temp II sensor to me.

Cosmo Kramer

You can check the specs of the Temp II with an ohm meter. Specs are as follows, check each terminal (both should be the same) and use the sensor body as a ground.

1.4 - 3.6 Kohms at room temperature
0.9 - 1.3 Kohms at 104 deg F
480 - 720 ohms at 140 deg F
250 - 390 ohms at 176 deg F

shane_b

That's uncanny, a pal of mine is a roadside assistance patrol and he came round tonight and we ran a couple of tests and he suggested I post asking for the resistance at normal operating temp and cold (at least that is what I think he said!)

Cheers!!

shane_b

Gutted!!

I ordered a new Temp II sensor from Porsche as well as a new fuel filter (just something that someone had suggested!)

Anyway, I have replaced both but it hasn't fixed the problem and I don't know where to turn next.

What I can't understand is, once the engine is warm and the engine starts throbbing before eventually cutting out after a period of time, if I remove the plug to the Temp II sensor the engine picks back up..... albeit with a stronger fuel smell in the fumes. It has to be a fueling issue. What else could make it run too rich once warm?

Also, there are two wires going to another "sensor" or something behind the Temp II sensor, and into the same unit..... what is that?

Any other suggestions?

Cheers

Shane

69gaugeman

Sounds like the cold start injector. Unplug that when warm and see if it starts.

shane_b

Ok, will do.

Something else I have stumbled across as I have been looking at photos of other fuse boxes and relays; I think I have a standard relay in position XVII.... Might be a 53 from memory.

Anyway, on most of the photos I have seen, it seems that most of them have a deeper relay than a standard cube shaped one.

I only know it is a standard one because I swapped it round with another one to test for a faulty relay.

Thoughts?