Dogberri

i was driving home today and it (83 944 n/a) quit on me. engine stopped running as if i ran out of gas. got it home and started trying to diagnose the problem.

1 have spark in all 4
2 fuel in all 4
3 battery connections good
4 air filter not plugged
5 have 1/2 tank of gas
6 timing belt not broken

when i pull the fuel pump fuse it starts after a couple turn overs. idles fine but then bogs out with any engine load. Im thinking i have weak spark, twelve volts going to the coil. whats next step? anybody have similar problems in past? any thoughts?

F18Rep

So then, are you saying it is starting on residual fuel pressure? Gotta be,right? I guess I would look first to quick make sure your o2 sensor isn't shorted out on the exhaust, I'm thinking that will take our the fuel pump bc they are on the same circuit - it might be loading it down so it pumps intermittently. Beyond that, then I would get a fuel pressure gage and pick up the trail to the problem - guessing at stuff always gets me in trouble... Bruce

Dogberri

thanks for the input, ill be sure to check when i get home

Legoland951

Does the car start and run/rev up high with a healthy amount of starting fluid every time? If you can answer this question it will eliminate a lot of guess work.

944_S_TYPE

DME Relay? Or perhaps the timing belt jumped a tooth in the belt?

Just my .02

Dogberri

T-belts not loose but i'll check that just to make sure. i can only get it started by holding the throttle wide open and even with that it sounds sick and struggles to get to an idle. i was going to try that DME relay jumper thing tonight to see if thats it. i have not tried any starting fluid. i know its not ignition components. when its idling, if i pull the AFM plug off it almost dies, it also starts easier with it unplugged.

Dogberri

would a bad DME temp sensor cause these symptoms? or speed senor?

Tom M'Guinn

Sounds like you should check your fuel pressure to see if it is falling off after starting it. Also, is it limited to the idle -- what happens if you start the car with the throttle partly open -- can you keep the engine running if the revs are up?

Legoland951

Don't waste time diagnosing things randomly. Get starting fluid and I can help you as I have not encountered a 944 no start I could not solve and I have dealt with many many 944s along with other types of cars with no starts.

Dogberri

thanks for all your advice everybody, found out what it was though. the PO put a potentiometer "in-line" on the DME temp sensor, positive tab broke off that thing. now i have a new question for you all though....

Is there supposed to be a jimmy-rigged potentiometer on the DME temp sensor? is there supposed to be anything there other than the sensor itself?

again, thanks to all the suggestions

Legoland951

The block temp sensor will cause rough idle but not cause the car to bog under load. Use the starting fluid. I can name 10+ possible causes of anything from a set of bad cap/rotors to bad DME and everything else in between. There is a specific order in diagnosing the problem and random guessing is not it.

I want to eliminate many problems by hearing your answer after using starting fluid and how the engine runs under throttle while someone spray pulses of the ether down the air box as the car is throttled up. Lets put it this way, a bad/out of calibration AFM, blown head gasket, intermittent short in the reference/speed sensor, bad cap/rotor/wires (yes I would want to know how you checked for spark and whether you watched all 4 wires spark in sequence and how regular/strong the spark is), etc.

We can eliminate most of that by simply using starting fluid.

Tom M'Guinn

There should not be any potentiometer in line. Sounds like the sensor may have failed and somebody got the bright idea to add a variable resistor. I'd start by removing that and testing the sensor. Even if that's not the cause of your current issue, you'll want to fix that.

Dogberri

im not sure what you mean by "random guessing". when i connect the broken wire the vehicle starts, runs, and revs just fine...

Dogberri

thats what i figured, ordering a new one tonight

ZR8ED

A potentiometer inline with the temp sensor wire, is an old "trick" to fool the ecu that the engine is still cold, and give it an extra boost of fuel. It doesn't really work on a stock engine, but it does have some effect on engines with very mild mods that the ecu is not programed for. It is very old school.