944S Intermittent running fault, injectors?
 

Hi guys,

My 944s has just started causing me trouble, i was 2 miles into a journey when in stuttered and then cut out as if it had run out of fuel!

it then wouldnt start! help came, we check there was fuel pressure and there was, there is spark, the signal from injector lead seemed to vary in strength, then it started again ran for a minute and stopped.

we noticed a burned wire from rear of distributor, can sensor? 2 wires with a wire shrowding them.

then car fired up seemed to run fine with this lead connected and disconnected. i assumed it was some sort of correcting signal? so i drived it home, i replaced this suspected wire from distributor it ran but died again then wouldnt start.

this morning it ran but was a bit rough.

what would be a good place to start now? get a diagnostic test? replace a particular sensor?

any advice would be greatfully appreciated,
thanks

Joe

I'm not familiar with the wires coming out of the rear of the distributor. The 2.5's don't have them. But there are many things that it could be. Cap, rotor, wire(s), coil (unlikely though), FP, FPR, FP relay, DME, DME relay, crank sensors, etc. Do you have any "tach bounce" when it doesn't start? There is only a very small amount.

I dont believe there is any tach bounce, i didnt notice any!

The signal stength did seem to vary on the lead to the injectors!is it the crank sensor which controls the injector signal? does it simply supply a pulse?

i did swap around the dme relay for a spare i had but it made no difference!

im parting an 1987 944s and can pull that part for you , not sure if your local but your welcome to stop by and try swapping it in and see if it makes any difference

Recheck the tach bounce, if unsure. It only moves slightly. But if you see no movement whatsoever, consider the signal not there. That would help narrow it down.

Low impedence injectors use what is called a "peak-and-hold" signal, where there is an initial spike in the waveform that opens it (quickly). Then the DME switches the signal down to a lower voltage, which maintains it open for the rest of it's designated open time.

I just recently had the same problem on my 944S. Check the "-" side of the coil for a ground pulse while cranking. Use a test light, Hook the negative up to the - on the coil and the positive up to the + on the battery.

If nothing, like I had, it's the Ignition Control Module. They seem to only be on the S models, so there isn't much info on them.

Pitcher, very good info to know for later. thanks

The 944S has a camshaft position sensor. How it factors in I'm not sure of, but I believe it allows the injectors to fire sequentially, rather than all at once. There is also an ignition module as mentioned that the 8v cars don't have.

Correct me if I'm wrong, but the 944 tach uses the voltage impulse from the collapsing magnetic field on the primary as the ignition coil fires to read engine speed. If that is the case, no bounce would indicate no spark. That could be caused by a couple things, including a bad coil, bad DME relay, or bad speed or reference crank sensor.

thank you guys for your feedback!

I dont believe it is anything directly related to the spark as the spark has always been present. From searching on the clarks garage website the most likely fault seems to be the fuel pressure valve. As my car starts and then after a couple of minutes dies then wont start, then after unplugging and injector lead it will fire up again this seems to relate to symptoms of a fuel pressure valve. The only difference is that mine doesnt die almost immediately albeit it lasts a couple of minutes! i can only pressume my fuel pressure valve is not stickign completely closed!

My next point of call is to purschase a fuel pressure gauge and see exacly what is going on with the fuel pressure!

will inform you of progress