macho_mango

Hi all, 1984 Porsche 944 NA.
New problem that recently started -> my car has a little bit of difficulty starting, sounds like its not getting enough fuel, but then will start up but idle erratically, almost like its lugging or pulsing. After a few minutes, it'll stabilize to its normal idle, and I can drive it normally, but then it will suddenly lose power, like its out of gas, and if I take my foot off the gas, it will die. The elctrical systems are all running as this is happening, and I can't restart the car for at least several minutes. Turns over fine, crank and everything, but it just won't catch.
Once my car does start and gets going again, engine seems totally fine, and won't have troubles with it until the next time I turn it off for at least a couple of hours.
Any ideas????????
Please help!

Yarf

I would start by checking the fuel pressure. Help can be found here.
http://www.clarks-garage.com/pdf-manual/fuel-01.pdf

Leonel_944

check reference sensors connections, DME temp sensor, the AFM, battery terminals also, and whens the last time you did a fuel filter?

J Berk

bad fuel pump

macho_mango

Hey all,
sorry, I forgot to mention, I've done a couple of things.

1) checked fuel pressure -> ok
2) checked spark -> ok
3) replaced fuel pump
4) replaced fuel filter
5) replaced fuel pressure dampene


How do I check the reference sensors?
My next step is going after the AFM, but before I go there, I want to make sure there's nothing else it could be.

Not sure if it electrical in nature - I already replaced the fuel pump relay with a used one, but newer. DIdn't seem to change things much.
I might try and get a brand new fuel pump relay just to make absolutely sure its not that. Any other ides???

J Berk

I said fuel pump because it's the same behavior my old 84 NA exhibited when the fuel pump was going.

It would provide enough pressure to run but not under load....it would crap out.....I'd coast to a stop and wait a few mins and it would start right back up.

Are you sure there are no leaks ? How are you checking fuel pressure?

Leonel_944

ref sensor connections are on the back of the intake close to the firewall just make sure there pluged in. the connections are probably really brittle so be gentle

DME temp sensor its right below the intake boot i think its a blue connector not sure though. It might be a bad connection somewhere which would cause it to be intermittent.

Leonel_944

The auxiliary air valve gave me a weird problem like this but it would burn out my fuel pump fuse. it underneath the intake manifold I don't think this applies to you but just throwing it out there

944Ross

When it dies, and you crank it, does it immediately re-start? Is the tach needle bouncing while you crank it?

RC713

I would suggest cleaning your grounds, I had an intermittent no start/random shut off situation that caused me to replace my ignition switch, plugs, wires, cap, rotor, ref sensor, spd sensor, ref ans spd sensor wiring back to the wiring harness, DME relay... You get the point. Turns our cleaning the grounds did the trick after all that (not saying all that other stuff didn't contribute to the car running better, I joke she "tricked me" into giving her a full tune up, but after cleaning the grounds the problem went away).

macho_mango

Thanks all for the advice so far.
After it dies, it does turn over and crank, but it won't catch.

The electrical system seems like its intact, and I can keep the car running as long as its coasting and engaged - the wheels turning can keep the the engine running.
I managed to drive home on the highway the other day, and when I could my engine start to die, I just dropped down a gear, and forced the revs up, and the engine seemed to pick up on its own.
Not very convenient if I'm at a light and this happens...
I talked to a mechanic, and he said fuel distributor - not sure if he meant the MAF though... any thoughts???

macho_mango

My mechanic had a look at the car, and he adjused the MAF tension. Before that, he checked fuel pressure using a fuel pressure gauge.

Cyberpunky

My car had similar symptoms and it was the DME box. We tested everything under the sun but eventually had to bite the bullet and replace it. If you can swap it for a known good one, that would eliminate it

944Ross

Adjusting the AFM tension seems like an extreme move, what basis was there for that?

whalebird

Put a new DME relay in. Of course a tune up might be in order - cap, rotor, plugs and wires, fuel/air filter. Stay away from the AFM spring and find a new mechanic.
If this persists, a determined diagnosis would be in order. What are you losing? fuel or fire? Yes the ref/speed sensor should be known good(i.e. new).
A faulty DME will act like this if all else is good.