M4A3E2

Hi All,

Got an 88 944 automatic that won't run for the life of me.
Replaced/Rebuilt:
Cylinder head
Water pump
Timing belt + Tensioner
Coil
Plugs
Wires
Speed/Ref sensors
DME
Distributor rotor
FPR
Fuel rail
Fuel pump
Fuel filter

I know my timing is set, I've got spark, and I've got fuel. It'll run every now and then but only if I hold it under WOT and then play with the throttle. I have a couple minor vacuum leaks that I am aware of but nothing that would prevent the car from running like this. Most of the time it sputters or tries to fire but never gets there. I've had it running and rev up to 6k RPM but it wont stay alive for more than 30 seconds. This car is driving me absolutely insane! I can post videos if that would be appreciated.

Jfrahm

Damper maybe. What do the plugs look like?

walfreyydo

Whats the fuel pressure?
Have you done a compression test?

M4A3E2

I’ll check when I get home. I haven’t done a compression test but seeing as I’ve replaced the cylinder head and the car has run I assume compression is good. I’ll still check both after work today

walfreyydo

Vacuum leaks can cause a lot of really severe issues (including a really huge imbalance of AFR), so I wouldn't overlook that as a possible culprit.

Fuel pressure reading is important to verify the health of the FPR, pump, etc and all components are working correctly - even though you said you replaced all that stuff still need to check it.

Also double check the obvious -
plug wires in correct order?
Timing set correctly? (I check the cam mark and prefer the TDC mark on the flywheel housing - not bellhousing port from top because its too hard to read - and make sure both are lined up)
Speed/reference sensors gapped correctly?
Compression, although seems obvious, must be confirmed (spark, fuel, air, compression, timing are all needed to run a car)

As @Rockerchief said, the AFM can cause some issues as well, since it meters air, youll want to verify/test the AFM unit and if needed, readjust the pickup arms (details on how to do this are on Clarks Garage)

Rockerchief

Try replacing your MAF. I know that sounds a bit weird but I had a reputable parts guy offer that up as a solution when mine was doing to same thing and it worked.

Pierregirard

Even though you've swapped out the fuel pump and filter, it wouldn't hurt to double-check the fuel pressure. If it's off, it could be causing the problems you're dealing with. A fuel pressure gauge is handy for making sure everything's pumping as it should in your 944.

Jfrahm

Before getting too far into the weeds, get it running badly and cut the engine. Quickly check the plugs to see if they are wet, and if they are dark from running rich. From the description it sounds rich, so maybe a leaking damper or hosing injector. Leaking or stuck FPR also but you say you replaced it (still worth checking).

Chalt

When you replaced all that stuff did you replace the DME Temperature Sensor? 944.606.125.00.M14 - Bosch 0-280-130-026
It's a $20 Bosch part that tells the DME to enrich the fuel when the engine is cold.
Mine went bad and was near impossible to start.

Notes:
DME Temperature Sensor
This sensor tells the Porsche 944 DME (computer) when the engine is cold. A cold engine is not as efficient at atomizing fuel as one that is at operating temperature. Because of this, a cold reading from this sensor will tell the Porsche 944 DME to add extra fuel until it reaches the optimum operating temperature.
This sensor fails by telling the DME that the engine is always at the correct operating temperature. When this happens you have a lean condition until the engine actually warms up.
You can see the effects of a bad DME temperature sensor as a cold start / idle problem. In some cases it can be so bad that the Porsche 944 will not run at all when cold.

M4A3E2

Thank you SO much for the advice and help everyone!

Spark plugs have some moisture but not enough for it to be fouled. The only vacuum leaks I have are the two little plastic lines coming from the damper and regulator. I’ll replace the head temp sensor ASAP and see if that changes anything.

here’s a video of when I did get it to run. Compression is good, fuel pressure may be suspect. Upon inspection I’m not 100% sure if my return line is attached underneath the car.

M4A3E2

Return line is hooked up. It tried to fire up but still acted the same.

walfreyydo

What
is
the
fuel
pressure?

M4A3E2

I don’t have a fuel pressure gauge at home that works for this style fuel rail, so I’ll have to get one tomorrow.

Chalt

Sounds like it has an exhaust leak. Not that that would prevent it from running though. You have spark, air/timing, and enough compression to run briefly. I'm thinking a fuel delivery problem.

M4A3E2

Found the source of a massive vacuum leak.
j-boot tore. Guess I’m replacing a good bit more parts!