1986 944 n-a cranks but wont start

[Orca]

I recently purchased a 944 and the previous owner said it cranks but wont start. When i spray starting fluid in the car it will turn over for a second. I have replaced the fuel pump and filter, fuel injectors, spark plugs, dme relay, speed/ref sensors, and tested the wiring harness to the injectors and they all worked fine. If someone could steer me in the right direction it would be greatly appreciated.

[Jfrahm]

I assume you are seeing the tach bounce when you try to start. if so I'd try a DME relay jumper wire, see if it starts. You should hear the fuel pump run.

Then if it doesn't, try clicking the injectors with 12v to the harness, see if it catches.
(I think you should have 12v to the injectors and the DME grounds them? Check this)

If tickling the injectors works all you are missing is a signal to the injectors. Maybe the injector driver in the DME itself is blown.

You can do this yourself, tickling injectors should dump some fuel into the intake which the engine can run on for a few seconds when you go around to turn the key. Just click the injectors quickly, do not hold them open. Like you are sending a few dots of morse code.

If this doesn't work, try a fuel flow test from the rail to an old soda bottle. It should hose out a lot of fuel. If not, maybe the tank sock is clogged.

[Orca]

I dont see tach bounce, do you think the gap might be off on the speed/ref sensors?

[Jfrahm]

Maybe but it does not make sense that it runs for a second with a spray of starting fluid, if that's what you mean by "turning over" (to me that means the engine is rotating). Maybe the tach is dead. If there is no good signal from the Speed/Ref there should be no spark (and no tach bounce) and it should not run at all, starting fluid or no.

If it's not catching when provided with fuel try a DME relay jumper first and eliminate the obvious and then I'd try to determine if the DME is working at all, providing power to the AFM and injectors and the like.

[Sebscst]

Are you sure the timing belt isn’t broken? That won’t be good. That’s the infamous “ it cranks but won’t start “ from a seller.

[DannoXYZ]

Doubt you can crank engine with broken timing belt as pistons will collide with valves and prevent further movement.

Take distributor-cap off and turn over engine by hand 720 degrees. If rotor spins complete 360-degrees, timing-belt is OK. Should still replace it ASAP as old belts can snap and cost you thou$and$ in repairs.

Check speed/ref-sensor signals at DME connector with oscilloscope. Will tell you with 100% certainty if they are adjusted properly.

[Sebscst]

Yes you can ask me how I know.

[mikseymono]

Sounds like DME relay...jumper the wires at the DME relay...and if it starts..voila....then get an OEM relay.

M

[Sebscst]

Any update?

[fitzpac3]

Sorry for the length, but I need to give you Porche 944 experts the full story. I am experiencing a mystery when it comes to getting my 86 944 started. I have followed every tip from Clarks to working with Edredas on Youtube and the car just won't start. It fires but won't start.

Background-decided to have the cylinder head rebuilt in the spring by Lindsey racing. I mailed it off and decided to go through the rest of the motor doing the following:

- Replaced all vacuum lines
- New FPR and Damper on rail
- Original fuel injectors rebuilt and flow tested
- MAF meter rebuilt and tested
- DME rebuilt and certified
- New timing and balance shaft belts/timing is set perfect ALL marks line up
- New rotor, cap, wires and plugs
- New gaskets all around including cam tower, head gasket
- New speed and reference sensors/tested their operation using multimeter
- Throttle body rebuilt and new o ring
- New DME temperature sensor and new DME relay in fuse box

And many more little new smaller parts. The fuel pump and filter are about 4 years old.

I had the car running but developed a sever oil leak. Discovered I had the wrong size seal on front of the cam tower. Still leaking and appears to be the old style OPRV and old oil cooler housing which Porsche tech bulletin said needs to be replaced with a 1987 version. I plan to do it as soon as the car actually runs. When it did run after all the above work, it did not accelerate very well.

So here we are today. car turnovers, tries to fire but won't start. I have checked the following:

- Fuel pressure by jumping DME-PSI spot on from fuel pump to end of rail.
- Used a spark tester on each plug and wire....and the coil. Getting spark all the way around

The speed and reference sensors must be working correctly if we are getting spark and fuel. I also get tach bounce. When I turn the engine over, I do smell gas from the engine.

HERE IS THE MILLION DOLLAR QUESTION:

From the list above of items and maintenance performed on the car, what would cause it not to start?

Thanks
Casey