87 944S Cranks but doesnt fire up

[mhariush]

Trying to trouble shoot my 944S.

The engine cranks but doesnt fire up. When I turn the key to "on" all instruments light up, lights work, everything. When i turn the key to start, it cranks but doesnt fire. Tachometer doesn't bounce.

The fuel pump doesnt start, listened for it and also unhooked the fuel lines to see if anything pumps out. nothing.

No sparks and don't hear the injectors click. The injectors are brand new OEM Bosch and the spark plugs are good.

Checked the coil, has 12V at + connector.

Checked the plug going into the Ignition Control Unit (Module), has 12V.

I've checked for loose wires and burned wires but can't see or find anything.

The DME relay is also good and working.

Any thoughts on what could cause the pump, spark and injectors to not fire up?

Thanks!

[v2rocket_aka944]

Originally Posted by mhariush

Tachometer doesn't bounce.

Sometimes metal particles or dirt will get on the reference sensor tip and will prevent it from working...no reference sensor = no fire...

[mhariush]

I was really hoping not having to pull it, because that means i need to pull the manifold again i guess. The sensor is new, but could have gotten something on it i guess. If it's dirty and not registering, would that also keep the fuel pump from engaging?

[kfray]

The Speed / Reference sensor is on the bell housing a the Hall sensor is on the front of the the Cam Housing, check the wiring of both sensors.

[mhariush]

Arent the speed sensor and refrence sensor together by the flywheel at the back of the engine? One connects to the throttle position switch on the manifold and the other connects on top by the fuel rail (on top of the cam housing in the back of the eninge)? I checked the conncetion by the fuel rail, this connector is also brand new, as the old one had cracked.

[kfray]

Yes you are correct the speed/reference sensor is on the bell housing. The Hall sensor is on the front of the Cam housing.

[v2rocket_aka944]

Hall sensors get fried sometimes by being next to the exhaust so long...perhaps your carwash got it a little wet and killed it...

Getting to the ref sensors of an S is a pain because of the stupid intake manifold design...Porsche dropped the ball on that one rather than making something that works just as well but much less complicated...

[rick13]

How do you know your DME relay is good. Did you try jumping it?

[mhariush]

I'm trying to get the speed sensor out today. The sensor is new, but could have gotten something on it when the starter was engaged while the car was running.

The hall sensor is new.

I have another 944, and I took the DME relay from that car and put it in this one, so I know it's working, also, the other car is running with the DME from the stalled car.

[mhariush]

I pulled the speed and reference sensor out, they looked pretty clean, cleaned them off, so they had nothing on them and put them back in. Still no bounce on the tachometer and the car doesn't fire. I checked all the connectors, the one by the fuel rail, the one on the underside of the mainfold and the hall sender (which is new).

Checked the coil again, used a test lead from the - to ground and it arched, so the coil is good right?

What is before the speed sensor? If the speed sensor tells the dme to fire fuel pump and sparks, what tells the speed sensor to start? Or is that magnetic and it just registeres no matter what?

[kfray]

Check for continuity of the engine harness for the Speed/Reference sensor.
DME/ECU connector pin 47 to pin 1 of engine harness connector
DME/ECU connector pin 48 to pin 2 of engine harness connector

[mhariush]

Kfray, I'm sorry, I'm somewhat of a novice so I'm a little unsure of what you're saying.

Check the continuity of the harness for the speed/ref sensor? I assume you mean just follow the wires to make sure they're not broken/damaged etc?

The DME/ECU connector Pin's I don't understand. What do you want me to check there? I opened up the passenger foot well and have access to the DME.

thanks!

[kfray]

In other words check the resistance of the wires pin to pin.
Do you have a meter capable of reading resistance, and do you know how to use it?
The DME / ECU is the Engine Control Unit, as you pointed out is in the passenger foot well. If you unscrew the ECU there is a release for the 55 pin connector, locate pin 47 and 48 and check the (continuity) Resistance to the engine harness Reference connector pins 1 and 2 with a meter, it should be just a few Ohms.

[mhariush]

Ok, I think I understand. I picked up a meter a couple of days ago.
So you're saying I disconnect the connector from the DME, check the resistance on pin 47 to 1 and then 48 to 2 on the connector?

Thanks, sorry for being slow about this.

[kfray]

No check resistance of pin 47 on the DME/ECU connector for to pin 1 on the engine harness connector where the Reference Sensor normally plugs in and 48 to 2.

[GreenWater]

Are the speed/reference sensors adjusted right?

Maybe a bad ground?

I hate when I fix something on my car and then I have problems like yours. Not firing for who knows what reason. Good luck.

[mhariush]

Could be a ground somewhere... there's no reason why the sensors are out of balance, the car was running fine for a day and they weren't changed after that.

but this all happened after the starter got stuck and was engaged while the engine was running. Burned out the starter. And this happened after i took the car through a car wash. I started the car up after the car wash, drove home, about 3 min and parked it, and that's when it wouldnt shut off, the engine shut off but the starter kept cranking it. After the starter disengaged and burned out the car didnt fire up again.

[mhariush]

I'll try to check the resistance on the pins tomorrow. Thanks Kfray.

[944Porker]

fuse number 34 (dme/fuel pump) is ok?

Just a thought, I didnt see it mentioned yet.

[guru944]

Mhariush;

Also check the Ignitor/amplifier which is located on the drivers front engine bay/ fender (behind the left front light). This goes bad sometimes.

***Make sure your Engine is properly Grounded to the chassis***

Ground-loops are very common problem on the German cars after a while.

Keep us posted, later.