Car starts then shuts off immediately

[chitown944]

my luck of 8k since ownership without a prob has come to an end. I was driving when all of a sudden the cart felt it wanted to turn off. So i pull over and thats what happened. I havent been able to get it to run since Friday. It starts cranks and then shuts off. A couple of time i was able to rev it but then it bogged down. I've done the following and still no dice.

1. Check for fuel pressure...at least 40psi
2. Checked coil & alternator with volt meter...so plenty of spark.
3. Checked fuses..all working
4. Checked plugs cap & rotor...all relativley new
5. Replaced performance chip back to stock...same difference

What's left...dunno I say bad DME relay my bro is thinking bad air flow sensor..or bad ignition switch...what else can I do before I haul it out to the Porsche dealer...

[TCMdocs944]

DME relay....


thats my vote.


What is the thing that you can do on the lates to jump it with the wire thing?

[Porsche944]

sounds like the AFM is bad/disconnected or you have a serious air leak downstream of the AFM.

When the engine starts the DME ignores the AFM signal until engine RPM reaches a specific set point. Once the set point is reached the DME 'polls' the AFM looking for a valid load signal. If the load signal is not within spec or is not there, the DME kills the engine.

[Paul Glasson]

Also check engine position sensor connections

[chitown944]

where is the check engine sensor thingy at

[Porsche944]

There is no "check engine sensor thingy."

The previous post refered to the Engine Speed and Reference sensors which are located on the driver side of the engine on the clutch bell housing.

The Reference sensor "tells" the engine management computer (or DME in Bosch/Porsche speak) when #1 cylinder is at Top Dead Center, or TDC.

The Engine Speed sensor "tells" the DME how fast (in RPMs) the engine is running.

Coupled with an Engine Load signal from the AFM (Air flow Meter), an Air/Fuel Ratio signal from the Oxygen sensor, and an engine temperature signal from the DME Temp II sensor, the DME manages the fuel/air mixture by altering the fuel injector duty cycle (how long the injectors are open) to insure the engine is running with high efficiency and low emissions.

Based on these facts, the symptoms you describe are an EXACT match for a disconnected or bad Air Flow Meter.

[chitown944]

ok what does it look like and how do i get to it

[Porsche944]

The air flow meter is attached to the end of the air box, where the air filter lives.

The AFM is a roughly square grey box with a black top.

For more info on the AFM try here: http://frwilk.com/944dme/

Once the page opens click on Air Flow Meter (AFM).

[chitown944]

sorry i was referring to the Engine Speed and Reference sensors which are located on the driver side of the engine on the clutch bell housing.

[Porsche944]

OK.

Stand on the driver side of the engine bay and locate the oil filler neck. Look down on the engine between the oil filler neck and the firewall.
You should be able to see a 1" square "window" in the bell housing.
Just below the "window" you should be able to see the Speed and Reference sensors.

If you follow the wires from the sensors you should find their connectors and the connector for the O2 sensor.

Hint: If either sensor were bad the engine would not start at all. This is due to the following:
1. The DME MUST know when the engine is at TDC on #1 cylinder.
2. During the cranking phase of the engine start sequence, the DME MUST see an engine speed >200 RPM before the injectors and spark plugs are fired.

Since the engine starts, both sensors MUST be good.

You can also rule out the O2 sensor because it is being ignored by the DME. The sensor does not develope a useable output until it is heated to about 600 degrees or so.

By the same token, you can rule out the DME Temp sensor II because the DME ignors this signal during start up and cold enrichment.

This leaves the AFM, the interconnecting wiring between the AFM and the DME, or a crack/hole in the intake boot (the rubber "tube" between the AFM and the throttle body) as the most likely suspects.

[chitown944]

ok i just took off the cone filter and had someone crank it...the lil door opens and wants to suck in the air...so is it safe to say the dme relay and AMF work

[TCMdocs944]

No.










That little door will open as long as the throttle is opening.
We are talking about electrical here....the stuff under the black cover on the AFM.

[s928s]

Check the connections at the air meter as TCMdocs944 noted. There is a large connector that attached to the meter, between the large rubber intake tube and your fiter cone. Hopefully the PO or whoever installed the "filter cone" may have damaged the clip to the connector or damaged the wiring when removing, or even luckier may have popped off.

[Paul Glasson]

Porsche 944,
You guys have more knowledge on the mechanics of these cars than me and probably the air sensor is the problem. My car however did exhibit the same symptoms as chitown944's car by starting and shutting off immediately and it turned out to be poor sensor connections. The car would run sometimes then would cut out and present the symptoms mentioned trying to start again. Just my penny's worth-someting simple to check.

[TCMdocs944]

Thats a good bet too.....some of these connections are quite sensitive after 20years of heat cycling.

[chitown944]

well it wasnt the DME relay...bout a new one same crapola...