Stalling 86 944

[Timmay!]

Symptoms:

86 944 revs up to red line freely in neutral.

Car drives/runs up to about 40mph and suddenly dies. No sputtering at all. Then you can't start it for a few minutes. DME relay feels warm. Temp is good. oil pressure is good.
DME relay was replaced and DME Computer was replaced while troubleshooting this problem.
2 injectors were recently replaced.

[drift a 944]

so if you are cruising along at say 35mph in 3rd or 4th gear and gently increase speed to 40-45mph, the car will just completely cut out?

[Tishabet]

Why was the DME computer replaced?

[Timmay!]

Nobody drives at 35mph in 3rd or 4th gear. Doesn't matter if it's 1st or 2nd, engine dies at 40mph.
The computer was replaced because the car was stalling........
Can anybody help? This is a friend's main source of transportation.

[AKCJ]

During the no start condition, is there spark? is there fuel?

It sure sounds like a DME Relay & I've heard that even a new one can be bad. You could do the DME Relay bypass the check?

During the no start condition, is there power to the fuel pump? If yes the pump is probably bad, if no then back to the DME stuff - DME Relay, speed & ref sensors (and connectors), DME.

If no spark that could be the DME stuff or the coil could be going bad (cuts out when warmed up).

These are the items that come to mind first. It sounds like changing the DME did not fix it so now you've got a spare, which is a good thing.

This could also be the AFM or the connector to the AFM - read Clarks & watch the U-Tube video.

[Tishabet]

Originally Posted by Timmay!

Nobody drives at 35mph in 3rd or 4th gear. Doesn't matter if it's 1st or 2nd, engine dies at 40mph.

FWIW, I'm definitely in 3rd or 4th if I'm going 35.

So you're saying that regardless of the RPM, the speed of the car is really and truly the sole determining factor for the cutout? That's really odd.

[Timmay!]

If the DME relay was bad it wouldn't even turn the fuel pump on, right. This car runs and drives. I have spark and fuel and good ignition timing up to 40mph.
Speed and ref sensors MUST be working because the car runs and drives. If the ref sensor were bad or the sensors were mixed up the engine wouldn't start at all.
AFM? No, again the engine runs and accellerates well up to about 40mph then dies. No gradual decrease in rpm, no sputtering. Just dies.

I'm leaning more towards fuel delivery rate, but didn't want to influence the possible answers. Sounds like the pump is weak or choked down? Could be the fuel pressure regulator not holding the correct psi in the rail?

[Timmay!]

Tisha,
You must have 944 option code 512, extremely short ratio gearbox!LOL!
No, but seriously, I didn't believe the guy when he said it cuts out at 40mph. I said it must be a certain rpm, not car speed. But, it's true. I've not seen this before.

[AKCJ]

Originally Posted by Timmay!

If the DME relay was bad it wouldn't even turn the fuel pump on, right. This car runs and drives. I have spark and fuel and good ignition timing up to 40mph.
Speed and ref sensors MUST be working because the car runs and drives. If the ref sensor were bad or the sensors were mixed up the engine wouldn't start at all.
AFM? No, again the engine runs and accellerates well up to about 40mph then dies. No gradual decrease in rpm, no sputtering. Just dies.

I'm leaning more towards fuel delivery rate, but didn't want to influence the possible answers. Sounds like the pump is weak or choked down? Could be the fuel pressure regulator not holding the correct psi in the rail?

OK, I was thinking that it was on again off again but you're saying that it does the same thing the same way every time? And you're thinking the fuel delivery system isn't right. Could be.

Could also be an intermittent failure under load - bad coil, what's the fuel pressure?, AFM could be hitting a bad spot? bad solder connection in DME (except you already replace it), bad (poor connection) at the speed & ref sensors? Bad connection at the injectors?

If the fuel delivery rate gets out of range at a certain point, wouldn't that point to he AFM more than anything else?

I'm just trying to give you some more ideas. Keep us posted.

[TibetanT]

Just a thought, but it could be a bad TPS (throttle position switch).

Might want to check that via Clarks Garage write up.

[TibetanT]

Never mind...I just re-read the original post. Duh! You said it revs up just fine.

sorry for my mindless response

Too quick with the mouse I guess

Sounds like fuel delivery problem. Fuel pressure regulator, fuel dampner, or fuel pump problems.

[Timmay!]

OK, got it fixed the other night! Boy, was he happy to have his 944 back and running!

Here's the story.
Sounded like a fuel delivery problem to me.
I was right. However, there's 2 components to fuel delivery: rate and pressure.
I jumpered the DME relay socket: Pump was kicking out over a liter in under 30 seconds. Good.
We drove the car again and made it fail. Remember, It would not restart on it's own for a few minutes? Pulled a vacuum line at the throttle body and squirted brake cleaner in. Tried to start it and it fired right up!
Ok, now we're sure the car wasn't getting fuel.
.......but the pump was great! Confused.
We tried a test run without the customer's "new" aftermarket fuel cap..... same failure. Tested again with NO fuel cap. Same failure. We did this because we thought the tank might not be venting correctly, thus preventing fuel delivery rate under load.
We connected a long clear hose up to the end of the fuel rail and stuck a portable pressure gauge on the end of that. Fired it up. ~29psi. I disconnected a vacuum hose to the regulator and the pressure jumped up to ~ 39psi. OK, that's fine.
Test run. Customer drove, I rode shotgun and had a light on the gauge. Just to be safe from the hose bursting, we made sure the entire hose was completely outside the car. Got up to failure speed and the fuel pressure jumped to up over 80 psi and stayed there!!!!!
It looks like the fuel pressure was so great that the injectors couldn't open.
.........what controls the pressure? ......the regulator.
Digging into my mountain of 944 racing spares at the shop produced results. Bolted it on in a few minutes, fired it up, checked for leaks, test drove.
Car went like a raped ape!
Morale of the story: Too much of a good thing...............

[AKCJ]

Thanks for posting.

So it turned out to be a bad fuel pressure regulator that is only bad during certain running conditions? An intermittent fpr failure?

Somehow I thought that the fpr was basically a diaphram & a spring. And, failure would be full time or none at all. During testing the pressure was good @ 29 psi and jumped up with removal of the vacuum hose. To me this would prove the fpr is good. I totally agree with running with the gauge hooked up - that's the way to show the thing who's the boss!

I'm glad that you found the problem but I'm not sure I understand it.

[SuperXRAY]

Was the FPR tested while it was at operating temperature? I had an FPR fail in the same way on my Mercury Villager. Would work fine when things were 'cold', but once the engine compartment heated up, it stopped regulating, causing the van to lose significant power and studder until RPM's hit about 3k, then it would take off like a Villager On Steroids!.

It's more rare than their normal failure, but it does happen. I ran a separate piece of hose from the discharge side of the FPR to the discharge line, long enough to run it and lay it on the windshield with tape, next to my fuel pressure gauge. That way I could see exactly what was going on. Went for the drive, pressure went way high and fuel stopped flowing through the discharge line. Further investigation found that fuel was shooting through the vacuum line and into the throttle body, making matters even worse.

While waiting for the part, you could drive the van, shut it off, and smell gas coming from the driver-side engine area when getting out. Took the boot off the intake to find the gas coming from the vacuum line that leads to the FPR. I found it quite interesting...and lucky to find it when I did, as that can be seriously hazardous.

[Timmay!]

Yes,
The off and on vacuum line test while static made it look like the FPR was good. But we knew something was failing under load......