1995 start\stall

[John Del]

I have a 95 3.8 that suddenly stalled while idling. The car was running perfectly, with no drivability symptoms whatsoever. The car will start immediately and run for 1 to 2 seconds (sounding fine) and then stall. Trying to add throttle kills it quicker, like it's getting no fuel. The pump sounds healthy with key on, and the fuel pressure is 42lbs.

I had it towed to my buddy's garage for further diagnosis. It stored codes for both banks lean, and no others. He pulled and cleaned the MAF sensor, with no improvement. With the MAF sensor disconnected, the car will continue to run, and it will rev normally. We installed a known good sensor, and the problem remains. Going further, my buddy started checking the data through the scanner, and found the barometric frequency at 159hz, instead of 150 (I may have these figures reversed from memory). He also found that it showed a load of 77%, with just the key on and the engine not running.

He's suspecting a bad eec, but has only replaced three in over 20 years. Anyone have ideas? Thanks!

John

[knl25]

It sounds like fuel issue to me. Did you check the fuel rail pressure at various conditions? Has the fuel filter been replaced on a regular basis?

[John Del]

I replaced the filter when the car stalled, with no improvement. Also, this occured with about a quarter of a tank left, and there was no problem with the other three quarters. Again, it ran perfectly until it stalled.

Fuel pressure at the rail is 42 lbs with key on, during cranking and start until it stalls. Never drops.

Again, the van will run with the Mass Air Flow sensor unplugged.

John

[knl25]

Just for reference my scantool shows a barometric pressure of 154.4 Hz (in the Boston area). I'm not sure what this means or how it is calculated since there is no MAP sensor in the windstar. My calculated load is about 14%. Just curious what your scantool shows for the MAF sensor reading (which is what the PCM receives) with your old and replacement one? Do they differ and change accordingly with different throttle position? Could there be a short circuit in your wiring harness from the MAF sensor to the PCM when it is plugged in?

[John Del]

Originally Posted by knl25

Just for reference my scantool shows a barometric pressure of 154.4 Hz (in the Boston area). I'm not sure what this means or how it is calculated since there is no MAP sensor in the windstar.

I believe 154Hz is what it's supposed to be, I mistyped. It is showing 150. My friend explained that the barometric pressure is probably computed from MAF readings, and that 150Hz is probably something like what you'd get at 7000 feet above sea level.

Originally Posted by knl25

My calculated load is about 14%. Just curious what your scantool shows for the MAF sensor reading (which is what the PCM receives) with your old and replacement one? Do they differ and change accordingly with different throttle position? Could there be a short circuit in your wiring harness from the MAF sensor to the PCM when it is plugged in?

My calc load is 77%. We'll get back to it in a few days and take more readings. Is your reading at idle? Mine is with key on, engine off. Yes, a wiring issue is something that we've considered. I'm guessing either a wiring problem between the EEC and the MAF, or perhaps an input buffer in the EEC itself is bad. I took the van out for a spin around the block with the MAF disconnected, and the freaking thing runs perfectly! Starts and runs immediately, no stumble, no miss, pulls hard to redline. (Odd how the EEC can come up with a fuel ratio based on internal mapping with no MAF feedback at all.) Reconnect the MAF sensor and it dies right after start, and tipping in more throttle just makes it worse. It's like the computer is figuring almost no zero air movement in the throttle body. I'm going to pull the air tube out and see if there is some sort of obstruction in the MAF tube.

John

Edit: Just to make this a bit more weird, when we took the van for a spin with the MAF sensor disconnect, the check engine light went out after a couple of miles!!!