Looking for help diagnosing a '93 stalling 3.0 engine

[Ray V]

Hello, all.

I'm looking for help in diagnosing a friends '93 3.0 that stalls immediately after starting. He just ordered a service manual off the internet but won't have it for a week (I am in Hawaii). I thought I might get lucky asking the forum members.

Background:
1) MAF is disconnected (it failed about 2 years ago so I unplugged it to get him home and he never replaced it).
2) I initially suspected a fuel issue so he replaced the filter
3) significant corrosion on coil contacts and the cap and rotor were badly worn - coil, plugs, wires, cap & rotor replaced (needed the maintenance).

Symptoms:
1) engine was running OK and then stalled while driving (~35mph)
2) starts normally, then dies after 1-2 seconds
3) fuel pressure is 40psi
4) engine runs roughly on its own with the IACV disconnected (will not run with IACV connected)
5) engine will run on starter fluid (with the IACV connected)

I thought that the IACV was bad, and he bought a replacement one for $80. Turns out to not be the valve. I want to diagnose this issue any not replace parts and hope to get lucky.

Any one have any suggestions. Could the EGRV be stuck open?

Thank you.

 

[Ray V]

I forgot to add - the check engine light is not on.

Ray V

 

[Ranger44]

The truck is going to need a MAF to run. Without it the computer will not know the incoming air and be lost as to what amount of fuel to use.

Probably why it will run on starting fluid.

Have you tried to plug in the MAF?

 

[ForOffRoadDriving]

clean the MAF of get another one on there, it wont idle well without it, but it should throw a check engine light and you said there isnt one so do you know that the bulb is indeed good in the dash? does it light up when you turn the key to the on position?

 

[Ray V]

The MAF sensor is indeed bad. The owner of the truck has been driving it for 2 years with it disconnected. His truck, along with the others that i have diagnosed with bad MAF sensors, ran 'fine' with the MAF disconnected. By 'fine' I mean that it would idle and accelerate well. I am sure that the engine was running rich - the cat may now be clogged now. The plugs that were removed had excessive black soot on them. If he was to replace the MAF, I would image that he would also need to replace his O2 sensor/s and his cat.

I do not know why his 'check engine ' light is not illuminated. The bulb does work (it illuminates with the key in the on position).

Regardless, the MAF is not what is causing the truck to stall now. Any ideas on the stalling issue?

Thank you

 

[Ranger44]

I don't understand how it could run properly without the MAF in the first place.

The only thing I can think is that the PCM eventually adjusted to a dying, then dead MAF, and just used the feedback from the HO2S's and other sensors to try to run even remotely well.

It's my opinion too, that the engine would run rich. Which would explain the soot.

I do know when I unplugged my MAF on my 94' 3L, that it would idle VERY poorly then completely stall.

You need to replace the MAF, the PCM is designed to run with it, and can't compensate and adjust for EVERY condition correctly without it. If it wasn't a needed sensor, then FORD wouldn't have made it a key sensor. The MAF is just as every bit important as the HO2S's, TPS, ECT, etc.

If it adds any weight to my words, I am not just a novice that tinkers around with cars, I am an actual practicing auto tech with a Ford cert.

 

[ForOffRoadDriving]

any chance the timing is off? its probably not likely, but it could cause stalling if the base timing is too far off? do you have any access to a scan tool to watch the live data for the few minutes that it is running?