My 1990 F350 with the 7.5L EFI engine won't start and I've changed the spark plugs and the wires and the coil, distributor cap, and rotor, and the fuel pump and still it won't stay running. It fires up for about 3 seconds and then dies every time and I'm running out of ideas.

I did a compression test on it and all the cylinders except cylinder 8 which is at 75psi

Here is how it all looked on the dry compression test
130.........75
123.........124
119.........139
125.........130

When I did a wet compression test on #8 it jumped up to 119 psi so I'm sure the rings or cylinder in #8 is worn.

I tested the fuel pressure and at the fuel rail I got 40 psi with the key off engine off and when trying to fire up the engine it got up to 44 psi which was the exact same reading I got for both front and rear tanks. I'm assuming then that there isn't a fuel problem particularly since I sprayed ether into the intake and it didn't change anything. Still only ran for about 3 seconds exactly the same as without the ether.
Also I pulled the plugs off and saw they were wet with fuel.

When checking for spark I can see spark on all the spark plugs but I'm wondering if it is a weak or intermittent spark (don't know for sure)

One other thing I'm wondering is if the ECM electronic control module might be faulty. Would a faulty ECM produce what I'm seeing? I'm seeing them on Ebay for like $19 for this truck so it's a cheap fix if that is even a possibility that this might be the problem.

I'd sure appreciate any advice on this thanks

 

Did you check for codes? If your CEL is not on it may still have a code or seven. The worn out cylinder doesn't help.

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Yes, and all I get is code 34.

I checked the EGR valve also and it was originally stuck so I removed it and cleaned it and now the EGR is working fine but that doesn't change anything as far as getting the engine up and running.

 

Some other threads the OP has started on the same subject (no start):

https://www.ford-trucks.com/forums/1...1990-7-5l.html

https://www.ford-trucks.com/forums/1...-question.html

 

Yes, but they don't answer the question.

 

Then post in the other thread so everyone does not have ask the same questions again. That wil bump your thread to the top again. An occasional bump is acceptable practice.

 

The injector on #8 may be leaking a little and washing the oil out and that will give the low reading.
Also 44psi is too high and should not be above 40psi (39.3psi with a very good gauge) with pin #6 grounded and the key on.
You might want to check for a blockage on the fuel return line to the tanks.
Also check or replace the ECT & ACT sensors. Those two sensor do not always give a code when bad.

 

Was the fuel pump external or internal to the tanks? For $15 off ebay, I wouldn't expect it to last very long at all.

Your fuel pressure is fine. Have you checked the timing or tried to run it without the SPOUT connector?

Bill would a bad ACT or ECT cause the truck to run briefly and then die? I didn't think those sensors were critical for the engine to run.

 

Andy,
Most of the time we hear of the truck not starting at all with a bad ACT or ECT sensor but once started I would think it would run.
But he is saying he has wet plugs and sounds like the truck maybe flooding out.
Those to sensors could make it rich and with no codes pointing to anything else I would look at them.
We had another poster on here the other day that had high fuel pressure around 44psi and turned out he had a kinked fuel return line and after he fixed the line the engine started.
So I would suspect that his high fuel pressure of 44psi might be the reason for it not starting.

 

I'm not sure where the fuel return line is. Maybe if someone had a picture?

 

It is dark now but if you still need one I could go out and take a photo tomorrow.

But it should be about the same as the left arrow in the photo below:


/

 

I'm just not sure what to make of the picture. If you could get another I'd appreciate it thanks