1992 4.0 OHV 4x4. This was an auction buy which needs brought back to life.
It was driving and running fine until I just replaced the lower intake manifold gasket and water pump.
Now a new issue. When I put it under load, either a hill or acceleration once I hit around 2000-2500 RPM engine sputters or stall or stops altogether.
Brand new CPS, so that's not the issue.
The MAF seems fine as when I unplug it the engine dies.
There are no vacuum hose leaks. I can find no manifold leaks with starting fluid being sprayed. The bolts are all torqued soundly to spec.
I cleaned the air filter with air pressure, so it is clean.
The fuel pump and filter have less than 1,000 miles on them. The gas tank has been cleaned.
Fuel rail has 32 PSI when the engine is running. With the engine off it climbs up to 35.
It has a rebuilt ECM with less than a 1,000 miles on it.

At idle it purrs like a kitten, but under load I have to feather it and shove it into neutral and rev it up before slamming it back into drive.

It does not backfire or give me any indication of spark plug fouling, it just sputters and loses power of dies.

Ideas?

 

Have you considered the FPR? Fuel pressure regulator.

 

Thank you for the suggestion, however The fuel pressure gauge lost no pressure for more than 10 plus minutes after engine turn off.

in addition I detected no presence of fuel in the vacuum line which attaches to the FPR.

this leads me to believe that there is no degradation to the diaphragm within the FPR.

 

Is there anyway you can hook your fuel pressure gauge up and drive it around? Just because you have 32 psi with an idling engine does not mean that you are staying in that range when engine is under load.

On another note, while you may use "new parts" that does not mean that they are good. There's been many instances where replaced parts were bad straight out of the box. Very few parts are tested anymore, especially aftermarket parts. Case in point, I replaced my front wheel hub assembly several years ago. All that work and it was bad.

 

I will attempt to drive while the pressure gauge is hooked up today.

true on new parts being sometimes bad straight out of the box.

 

I drove with the fuel pressure gauge attached.

When the engine was running fine the gauge read 30-32ish PSIs.

Whenever the engine began to sputter the gauge would jump up to 40-42 or so PSIs.

In either case, if the engine remained running or if it quit the PSIs would return back to 30-32ish.

So two possibilites. Either the surging fuel PSIs cause the engine to sputter and die or when the engine is struggling the ECM is trying to overcompensate by giving it more fuel.

Which though?

 

… or is it standard for the fuel pressure to increase during those times of increased load either going uphill or when shifting to the next highest gear at 2000 rpm?

 

Does the throttle move evenly and thoroughly -matching what you're doing to the pedal?

 

Up until the point where it begins to die, then as I press the pedal further down, the power (throttle) loses enthusiasm.

 

For anybody having the same issue perhaps getting your ECM bench tested and repaired is warranted.

consider:

After much testing and trial and error as listed above, plus replacing more sensors than needed ( including the MAF and cleaning all of my injectors) I actually considered scrapping the truck. But then I thought about my EEC-IV once again… even though the rebuild had less than 1,000 miles on it. One thing I remembered from a YouTube video I saw in 2024 was that one symptom of a faulty ECM is a fuel pump that will not shut off while the key is on but the engine is off. I thought my ECM was too new to fail like that and thought perhaps there is a short somewhere in the FP wiring system.

but no…

Turns out my ECM had some faults. Even though I had a remanufactured unit from Mexico via RockAuto which was less than 1.5 years old something happened to it. Shoddy original repair? I don’t know, but when I opened it I didn’t see any obvious signs of capacitor degradation as I had a year and a half prior. Regardless, I called all the shops in my area and asked if they could bench test or if not, did they know if anyone. Nada… not even Ford… they said nothing older than 1997 due to liability issues. I did some research and found a place in Richmond, VA called “Keyworks.” I sent my ECM to them and they sent it back to me fully repaired less than a week later.

Reinstalled it today and drove the heck out of it. All previous symptoms disappeared.