My '92 currently runs extremely rough at high RPM, and it has been parked because it's not safe to drive. Best symptom I can describe is the engine bucking/sputtering at highway speed -- generally 50 mph and above. The truck starts fine and will remain at idle with no hiccups. Low to moderate speed driving is fine in the lower gears, but reaching highway speed and highway cruising gets problematic. I'm wondering if it could be a fuel issue or the VE on its way out. Truck is the '92 listed in my signature and now has about 570,000 miles on it.....so could be premature failure on the VE, hahaha.

Any thoughts are greatly appreciated. The truck is just a daily driver, very light pump adjustments, and always treated very well, so no issues of it being heavily modded/abused.

Thanks in advance,

Dawson

 

Take a sample from the fuel/water separator.

Mine did something very similar, and I had a few gallons of water in the tank.

I'm amazed it idled, or even ran at all, with what I found.

If it's clean fuel, I'd put a pressure gauge on the lift pump. I just changed my original pump (gained 1 psi of pressure)




Mike

 

Thanks for the information from your similar situation. I checked the water/fuel separator and appears to be clean diesel fuel with no signs of water/gunk. I did not do a pressure test yet on the lift pump, although it was just installed and has less than 200 miles on it.

Not sure how this can relate, but I did find one wire pulled loose on the oil pressure sensor plug on the side of the engine block -- so I repaired that wire. Engine still cranks and idles like normal, so I took it for a test drive down the county road.....and of course, it now doesn't choke/buck at all, yet I don't trust that it's resolved . No codes stored in the ECM, for what that is worth.

I do have two existing leaks from the injection pump (had those LONG before this recent fault). Both have greatly progressed recently, so I likely will be replacing the pump regardless.

Thanks again for the input.

-Dawson

 

Did you change the fuel filter? You need to dump the contents into a clean white bucket to see what is in there. You say you changed the lift pump. A small air leak in the line between the inlet of the lift pump (including the fitting) and the tank can allow air into the fuel. Considering that line is under an increasing vacuum by RPM, a small leak may not be noticeable at idle but get worse as engine RPM increases.

 

It has a new fuel filter that was installed at same time as the lift pump (less than 200 miles on both).

The bucking issue began some time ago, before replacing the new lift pump that it has currently. At first occurrence, I initially changed the fuel filter as a starting point. Symptom continued, then did the lift pump (and current new fuel filter) hoping to get some progress. I can recheck lines for secure connections.

Thanks,

Dawson