Hesitation at 1800 RPM

[Ben10]

My 1999 C2500 Suburban will hesitate at cruising speeds (65-70+MPH), RPM's are usually anywhere from 1800-2000 when it will hesitate. This will occur during the first 30 minutes of driving, but will not occur after about 30 minutes. Ambient temp has been anywhere from 84 to 98 degrees, and the engine temp is normal. This occurs with the cruise on, and with it off. I have tried third gear as well, same result. One suggestion from a Ford diesel truck owner was a exhaust back pressure sensor. I don't even know if I have one.
Has anyone seen anything like this and repaired it? Thanks.

[Ben10]

It now misfires at idle while warming up, then smooths out unless the 1800 RPM threshold is broken. Any ideas?

[ronniejoe]

There is no exhaust back pressure sensor on your truck.

The hesitation could be one of many things. First, I would check to make sure that the lift pump is working properly. With the truck running, open the thumb screw bleeder valve on top of the fuel filter. If fuel gushes out, the pump is running as it should. If no fuel and the truck stumbles, the lift pump is not working. If it's not, troubleshoot and fix that first.

[Robyn]

When was the last time the fuel filter was changed ???

The filter on these is fairly small and can become plugged quickly with a couple bad loads of fuel.

If you have not changed the filter in a while (couple months or longer) install a new filter and , as RJ mentioned check to be sure the lift pump is running properly.

The filter gets overlooked a lot and can cause all sorts of subtle problems that tend to fall right in with what you describe.

Any DTC's showing (SES Light coming on) ???


Keep us posted

Robyn

[Ben10]

I will change the fuel filter and check the lift pump at the same time. It's been about 8,000 miles since last change.

A local shop felt it might be the injection pump, does this sound anything like IP failure?

Thanks.

[ronniejoe]

It could be, but there are a lot of other (cheaper) possibilities to eliminate first.