2002 FlexFuel 3.0.

Last month while driving cross country my truck started shuddering while climbing a long grade. Since I had it on cruise control I immediately disengaged it and let it slow down. The shuddering stopped. When I tried to accelerate back up to 75mph it began shuddering again. It continues to do this and almost only when encountering a long grade at 70 plus mph. Additionally, the symptoms occur only in the 3200 to 4000 rpm range. If I can force the transmission to gear down and the engine to run above this point it will smooth out and pull as it should. While in Knoxville, TN I brought it by the dealership to have it checked for error codes and to find out why it might be doing this. Unfortunately, what they thought, and I paid for, was not the cure: plugs, wires, intake servicing. It can't be bad gas after filling the tank so many times since then. I'm suspecting O2 sensors at the moment, but realize it might be other problems, too.

I've seen similar symptoms in a few threads here but nothing that fits perfectly. Any ideas on what else to check?

 

Hey man, I have little knowledge on it but mine was shuddering at idle sometimes. Plugs/wires/IAC/o2 Sensores were replaced and it seemed to help, but it was still there. I read around and thought maybe EGR components but while fiddling around I found that my PCV hose was actually split. Replaced it along with the valve. Just did that today so I can't confirm it fixed the problem. But maybe it's a good starting point for you?

 

First off, I'm not a car/truck guy so this is FWIW

Sounds similar to my issue, bad injector. Was intermittent and my first guess was bad gas/ fuel tank sediment, as it first happened not long after I ran out of gas. Same deal on hills, also ran really poorly if slowing to point where it almost lugs before downshift. Shop said probably bad ECU but my"expert" said they rarely fail, ECU was sensing the bad injector and not sending impulse to it. All better now after injector replaced. (one shop wanted $50 for the intake manifold GASKET, $110 for injector, I got it them for $21 and $94)

Injectors are difficult or worse to test w/o removing intake so I'm thinkin' mechanics want to throw everthing at the problem besides that.

Good luck.