I have an '02 1500 Laramie 5.9 non hemi with an ongoing problem. I noticed at around 65-70mph it would hesitate back and forth very quickly. The tranny shop said it was a TPS which was replaced, no change. The garage said cylinder misfire so they replaced some of the plug wires (which were not that old), no change. We replaced all the plug wires, plugs, cap and rotor, it got worse. Now it happens around 30mph and feels like someone is turning the ignition on and off. The gauges all stay normal and the radio/lights all stay on so its in the power train or electrical for the power train.
Also I have a noise/vibration sounds like it is coming from the rear. My mechanic said he thought it was a wheel out of balance. All the wheels were balanced and no change. He checked the u joints and rear end and said they were fine.
Any ideas??

 

Sounds like an intake or vacuum leak since you already ruled out the ignition system.

Rear vibration can only be from u-joints, ring/pinion or tires. Have you had the rear diff fluid changed recently? And did he remove the cover and inspet the gears or just spin the tires on the lift and say...yeah, they're good?

 

CKPS almost without any doubt....

 

Ckps?

 

CrankShaft Position Sensor....

 

thanks Carnage!

I was on the phone when I responded earlier..

the CKSP watches the flexplate and keeps up with the location of the crank so the engine knows when to fire the cylinders.. when it goes wonky, it will do precisely what you described: feels like the ignition was turned off..

it will also cause misfires- maybe enough to trip a code, or maybe so intermittent that the PCM doesn't call it out.. when that happens, it feels precisely like a vibration/bump in the drive train.. you will feel it most prominently when the engine is not under load- such as 40~45ish, and when she shifts to fourth.. it gives the same sensation- by my way of explaining- as torque converter shutter does when the lock engages..

the 'turning off and back on' is what gave it away... almost with certainty it's the CKPS.. here is the kicker- and pay heed to this and save yourself some frustration: BUY ONLY FROM DEALER.. this is one of those sensors that the aftermarket can't be trusted on- this one, the cam position sensor, the MAP, and the transmission governors/solenoids..

 

That sensor was a real PITA for me to replace, but mine was starting to go out and threw codes, but it only made for hard starting at times, once it would start it would run fine. But I replaced that and the camshaft sensor aka distributor pickup sensor and all has been well for a few months.
I don't know if anyone has any good install tips, but I needed an extra pair of hands, the sensor wasn't lining up perfectly, so I had to move it around from under the truck while my partner was up top trying to get the bolts started. I got that one from rock auto, so maybe that's why the install gave me trouble...

 

Thanks I'll replace the CKPS and let you know how it turns out.

 

Ok so I had the CKPS replaced, no difference. Replaced the coil, no change. Any other ideas? Mechanic says he's 99% sure its not fuel system related. Could it be the computer? HelP! I am out of ideas and I think my professional mechanic is to!

 

if it's NOT the CKPS, I'd second guess your mechanic and borrow a fuel pressure gauge from advanced/autozone/o'rileys or the like.. test for fuel pressure at the rail.. you'll be needing 45~50psi for the engine to operate properly, with a target of 49psi as what it should be.. atmospheric pressure can sometimes mess with it, but it's gotta be in that range..

there is a schrader valve test port on the drivers side fuel rail.. looks like a valve stem on a tire.. it's a real easy test to perform..