This thing is nearly undrivable...

I can accelerate. I can decelerate. thats it. no inbetween.

I have comfirmed that it is not a trottle sending unit issue by borrowing one off a guy at work. Same symptoms with either installed, and mine works ok on his truck.

Heres what it does....

at idle, the engine will fluctuate a few RPM on an constant 1 cycle per second pattern. in neutral you cannot control engine rpm with the throtte. enough throttle to bring it up off idle will send it to the red line.

In gear, the slightest amount of throttle will cause quite a bit of accelration. the RPM will fluctuate as well (I hate to call it a surge becase its only maybe 50 rpm total change). Holding the throttle open at that same setting, the truck will slowly keep accelerating until it is doing 85 plus and in the redline in top gear. Its like at each 'surge', the RPM dont come all the way down to the original position, and they accumulate until you are screaming down the hiway.

Filters are new. the lift pump is confirmed working. The FSD appears to be ok. The SES light is erratic. sometime it comes on, sometimes not, but the truck drives exactly the same either way. I have yet to pull codes. I should be able to get them tonight.

I have heard of trucks where someone got a little carried away with the optic bump acting like this, but I never touched it, or the resistor. This problem has gotten progressivly worse over the course of a couple weeks.

I will crack open the top of the pump this week and try de-bumping the optic a bit, but I am really concerned about why or how that might have changed.

Any other ideas would help.

Thanks.
Tim

How old is the IP?

Do nothing before you pull the codes - the FSD can cause that, and the FS can cause that

Varying rpm is probably Cyl Imbalance - which doesn't set the SES, but does DTC and can be observed

Screw in selonoid inside the head of the IP has broken loose. No throttle control when that happens from what i understand.

Do you have an aftermarket chip installed? When I had the HYPERTECH in mine I had those same issues above 2500 RPM.

Solenoid Armature shaft screw is broke or loose. Quantum had some good pics.

Quantum post
http://dieselplace.com/forum/showthread.php?t=89886&highlight=broken+armature

And #6
http://dieselplace.com/forum/showthread.php?t=13455&highlight=broken+armature

My wording may be wrong but what DP said is what i was getting at.

Screw in selonoid inside the head of the IP has broken loose. No throttle control when that happens from what i understand.

Hmmm. But I have throttle control! It idles fine, other than the slight surge. I can put it in 'high idle' and it idles at the high idle speed just fine as well, again with a slight surge or flutter.

I can drive it a slow speeds (enigne rpm) and maintain a reasonable amount of control. But at fast speeds it is either decelerating when at idle or accelerating when I come up off idle. If I just barely come off idle, it gains speed slowly (but surely) and I can definatly vary the power level by increasing the throttle, but if I come off the throttle to a cruise mode, it falls all the way back to idle and the cycle repeats.

I would think that if the screw on the armature broke, the enigne would have ZERO resonse to the throttle. That sound right?

The regular surging makes me think that its electrical somehow. I havent had a chance to look at it yet (working on my sons car this week), but I am wondering if there is a failure mode in the FSD that would do this.

Again, it started as a very slight problem and progressed over the course of a week or so to a bit of a monster.

I'll keep ya informed what I find, when I can get time to work on it.

tim