[601HP]

REVISED

While idling, whether in Park or Drive, the engine has begun to gain rpm's and then drop back to idle. It occurs almost every second or two. The idle increase is small, maybe 100+ rpm, but very noticeable. Up and down, and it is constant. I noticed this very recently, within the past weeks. Possibly ICP?

58,000 miles on the truck.

Thanks for any input,
David

 

[TKOPerformance]

No, probably the effects of FICM compensation on an injector that is dropping out. If it only has 58k on it I'd run a full bottle of Diesel Kleen in a full tank of fuel through it and see if it goes away. If that doesn't fix it then you need to run a contribution test to find the injector that's causing it.

 

[601HP]

Thank you TKOPerformance,
I'll try that.

David

 

[CameronP.]

How'd it work out for you, 601HP?

 

[601HP]

How'd it work out for you, 601HP?

I had planned to update this thread after driving through at least a full tank of fuel, but since you asked, here's a small amount of info. I'm sure its too soon to tell if there's progress as I haven't put more than 20 miles on the truck since I added a quart of Diesel Kleen in the tank, and 16 oz. of Archoil 9100 in the oil. 10 of those 20 miles were driven today. I'm retired now and don't put a lot of miles on the truck.

Between the time I initially posted about the RPM surging issue, and just before I added the 2 liquids, the RPM surging actually stopped, and I don't know why. The surging had been obvious every time I drove the truck for about a 2 week period when I first posted.

Coincidentally, there has been and still is, an obvious difference in the fuel pump's pitch. Its normal constant pumping sound has changed, it has a slight but consistent up and down pitch change. That up and down whine was there this morning during the cold start (30 degrees) and continued for a good portion of my 10 mile drive today. However, by the time I returned home at the end of the 10 mile drive, the cyclical whine was gone and the fuel pump sounded normal. This is the first time in a few weeks that I noticed the variable fuel pump whine had disappeared.

If any of you folks have an opinion, please share it. :laugh2: I'm expecting more little surprises from the truck!

David

 

[TKOPerformance]

In my experience that fuel pump noise is normal when the temperature outside is cold. Mine does that too.

 

[jimmy]

The HFCM will redirect fuel to warm it and the load on pump varies when it is cold enough for this to be happening. I think most never her the pump noise change. I only hear if the truck is parked in certain places with a wall to reflect noise.

I have never noticed oscillating idle speed at the same time.

 

[601HP]

Good to hear regarding the fuel pump. I'll respond to the original rpm issue after another 500 miles of driving.

David