Knocking

[Ted a.]

Wierd situation. I am not a diesel god, so I am learning a lot about these things to date. I had my 8 injectors replaced at 38k. Truck is a 03 GMC. I noticed after pulling out from the Sunoco on the Ohio turnpike that I had a significant "knock" as if spark knock on the drivers side at about 2200 rpms at medium acceleration(coming on to highway off ramp). I let out a little and there is no noise. I must stress it is not mechanical valve train noise. Anyways, at times when there is no trailer, I get the same noise when I am accelerating and it always starts at about 1800 RPM up to 2200. There are days it does not do it at all, sometimes for days. It only does it when engine is at full temp. Any ideas??

P.S. I have tried every different fuel out there too. They all react the same.

[Jim Brzozowski]

Just my idea, but after sitting at a station, assuming you shut down while fueling, restroom stop etc,when you start back up again the steel block has retained the heat that was there before you shut down. The Aluminum heads have drawn heat out of the aluminum pistons and as they contract away from the cylinder walls there is more clearance, thus more noise. Once up to operating temp again it all evens out again. The clearance closes back up to normal operating clearance and you don't hear the louder noise anymore. Also an additive with Cetane improver helps to smooth out the combustion spike and really is one of the better ways IMHO to keep the engine running quitely, relatively speaking.

[deerhunter7]

I wonder if your pre-injection is cutting out early. I don't know what controls it, but that would explain the extra noise. I would think there is a test for that..

[madmatt]

pre injection(pilot injecton) is controled by the FIMC. replaced one for a intemittant low power complaint.

[madmatt]

FICM...sorry!

[Ted a.]

Well, I replaced the K&N filter back with a stock one and hit the MAF with some electronic parts cleaner. The MAF did not look oily. The noise is almost gone, the acceleration seems to require a little more "gas" now and maybe it was running leaner causing some "knock". I still think there is a problem somewhere. I'll keep you guys posted.

[DmaxMaverick]

....maybe it was running leaner causing some "knock". Diesel engines don't/can't run lean, like a gasser. The quantity and timing of the fuel determines the RPM and power output. The fuel/air mixture is incidental.

You can have individual injector(s) that are getting less fuel (lean), or is out of time, and that causes knocking. In that case, repair is in order.

[Ted a.]

Maybe round 2 of the injector game. I did not know you can't run them lean. I figured if they were in fact lean the cylinders would run a little hotter on the effected ones.

[DmaxMaverick]

An injector that is injecting less fuel than the majority, it will be cooler. An injector that is injecting more fuel than the majority can run hotter. So much hotter in some cases they can actually burn holes in pistons.

[madmatt]

Bulletin No.: 02-06-01-022C

Date: January 26, 2004

INFORMATION

Subject:
Information on Engine Ticking

Models:
2001-2004 Chevrolet Silverado
2003-2004 Chevrolet Kodiak C4500/C5500 Series
2001-2004 GMC Sierra
2003-2004 GMC Topkick C4500/C5500 Series
with 6.6L Duramax(TM) Diesel Engine (VINs 1, 2-RPOs LB7, LLY)

Supercede:

This bulletin is being revised to update the engine information. Please discard Corporate Bulletin Number 02-06-01-022B (Section 06 - Engine/Propulsion System).

Some of the above vehicles may exhibit a random ticking noise that is most audible on an engine with a coolant temperature of 70