2001 Duramax: Suddenly diesel knock & high idle speed

[portcity05]

A louder than normal diesel knock has started for no apparent reason this week while on a 40km trip & has not gone away since then.
The engine is noisy at idle & right through the rev range as though it has somehow advanced the timing or something.
Also the idle speed has increased slightly.
When you rev up the engine it comes back normally until it gets to about 1200 rpm when it picks up slightly before coming back to idle just like you gave the accelerator a small blip.
The vehicle is a 2001 Silverado crew cab long bed, Duramax / Allison converted to right hand drive 4 years ago, 265,000km (no add on extras)
I changed the fuel filter yesterday which looked perfect anyway (no change), the injectors where replaced at 180,000km.
This has always been a great truck & regally tows a 30-ft gooseneck & race car around the country without any problem until now.
Hoping someone has an easy answer?
regards Terry

[Mark Rinker]

Sounds like injector problems, without more information. If you have access to a scan tool, or Predator programmer, check the cylinder return rates (at warm idle) and post them here.

I would suspend towing and try to get the truck to an experienced mechanic immediately - engine damage can occur under the wrong conditions, although most Duramax engines come back fine - after all 8 injectors are replaced.

Alternately, there is an article on this site detailing the 'do-it-yourself' approach to LB7 injector replacement...

Good luck, stay in touch.

[portcity05]

Thanks Mark
I hear what you have to say about the injector problem although after having the experience some 80,000km ago this seems completely different.
The symtoms from our earlier injector problem was first the warning display gave out codes which we ignored because we could not find the answers at the time followed by low oil pressure (after 1000km towing) caused by about 20 litres of diesel in the sump & finaly a trail of white smoke, no driveabilty or noise issues at all.
This time we have no addition to the sump dip stick & no warning centre codes or service engine soon warnings.
Because of the manner the idle has changed & the diesel knock that is present I wonder if there is anything worth checking with electrical sensors or connections.
Also this problem began while on a short trip all of a sudden & not over a period of time.
regards Terry

[Mark Rinker]

Hard to tell, but the knock is something NOT to be ignored...

Search this forum for 'diesel knock' and see what you think.

[portcity05]

Hi
I can get access to a Tech-2 scan tool used on 6.5L engines, will that work on a 6.6L Duramax to check injector flow rates ???
We are limited to available equipment here, we are in Portland, Victoria, Australia.
Also I see mentioned a software update on 2001 trucks, is it worth getting hold of & where can I get hold of this.
regards Terry

[Kennedy]

Checking injector balance rates on a warm engine (Tech 2) is where I would start. Also check that desired rail psi and actual match. If the psi and pump regulator duty cycle are not steady this can affect balance rates.

[Rabbler]

It could also be a bad fuel pressure regulator.
If the rail pressure is sky high at idle (23,000 psi) its likely the regulator has failed or the wiring to the regulator.
Does it rattle even at idle?
Good luck

[portcity05]

Thanks.
I am waiting to have it checked on a tech-2 machine, I hope that will show up & I will let you know.
Something I have noticed occasionly is when you come up to an intersection & are only slightly moving (about 5-mph) when you start to accellerate the engine revs build but the trans does not engage straight away.
You can take your foot of the gas & let it catch up or leave it down a bit & it will engage very agressivly.
I believe there is a computer upgrade on the early Duramax, can anyone tell me where I can get one & how to go about installing, there may be a fix in there somewhere.
regards Terry

[lb7lbz]

had very similar condition on my 01 w 250k on it. replaced fpr and a few fuel hoses that looked a little dry rotted and fixed the prob.