2001 Duramax LB7 Knocking

[rpaoness]

Both in fall trips up to VT and my recent run to PA to pickup a Jeep, I've noticed the 2001 GMC K2500 HD LB7 Duramax sounding like it has a bad exhaust manifold leak under heavy load. Anecdotes, internet reading, and discussion with a local mechanic tells me that it is most likely injector knock. It doesn't appear to match any common injector failure symptoms that I'm familiar with - there is no evidence of hard starting, no noticeable smoke (although I have failed emissions several times for excessive opacity, each time I ran injector cleaner/lubricity additive and retested successfully (barely) ), or what I would consider poor fuel economy.

I need to start with a fuel filter change since it's been a while (probably only like 8k mi or less, but more than 2 years). As long as the filter change doesn't resolve it (which I think is highly unlikely), I'll consider doing a replacement set of injectors. Injector testing is $25-$49 each, but I think unlikely worth the investment since I believe the injectors have more than 135k miles on them.

Spoke with Metro Diesel, a local diesel injection shop. They recommended there reman injectors using Bosch components. Said they have few returns and have them in stock. Also recommended new lines if there's any evidence of scoring on the line sealing surfaces. They sent a quote for parts needed (attached). $3521.41.

Here's a kit. Should include OEM (Bosch) parts, that raises it to $2149, but includes lines and glow plugs (my glow plugs are probably shot - the electrical connecting rail rotted off a while ago. Since I've had no cold weather starting issues at all I've just let it go.

https://www.dieselogic.com/p-353-lb7-20 ... PDEALw_wcB

[kevm14]

(although I have failed emissions several times for excessive opacity, each time I ran injector cleaner/lubricity additive and retested successfully (barely) ), or what I would consider poor fuel economy.

Geez, talk about flashbacks to your 6.5TD days.

Could also consult Area Diesel Service since they were helpful last time.

Since it is common rail, does that mean the timing is a PCM/injector system and not, say, the pump or something?

[rpaoness]

I believe fully ECM managed - I think it's just a mass-volume high pressure pump that just keeps the manifold at full injection pressure and the ECM signals each injector. If I recall correctly the injector driver hardware is a pretty big ECM-looking box. This is the first time I'll have done anything to the on-engine fuel system since like 8 or 10 years ago I replaced the fuel pressure regulator because of a recurring CEL.

[rpaoness]

I did look at Area Diesel's website - they're pretty high for stand-alone injector pricing. I didn't see this kit earlier:

https://shop.areadieselservice.com/Cate ... B7-(VIN-1)

Their magnum line doesn't seem to indicate using Bosch parts, and $2689.80.

[kevm14]

I just meant as a second opinion on the likely source of the knock. If they also seem confident in the injectors as the cause, get their opinion on a cost-effective way to proceed (i.e. test them first, replace as needed). The LB7 is old so they SHOULD have a fairly strong opinion but you can insist that you don't want to spend money you don't have to, and see what they say. It's a confidence thing. If a second source basically says "it needs injectors, this is very common, you will have bad results trying to chase one or two" then you should feel pretty confident in doing all 8. Or, they could say "these are the symptoms of failing injectors" and perhaps you don't have those symptoms, so maybe they could recommend a way to determine the cause that doesn't require pulling 8 injectors and mailing them somewhere.

[rpaoness]

Replaced the fuel filter yesterday - date on the filter was from 2014 (probably 4+ or more years old when I installed it - I always have one under the back seat, reorder whenever I change it). The replacement had a 2019 date code, so I guess it's been 5 years. Didn't appear to have any issues - clean fuel out of both ends during the swap. I can hear the tick at idle/low load in the driveway now, so I think it's getting worse. I had run lubricity additive during my trip out to PA and back hoping that might help. I think I'm headed toward just doing a set. The knocking has me worried about uneven in-cylinder/piston circumference temps and possibly uneven cylinder loading/wear. I think I should just do a "preventative maintenance/tune-up" injector set since they have about 140k miles on them and are at least 16 years old. I don't think I'll pre-emptively redo the CP3 pump, but dieselogic.com does offer a super-duper set and an ultimate fuel system replacement set that include it.

https://www.dieselogic.com/m-23-2001-2004-66l-lb7.aspx

[rpaoness]

My local-shop quote comparison above isn't quite fair - I didn't realize the $3521.41 included core. w/o core charges, the total is $2375.16 for lines, gaskets, and injectors. I wonder if I should do injector cups also. And should I tackle the glow plugs at the same time... probably.

[rpaoness]

Looks like sometimes the cups come out with the injectors. I'm leaning more toward the "complete" dieselogic kit.

https://www.dieselplace.com/threads/inj ... ce.341432/

[rpaoness]

Changed the fuel filter and saw no real improvement - still knocking/pinging under load. I guess I'll take the truck offline and pull the injector set and see if the cups come out with the injectors before I decide what kit to order.