LB7 Injectors...

[More Power]

Was listening to local radio the other day when I heard an ad form a diesel shop offering to replace the injectors in an LB7 truck for $2900... This is a shop I hadn't heard of before.

Got me to thinking about injector service in general. What are people paying for a Duramax injector replacement using good parts, and by a shop that does it right the first time?

[Kennedy]

I'll throw in my $.02

The price of the proper Bosch remans alone pushes pretty close to that price so the injectors used would undoubtedly have to be 3rd party remans. That price certainly could not include new supply lines, and I would be suspicious about coolant replacement. We also as a matter of practice do thermostats because we are there and have the cover off and system drained. Realistically it takes 12hrs to do the job provided no major speed bumps along the way. Some can and may do it in less, but haste makes waste with these type of projects.


Add to that we've seen SO many LB7 injectors fall to the blue smoke issues after a mere 40k and sometimes less. For this reason we are favoring the SAC type nozzles.

[More Power]

Tell us about SAC type nozzles and how they are better choice. I did a little reading online, but it wasn't completely clear. I plan on replacing the injectors in my truck this spring. More info is always better... Thx

[Kennedy]

The LB7 is unique in the Dmax lineup as it is the only model that uses the VCO style nozzle. The SAC nozzle is the mainstream nozzle used by Bosch on all other Dmax. It is my understanding that the SAC contributes a small amount of additional hydrocarbon emissions due to fuel lingering in the SAC. The VCO nozzle was designed to eliminate this. The catch is that with the VCO is that not only does it have to close off all 7 spray holes simultaneously, it also needs to deliver/distribute the fuel evenly. The SAC type just turns the fuel off and on.

[More Power]

Here's a YouTube video that does some show-n-tell comparing VCO to SAC...

https://www.youtube.com/watch?v=LR6Sq1oridc

[More Power]

The LB7 is unique in the Dmax lineup as it is the only model that uses the VCO style nozzle. The SAC nozzle is the mainstream nozzle used by Bosch on all other Dmax. It is my understanding that the SAC contributes a small amount of additional hydrocarbon emissions due to fuel lingering in the SAC. The VCO nozzle was designed to eliminate this. The catch is that with the VCO is that not only does it have to close off all 7 spray holes simultaneously, it also needs to deliver/distribute the fuel evenly. The SAC type just turns the fuel off and on.

I know this is an older thread, but the relevance is still there/here.

Regarding the statement that all 2004.5 and newer Duramax engines use SAC nozzle tipped injectors, where the LB7 used VCO - I'd like to know how the newer engines can run so quietly. I know that the SAC injectors in an LB7 produce a lot more combustion rattle. And, I know that VCO injectors are more precise in fuel delivery. In my truck, I saw an average of 1-mpg lower fuel economy over the long-term with SAC.

That said, the SAC injectors I installed in my GMC in June 2021 - 4 years and 19,000 miles ago, have been producing out of tolerance balance rates, rough running and periods of objectionable smoke for a year or two and 5k miles. How the engine runs on any given day can vary somewhat. The out-of-spec balance rates have improved a bit with a couple hundred miles of hard towing, better but the numbers are still way out of spec. Other running symptoms (sometimes sounds like a miss at idle, more haze & smoke, exhaust stink, etc) all of which can come and go... which got me to thinking...

Logic would suggest that a wear problem or some other type of a mechanical failure would produce symptoms that wouldn't vary that much on a day to day basis. Which also got me to thinking...

What if some of these injector balance/smoke/haze symptoms are due to injectors that suffer from carbon/varnish - which could change over long/short periods of time? I've been watching some Youtube videos that appear to show that balance rates (before/after) and engine smoothness can be helped with an injector cleaning like this one... https://www.youtube.com/watch?v=_Cx76abhM3E

I also know that back in my 6.2/6.5 days that those engines always ran smoother after a hard towing trip (injector nozzle tips burned clean). And, then there's the fact that I usually drive my diesels for fuel economy, which means always light on the accelerator pedal. I imagine this could contribute more fouling on/in the injectors.

Just thinking out loud... I do plan to do a complete and thorough repair - that includes an engine cylinder compression test, re-evaluate valve lash/valve integrity, injector electrical test, and finally I'll likely install another set of injectors (insert grumbling here) before the cold weather returns later this year. In the meantime I may try the injector cleaning just to see what happens...

The summer 2021 head gasket replacement projects for both my GMC and Lil Red are still fully 100% OK (no coolant loss and normal cooling system pressures), and Lil Red runs like a watch either cold or at operating temperature with its GM original VCO injectors - it is amazingly smooth.

My GMC ran to about 120,000 miles before the original factory-installed VCO injectors were replaced due to a P0302, haze & miss at idle, smelly exhaust, etc. It ran pretty well after replacing all 8 injectors, for about another 20k miles. Then I started noticing a bit of bluish/whitish smoke at a cold start. The GMC got new Mahle head gaskets (due to over-pressurizing the cooling system), 8 new SAC injectors, brand new high pressure injector lines, and a set of ARP head studs at 140,000 miles.

What do you think?