2001 lb7 injection issue but unsure - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 3 (permalink) Old 01-14-2020, 01:11 PM Thread Starter
Join Date: Jan 2020
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2001 lb7 injection issue but unsure

I posted once about this and havent gotten any response. hoping i could explain a little better this time to see if anyone could point me in the right direction. I recently replaced my cp3, ive had several fuel issues, some as simple as the fuel filter, ive had several leaks, the biggest one being the cp3, anyway. this time ive tried every thing i know to when narrowing it down but ive had no luck. the issue i have now has me lost. im currently going to a tech college for diesel, ive done a set of injectors on an lb7 before just not on mine. the symptoms its having is very similar to the lly injector pig tail problem but its only showed a code once an it was p0203 if i remember right which would be cylinder #3 injector fault of some sort. ive researched all over trying to narrow it down with out taking anything apart, i had been running it with only one battery so im wondering if it could be the ficm rather than injectors, because i know if you dont have enough voltage it can mess with the ficm. however i know its getting close to needing injectors any way it has a slight has at idle but not while driving. ive got nearly 160 thousand on it so its getting about the time for injectors. the injector rates were all with in the range of -4 and +4 all of them being -4 except cylinder #s 1 3 and 7 which were + 1 or 2. the problems were instant rather than over time, there no blow by at all so i dont think it dropped an injector tip. if anyone could give me some advise thatd be wonderful thanks
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post #2 of 3 (permalink) Old 01-16-2020, 07:12 AM
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Hello, welcome to the Forum and apologies for no earlier response.

Congratulations on advancing your education in diesel technology! I trust you will be looking for a position with a fleet operator or government.

To be clear, you have an intermittent P0203 and slight haze at idle, which clears up on-throttle, But no other performance issues, correct?

Sounds like you have already spent time researching the MIL and sorry, but I have no knowledge of that particular situation.


Regarding haze at idle, what is most likely happening is the VCO (Valve Covered Orifice) injectors in your LB7 are aging and no longer shutting off completely. As you may know, VCO’s were only used in the LB7 and were replaced by the much more reliable SAC type injectors in all later Duramax engines. Until not long ago, only higher flow SAC’s were available for LB7’s, which required a tuner for best performance, but those injector types are now available in OEM flow rates and are an excellent option for R&R, with good reports from owners who have installed them.

And yes, that’s what you are looking at .

What happens is fuel dripping from an “off” injector begins to carbonize on the injector nozzle and not only disrupts the flow pattern, but also causes a small amount of excess fuel to constantly enter the combustion chamber and at idle, even that tiny amount of fuel is more than the engine can burn, resulting in a smelly haze of raw diesel coming out the tailpipe.

While a variety of chemical treatments are available (Stanadyne, endorsed by the GAO for government vehicles comes to mind) and may mitigate the problem temporarily, once hazing presents, it’s all downhill and injector R&R needs to happen. Around 60k seems a typical life expectancy.

BTW, haze disappears off idle because the small amount of dripping fuel is inconsequential compared to normal fueling and other than some loss of MPG, may not be an issue. The engine will continue to perform adequately but a major concern is fuel leakage will begin to wash cylinder walls, with obvious consequences (not to be confused with “making oil”, which is generally a failure in the return circuit under the valve covers). At night, you may see haze in the headlights of following cars and will also likely blow a cloud following periods of idle. (Not to be confused with vaping ).

Lots of 411 here on injector R&R, so unless someone has a better idea on a chemical solution (fairy tears?), you know what you gotta do.

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post #3 of 3 (permalink) Old 01-16-2020, 08:06 AM
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Location: West-Central Indiana
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So what exactly are you trying to figure out? The code, a smoke issue, an intermittent miss? I'm having trouble following exactly what you're trying to do...

P0203 is injector 3 control circuit so that could be ficm related or a bad #3 injector solenoid. Could have been a bad connection, could be a rub spot in a wire-check the ficm harness next to the alternator, sometimes they rub on a bracket there and can create issues.

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