lb7 injectors loud under load and completely quiet once I hit 2900rpm ...???
- Thread starter rcfreak24
- Start date
I'm glad other people know what I'm talking about. It's just plain annoying. ...
Yep! And I try to point it out to people riding with me and they act like they can hardly hear it. A guy that was a GM tech for years and now owns a shop heard it when I was racing him and said it was injector knock and I should take care of it asap.
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I replaced my injectors when I bought the truck because it failed emissions. Same noise before and after. My lift pump made the idle smoother but that's all and when people ride with me they say I don't hear anything. I also run additive in every tank. I don't know what the noise is but it drives me crazy, sounds like the engine is going to rattle apart! Lol
I don't think it's the cp3 because mine holds rail pressure very well. I also don't think it's tuning related because mine will do it with a bone stock factory tune or any of Rob's tunes. My truck is a freak, once in a great while it will run smooth and quiet. Than it will change its mind and start rattling again lol
It could be main timing (but not on a stock tune), pilot timing, too much fuel pressure, or injectors.
Word of warning: almost all larger than stock injectors are noisier than stock injectors. If you didn't like the sound now...
I played with the pilot timing and fuel quantity, and I was able to quiet my 60% injectors down like stock, but it hurt the mileage a bit (not much, but measurable). So I re-did the timing for efficiency, and just live with the ticking. It doesn't bother me, though.
Word of warning: almost all larger than stock injectors are noisier than stock injectors. If you didn't like the sound now...
I played with the pilot timing and fuel quantity, and I was able to quiet my 60% injectors down like stock, but it hurt the mileage a bit (not much, but measurable). So I re-did the timing for efficiency, and just live with the ticking. It doesn't bother me, though.
x2 . . . some mornings it will run quiet for a while and then all of the sudden it will start ticking. Doesn't matter outside temp or engine temp.
Shoot....my LB7 is the loudest Duramax I have ever been around. Damn thing snarls and growls all the time, but nothing was wrong with it. Still sounded the same after the rebuild.
On the other hand, the donor LB7 engine I bought sounded quiet and smooth, like an LBZ.
On the other hand, the donor LB7 engine I bought sounded quiet and smooth, like an LBZ.
Mine does the same thing, has ever since I bought it. Sometimes it's absolutely quiet, other time it rattles, sounds like pilot injection turns off at low RPM. Wierd, sometimes it starts immediately following a left turn. I checked, cleaned & picked the injector harness and replaced the #2  connectors but still the same. Whenever I bleed the filter, I always get a little air but it doesn't seem to quiet down. I'm thinking there could be air getting in somewhere, I'm going to try a lift pump next.
When common rail injectors get deposits in them from poor fuel or lack of maintenance, or just over time... It is the pilot injection that suffers, because the injector becomes "sluggish" and sometimes can get to the point of hardly injecting anything because of the delay, so it becomes just like reducing or eliminating the pilot injection, which is of course going to be louder...
Here is something I found about the pilot injection:
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.
Condition/Concern:
The customer concern may be a fuel knock type noise heard at 2500 to 2600 RPM, or when the vehicle is accelerated with a throttle angle above 80%.
Recommendation/Instructions:
The following is an explanation of the fuel knock noise. The Duramax Diesel has what is referred to as pilot fuel injection at lower engine speeds. Pilot fuel injection is defined as a preinjection of a small quantity of fuel, five to twenty crankshaft degrees, before the main fuel injection. This preinjection softens the main injection pressure rise. When the main injection is softened, normal diesel engine combustion noises are less noticeable. At engine speeds above 2600 RPM and a fuel quantity supply greater than 35 cubic millimeters, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above this engine RPM range, main injection combustion noise may be noticeable. It is normal and not harmful to the engine. When traveling in fifth gear the pilot injection to main injection transition is typically in the 136 kilometers per hour, or 85 miles per hour range. However, it may also be heard under heavy acceleration with throttle angle at or above 80%, when pulling loads up a hill, and during shifts at or above 2600 RPM. Customers that utilize the fifth gear inhibit switch may encounter the pilot injection to main injection transition noise at speeds around 107 kilometers per hour, or 67 miles per hour.
This sound is considered normal and no repairs should be attempted.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.
Condition/Concern:
The customer concern may be a fuel knock type noise heard at 2500 to 2600 RPM, or when the vehicle is accelerated with a throttle angle above 80%.
Recommendation/Instructions:
The following is an explanation of the fuel knock noise. The Duramax Diesel has what is referred to as pilot fuel injection at lower engine speeds. Pilot fuel injection is defined as a preinjection of a small quantity of fuel, five to twenty crankshaft degrees, before the main fuel injection. This preinjection softens the main injection pressure rise. When the main injection is softened, normal diesel engine combustion noises are less noticeable. At engine speeds above 2600 RPM and a fuel quantity supply greater than 35 cubic millimeters, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above this engine RPM range, main injection combustion noise may be noticeable. It is normal and not harmful to the engine. When traveling in fifth gear the pilot injection to main injection transition is typically in the 136 kilometers per hour, or 85 miles per hour range. However, it may also be heard under heavy acceleration with throttle angle at or above 80%, when pulling loads up a hill, and during shifts at or above 2600 RPM. Customers that utilize the fifth gear inhibit switch may encounter the pilot injection to main injection transition noise at speeds around 107 kilometers per hour, or 67 miles per hour.
This sound is considered normal and no repairs should be attempted.