Need a diagnosis

[ElwoodB]

Not sure what to do-bought a 2004 2500HD 6.6 and here is my dilemma.

Bought this truck with a Airaid cold air intake and MBRB 4" exhaust but no chip. Truck seemed doggy, so I took it to my dealer. He suggested two things- One, lose the CAI and put the stock box back on and two, the LB7 was warranteed for new injectors. Did both, and it changed nothing.

Truck smells heavily of diesel. I know it IS a diesel, but every other truck I am around does not smell that much.Seems to require WAY too much pedal pressure to make truck respond (have driven several others to verify). This is my first Duramax and I don't know if there is something wrong or if there is that much variation from year to year. I just pulled onto a highway on flat ground and my foot was an inch from the floor just to get the truck up to 70mph. No codes, just replaced the fuel filter as well.

Is my turbo not working correctly? Should I just put the Airaid back on and get a programmer? The factory mechanic said he drove it and it was fine- I think he's nuts.


Someone please enlighten me......

[Mark Rinker]

Hello - welcome aboard. First a couple more questions:

Do you see any white smoke during warm idle, or smell unburned raw diesel in the exhaust?
Were all 8 injectors replaced under warranty? How many miles ago?
Do you see any black exhaust smoke under full pedal acceleration?
What shape is the air filter in? Could it be plugged and causing the intake air tube to collapse during high intake air demand? (One quick test is to remove it altogether and take it for a quick/short test drive, to see if your acceleration performance changes.)Please fill out your signature block with year/make/model/options/miles/etc... information it helps with troubleshooting.

[ElwoodB]

No smoke at idle
Smells like fuel all the time when running
All 8 injectors new
No black smoke
Acts the same when trying Airaid, just k+n filter, and current brand new stock filter.

[Mark Rinker]

Sounds like you have a fuel leak somewhere. I'd be looking carefully at every fuel line, fitting, etc. that had a wrench on it during the injector replacement.

Also, check the seal at the fuel filter - that would have been replaced at that time, as well. There is a small plastic fitting and small Oring for the water separator at the bottom of the filter, and a large Oring at the top where it meets the filter housing. Either can leak if not installed properly.

How is the mileage? Could it be something totally unrelated, like dragging rear brakes, or blocked exhaust?

[ElwoodB]

mileage is around 15.
diesel smell is from exhaust only.

[Mark Rinker]

Hmmm...so it smells like fuel when idling, but not enough to smoke. Sounds like a normal diesel truck to me.

If your turbo boost was low, you'd see black smoke under acceleration. Do you have any SES light or codes being set?

I'd start a regimine of a quality fuel additive, and use a premium synthetic oil. If the truck was a daily driver, and the previous owner used low quality oil, it might simply be sludged up and and in need of being "pulled hard and put away wet" with some good fuel and good oil in it to get the intake, exhaust ports, turbo, etc. de-sludged, de-carboned and the whole package simply flowing more efficiently.

NOTE: BE CAREFUL IF YOU DECIDE TO USE ANY KIND OF EXTERNAL 'THROUGH THE INTAKE' CLEANERS - THEY MUST BE FOR DIESEL USE ONLY - ANYTHING MEANT FOR GAS ENGINES CAN CAUSE A 'RUNAWAY' ENGINE AND CAUSE MECHANICAL OR EVEN PERSONAL DAMAGE...

[Runaway_Dmax]

Might want to check your oil level as one of those new injectors could be leaking.

Why were the injectors replaced? Did they test them and found problems? Were the injectors in deed replaced. Can you tell if the valve covers were removed? Was the fuel filter replaced when injectors were replaced. You should be able to see what was done and replaced on your WRO.

Don't know your driving habits, but 15 mpg seems low to me if this is highway mileage. You shouldn't smell raw fuel in these newer diesel p/u's. I would agree with Mark in that you have a fuel leak. With a 4" exhaust and an CAI I would bet the previous owner had some kind of power adder on the truck. If you could contact the original owner, he/she may be able to shed some light for you.

On another note if this is your first diesel, they don't come off the line like a gasser does. You will find these trucks performance in stock form shine when towing. You said you had it almost to the floor to get it to 70 mph. Distance wise, how far did you travel before reaching 70? The LB7 has a standard vane turbo on it so it takes awhile to build boost before you notice any noticable performance. Starting with the 04.5 the DMaxes (LLY) they have variable vaned turbos on them and low end performance increased.

Like Mark suggested, fill out signature so members here can help further diagnose your problems. ;)

[ElwoodB]

Going to do the quality oil and additive routine first.

I think you hit it on the head- I've had so many people tell me duramax diesels were the best thing since sliced bread(one of my friends loves his so much I expected to see a red cape and boots on it) with my inexperience I may be expecting too much.

I do drive a 700 horse Camaro during the summer months.

Maybe it's me and not the truck at all.

Power adder on the horizon? Hmmmm.......

Thanks for all your input. Going to leave it alone until race season and see how it pulls the race car trailer.