04 LB7 DMax throwing fuel

BillB3857 · October 11, 2004

Just came back from a weekend camping trip with our 04 Silverado CC D/A 3500 Duallie. Found a lot of sooty green stuff strung all over the front of our 5th wheel and also in the bed of the truck. (We travel with the tail gate removed) My question is whether it is normal for the DMax to throw raw fuel out the exhaust. Our milage has also dropped. Normally, when towing, I get about 11.5 mpg but on this trip it was about 9.7mpg. All the dealer mechanics are on strike in the St. Louis area so getting a straight answer from the shop is unrealistic. Any ideas out there? BTY, when towing, our gross weight is around 18,500 and we were towing in the Missouri Ozarks at mainly interstate speeds and the truck has 14,000 miles on it.

Thanks in advance for any suggestions or ideas.

Bill

1BADHD · October 11, 2004

Just came back from a weekend camping trip with our 04 Silverado CC D/A 3500 Duallie. Found a lot of sooty green stuff strung all over the front of our 5th wheel and also in the bed of the truck. (We travel with the tail gate removed) My question is whether it is normal for the DMax to throw raw fuel out the exhaust. Our milage has also dropped. Normally, when towing, I get about 11.5 mpg but on this trip it was about 9.7mpg. All the dealer mechanics are on strike in the St. Louis area so getting a straight answer from the shop is unrealistic. Any ideas out there? BTY, when towing, our gross weight is around 18,500 and we were towing in the Missouri Ozarks at mainly interstate speeds and the truck has 14,000 miles on it.

Thanks in advance for any suggestions or ideas.

Bill

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Hey fellow Missourian! I live in Ste. Gen about 50 miles south of STL.

To your question. It is not a common thing for your truck to be throwing raw fuel. Does it feel like you had a loss of power whiel this was going on? Any tuners or chips installed on your truck?

whitesnake01 · October 11, 2004

That is not normal. Is this an LB7? It could be a leaking (stuck) injector that has caused diesel to get into your crank-case and subsequently overflowed it. Check the oil-dip stick for starters. If the level is higher than it should be you, that may be what has happened. I have seen stories of owners draining 16-20qts from the engine. I would call the dealer for advice on how to get your truck to the dealership. I would not drain it myself as this appears to be a warranty issue.

1BADHD · October 11, 2004

I just thought of somthing else. Are you sure its fuel? Maybe your rear diff is spewing oil for some reason. It is a really thick nasty looking yellow/green color.

BillB3857 · October 12, 2004

I just thought of somthing else. Are you sure its fuel? Maybe your rear diff is spewing oil for some reason. It is a really thick nasty looking yellow/green color.

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I'm reasonably sure it is fuel. The only difference is that it has what looks like a lot of soot mixed in with it. On the front of the trailer, it leavesl little soot trails as it runs down. In the bed, there are some strings that seem to pool and settle. The soot seems to congregate in one area and relatively clear, green tinted stuff around it.

A check on the oil level shows full, not over. Power seems to be somewhat lower than it has been. I thought it might have been caused by a tank of stale fuel. Truck is 100% stock LB7 with no tuners/chips/propane/etc.

I really hadn't thought about the diff because of the soot content. I guess it could be picking it up from the exhaust stream before it blows all over everything. I'll check it out and see if it is the same color but if it is thick, I'm sticking with the fuel theory just due to the consistency of what is pooling in the bed.

Thanks to all that have responded. I'll post the final outcome when I find it.

Bill

Haulin' 8.1 · October 12, 2004

I should have known this one but I admit it had me stumped for a couple of days. I'm a mechanic and a pretty good one at that so it kept turning over in my head until it came to me.

It's a leaking injector, I'm so used to gas engine diagnosis I had a hard time realizing how raw fuel would be blowing out your exhaust in a engine that can't misfire (diesel). But I finally remembered that the Duramax is direct injection, meaning the injectors fire directly into the combustion chamber and fuel dosen't flow around the intake valve with the air like in older design engines and most gassers. This increases effeciancy and power while reducing noise. But being as that the injector is in the combustion chamber, if it is leaking it will leak during the exhaust stroke also. With remote type injectors (the other kind) any leaks will cause excess fuel on the intake stroke when the intake valve is open but the following combustion stroke prevents raw fuel from making it out the tailpipes. But any fuel leaked from a direct type injector (like the DM) that doesn't get to participate in a compression stroke and then combust will just be blown out of the cylinder with the exhaust gasses as it leaks. Hince your problem. This would explain your other symptoms as well, reduced milage and power but no major running problems.

I hope you still are under warranty, I would think you would be, but I got into this big truck scene with a used '01 and don't know exactly what your warranty is. In any case have it fixed before it gums up your turbo and exhaust.

Good luck,

Vernon

lovette · October 12, 2004

Raw fuel dumped into the exhaust--> you've got an afterburner!

BillB3857 · October 12, 2004

I should have known this one but I admit it had me stumped for a couple of days. I'm a mechanic and a pretty good one at that so it kept turning over in my head until it came to me.

It's a leaking injector, I'm so used to gas engine diagnosis I had a hard time realizing how raw fuel would be blowing out your exhaust in a engine that can't misfire (diesel).

{SNIP}

Wow, Vernon! That makes a lot of sense. Yes, the truck is still under warranty and I'll give the dealer a call tomorrow, even though their mechanics are on strike. Will probably be good just to get it documented with them. I have pictures of the mess in the bed and mopped a lot of it up with a paper towel that I stuck in a zip-lock bag. Maybe that will convince them since it has only done it when towing 11,000+ trailer at interstate speeds. You know the dirll of, "Unable to duplicate problem."

I wonder if I would get a new LLY if it flodded a cyl while parked and hydro slammed or is that only a problem with the F**d 6.0?

Other than this, the only other problem I've had with the truck was a turn signal problem where all four corners would flash when trying to signal a right turn. One dealer in TN replaced the switch after telling me they were going to replace the flasher module. It did it again after I got home, but very intermittantly. Found that it would do it after about 1/2 hour of driving, so timed a trip to the dealer. Got there a few minutes early and sat in the lot with truck running. Lo and behold, it started acting up on schedule, so wheeled it into the check in bay and got the service writer over to witness the event. They replaced the flasher module after contacting engineering and no more problem with the signals.

Again, thanks to all the responders. This is a great forum!

Bill

Machine · October 12, 2004

Raw fuel dumped into the exhaust--> you've got an afterburner!

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All joking asside, and if a faulty injector is the case, it can only get worse if not looked at. Keep us posted, please.

Redapple · October 13, 2004

You are still under warranty. Take it back to dealer, they will replace all 8 under warr, and warrant the replacements for 200k.

Bill

bigdogs · October 13, 2004

You are still under warranty. Take it back to dealer, they will replace all 8 under warr, and warrant the replacements for 200k.

Bill

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I don't think they are doing ther 200K warranty on 2003's or 2004's (yet??), just the 2001-2002's

BillB3857 · October 18, 2004

Just an update: Strike in St. Louis is OVER.. Truck goes in Wed. Will let you all know the outcome.

Again, thanks for all the responses.

Bill

BillB3857 · October 20, 2004

Well, it is in the shop. Service Writer said he had talked with the diesel tech and the general feeling is that the truck has probably been throwing fuel all along and will need a new injector or a full set. Sure has a familiar ring to it since reading the responses on this forum. Will let you know whether it is one or more that get replaced.

While they have it, I'm having them check out the bumpy feeling in the steering when making low speed turns as well as checking the fit on the doors and hood. It's probably the intermediate shaft I've read about here. Also, both front doors have rub marks where they are bumping against the back doors and the hood is bumping the top of the fender on the drivers side whenever the hood is closed.

BillB3857 · October 21, 2004

Here is the latest. Took truck in to dealer. Their first impression was some sort of injector problem, as had been the opinion of most replies to the original post.

After having it a day, they called and said all the flow rates, etc were right on the money and since my crank case wasn't being contaminated, they were ruling out the injectors. They did, however recognize that I had raw fuel/carbon in the bed of the truck and called GM Tech Support today. Answer from GM was to replace the Mass Air Flow Sensor. If it is sensing more air than is really going into the engine, it will allow the injectors to over-fuel for the load conditions. Problem is that I will need to hook the 5th wheel up and get into the Ozarks to check it out.

Will keep you posted.

Bill

BillB3857 · October 25, 2004

Well, it seems to be fixed. Dealer contacted GM Tech Support and they had them change the Mass Air Flow sensor. Took almost the same trip as before and really worked it hard. No fuel in the bed, although mileage was the pits. Held 70 mph through the hills on I-44 from St. Louis to Lake of the Ozarks get off at mile marker 150 and had a strong head wind all the way. Pulling 11,000+ lb trailer that is 11'10" tall creates quite a wind and weight drag. Got 8.6 mpg on the way down. Came back via Hwy 54/I-70 and kept the speed down to 60-65 and noticed little or no wind. Got over 11mpg. Speed makes a big difference.

Again, thanks to all that respoonded. Hope my experience may be a help if others have a similar problem.

Bill