August 1

2006 GMC Sierra 3500, 6.6L Duramax, Fuel Injector Replacement

GMC Trucks, Podcast


Mark: Hi, it's Mark Bossert, producer of the Pawlik Automotive Podcast and Video series. And we're here with Bernie Pawlik. Pawlik Automotive in Vancouver, Vancouver's best automotive service experience and 20 time winners of Best Auto Repair in Vancouver as voted by their customers. And we're talking cars. How are you doing this morning, Bernie?

Bernie: Doing well.

Mark: So 2006 GMC Sierra with the Duramax diesel. What was going on with this vehicle?

Bernie: So this vehicle came to our shop with the diesel engine running extremely rough. A lot of knocking noises coming from the engine and a lot of smoke coming out. I mean we're talking like a hideous amount of smoke pouring out the tailpipe when the engine was running.

Mark: Well, I know there's different types of smoke. What sort of smoke could you tell from... Was it inky black or was it cloudy white?

Bernie: Yeah, there was a lot of black and greyness to it. And with a diesel, you know, as you're alluding to, you can do a lot of... A lot of the diagnosis with the diesel is done through the smoke that comes out the exhaust. If it's really white, usually indicates that there's not enough fuel, too much air. If it's really black, it's too much fuel, not enough air. You know, grey is kind of a... Often we get grey in diesels that are over fueling or the injection process isn't working properly. And then of course the blue smoke that can be from over fueling as well or it can be, you know, from a worn out engine. A bad head gasket of course can cause a lot of white smoke. So we have a little tricks and ways to figure out what, you know, whether it's diesel fuel or whether it's engine oil. But in this case there was just a lot of smoke coming out and figured, you know, there's most likely a fuel injection problem of some sort.

Mark: So what diagnostic tests did you run?

Bernie: Diagnostic tests?

Mark: Yes.

Bernie: Well a scan tool is very useful in this vehicle. So this is a common rail system electronics. So the scan tool works fantastic to do it. There's a number of diagnostic tests we can do. One of them we did was there's a cylinder, a power contribution test to see which cylinder is contributing power to the operation of the engine. And it was pretty clear that number four cylinder, as soon as we killed that cylinder and shut it off the knocking noise in the engine disappeared. Smoke was reduced, not gone, but the knocking noise in the engine disappeared right away. And even though the engine was still a bit shaky because it's only running on seven cylinders, it was a definite noticeable difference. So we're on to something there for one cylinder. And there's also an injection balance rate, I believe. I'm trying to think of the right term. Anyway. So there's another PID to look out on the computer where it can tell how much the injectors are being compensated in terms of how much fuel they're delivering. And you know, there was another injector in a different cylinder that was quite a bit out of range for that as well. So we knew there was at least two bad injectors. So at that point we have the option, we can remove all the injectors, send them up, and have them tested. But in my past experience with doing that is like nine out of 10 times every injector is going to have some kind of a, you know... Not malfunction, but you know, it's not going to meet the specs. And so, with the age of the truck, it's, you know, well over 10 years old, quite a bit of mileage on it. It's time to just change all the injectors. Once one or two go bad, the others are, you know, probably not operating at 100% performance and need to be replaced.

Mark: So you concluded that the injectors were bad?

Bernie: Absolutely. Yeah. There was no doubt the injectors were the cause of the problem.

Mark: So how difficult is injector replacement in a Duramax?

Bernie: Well, it's not too bad on this particular model. The first generation Duramax, so it'd be a couple of years older than this model, required removing the valve cover. There's a lot of fuel pipe plumbing that needed to be removed under the valve cover. It's a very... Quite a large job. I mean I love Duramaxs. They're good engines, but that was definitely a downside of that particular engine. This one, however, the injectors are accessible without taking the valve cover off. It's still a fair bit of work, but you can undo all the injection pipes and change the injectors. A much simpler operation than in the previous. And there's no injector cups that go bad on these. It just... Just everything just fits together a lot better. It's made for much easier servicing on this particular generation of Duramax.

Mark: And do we have some pictures?

Bernie: Yeah, we do. Yeah. Thank you for reminding me. Let's get into that. Okay.

2006 GMC Sierra 3500, 6.6L Duramax, Fuel Injector Replacement
2006 GMC Sierra 3500, 6.6L Duramax, Fuel Injector Replacement

So there's our truck, a nice dually for hauling big loads, you know, with that big diesel you can haul a lot with this particular vehicle. Next photo we've got is the fuel injector. So this is one of the old injectors removed. As I said, you can see it's pretty simple. It's just one high pressure fuel line going to the injector, the electrical contact connection is there. And then the injection nozzle fits down into the cylinder there. There's the high pressure ceiling ring, and then there's a couple of other little seals that just kind of keep dust and dirt out of the injector bore. So that's basically it. A nice simple slideshow. I mean, you know, what goes wrong... I mean there's electronics inside here that fail. Also the injection nozzles can fail as well to deliver the right amount of fuel or they can be stuck open and just keep, you know, pumping like a fire hose. So that'll, you know, either... It's hard to know exactly what was wrong with this one. As I said, if we tested them, we could find out. But the testing in this case is really in the way the engine ran.

Mark: And how did the truck run after the repair?

Bernie: What was... Well there was a couple things. So immediately upon starting it up, the engine was, it was a V8, ran nice and smooth, no more knock, knock, knock, knock noise. But one thing that was a little disturbing is that there was still a lot of smoke coming out of the exhaust and it seemed like, "Okay, what else could be wrong with it?" But what we determined... We shut the engine off for a while and let it cool down. It started up, there was no smoke but after driving it for a few minutes the smoke would increase and what we determined pretty quickly is there was just a lot of excess fuel. And the engine had been running so rich that it had been dumping fuel down into the exhaust system. The other issue too that we noted was that the engine seemed to be a little gutless. Like when you go to boot it, it would tend to lack power.

So immediately brought it back to the shop and just made sure we didn't leave any turbo ducts loose cause that... You know that does happen from time to time. A duct will pop off. Verified that was all good. There's no leaks of any sort. So the best thing we did, we took it off for a good hour, hour and a half drive on the highway up and down hills and after doing all that, the smoke cleared up because we burned everything out of the exhaust. It was embarrassing for a little while getting rid of that smoke. Once it disappeared then the turbo... There's a couple of codes that kept returning for a turbo under boost, but after driving it for a while and just getting it really hot and burning everything out, it actually cleaned everything up in the turbo and the engine at full power ran just fantastic.

Mark: So was that soot and build up in the turbos from the over fueling situation?

Bernie: That's what we figured probably happened. You know, this is a variable geometry turbo. There's a vein that operates and moves in it. It could have been sticking. So I actually took it out for the road test out in the highway and I could see on the scan tool... There's different things we can look at to see if it's actually responding the way it's supposed to. And initially it wasn't and then it started... It cleaned itself up.

So this is one thing that, you know, I realized a lot of times when we take on a repair like this, we think, "Okay, it's got the bad fuel injectors" and we need to remind our clients that, "Hey, by the way, there could still be other things afterwards because you never know if you've been driving it for a while like this what other... I don't want to say damage, but what other issues may have occurred because of this." Fortunately, it was good news. It just required an extra long road test to clean everything up. But we're kind of concerned that maybe the turbo had been gummed up to the point of needing replacement, but it didn't. So...

Mark: And how are Duramax engines for reliability?

Bernie: Well, I'd say they're good. They're certainly my first choice in terms of the American diesels, especially for the 06 model year. When you think, you know, what did Ford offer? Well they had their six litre and you can look at our plethora of podcasts and videos about the six litre. You won't see much about a Duramax. And the Cummins are really good too. But I like the Duramax. They just seem to have that little extra edge of reliability. And we very rarely ever do a lot of work on them. So that's, you know, maybe not so good for us, but good if you own a diesel, a Duramax.

Mark: So there you go. If you're looking for service for your Duramax in Vancouver, the guys to see are Pawlik Automotive. You can reach them at (604) 327-7112 to book your appointment. You have to book ahead. They're busy. Or check out the website, On the blog, there's literally hundreds of videos and articles about repairs, maintenance of all makes and models of cars over a lot of years. A YouTube channel, Pawlik Auto Repair. Same thing, hundreds of videos. And of course we really appreciate you watching and listening to the podcast. Thanks, Bernie.

Bernie: Thanks, Mark. Thanks for watching.

About the author 

Bernie Pawlik

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