LLY Duramax Common Problems

All right, the first subject I’m going to talk about is overheating. The LLY has an adequately sized radiator when it’s clean. Now the LBZ had a much larger radiator and those do not tend to have overheating problems, but the LLY. If you have a truck, that’s you know, 15 years old has all kinds of leaves and dirt and crap in the cooling stack. You hook a trailer up to it in the Summer, with the AC going uh that truck’s going to run hot.

This can be solved for free simply by cleaning the cooling stack on these trucks. You can search for other videos and things explaining how to do that, but basically you’re going to take all this plastic off you’re, going to kind of pull the headlights off and get to where you can get in between the radiator and the AC condenser. And everything get in there with a hose and some compressed air and clean everything out, really good. That’S going to solve your overeating problem, like I said, I’ve towed, you know 8 000 pound Trailers, Plus with this thing in the Summer, with the AC running it’s 100 degrees outside I’m going 80 on the highway. No overheating problem here, but that’s because I’ve cleaned out my cooling stack so, like I said it’s adequately sized but um over the years you get a bunch of leaves and junk in there.
You might run into some overheating issues now the next subject. I want to talk about is head gaskets and these two are related: the overheating in the head gaskets and what comes first, the chicken or the egg. I’Ve taken care of three of these vehicles. Three LLY Duramaxes two were uh part of a friend’s business and then this one, all over 200 000 miles, one has had a bed head gasket, and that was because the truck, I believe, overheated first um uh. It was running hot guys.
Employee, probably wasn’t paying attention to the temperature overheated, the truck, pretty good um, and then you know surprise, surprise about two months later: uh notice that the head gasket was bad. So if you can keep your coolant sack clean, don’t overheat, the truck. You should never have any problems with the head gaskets. Now here’s uh some ways to check for a bad head gasket. If the truck is cold and ran yesterday, you want to make sure that there’s no pressure lingering in the system.

So this truck I drove yesterday, it’s been sitting overnight. I’M gon na check this top radiator hose right here. It’S nice and soft there’s no pressure in the system, I’m gon na pop the cap off here. I don’t have a rush of air coming out um. Other thing you want to check for, if you’re, like looking at a new truck or looking to buy a used truck, is when the truck is cold and when it’s cold, don’t pull this off when it’s hot pull the cap off of it start it up.
Um. On the trucks with bad head gaskets, if the head gasket’s really bad, when the truck is running when it’s cold you’ll see bubbles in here in the radiator uh the coolant, also, it just smelled like exhaust that that one that had a Bed Head bad head gasket. So check that before you buy a truck, it’s pretty obvious if the head gasket is bad all right guys next subject: I’m going to address here is injector wiring issues, fuel injection control, module and the truck going in the limp mode, um. So basically, the way the fuel injection system works is there’s two Banks of cylinders that are all the injectors are all Daisy, chained together on the same wiring circuit and if there’s any kind of a break in the connection on that circuit, it’s going to throw the Whole thing into limp mode, you’ll hear some people talk about it as a tractor mode. Basically, the truck’s going to have about 20 power and it’s going to sound awful.

It’S going to be in some kind of like barely running condition. It’Ll get you off the side of the highway, but that’s about it, so the main causes for that these are pretty simple things: to chase down the number two and number: seven cylinders the pigtail right here I don’t know if we can see that very well right. There, the pigtail for the wire that bolts to the actual injector itself, the these due to vibration over time these tend to go bad. You can get new pigtails online, pretty cheap. I just got some aftermarket ones.
I went ahead and replaced both of mine number two and number seven, the pigtail right here. You can it’s two wires. I don’t even think it matters which way you hook it up, but basically you just cut and the best way to do it with like a butt, crimp and then uh heat shrink all right. So the number two number seven cylinder pigtails go bad. That can cause those uh tractor mode and all those codes.

The other thing to check is the um right here. This is the wiring harness and I’ll get get rid of this flashlight uh. This right here there’s a plate and this thing is going to be zip, tied, I’ve already kind of messed with this one, but um the wiring likes to chafe right here. So you’ll pull the wiring loom back, spread all the wires apart, make sure that none of them have chafed through and then uh zip tie back and use some electric tape whatever to keep it from chafing. So number two number seven now the other thing that can cause the limp mode is the fuel injection control module.
That is actually this thing right here. This is a computer, that’s bolted to the engine uh, it’s got some little rubber, isolators and it all. It is also cooled with fuel uh. There is diesel fuel runs through this computer to keep it cool. The fuel temperature when you’re on the highway tends to stay around 150 degrees.

It feels constantly circulating that’s kind of a Band-Aid fix. I think this is a bad place to put this thing, but that’s just how the engineers designed it. So this computer is bolted to the engine block. It controls the fuel injection, ficm fuel injection control module, and these can go bad internally. They have capacitors that can um that can go bad inside the circuit board and if you’re lucky, they can be repaired for between 250 300 somewhere in that range I had mine done.
I had a problem with this one. It went bad it kept going into tractor mode number. Two number seven injectors were good. The wiring was all good, and finally, I realized that it only did it when it was hot, and I found out that if I poured cool water on the computer, the engine would run fine, so that was how I traced it down. Actually, anyway, these can be removed, sent out repair for 250 to 300 bucks.

Sometimes they go bad. If the circuit board itself is fried, you’ll have to get a used one and a good used. One of these runs 1000 plus I’ve seen them 1500 bucks they’re, not making them anymore they’re hard to come by so uh just hope that your fuel injection control module doesn’t go bad all right. Y’All next thing I want to talk about is the air intake system. This is where you can really inexpensively, make some Big Time Performance gains and get your truck running a lot better, better miles per gallon and running a lot cooler too um.

So the factory air box is good. I’Ve seen statistics saying this thing: they’ve flow tested these online people have done some real scientific work um, and these things are good up to 500 horsepower stock. They make about 300, so uh. Unless you’re going real high performance, you don’t really need to modify that just make sure your air cleaner is getting clean, um right here. This piece I have this – is the air intake, horn or intake elbow that bolts to the turbo.

This is a replacement um. I got this off Amazon for 60 bucks. I thought the quality was actually really good. It seems like it’s a knockoff of the s b. 200 intake horn.
If you look at pictures of this intake horn next to the stock one, you can see that the stock horn is really restrictive, and by replacing this one piece you can really open up the amount of air your turbocharger is able to to get all right. So there comes in here goes through the turbocharger goes down here into your intercooler comes across this way through the intercooler comes back up right here all right now, this pipe right here is an EGR delete pipe. So basically, what happens right here with your stock uh engine is. This is where the EGR is exhaust gas for circulation, and what happens right here is that hot exhaust gases come from back here, which I’ve blocked this off. You can see like a block off plate if you kind of look really hard in there.

Hot exhaust gas comes through here, comes through your EGR and then it meets the uh. The high pressure air. That’S going to go into your engine, a high pressure air has um the on the stock setup, the PCV crank case ventilation, it’s kind of like you know, oily gases from your engine crankcase goes in there. What happens over time is those two gases meet the hot exhaust gas meets the oily crankcase fumes and you get a bunch of soot and crap in the EGR um. So the solution to do that is to pull the EGR off the truck clean it out, and you can put it back, as is my state, doesn’t do any kind of emissions inspections.

It was easy enough just to put it a lead pipe honestly, if I had to do it over again. What I would probably do is pull the EGR off. Put it back clean it up, put it back on just block it off to keep it from coking up in the future. But if your state does, you know, have emissions and you you are concerned about that. Simply pulling that thing off every 50 000 miles and cleaning it out, uh that’ll do the EGR itself isn’t really restrictive.

It really is just the build up of stuff over time and when I say restrictive, I’m talking about 30 40 clog. This truck had 200 000 miles on it. When I got it and the intake was about 30 to 40 percent clogged, I mean it was really having trouble so uh doing those two things I did them at once. It really woke the truck up uh. This thing gets gray miles per gallon.
I get like 20 miles a gallon on the highway unloaded, so take care of that stuff. All right next thing under the hood. Probably last thing under the head, I’ll talk about is thermostats. When I got this truck um, the therm one of the thermostats was stuck open. The truck wouldn’t get up to temperature on a cool day and uh right here is the thermostat housing.

You can check out how to do this. It’S really not that hard. You got to pull the thermostat housing off, there’s two thermostats in there replace them. Both trucks gets back up to temperature. It seems that’s a common problem um and if you don’t have that, if your truck’s running cool you’re kind of missing out on some miles per gallon, all right y’all next up is the factory cluster right here these guys they tend to go bad.

I had mine rebuilt uh. The solution is to pull the cluster out and send it off uh. You could do it yourself, but there are Services out there between 100 and 300 that’ll rebuild your cluster um. The the issue is that over time, the gauges they tend to read, inaccurately. So if you think that a gauge is reading, inaccurately um, it’s probably just a gauge – and it’s probably this cluster itself – so pull the instrument cluster out, send it off.

Have it rebuilt that’ll. Take care of your problem all right. If you really want to go for some bonus points with your LLY, I suggest replacing the cab mounts. Um, you you’ll notice, with a lot of these trucks, it’s just natural over time. The stock body mounts they kind of sag and you’ll, see that there’s an alignment issue between the bed and the cab will start to develop or the cabs sitting lower than the bed um.
I replaced him with s b, silicone mounts here and I was super happy with that kit. Um. One of the things I noticed immediately is that the truck uh seems smoother. It seemed like the engine was running smoother and I realized it was just no. The engine’s not running smoother, it’s just a lot less vibrations getting to the cab after I replace those mounts uh I did the math and I looked at buying OEM mounts versus that SMB silicone kit, I’ve at the end of the day that Kit’s really expensive.

I think it was about 700 bucks, but it was worth it just to go with the kit. All the parts came with it: the OEM Parts, they’re kind of hard to track down, um all the parts that you need and, like I said it was worth it just to buy the silicone kit. All right. We are looking at the Allison 1000 transmission. They give you a spin-on filter and a drain plug.

I suggest you use it now. There’S lots of uh. You know sort of old wives tales about changing transmission, fluid on an older vehicle, how it’ll mess it up now that that’s might be true for a a car, that’s got a transmission, that’s already kind of going bad. If you change the fluid it’ll get worse, that is true. However um these were designed to be changed.

When I got this truck, I had about 200 000 miles on it. I drained and filled the fluid three times and I put a new spit on filter and it shifted smoother just immediately so big difference there drain and fill three times change your filter make your transmission happy. Well, I thought I was done under the hood, but I have one more thing to talk about. Uh Hydro Boost mine was leaking, I had the stains are still not gone. I’Ve got a bunch of kind of oil stains down here from leaking power, steering fluid um.
It turns out my one or two of my lines were leaking. The Hydro Boost unit itself was leaking, so I went ahead and swapped the Hydro Boost out for an LML unit. Uh 2011 one will bolt right in there. You can look it up. There’S a slight modification: you need to do it’s really easy, but for the most part It Bolts in there and it gives you some extra braking power.

So um, you know it’s not it’s not probably confined to the Duramax all these 2500s. I suggest doing all the lines and everything at once. I had two lines leaking and the Hydro Boost leaking all at the same time um, but I spent an afternoon swapped it out. I used a Cardone reman from Rock Auto. It was about 115 bucks and then I used Gates lines from Rock Auto and actually I think the quality is pretty good.

I go OEM when I need to for quality, but um. I was pretty pretty pleased with how all this went together all right guys before I go. One final thing I want to point out uh the factory hitch on these trucks is only rated to 7 500 pounds. I’Ve probably towed more than that with it and the hitch is held up fine, but I’ve seen pictures online of people bending the factory hitch. I went ahead and got a class five Curt hitch, I’m gon na put on, and we all know these trucks like lift pump.

So I’m gon na put that on too so, maybe in a future episode I’ll do some uh video of adding those two things. I hope this has addressed some uh questions you all might have had about the LLY and thanks for watching