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Just want some insight as to what I should or not do to the truck. Well just purchased an 05 -2500 with over 350,000 miles. Everything is stock and the previous owner claims all he ever had to do was replace the the injector wires for the 2&7 injectors. The truck runs good tranny shifts smoothly. So my question is should I do any of the mods that are recommended to do to kinda prevent issues that are common with the lly’s.
 

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LHN...We ARE the Joneses
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About the only mod that's necessary is to change out the Turbo Duct Inlet (a.k.a. mouthpiece) to the larger nonrestrictive '06-'10 style (under $100).

"all he ever had to do was"
surprised at the mileage and never having the head gaskets replaced.
 

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LLY is a good motor. Do what Hook 'em sez, I would also add a lift pump and just drive it.
 

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The 5speed of 2004 is a bit less robust than the 05+ six speed. From the guys I've talked to about rebuilds the converter is one of the first things that indicates issue. If the trans Limps think seriously about a triple disk /billet cover converter.
Search trans service for the double drain if the fluid smells suspect.
 

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Well, since you asked... I made a file which I've probably posted before with many of the known LLY problems... Here goes:

I usually warn that while these are GREAT trucks, they have a LOT of potentially big problems. If you do your own work, then they can be manageable. That said, I took mine on a 13k mile trip in 2014, several 3300 mile trips, and my truck was flawless (until 2017 when injector #2 connector went bad). But, I’ve had it since new, have never overheated (and added an aux radiator to make sure it doesn’t), have never ran a tuner (which can also lead to transmission problems), and I live in southern California so there is NO rust under the truck. At 107k miles, I replaced the water pump, serpentine belt (and idlers and tensioner) . . . not because there was a problem, but because I don’t want to wait for the problem to show up when I’m on a trip.

Unless you need the diesel to tow or haul a load, then it’s hard to justify the diesel. If you drive 60 miles a day and want better mileage, then a small economy car (I’m partial to Japanese makes for this) is the way to go. That said, here’s a partial list of issues with the 2004.5/2005 LLY Duramax trucks . . .

Short or Long bed? Standard, Extended, or Crew cab? Short bed has a 26 gal. tank; long has a 34 gal. tank. Crew cab with long bed has a 2-piece driveshaft and the carrier bearing/mounts can be a problem.

Wiring harness – may rub through where it goes over the alternator (near FICM) bracket on front of motor, passenger side. It needs to be protected where it rubs, usually with a piece of heater hose. Other potential chafing spots exist, and some connectors can have contact problems.

Injector connectors - #2 and #7 are common culprits, but it can happen on any cylinder. They can be replaced or “ice picked” to make sure they make a good connection. I finally had #2 go bad while on a trip 2 years ago. I bought cheap connectors on Amazon (about $16 for 4) and soldered in 2-way connectors so I can easily replace a connector on the road with a new one. My cheap connectors (just on #2 and #7) have worked great for 2 years now.

Overheating – worse on long, hot climbs (especially in the west). Some trucks are worse than others. An auxiliary radiator kit is available.

Head gaskets – mostly a problem if it’s been overheated or had a tuner. Expensive to fix ($6K?) and should include replacing torque-to-yield bolts with ARP studs.

4x4? – If so, magnesium transfer case can get a pinhole from “pump rub”, leak out the ATF, and ruin the transfer case.

Water pump – failure-wise, no worse than any other vehicle, i.e., will probably have a problem sometime after 100k miles. More difficult to change than most (must remove harmonic balancer on crankshaft; o-ring on tube from pump to thermostat housing can be tricky).

Serpentine belt idlers – usually make noise or bearing gets sloppy before going bad. Not expensive or hard to change (probably should do tensioner, too, along with serpentine belt). This is no worse than any other vehicle on the road.

Fuel filter head – pump may leak, or need new o-rings for pump to work, and some have cracked. BTW, fuel filters are expensive and can be tricky to replace. Some have had problems with certain brands/types of filters, especially the ones with plastic housings. I use Racor.

Some problems will be worse if the truck has resided in the rust belt, e.g., rusting brake lines, abnormal brake wear, speed sensors affecting ABS (truck could be hard to stop).

Automatic Climate control system (if so equipped) is, um, maybe too smart and does stupid things when it thinks an actuator door is “out of range”. It may be reset by turning off/on (mine does, and has since new), or it may require changing an actuator door which is a difficult task.

Allison 5-spd automatic – a great transmission, but can have failures if engine has power tune added. Also, it originally used Dexron-III ATF which is no longer available (or hard to find) with that spec. GM replaced with Dexron –VI ATF but there may be a seal problem if used. If the truck has been serviced at a dealer, it will almost certainly have Dexron-VI. It should be replaced with a “synthetic Dex-III” (e.g., Mobil 1 Fully Synthetic ATF “for 2005 and older GM”) or TES-295 (Castrol Transynd, Mobil Delvac ATF, etc.).

Lift Pump and auxiliary fuel filtering – highly recommended!!

Cluster – stepper motors go bad and needles go crazy. While often the speedometer, they are all the same so any of them go. Both speedometer and fuel gauge went on mine, probably 10 years ago.
 

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I would definitely try and replace the turbo downpipe if budget allows. That thing is like a pancake. I used a Flo-Pro. Fit perfectly.

Rear tires and front brakes are always a problem as well.

Congrats and Enjoy!

Sent from my LG-H831 using Tapatalk
 

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Discussion Starter #7
About the only mod that's necessary is to change out the Turbo Duct Inlet (a.k.a. mouthpiece) to the larger nonrestrictive '06-'10 style (under $100).

"all he ever had to do was"
surprised at the mileage and never having the head gaskets replaced.


Does the brand of the mouth piece make a difference?
 

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Only to your pocket. And/or convenience.

Convenience, as in the aftermarket replacements are a drop in, no mod item.
But they're the more expensive route. And they're not the biggest choice.
(if bigger is better)
See pic below;

As you can see in the pic, The LBZ is considerably LARGER than the LLY version. In order to fit, the inlet flex duct needs to be cut back just past the yellow warning tag, adding a 4" coupler to complete.
Part #98011738
The stock LBZ/LMM acDelco inlet duct is (I see a new one on fleabay for $90 free ship).

Another option is/was the Kodiak version.
No cutting or mod is/was needed as it will/would just drop in and fit.
However, it does not have the tube for the Turbo Resonator on top.
You can still mount it where it was, using the T-30 bolt in front, it just won't attach to the inlet tube as before.

GM part #98011736
But doing a search now, it seems the world has gone nuts, as the only ones people are offering, they now want anywhere from $450-$700. 'uhNo




And here, you have the LBZ inlet duct installed on the LLY air intake tube that's been cut back in length. Best to install the inlet duct loose, then place the intake tube next to it to mark the cut off point. Measure twice, cut once.



There is one other trim needed.
(seen in the 1st pic above, on the inside bend)
On the underside of the LBZ inlet duct is a casting fin that protrudes.
Where that fin comes in contact with the inlet tube for the EGR cooler, it needs to be notched/trimmed back, so there's no pressure on that tube.
Lest it springs a coolant leak where the weld breaks.
(engine moves, airbox/inlet tube doesn't)

 

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Another route is to find a complete LBZ intake. No mods necessary other than EFI Live for the MAF due to increased airflow. But you should do EFI Live anyways. Cleans up some things. I'm super happy with the intake and a modest 60HP tow tune/fun daily driver.

My .02 anywho.

Edit- sorry I just remembered..one mod is to cut open the inner fender dynamat with a knife where the filter would sit. There's an opening behind it. Not sure if it actually helps or not. Can't hurt.

Another is swapping the mount platform for the filter. The LBZ one has drain tubes on the bottom.

Wow. I hit post button a little prematurely haha
 

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I personally am a believer in an EGR delete and PCV reroute. I took one look at the walls of the intake (after the EGR), ewwwww. looks like covered in tar! I am on my 3rd LLY and all were the same. I have seen other posts where they talk about cleaning from time to time, but what a headache that is (IMO). Getting rid of the EGR and the PCV reroute (I ran mine down the frame and kick out near the from step mount).

Like AxysAssault said, EFI live (I personally like a near stock HP tune, it just cleans things up and improves fuel economy and performance). And if you are doing EFI live, the EGR and PCV mods work hand in hand.

As others have said, a lift pump/aux filter is a VERY good idea too.

I am also a believer in battery interconnect and extra grounds. What I did, left all stock wiring, added a junction block mounted on the firewall and ran positive cables (0 AWG) to the junction block from each battery and one to the starter and a 2 AWG wire to the alternator output. For grounds, I ran one from each battery to the engine, one from each battery to the frame (all 0 AWG), one from engine to firewall (2 AWG), and frame to body (4 AWG). I needed longer batter studs to make it work. It really does sound like overkill, true and I might be, it is just what I have done on my last 2 trucks, and I have never had any issues (electrically).

Like many have said on this website, if you can do the work yourself, you will save a ton of money (and you know exactly what has been done... I don't have much faith in the dealers and many mechanics... they don't like to admit if they damaged or screwed something up, or if they don't know... their learning on my truck - I don't think so!


But, that said, Welcome to Duramax ownership! They are great trucks, and will treat you as well as you treat them!
 

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.........if you can do the work yourself, you will save a ton of money (and you know exactly what has been done... I don't have much faith in the dealers and many mechanics... they don't like to admit if they damaged or screwed something up, or if they don't know... their learning on my truck - I don't think so!
DITTO!!!! This is becoming a bigger and BIGGER issue. Not to take anything away from the honest experienced mechanics out there,, but as these trucks age they develop quirks,, ( just like we humans do LoL) And it seems the new generation of flat rte mechanic knows ONLY what the computer tells them. Well and what 'tricks' the more experienced 'flat-rate' mechanic teaches them on how to CUT CORNERS!
These are not a low maintenance vehicle by any means. And maintenance, parts, pieces and service cost substantially more than lesser vehicles i.e. oil change = 2 gallons of oil and a $16 filter vs. 5qts and a POS $1.79 fram filter on a SBC... OR $15 fuel filter once or twice a year,, vs. a 5.3 GM gas rig from the same 2004-2005 era DOESN'T EVEN HAVE a serviceable inline fuel filter!!

Point here is even though these trucks are SIMPLY AWESOME and made to be worked, and worked HARD, and even if you do twist your own wrenches,, You should ask around, visit shops and find a GOOD RELIABLE HONEST shop for those things that are beyond your abilities, patients, and expertise. Like everything, plenty of boo-boo's can be made that will just cost you dearly in botched repairs.

Ask around and find that shop that others with this era of Duramax go to when they need substantial repairs. No matter what the experienced reliable shop charges, may be money WELL spent vs the cut-rate, flat-rate, "It's just changing the part the computer tells me " mechanic. If your prepared with WHO that is in your area,, can save a LOT of headache.
 

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I also believe EGR delete/PCV reroute is a must. With the LLY donor truck I bought, the intake valves were so plugged, I'm surprised it even ran. Intake manifolds as well. Just coated in sludge. Even a hot tank at the machine shop couldn't get it all out.

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I posted this on another post, but it might be a good maintenance item to do for a truck with as many miles as yours. The way the radiators are setup they get really dirty.

I would also look at removing the intercooler and cleaning the fins on it, the radiator, trans cooler and ac condenser. The easiest way you can clean all 4 by removing the intercooler, you don't need to remove the radiator. There are some videos online.

My truck only had 120000 on it when I bought it and I could not believe how much dirt was in there blocking air flow. There are some videos online.
 

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