Jmantx

As the title implies, I recently bought a 2003.5 Silverado 2500HD to pull a travel trailer. Within a week I was having issues - reduced engine power, random misfires, and half the time the check engine light is blinking and claiming a misfire, as well as randomly running on only one bank of cylinders. I assumed the grounds were an issue and started trying to test grounds when I noticed that the cylinder heads were stamped as 706s. I knew the lq4 should have had 317 heads on it, so you can imagine my dismay when I found the stamping 12551358 on the block. From what I can tell, a previous owner swapped in a 5.3. I don't have a shop or a way to swap back in a 6.0. My best idea is to try to flash it with 5.3 programming in hopes that it will run correctly. Before anyone asks, it does still have a 4l80e in it.

68Formula

A 12551358 could be a 4.8 or 5.3L. If it was running fine for a week, and then suddenly started showing issues, I don't see how reflashing is going to fix it.

LS1 TJ

Assuming its a stock 5.3 you could try a mail order tune but best would be a chassis dyno tune to adjust the ECM. Or maybe a 5.3 ECM out the salvage yard?
Have you done the basics like spark plugs, fuel filter and maybe a compression test?

Ls7colorado

iTrader: (3)

A 5.3 ECM would not help because it would still need to be segment swapped to make the transmission shift and remove Vats.

Sounds like a ground or low voltage problem.


how big is the camper your towing?

Jmantx

I wondered about a ground issue. I added a ground wire to the driver side coil harness because there was no ground to it. Upon inspection I found a large mess of grounds in the loom from the PCM to the top of the intake manifold.

The trailer is 32' long, gross weight is 8600

Full Power

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' Obvious solution is MANIFOLD PRESSURE. I'd recommend a Magnuson TVS1900.
Around 11 PSI should help towing a bunch.

Ls7colorado

iTrader: (3)

That would certainly make up the difference but id say 11 might be a little much lol

My biggest concern would be getting 6-8mpg AND having to use premium fuel while going any sort of long distance.... yikes

hopefully your truck atleast has 4.10's instead of 3.73's

Tuskyz28

6 mpg i would cry literally. Im frustrated now with my 87 R20 Camper special 454 truck with 4.10s and turbo 400. I barely see 10 mpg

Kjduvall

did the guy that sold it to you say anything about it ? id be a little pissed myself. i kow that wont help your problem but damn dishonest people these days.......

Ls7colorado

iTrader: (3)

Im just guessing... my slightly modified and tuned 6.0 with 4.10's will be in the 9-10MPG range towing a 7-8000lb tractor
So I can only assume towing a wind catching 9000lb camper with boost would certainly be worse lol

Jmantx

He claimed it was a 6.0.

Jmantx

Personally I'd start with more displacement so that I could at least go to a 2650 I have an empty 6.0 block sitting at my dad's house, so I could work a little magic and get it put together and in the truck.

strutaeng

Well, that sucks. I guess you really can't do much about it having a 5.3 now?

Some very early GMT800 2500s (non HD) did come with the 5.3s, but they were very few and IIRC were like regular or extended cab options.

I would say, just try to diagnose the apparent misfire for the time being. A flashing check engine light is warning you your catalytic converters are likely going to be damaged from the misfire. A good running engine is obviously better than any engine that's misfiring...

Jmantx

Yeah, mine is an 03.5 and an HD so I'm pretty sure it's supposed to be a 6.0. I'm going to try to diagnose the wiring issue soon, I may even swap the entire engine harness to get a better start on repairing it. The current harness has some rather questionable mods/repairs to it.

Forcefed86

iTrader: (4)

could check your local lemon laws. Selling a tow vehicle with a smaller engine is def shady stuff. May be able to force him to give you a refund. Boost is the cheapest option by far. Though thats def not from a blower. Little T4 turbo back where the muffler is running 4-6psi would do wonders and isn't going to kill mileage that much. Could do it very cheaply compared to a blower. Prob around $1000.

CattleAc

iTrader: (7)

Bottom line...you're never gonna' be happy with a 5.3 no matter what you do to it unless it's boost...

Jmantx

Dang, ok. I do have an lq4 block sitting at my dad's house, but it needs to be bored and of course would also need pistons and rods. I've thought about buying some LS3 rods and pistons and just boring it to 4.065, but life got in the way and I had nothing to put it in.

Forcefed86

iTrader: (4)

Adding a turbo to what you have would be cheaper and pull better than an stockish 6.0.

Full Power

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. Turbochargers are cheaper than pistons + machine work.