GMCtrk

iTrader: (27)

So, I was on a long road trip today with the cruise control on and any time the engine went into load (i.e. up a hill) you could hear a whistling noise. Air is going in somewhere. I have both throttle body and intake manifold gaskets off an 05HD ready to go in, but i was wondering, is it possible that anything else is leaking causing this? It is really screwing up my engine at WOT, and due to this I can't get a blackbear tune until I fix this leak! I have the coolant bypass on my TB. Do the open ends where the coolant goes in need to be plugged off? Mine are just open. Are there any other common places where air can get in? I've sprayed flammable brake cleaner everywhere copiously with no change in idle.

Also, I'm f*cking fed up with the throttle response on my truck. It seems to do okay up until 75mph, but after that going up a hill or anything it can't accelerate, and these damn GM tunes wont kick down to 3rd until 75% TPS. I refuse to be have to go WOT any time I want to accelerate up a hill. Really sorry about this reant but I was ready to drive my truck off the road today pissed off about this and determining what I need to do about it. I'm hoping a turbo setup will remedy it and if need be I am looking at a 215/215 cam, but I haven't seen much feedback on small cams in 6.0s and gains in cruising power. What I really want to know is how in the hell is a 6000+ LB 2500HD with a low compression 6.0 and 4l80e tow on the highway without going WOT all day long and getting 10 mpg.

hirdlej

iTrader: (31)

Dude did you ever change the intake mani gaskets? Did you check the intake mani flanges to make sure they're true and flat? Otherwise how much are your TSP heads milled? Perhaps they're milled enough that the manifold can't seat properly.... Just a few things to thing about........

BlackGMC

iTrader: (31)

Do you have tuning software?

GMCtrk

iTrader: (27)

I have the software. But I can't do anything until the leak or whatever is fixed. My logs @ WOT are an absolute mess. The engine made the hissing/air whistling sound before I ever had the TSP heads, and it all seemed to start after I put on a ported TB. But now I'm running the stock one again.

I can't remember or not, but do tunes normally pick up at part throttle or crusiing? All I could remember from my Wheatley tune was that it picked up at WOT but part throttle felt like stock.

BlackGMC

iTrader: (31)

OK, since you have tuning software this is what you can try. Let the truck warm up to operating temp, hook up your laptop and drag it around to the front of the truck, i placed mine on the fuse box. Log STFTs and LTFTs both bank, open up the scanner so you can see the trims... Get a can of carb cleaner and start start at one spot. For example spray each injector at the base, look at the scanner to see if the trims change. Spray small sections and watch the scanner, also when spraying make sure you spray ALOT in one spot. I used about 2 cans... After finishing i determined my injector Orings were leaking and one of the connections on my intake.

GMCtrk

iTrader: (27)

I already did that a while back. I couldn't find anything. On one tiny occasion the STFTs did blip to -8 but I could never reproduce it and I sprayed a ton of cleaner in there. I'm gonna replace these gaskets and go from there. I wonder if my EVAP is leaking.

BlackGMC

iTrader: (31)

I have never used brake clean before but I know carb cleaner works. Also when your doing it the idle probably won't change at all, all you doing is basically plugging a small hole with liquid until it evaporates. IMO get out there and do it again and again until you find the leak... test everything post MAF, the entire intake track, brake booster and line, etc...

GMCtrk

iTrader: (27)

I'll do that if the "new" gaskets fail to correct the problem.

I'm gonna pull the whole manifold off, clean it and inspect it.

budhayes3

iTrader: (19)

FYI, we've used flammable brake cleaner to find vacuum/air leaks at work with good success. The coolant passages on the TB don't need to be capped, no vacuum goes through there.

Replace the gaskets as you mentioned, paying special attention around the throttle body. It seems to coincidental that you started hearing the hissing noise after the throttle body swap. If the mani and tb gaskets don't fix your problem, spray all of the injector o-rings as Corey mentioned, and check any vacuum lines going to the intake, such as the brake booster hose, PCV hose, and EVAP, and closely inspect the air intake tube since it was disturbed during the tb swap. Check the rubber gasket that slips over the tb to make sure that it's not torn or deformed, and check the tube for cracks or anything of the sort. I guess it couldn't hurt to check and make sure that the MAF isn't cracked or anything like that either. You're still rockin the stock air box right?

BuyAmericanIron

While you have the intake off, I would check it closely for a crack somewhere on the bottom side. You said when the engine goes into load you hear it. That indicates less vacuum and a slightly larger opening in the TB. That would lead me to take a close look at the TB. I have not seen it in GM, but have seen several cracked or broken Ford intake manifolds on the 4.6L. The defect always showed on the bottom for some reason. As for your question about the coolant passage in the throttle body, I can't imagine any way for an air leak there unless it has an internal defect which would have shown up before the coolant lines were removed. You could always plug them and see what happens. I agree with Corey, I would chase this one until you find it. Good luck!