03sierraslt

iTrader: (22)

It doesnt take much of leak to throw off your fueling.

Atomic

iTrader: (42)

The biggest give away for an intake leak is a high idle...

PSM

iTrader: (3)

at initial startup it would idle around 1000 rpms, then 30 seconds later back down to 650 or so.

Atomic

iTrader: (42)

Your fuel trims sound pretty normal, as does the idle speed....I am really doubting that small intake leak is your issue. Even a small leak will make the idle stay at at least 1000rpm.

Let it idle and spray some starting fluid around where you think its leaking, if the RPMs rise, then its definitely a leak. Also, try cleaning your MAF with some of that cleaner they sell at autozone. If you are using a K&N or similiar oiled air filter they often get the MAF dirty and make it act funny...

PSM

iTrader: (3)

I do have a k&n and clean the maf every oil change with the autozone maf cleaner as preventative maintenance.

I also bought some starting fluid, but haven't tested that yet

Also warm idle is around 14.5-15" vacume which is way low for the gt2-3 cam. Crusing at 70 vacume is around 8-10, but I do have heavy tires/wheels (about 90 lb a pop) and have awd.

When I first did all this to the truck the throttle was very touchy and the engine had spunk. Now its very doggy and stumbles so its gotta be some sensor thats going or a leak or something. I did swap maf's with an 01 5.3 and it didn't cure the problem. Also a Maf reading wrong wouldn't explain the lack of boost either. Also as a sanity check, should I be able to roll into the throttle and dial in boost .1lbs(digital gauge) at a time? I thought once you get within -2in vacume the bypas should close and you should get right into boost?

My spare vehicle is also down, so I can't take this truck outa commission till I get the spare back up and running. Once I do I plan on trying to iron this all out.

03sierraslt

iTrader: (22)

You should have more idle vac then that, i see 14.5" vac at idle with a decently larger cam. Off the top of my head i would expect a gt2-3 to be around 19" or so at idle.

PSM

iTrader: (3)

I decided to make my own vac leak tester. I used couple plumbing parts including a 2” plastic pipe plug that I threaded an air line QD into, then that went to a rubber 2”-3” adapter that go clamped to the j tube. I then put just under 10psi into it to pressure ize the entire engine from the j tube back and sprayed down the whole engine bay with Windex. I could see the leaks bubbling like crazy. The leaks were between the lower and upper housing for the blower

I replaced the gasket between the upper and lower intercooler housings. The new gasket was visually a bit bigger and had a circular cross section vs the old one was smaller and was more square. After I pressure tested it, I could not see any leaks. Also did a compression test of all cylinders, and they were all between 125-130psi. I did not hold the throttle body open, so that was just with cranking. All the plugs were a nice golden brown, and I regapped them to .035” (they all were a little out, but still under .040”)

I also noticed on cylinder 2 and 7 black marks on the head coming from under the header flange, so I’d assume that means its leaking at some rate. Also you can hear leaks at every clamped joint in the exhaust. Could these be messing with the 02’s enough to be causing the stumbling and hesitation I’m feeling at part/very light throttle? When it stumbles at idle, the afr swings down to 17:1 mostly, but sometimes it goes rich too, maybe 13:1.

Also some times when I give the throttle a quick poke the maf value will jump, and some times it won't. When the value doesn't spike up, the motor bogs. Not sure if thats giving me a hint that the maf isn't working or not.

What should I be idling at for a MAF flow rate? I seam to idle around 1.7-1.9 lb/min when the truck is warmed up with an idle rpm at jsut above 600rpms