Still having issues with our 408 build

[mr2cam]

Hi guys, we started a build for my dads work truck a long time ago, it is a 99 Silverado 1500 that had a 5.3 in it. We bought a junkyard 6.0 and stroked it to a 408. Anyway I will get right to the problem and then list all of our modifications. First off cold starts are horrible, we believe it is running too lean, anyway you have to keep the rpms up to about 1500 for about 10 seconds and then slowly let it down otherwise it will die.

Ok now on to the next problem, about 90% of the time when you start it up (even if it's warm) and go from park to drive or reverse, it will die on you.

Our tuner said that it is common for LS motors to have issues when you put a bigger cam in and they can be kinda a pain to tune, he worked on it for hours and it got better but after we drove it back home (4 hour drive) it decided to go back to wanting to die all the time on us. The cam is only a 224/220, but we have 1.82 comp rocker arms (we bought some 1.70 adjustable ones and are going to install them to see if it helps our problem). My dad seems to think that the rocker arm ratio is too radical and that is causing it to be such a big pain in the ass.

The truck also has a FAST 102 LSXr intake manifold and a FAST 102mm throttle body, were not sure if that is also causing the idle issues. We have replaced every part you can think of and we still can't get it right. The truck runs like a raped ape WOT, but other then that it is almost undrivable. Has anyone here had a similar issue and might know what could be causing our problem? Any ideas would really help, thanks guys!

[country_3030]

it sounds like you need a new tuner. that is a baby cam for a
408

[mr2cam]

it sounds like you need a new tuner. that is a baby cam for a
408

Hmm.. He does a lot of GM products with cams and what not, he did say this one has been the biggest pain for him to do so far. The problem is that we live in Washington state and I was told to go to this guy by MULTIPLE people.. I would rather not say his name in case it does come down to it being a tune problem.

[bangbangskeetskeet]

I agree that the tune is not right. Ive got a 219/230 cam in my truck and it idles perfectly. Never has cold start issues.

[Botlfed]

Spend the money, call nelson, get the truck going right, never heard well cammed LS motors die after being cammed, sounds like the tuner doesnt know his ass from a hole in the ground.

[Frenchy]

I have a bigger cam in a 5.3. Here's a video of it idling at about 850 rpm (my coolant temp sensor was fubar'd, truck thought it was -40, hence the high idle) on a stock tune. (With the exception of the injector tables)


I've heard the FAST intakes can be a pain in the ass to tame, but a competent tuner can do it. You clearly don't have one of those.

[skeet]

id have to agree sounds like a tuning issue, i run the same intake F.A.S.T LSXr intake/TB on a stroked 410 my cam is somewhat huge by others way of thinking 252/263 you can go to youtube and look up nitrous fed 410, Quik tuned this truck and it didnt take him but a couple of times to nail the idling and the overall tune is dead on


might wanna check and make sure you dont have any vac. leaks or intake leaks also. did he tune with the MAF or is it SD tuned?

[farmtruc]

Frenchy, you need to freak'n sweep and mop that damn floor, lmao.

[George C]

if saying the mechanical part is 100% correct then its the tune. the 408 itself should easily swallow up that 220 cam to point it should of idle very well. I had a A trex in a 4.8 idle very well. the 1.8 rockers is only going to give you a out .030 lift gain but nothing on the durations.

we could sit here and blame everything to end and back but first check and make sure everything is legit

[farmtruc]

Check for vacuum leaks, not sure if you posted that already, but that will cause surging and headaches.