Tekprodave

I'm trying to brainstorm and I'm looking for ideas on what could be possibilities for my low RPM issues. The symtoms are irratic running from idle to 3800rpm with severe hesitation right at 3800. After 4k RPM she runs strong and perfect all the way to redline. It's an LT1 383 with Vortech s-trim blower. One thing I'm suspecting is blown header gaskets since it sounds raspy. Any other causes? It also blew the dipstick out but I found info on PCV routing that should help. Also leakdown test was favorable with about 5% on every cyl.

mrmint69

Do a vacuum test. It will give a ton of info. It should hold steady between 14-25 depending on the cam you have.

Tekprodave

Vacuum test huh. Hadn't thought of that. Thanks.

BTW I'm running a Delteq ignition.

mrmint69

I have a list of all the things it can be if you give me the exact description of what it does during the test. If the needle jumps around or moves you have a problem.

Tekprodave

cool. So what's the best way to do it?

mrmint69

Schuck's has a vacuum gauge for $19 and i hooked it up to the drivers side manifold vacuum hose i added for the msd box. Any small hose will work, i tapped into the middle one right over the pcv valve U hose. Then let me know the results here.

Tekprodave

I'm a knucklehead. I realized I have a vacuum/boost gauge already hooked up. Duh. Anyway as I recall it's usually around 20 at idle but I'll try to remember to check it again this weekend.

Tekprodave

OK the vacuum gauge is steady at 17 at idle. I took out the restrictive filter in the PVC setup and the car is running much better but there are two issues:

1. Valvetrain noisy on drivers side only. I can look into this.

2. stumbles hard at about 3800 rpm. What could cause this????