i only have 14 in/hg in park and 13 in drive at idle. does that sound like a vac leak? i have a light throttle skip that i have been playing musical plugs and coils with for 3 weeks now. well this week i replaced all 8 coils and 8 plugs, i still skip. i unhooked boosta spark completely still skips. tomorrow we are gonna replace fuel filter and check pressure on system during driving to make sure there are no fluctuations. then i guess im gonna have to start pulling supercharger and upper intake off to check gaskets. we couldnt find a leak anywhere but it just acts like its a leak. any ideas?????????

 

mine read about 18 in idle and 17 in drive.

 

If your engine is sound, and the valve timing is correct, you do indeed have a vacumn leak. Save your self time and effort, and have a local shop smoke test it (they use a machine to pressurize your intake system with 2-3 psi of a safe smoke). The smoke will come out of any leak, and easy to spot. That machine has saved me alot of headaches, and has saved my customers loads of money.

 

well unfortunately no one round here has a smoke tester that i know of. i wish to god they did b/c im really thinking i do hAve a leak. the truck runs great under full throttle or atleast it seems to but, light pressure especially round 40 mph in overdrive it has something wrong. and it definetely is not timing b/c i just had the problem recently when it jumped time with me that my friend sounds horrible and it does it under boost. it would spit back through the breather and pop real bad. so i dont think that is it. but if yall have that much vacuum and i think i used to, then thats just bout got to be it.

 

Your vacumn should be a minimum of 17, usually around 18-19. With it running good at full throttle rules out plugged cats, or mechanical problems, so I think your on the right track. Thats pretty low vacumn. Some common causes are EGR leaking into intake, and of course the intake ect... Good luck, and post what you found.

 

Rusty
If your sig is right it looks like you have a set of Comp Cams in your engine.....I'm pretty sure thats what Johnny sells.

How long have you noticed the low vacumn ?

Have you talked to JL about it ?

You realize that when you put cams in a motor the vacumn drops right ?

Does it have a lope at idle or does it have a flat spot off idle, we need more info.
Dale

 

I have the Crower stage 3 cams. My vacume at idle is 9-10 inches....

 

I have mild cams, something in between the Crower stage 1 and 2. My vacuum at idle is 14-15" I consider this normal.

 

yes i have the stage 1 jl cams. i didnt know how much this affected vacuum. it doesnt hardly lope except when it is skipping. normal idle is about 700-800 and you can hear very very little lope thru the exhaust. heck now u guys got me thinking its not vacuum leak i dont know. by the way cats cant be pluged b/c there are none haha. i am running 116 gas is it possible o2 sensors can cause this that im describing????? i will post problem if i ever find it i promise.

 

u might have kinked the line i had the same thing happen to me

 

20 in park and 18 in drive. I have the stock cams.

 

Vacuum leaks suck....or something!

 

Rusty: When you change the fuel filter out, save it and if that fixes the problem, saw the old one in two and tell us what you see or post a pic.

Dan

 

Rusty
Depending on how much leaded race gas you have run with the o2 sensors then Yes this could be your problem.

Here's a little tip......If you are going to continue to run race gas all the time, try turning the key to the on position and wait for 30 seconds or so then start the truck. This will give the sensors time to warm up and will keep them running cleaner. Most damage done to the o2 sensor is when it is cold, it can't keep itself clean. I learned this from the turbo buick guys, a lot of buick guys run heated ford sensors and run race gas.
Dale

 

ok here is what we did, change fuel filter, then hooked up fuel pressure guage and it showed 28 lbs of pressure at idle when i held the brake and bowed it up from 1000-2000 rpms pressure dropped back to 22 then bounced back and forth to 28! so after i good ole chat with jlp (THANKS JOHNNY YOU THE MAN!). my 3 week problem is finally fixed!

jl said when u run big motors and power u get under front bumper take the resistor wires off unhooking it and butt connecting them together and that would fix it. so we did it in bout 1 minute and bam no skip and fuel pressure is round the 50-55 mark. i never would have thought it was a fuel problem but as ron white would say i was wrong! by the way after all that i went to the track and improved on my best time b/c it actually hooked check out that post.