95BlackTA

I may have a vacuum leak thats causing the car to run like its on 7 cylinders....Im guessing you have to buy some kinda vacuum(compression?) gauge to check it?
How much are these and how does that work?

Fastbird93

If you're talking about just hooking a vacuum gauge up to it then that's very easy. You'll need a hand held vacuum gauge, costs about $20. Just take a fitting off of the intake manifold, let's say the EGR vacuum hose for instance. Then just press the vacuum gauge rubber hose onto the fitting that's open on the intake manifold.

Geoff Chadwick

You can buy a small pump with gauge at the auto parts store (or walmart if you're lucky) for like $25-$30. You'd tap it into a vac line that goes to the intake manifold, cover over the Throttle body, and pump away. I typically use sheet of rubber (gasket maker material) and a nice wormdrive clamp to close off the TB. While the engine is running however, hook the intake up, leave it tapped to the intake manifold, and see what it says.

The other thing you can do is order a vaccum gauge from one of the parts sites and hook it up. That will only work while the engine is running, but it'll let you know how much vaccume you're pulling during idle and cruise.

On a side note - I dont know quite how a vacuume leak would make it seem like it's running on 7 cylinders, perhaps you mean it's just running like crap? Any guesses so far to where you're problem is? (running pig rich perhaps?)

Straight vaccum tester:
http://www.actron.com/cgi-bin/web_st...=2672219_15814


Vaccum pump:
http://www.actron.com/cgi-bin/web_st...=2672219_15814

95BlackTA

Yea its just running like crap....almost like when I had one of the rocker arms come loose. But I checked that today and its fine. It idles rough, engine shakes...and when I drive it runs just as bad throughout the entire RPM band. I tried to take it to school today but never got outa the neighborhood it was soo bad. It just happened all the sudden. Well the battery died, so I recharged it, started it up, and it has ran like this ever since. Im at a complete loss.
A bad opti wouldnt make it run this bad would it? I jsut replaced it like 2 weeks ago, and maybe it failed cause I had a coolant line leaking a lil bit of coolant on it before I fixed that.

Geoff Chadwick

Any CE lights? If either the high resolution or low resolution Opti Signal are bad it'll trip a CE light... It COULD do it otherwise, but that doesnt seem likely without throwing a code if it was new.

Right after charging the battery? hmmmm

Injuneer

Just curious.... how do you insure that all the intake valves are fully closed, PCV valve is not leaking, vent line from valve cover is sealed, etc. so you can pull a vacuum on the intake manifold?

95BlackTA

No codes...and scanmaster is showing everythign is just fine and dandy(like Block learns, o2's etc)

Injuneer

If you have a ScanMaster, you have the ability to measure intake manifold vacuum. You don't need a gauge. Vacuum = BAR - MAP.

importeater

Just out of curiosity, what should your vacuum reading be on a stock LT1 tapping into the nipple on the drivers side of the manifold that goes back to the EGR?

Geoff Chadwick

Breather on the valve cover would eliminate the cross line, then block the others. Only issue I ever had was open valves, and I solved that one by taking the appropriate rockers off. For me that was the easiest method as I didnt have any other really good tools to work with and I had a leak somewhere that I couldnt find. Turns out thats how I found out one of my valves wasnt seating properly as well.

The other method I used to do a lot was for my DSM, which is where I'd put 20psi into the output of the turbo compressor and seal the compressor inlet with a silicone cap. Block the throttle blade WOT and the whole intake line was under pressure to check for boost leaks. There were some issues with open valves, but in such situations that wasnt too loud, it was more the huge hissing that gave leaks away. But I didnt try that on the Lt1 as I wasnt sure at the time if it'd blow any lines or hoses off. (That and a rubber sheet wouldnt hold a seal too well)

I know there are other methods for finding leaks, sure, but it made the most sense at the time, espicially considering I had the valve covers off.

Injuneer

At idle, the stock LT1 will pull 20 to 21"Hg vacuum (= 9 to 10"HG MAP; 30 to 35kPa)

Interesting concept on isolating the manifold for vacuum pump testing..... not sure if my Mit-E-Vac pump would handle that much volume.

Geoff Chadwick

For me it worked... honestly looking right off the bat to a turbo 4g63, every single line and hose was silicone and clamped, and could handle getting pressurized (turbo... duh). Then an LT1 can probably handle it as well, but call it a hunch, without replacing lines and clamping them all, some would blow off the manifold.

(Also at the time I didnt know how strong the gaskets were before they'd blow out, so I did it that way)

And the person who gave me the idea of vacume pumping the intake was an RX7 guy... but in his method he has no valves...