BlackMetal
Active Member
- Joined
- Sep 29, 2005
- Messages
- 4,688
Alright... my car has been running at 12-13" of vacuum for a while now (stock internals), finally built up the motivation to try to tackle the issue (would like to run vac brakes).
I know the basics, i.e. spray areas with carb cleaner and listen for changing idle, replaces lines, etc, so I don't need any tips like that. I'm trying to dig a little deeper than the "beginner" ideas.
I came across a suggestion, searching through old threads, that seems completely screwy to me. The idea was to take a blank piece of gasket material, unbolt the vacuum block from the top of the plenum, insert this piece of gasket material, and then bolt everything back down. Basically you're blocking flow through the vacuum block and eliminating any vacuum "accessories" from the equation. You're "supposed" to watch your BLMs, and if they decrease, you know one of your lines is the source of the leak. This idea sounds like complete garbage considering you'd be stopping vacuum from reaching your fuel pressure regulator, without vacuum the diaphragm in the regulator is going to allow more fuel pressure, the car will run rich, and your BLMs WILL drop as the ECM tries to correct for this incorrect fuel pressure. Am I completely misunderstanding something? Maybe it's because it's 4:30AM. But that idea doesn't seem to work in my book. Maybe if the leak is bad enough I'd hear an overall change in idle quality, but I do not see the point to watching BLMs when you're messing up the fuel pressure like that. My boost/vac gauge is also fed off of the vacuum block, so watching that for a direct change in vacuum is out the window too.
Anyways, I ordered some vacuum caps to block off the lines one at a time. The other day, I thought I'd get lucky (yeah right), and I blocked off the line that feeds EGR/cruise/HVAC, but saw no change. Guess my leak isn't there. That seems like the vacuum circuit with the biggest potential for leaks (T's, check valves, brittle HVAC lines). When I get more free time, I will go back and block off the rest, PCV, MAP, Canister. I'd block off the line to the FPR but if you read the last paragraph you'll understand why I have a problem doing that.
I will AGAIN try to spray carb cleaner at the back of the dog house, I did feel the infamous thread slip when I installed a PowerPlate and bolted the plenum back down. I left it snug and tried to avoid pulling the threads out completely, but this is a good area for a potential leak. Sprayed this area before and got no results, I am not a fan of the carb cleaner trick so far.
I am also planning to check the bolts on the intake itself, as I have read some guys with vacuum leaks go check the bolts and find out that they've backed themselves off quite a bit just over time and miles. Also will try to check the intake gasket with the spray method.
That's where I'm at right now. I wanted to see if anyone else understands what I'm saying about blocking off the vacuum tree and how watching the BLMs would be misleading. My plan of attack is to block the rest of the lines one-by-one using the rubber caps, then check for actual plenum or intake leaks using carb spray. Any other ideas are certainly welcome. I refuse to swap to vacuum brakes at this point.
I know the basics, i.e. spray areas with carb cleaner and listen for changing idle, replaces lines, etc, so I don't need any tips like that. I'm trying to dig a little deeper than the "beginner" ideas.
I came across a suggestion, searching through old threads, that seems completely screwy to me. The idea was to take a blank piece of gasket material, unbolt the vacuum block from the top of the plenum, insert this piece of gasket material, and then bolt everything back down. Basically you're blocking flow through the vacuum block and eliminating any vacuum "accessories" from the equation. You're "supposed" to watch your BLMs, and if they decrease, you know one of your lines is the source of the leak. This idea sounds like complete garbage considering you'd be stopping vacuum from reaching your fuel pressure regulator, without vacuum the diaphragm in the regulator is going to allow more fuel pressure, the car will run rich, and your BLMs WILL drop as the ECM tries to correct for this incorrect fuel pressure. Am I completely misunderstanding something? Maybe it's because it's 4:30AM. But that idea doesn't seem to work in my book. Maybe if the leak is bad enough I'd hear an overall change in idle quality, but I do not see the point to watching BLMs when you're messing up the fuel pressure like that. My boost/vac gauge is also fed off of the vacuum block, so watching that for a direct change in vacuum is out the window too.
Anyways, I ordered some vacuum caps to block off the lines one at a time. The other day, I thought I'd get lucky (yeah right), and I blocked off the line that feeds EGR/cruise/HVAC, but saw no change. Guess my leak isn't there. That seems like the vacuum circuit with the biggest potential for leaks (T's, check valves, brittle HVAC lines). When I get more free time, I will go back and block off the rest, PCV, MAP, Canister. I'd block off the line to the FPR but if you read the last paragraph you'll understand why I have a problem doing that.
I will AGAIN try to spray carb cleaner at the back of the dog house, I did feel the infamous thread slip when I installed a PowerPlate and bolted the plenum back down. I left it snug and tried to avoid pulling the threads out completely, but this is a good area for a potential leak. Sprayed this area before and got no results, I am not a fan of the carb cleaner trick so far.
I am also planning to check the bolts on the intake itself, as I have read some guys with vacuum leaks go check the bolts and find out that they've backed themselves off quite a bit just over time and miles. Also will try to check the intake gasket with the spray method.
That's where I'm at right now. I wanted to see if anyone else understands what I'm saying about blocking off the vacuum tree and how watching the BLMs would be misleading. My plan of attack is to block the rest of the lines one-by-one using the rubber caps, then check for actual plenum or intake leaks using carb spray. Any other ideas are certainly welcome. I refuse to swap to vacuum brakes at this point.
