vacuum reading and fuel pressure
- Thread starter 95mustang_gt
- Start date
Swarzkopf
Member
Someone correct me if I'm wrong here:
You checked this at idle? Your vacuum reading should NOT be moving by 3lbs at idle! That is a dead on indication of a fairly large vacuum leak.
Furthermore, with stock heads and a stock cam, you should be seeing 17-22lbs of vacuum at idle.
So...you probably have a significant vacuum leak causing idle problems.
You checked this at idle? Your vacuum reading should NOT be moving by 3lbs at idle! That is a dead on indication of a fairly large vacuum leak.
Furthermore, with stock heads and a stock cam, you should be seeing 17-22lbs of vacuum at idle.
So...you probably have a significant vacuum leak causing idle problems.
vacuum and fuel pressure
I just added a vacuum can from comp cams. I created about four extra inches of vacuum at idle and about 10 when reved to about 2 thousand rpm. before my idle was about 6 inches now it's about 9 to 11. I have the aeromotive adjustable fuel pressure regulator and i have I think your almost right on with your fuel pressure everytime muscle mustangs and fast fords or 5.0 and super fords magazines publish dyno results they usually end up with about 40 to 42 psi fuel pressure at idle. I set my fuel psi to 40 and it seemed to drive better. It drops about 4 or 5 psi when under load. I got the little fuel pressure 1 1/2" auto meter fuel psi gauge. it's pretty cheap from summit like 30 bucks with the fitting I think. It works great. don't get a liquid gauge I hear If the liquid heats up causing the reading to be off. I hear you need a minimum of like 15" of vacuum for your brakes to work a 100 % but I'm not sure about that. I know my peddle is definitely firmer now with the extra vacuum. If the gage is bouncing then you have a leak somewhere. your stock vacuum cannister is near your ac blower fan take that stuff apart and check the hoses and connections. check your charcoal cannister hoses for deterioration. I know my hose is about to crumble away I'm sure I could my vacuum to stabilize a bit more if I replaced mine. I plan on doing it soon. If you removed your egr pump or any of the egr stuff like me then check all those hoses. make sure your valve cover breather seal is good and mak sure you have the hose in place that goes from the passenger valve cover breather to the cold air intake pipe connected or your vacuum will be off. I would just check everything you can before you do anything with your engine. once your do everything else then get a leak down tester if you don't have one and then you can see how well the seals in the engine are. Oh i forgot to say that the vacuum can actually stabillized my vacuum a bit too. so if all else fails you can get one of those they aren't as big as they look. I mounted mine right above my brake booster. I have a double cowl hood and therefore the clearance but it's screwed into the plastic in front of the winshield wiper motor.
I just added a vacuum can from comp cams. I created about four extra inches of vacuum at idle and about 10 when reved to about 2 thousand rpm. before my idle was about 6 inches now it's about 9 to 11. I have the aeromotive adjustable fuel pressure regulator and i have I think your almost right on with your fuel pressure everytime muscle mustangs and fast fords or 5.0 and super fords magazines publish dyno results they usually end up with about 40 to 42 psi fuel pressure at idle. I set my fuel psi to 40 and it seemed to drive better. It drops about 4 or 5 psi when under load. I got the little fuel pressure 1 1/2" auto meter fuel psi gauge. it's pretty cheap from summit like 30 bucks with the fitting I think. It works great. don't get a liquid gauge I hear If the liquid heats up causing the reading to be off. I hear you need a minimum of like 15" of vacuum for your brakes to work a 100 % but I'm not sure about that. I know my peddle is definitely firmer now with the extra vacuum. If the gage is bouncing then you have a leak somewhere. your stock vacuum cannister is near your ac blower fan take that stuff apart and check the hoses and connections. check your charcoal cannister hoses for deterioration. I know my hose is about to crumble away I'm sure I could my vacuum to stabilize a bit more if I replaced mine. I plan on doing it soon. If you removed your egr pump or any of the egr stuff like me then check all those hoses. make sure your valve cover breather seal is good and mak sure you have the hose in place that goes from the passenger valve cover breather to the cold air intake pipe connected or your vacuum will be off. I would just check everything you can before you do anything with your engine. once your do everything else then get a leak down tester if you don't have one and then you can see how well the seals in the engine are. Oh i forgot to say that the vacuum can actually stabillized my vacuum a bit too. so if all else fails you can get one of those they aren't as big as they look. I mounted mine right above my brake booster. I have a double cowl hood and therefore the clearance but it's screwed into the plastic in front of the winshield wiper motor.
95Cobra302
Founding Member
I just checked my vacuum and i'm getting a steady 19. That's with a pretty much stock engine. What else are you all getting??
Swarzkopf
Member
Yeah....a bouncing vacuum reading is NOT normal or okay for a stock cammed car....according to Haynes, it is indicative of a vacuum leak.
slocomo said:
Well right not my idle is not perfect so when i was doing the vacuum test the rpms were moving.I reset the iac and got it to idle at 900 but its still a little boucing going on and cleaned the maf.I still have to check the tps.Right now for the valve covers i had to plug all the holes with grommets untill my oil filler from trickflow comes in,so there is no hose going into the valve covers.
thanks
Jesse
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