Vacuum leaks?
- Thread starter zZsKyZz
- Start date
Swarzkopf
Member
Vacuum leaks can be real hard to pin down.
If I were in your shoes, I'd check the vacuum at idle with a vacuum gauge...it should read steadily somewhere between 17-22 for a stock 5.0. If it's lower than 17 at idle or if it's jumping below 17 and then back up there's probably a leak.
As far as the basic larger vacuum lines...there are two that plug into the lower side of the upper intake manifold, and three that plug into the "elbow" area of the upper intake...I'd imagine a leak at one of these points would create pretty major symptoms.
If I were in your shoes, I'd check the vacuum at idle with a vacuum gauge...it should read steadily somewhere between 17-22 for a stock 5.0. If it's lower than 17 at idle or if it's jumping below 17 and then back up there's probably a leak.
As far as the basic larger vacuum lines...there are two that plug into the lower side of the upper intake manifold, and three that plug into the "elbow" area of the upper intake...I'd imagine a leak at one of these points would create pretty major symptoms.
Have you guys had a vac leak create knocking? I've only had them cause a hanging idle and then when it finally falls, it dips too low and might surge a little.
The vac specs Shawn quoted are right on.
Have you pulled codes yet? You just need a paperclip to do it. That's the place to start - it might save you some time bud (and no, the CEL doesnt have to be or have been on for codes to be stored).
Good luck.
The vac specs Shawn quoted are right on.
Have you pulled codes yet? You just need a paperclip to do it. That's the place to start - it might save you some time bud (and no, the CEL doesnt have to be or have been on for codes to be stored).
Good luck.
Swarzkopf
Member
Not a real "knock" in the detonation sense of the term...
But a definite "knock" type sound whenever my lower was cracked. That was a major vacuum leak. The engine felt out of balance, was backfiring, and wouldn't run without the throttle halfway open.
If you have a factory GT, you are OBD-I and the test connector is on the passenger side of the engine compartment between the firewall and strut tower. We use 3 digit codes.zZsKyZz said:
Here's one site (there are tons of them). You can check your repair manual as well (in the emissions chapter).
Good luck.
Methodical
15 Year Member
yellowstang1994
New Member
- Sep 9, 2004
- 338
- 0
- 0
Is your car running hot? I know this hot weather is killing my car. My low fan isn't turning on and since my car is running pretty hot it keeps turning my sparkplugs white and causing all this detonation. Just the other day I gave it a little more gas then usual in 3rd and it detonated to all hell and poured out a bunch of whitish/blackish smoke. Time to do a compression check and i'm trying like hell to get my car cooler with this little bit of money I have. But all in all, cooling is one of my biggest culprits for detonation.
Swarzkopf
Member
If it's before the 02 sensors, yes, definitely.
Like you said, the header/head point probably isn't leaking, but you do have an aftermarket H-pipe...check where the headers meet the H-pipe. I had a leak there when I first put my BBK on, and the car was idling poorly (though not half as bad as your describing).
I still think it's a vacuum leak or a combination of a vacuum leak and ****ed timing, but you should check everything you can to isolate the problem.
Similar threads
