View Full Version : vacume issue

T-bird Tim
12-07-2005, 02:45 AM
I have a 92 sc, heavily modified with stock computer. I am getting only 8-10 inches of vacume at idle and 10 -12 under acceleration. Cant accelerate hard or it will bog and miss. I also notice a miss at idle. The engine was rebuilt 6000 miles ago and has larger mafs and t-body as well as custom grind cam. I resealed all the IC connections and took it to auto zone for a scan. They told me the 0-2 sensors were bad as well as the air charge temp sensor. I replaced all of these and it still has the same problems. When starting the car when its cold, it will run for a few seconds then idle down so low that it dies. It takes me two to three tries to keep it running. And then I have to let it warm up before I can drive it. I am still getting a check engine light. I tried checking the vacume lines behind the intake but am unsure if they are actually hooked up where they are supposed to be. If anyone has a vacume line diagram they could send me it would be greatly appreciated as would any other ideas on the problems. DIS maybe?:confused:

12-07-2005, 03:04 AM
Sounds like you just need a tune.

12-07-2005, 04:50 PM
You most likely have a vacuum leak, 10-12 inches of vacuum is way too low at idle. It's possible that your reground cam has charicteristics that make low vacuum but my bet is a leak. John
edit: 8-10 vacuum at idle = vacuum leak, you should not really have vacuum under acceleration, only boost or zero vacuum.

T-bird Tim
12-07-2005, 09:27 PM
Thanks for all the input. I had it checked out by the Ford dealership today. There was a vacume leak at the air bypass valve at the supercharger and another somewhere at the rear of the intake. I have repaired the one at the throttle body but am unsure where to start for the one behind the engine as I have no clue as to where all of the lines are supposed to go. Does anyone have a vacume line diagram? That would be of tremendous help. Thanks everyone!

12-08-2005, 02:26 PM
As was mentioned........

DUDE GET A TUNE!!!!!!!!!!!!!

Even if you fix all your vacuum leaks, you are still going to have problems as you haven't told the computer how to deal with the new cam, t/b etc you have put in.... and you could even end up killing your motor right quick because your air fuel ratio could be dangerously lean or rich......


T-bird Tim
12-12-2005, 12:27 AM
Changed the plugs yesterday and the miss went away. Tore down the whole top side of the motor and resealed everything, still have low vacume but am assuming its due to the cam and other upgrades. Getting a chip burned for it next month, hopefully I'll see the desired results.