Lower Vac At Idle

FORSFED · 12-14-2003

I was doing some more thinking, and noticed my car (the one with the high rpm misfire) has a lower vac reading than what the norm is but it idles perfectly at 750 and the timing is right on. It reads 13-14psi where normally they ride around 18-20psi. This isn't a huge difference, but could it be an indication of a leak or bent valve? I've tried listening for leaks but haven't heard anymore after the couple small ones I fixed. Any other thoughts or easy checks?

MATCHBX · 12-14-2003

Just for clarification, you are talking about inches of mercury (In Hg) instead of PSI. Mine reads about 15-16 In. Hg. at idle. It reads about 20-21 In. Hg. when I'm decelarating and the engine is slowing me down (foot completely off of the gas pedal and also off of the clutch pedal). The only time mine hiccups at high rpms is when my boost creeps up past 18 psi and I hit a little bit of fuel cut. Otherwise, when I'm running around 15psi there is no problems.

What psi are you at when it misfires at high rpms?

A//// Guy · 12-14-2003

When my timing used to be off by one tooth my idle was around 12-15. Now with good timing it idles at 18-19 and decels at 22-23. I never had a problem with drivability.

FORSFED · 12-14-2003

I know I meant inHg, but anyway. If there is any amount of boost the car will misfire. Whether there's 4psi or 14psi by the time it is creeping, the car seems to misfire at around 4800 and above.

Just as a side note, with the cooler weather, it doesn't seem to misfire nearly as bad as it did when I got the car in September....leaner conditions in the cold = ?

john · 12-15-2003

Have you done a boost leak test yet? Those numbers are a little low but not too bad. Somedays my car would read those numbers and the next day be fine. Maybo because of the weather. Have you done a compression test yet on the car? Have you pulled the timing belt cover to check if it is off a tooth?

ipt · 12-15-2003

If your car is misfiring at higher rpms try closing up the gap on your spark plugs some. With the higher boost the car might be adding too much fuel and then the plug can not ignite the mixture and you get a misfire.

A//// Guy · 12-15-2003

All this has been covered.... over and over and over and over. Everything has been tryed. It still misfires. You keep forgettting to state this when you keep bringing this up. :stick:

FORSFED · 12-15-2003

I apologize for not repeating it every time, however that would get quite annoying as it is a mile long list. I am getting the impression that this really isn't worth mentioning anymore so I'll quit bringing it up.

BTW, boost leak test ok, timing ok, compression test soon to be done.

Jakey · 12-15-2003

For those interested here are the other threads in which this car's problem has been discussed. Hopefully this will avoid any confusion....

Looky #1
Looky #2
Looky #3
Looky #4
Looky #5

john · 12-16-2003

damn, if that were my car I would have given up and surrendered it to a mechanic. That car has never run right for you.

FORSFED · 12-16-2003

I refuse to lose!! Besides, I think that there is a new lead thanks to Josh and Mike :bounce: But that can be discussed at a later time.