Hi guys,

I put a rebuild motor in my car last august. The car now has approx 4000miles on the motor.

Last week, my vacuum at idle was sometimes at 12inch and sometimes up to 16-17inch. I have a stock port engine.

My mechanic and I decided to do a steam clean on the engine. After this, the vacuum jump to 18 inch and stayed at 18 inch rock solid. We took the compression and front rotor is 110psi and rear rotor is 114psi... and it looks to be really healthy.

I run 10 psi with stock twins and a few bolt ons.

But, after getting it back to my house, I shut it off. 1 Hour later, I started it again and it went down to 14inch even when it was on operation temperature...

Ok, now it doesn't go down like before at 12inch but it's fairly unstable...

Could it be a broken side seal? My compression on each face is really nice...

I also think something is wrong because it's spitting oil when I boost the car. (just under the elbow near the oil filler neck)

any ideas??

Thanks,
Max

 

Hot starts will pull less vacuum. How do you have your crankcase ventilation hooked up?

 

I should verify this.

What is weird is it can be at 18inch and runs very smooth with a 13,1 AFR at idle and then the next stop it drops to 14-15inch with a 14,8 AFR.

Max

 

Changes in afr and rpm will change your vacuum. As mentioned hot starts will also pull less vacuum until you go for a cruise to cool everything down. Sounds like a tuning issue to me with your last post.

thewird

 

A 14.8 AFR at idle on a rotary probably will cause a lean miss. If the idle speed does not increase under these conditions, it is probably not due to a vacuum leak. This situation will cause low vacuum. Therefore, I suspect an intermittent fuel supply problem: low fuel pressure, sticky injector, etc.

 

ok.

and also, when removing the spark plugs, they looked like it was running lean (a little bit of white)..

Could it be a defective injector so it doesnt get enough gas?

My innovate wideband shows low 11's on WOT.

 

Unless your running stock ECU on a stock engine, the 14 AFR at idle would indicate the problem is very likely a tuning issue. There is no reason to try to figure something out by looking at your plugs with a wideband in the car.

thewird

 

If it is a tuning issue, why is it intermittent?

Dave

 

What type of boost/vacuum gauge are you using? I don't like to rely on the boost/vacuum gauge for vacuum reading. There are a lot of variable that will make the vacuum to read different including climate, sea level and the actually quality of the gauge.

 

I have a autometer boost gauge + my apexi avc-r and my power fc. What is weird, my avc-r reads a different vacuum reading than the power fc.

Normally on idle I see -425 sometimes and -515 when it's running good on my AVC-R.

Max

 

It may only be a certain part of the map that doesn't have enough fuel and it only goes there when load changes for whatever reason, brake lights, fans come on, car heat soaks, A/C cycles, RPM drops etc.

Since he seems to be doing fine under WOT fuel wise, I wouldn't look at the pump or injectors just yet.

Gauges almost will never read the same with each other, especially in vacuum conditions. Go off the powerfc as that one is the most accurate one (and the one that matters for fuel/tune).

thewird