Say a splined opti is installed incorrectly... say off by a tooth, (which seem to be quite common, with the thought that it can only be installed one way), how much would that lower vacuum? I know it equals running like crap, but 7-9" hg of vacuum lower than where it should be at idle.... is that possible with just the opti being installed improperly? OR is my problem more likely be the valve timing being off being that the vacuum is that much lower than where it should be?

 

ttt

 

hmm... sounds like no one's hooked up a vacuum gauge here after installing their opti wrong.

How about this.. anyone notice their car running excessively rich (due to low vacuum/high MAP telling the pcm that the car is under load) after installing a opti incorrectly?

 

7-9 inches vaccum at idle will surely make the car run like crap. It will be excessively rich (will foul plugs immediately). This low amount of vaccumm (high map) will trick the ECM that the engine is under load, when it is not, and dump excessive amounts of fuel into they cylinders.

On a 93 ECM, this is much more apparent then later models, because it does not have a MAF sensor.

Things to check for:

-Dead cylinders will cause lower vaccumm, check for low to zero compression.
-Incorrectly installed OPti will cause it too, (timing will be late, which will result in incomplete combustion).
-Incorrectly installed timing chain. If its off a tooth, valve opening/closing relative to piston position will be off, which will cause low compression and hence lower vaccum.
-Vaccum leaks, but for such low vaccumm, it would be really apparent.
-Weak spark will cause it too, but is not usually the case.
- If you have a very big cam, the only is to compensate with tuning (proffesional help).

 

Yup, that sounds about like how my car runs including the plugs completely fouling out.

I actually just had the engine rebuilt and put back together with a LE 1 head/cam package by this guy thats the top mechanic at a mistubishi dealership out here, so I would think that he would have atleast got the timing and valve lash correct (compression checked out well higher on all cylinders than were it should be, but all within 7% from highest to lowest cylinder). The leak at the intake would still be a possibillity. The main reason why I was suspecting the opti being installed incorrectly is because he said that this was his first time working on a LT1, and somehow I get the feeling that he most likely just put the opti in with the assumption that it can only go back in one way, which is theoretically true but not the case with most people that assume this apparently. I actually did a mail order tune on the car, so I am guessing that MAP is set to compersate for around 14-16" hg of vacuum at idle, which is what I should atleast have with the cam I got. The only thing is I just didn't know if a improper opti install would've caused that much loss of vacuum.. That's a whole 7+"hg of vacuum less than where it should be...