My car has had a super weak vacuum and stalls once it warms up and the only thing I can think of is its a bent valve. I did a compression test and the results were 185-195 across the board. I couldnt do a leak down because I dont have the right fitting for my compressor. What are other indications of a bent valve that I could look into before I pull the head off.

 

it wouldn't hold compression if the valve was bent. Sometimes they make a ticking sound also.

 

What else could explain the low vacuum then?

 

Plugged up exhaust....

 

what makes you think you have a weak vacume? stalling out after operating temp is up could be numerous things.

To answer you question, 60psi indicated a bent valve.

oh ya, dont bother telling us what your set-up is. We really dont need that to help you trouble shoot.

 

Setup is a stock b18b in an 93 si hatch run by a stock ls bin on an uber p28.

What makes me think I have a weak vacuum is the fact that my boost guage reads -10psi at idle and not 20.

 

Have you tried disconnecting the exhaust from the cat back? If the cat got hot enough to melt, it'll plug things up. If you happen to have a pressure gauge, you could remove the primary O2 sensor and read exhaust pressure at idle and then at 2-3k.

Tight valves cause a low vacuum reading as do cams with some decent overlap (but you say you're stock).

Plugged up intake or clogged air filter.

Anything that prevents air from entering/exiting the engine will cause low vacuum readings.

 

Well im sure its not the exhuast because up untill yesterday the exhaust wasnt even hooked up while I was trying to troubleshoot it. I did a compression test and found it to be 180-190 across the board so would this be enough to rule out valves compleatly? The car idles ok (low no matter how much I up the idle in uber) but as soon as it warms up it will stall.

Is it possible to mess up cam timing enough to cause this? I never pulled the motor apart I just stuck it in so I wonder if there are any issues with this?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 5.0 Killa &raquo;</TD></TR><TR><TD CLASS="quote">
Is it possible to mess up cam timing enough to cause this? I never pulled the motor apart I just stuck it in so I wonder if there are any issues with this?</TD></TR></TABLE>

yes bad cam timing will effect your vac readings

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 5.0 Killa &raquo;</TD></TR><TR><TD CLASS="quote">The car idles ok (low no matter how much I up the idle in uber) but as soon as it warms up it will stall. </TD></TR></TABLE>Just a guess,but if the valve lash is too tight it will effect the valve's seal when it warms up,things grow when hot and the lash is smaller when hot then cold.Who set the lash and do you know what it is?

 

The guy who had the motor before me (and he couldnt get it to idle properly either) may have dicked around with the lash so im not sure what its set at. What should it be stock?