Low comp (head shim) and idle problems... please read!

[Oak Hill]

Low vacuum and low compression = Valve Timing!

 

[TWIN TURBO]

I installed a head shim on an Apex brought compression down to 9.3:1 and cylinder pressure to 165lbs. Intake cam would have to be pretty far retarded to bring cylinder pressures down that low, advanced cam timing would raise compression which is what is happening when you add a head shim by 2-3 degrees. Exhaust cam has little to no effect on cylinder pressure.
I think Hammer is right, if I remember correctly vacumn isn't real high on these engines anytime. Cam timing should be checked to eliminate that possibility for sure. LOL

 

[Anonymous]

Will check cam timing.

 

[efiguy]

We experienced a similar problem - sled idled bad, we kept having to add fuel as boost came up, then we started seeing code 14's. Turned out we had a leak on one of the lines on a throttle body that also goes to the MAP sensor. Look at all your vacuum hoses and fittings carefully - our line had a small crack in it so we missed it the first time. When running high boost, it's a good idea to zip-tie or wire-tie these lines on so they don't blow off.

Code 14 means the sled isn't seeing enough vacuum at idle. If your vacuum really is that low (should be at least 4"Hg) and you're sure there's no leaks, check your cam timing!

 

[polarisconvert]

Poor idle

I would bet on cam timing.

 

[Need for Speed 2]

muloth dont get distracted by too many things at once . go to cam timing first verify what should be right first. you mention grinding on the intake cam sprocket. im puzzled as to why . you should only have to move the exhaust cam sprocket. warm engines change vac signal dont be alarmed yet cant create vac signal till valves will allow it to.

 

[Need for Speed 2]

disregard the cam timing was thinking another eng we just done. it was naturally asperated. sorry for the no brainer. is it possible your off a tooth

 

[Anonymous]

Yep, exhaust cam gear left untouched (the shim advanced exhaust cam a bit) and I ground the intake cam gear to retard it...

The way I did it, at the TDC mark, the dot on the exhaust cam was pointing a bit toward the rear of engine and the intake was a bit toward the front of engine....

maybe I did something real wrong in there.......

 

[vcrash]

I realize that your sled is an apex and not a rx1 but mine does that same thing if the throttle cable is not adjusted properly, sputters as soon as the boost comes on and sets the engine light on.
vcrash

 

[Need for Speed 2]

dots on cam gear usually end up ex at1 oclock intake at11oclock roughly my mind is not as bad as my wife thinks. can remember some things.

 

[Anonymous]

Needforspeed, I will reverify, but that was exactly how it looked like when I closed the cam cover.

 

[Anonymous]

What puzzles me the most is the fact I had 10-12in-hg of vac saturday morning, and got down to nothing during the dyno day....

Can it really be a head gasket leak uniformly on all 4 cylinders a same time?

 

[TWIN TURBO]

Maybe something hurt itself. Check the chain tensioner and chain guides. First pull the cam cover off and look at the tension on the chain so you know if there is a problem, once you remove the tensioner you won't know. One thing this all sounds like to me is like when you blow the throttle body's out of the boots, it does exactly what your describing, low vacumn hard starting and if your certain you had vacumn and something changed they could have slipped out maybe on the bottom where you can't see. Check it out before you pull cam cover.

 

[Anonymous]

Ther are still tight because they are bolted to the head!! I am sure...
I will begine checking it tonight!

 

[slymax]

Trade 'er in