Ok so here's the deal. The shop just finished putting my motor in my 94 Z28. Here is a list of the mods that were done at the time:

Eagle crank
Scat 4340 Rods
Speed Pro pistons
CC305 cam
Comp valve springs
Comp hardened pushrods/ Guide plate
Crane Gold Non- SA roller rockers
Lunati Timming set
Mac Headers
New plugs and wires.

Heres the problem. The car starts and idles fine. Whenever you drive it Runs pretty good untill it gets warmed up. After it gets warmed up it runs like absolute crap down low. Under 2500 RPM's it has no power and pops back through the intake. It doesn't do any of this when it's cold.


Now i have checked several things first being the vaccum. It has around 7-8in when cold and stays around 8-9 when warmed up at a idle of 750 RPM's. Does this sound normal? I have been told stock should be around 20in/hg

Second fuel pressure shows normal at 42 psi idling.

No SES light

Am getting some knock up to around 8 probably because of the headers/ rockers.

Noticed timming was jumping around a bit. from 18 up to 22 idling

I am on stock tunning and stock inectors. I have already ordered PCMFORLESS tunning.

I think it is one of 3 things, Vaccum leak, tunning, or a dying opti.

What do you guys think?

thanks
Shawn

 

Sounds like the problem occurs when the car enters closed-loop operation. Since you're not getting a SES light (like bad O2, etc), I'd say that programming is the issue. But, I'm not an expert so take this at face value.

 

Idle timing is way low first of all. I gaurantee you it will idle better at 30-32 degrees and will consume less fuel and the idle vacuum will increase.

I see about 15.5 or so out of mine idling at 850 in neutral. So I would say you need to up the idle speed a little more too.

 

Should be at least 18" with that small of a cam. I would double check your rocker adjustment... an intake rocker too tight might cause the symptons you have. Could be the opti but, I would try to eliminate easy stuff first.

 

Yeah it definately starts running crappy when the car goes into closed loop mode. Just gotta figure out whats causing it.

Thanks
Shawn

 

Oh and how do i adjust the ilde timming up some? sorry just can't remember right now.

Thanks
Shawn

 

Hey man, I am in the same boat?

I am getting up about 9 psi with a XE 230/236 cam, 112LSA. It sucks, becasue of it it idles rough.

I have a new opti, dont seem to have any external intake leaks, 43 psi of fuel pressure, idles around 800-850 rpm (no load). I did the heated 0'2 Conversion, and verified my 0'2 and they work fine. I also re-adjusted my valve lash, and it did not help.

Sometimes after a WOT the car just plain dies.

This next week-end, I am going to take my intake of, and inspect, it quite possible be an internal vaccumm leak.

Good Luck.

 

I was in the same boat as you guys a ways back with my cam.

I had it installed a tooth retarded Hate to say it, and you wont listen to me at first, but your symptoms are identicle to mine. Have to pull the timing cover and see whats up. I fixed mine in about 4 hours.

 

Atljar,

You mean you installed the timing chain one tooth off?

That could be our reason for this problem, but I never thought it possible, because other wise the car feels good (although it definetly down about 75 - 100 HP).

I will check that.

 

Get the new tune in there and things should improve.

 

Yes, the dots on the cam/crank gear were not lined up. Its easier to mess up than you think.

My car pulled 4.5 inches before the fix, now pulls ~12, much bigger cam than the 305 however.

When cam was installed wrong, i was running low 14s, where i had been running 13.1s before the swap. Down BIG time on power. Car idled ok, but not steller, off idle you had to give a TON of gas to get going, wouldnt turn over tires with 4.33 gears.

Intake would backfire off and on. I also was getting tons of knock, where when i fixed the cam, i didnt get any.

 

did it do it all the time or just when it was warmed up like me? Mine only does it when warm. Leads me to believe it is somehting electrical like tunning since it starts doing it when it goes into closed loop mode.

I have my PCMFORLESS program now i am just waiting for the cable.

Thanks
Shawn

 

I say get the programming and make sure your valve lash is adjusted correctly first. Those are easy to do. My car had the lash too tight and it was a dog when I ran. Took a lot of gas to get going and just didnt have the power. It also made me think it killed the coils but in actuality, it was only when it got warm. Then mine wouldnt even start!!!!!

I adjusted the rockers and everything ran great. I even have an opti I bought b/c I thought that was the problem.

 

If you are only getting 8 to 9" vacuum with the CC305 cam then something is definitely wrong. I ran this cam for several years and always saw 14-16" vacuum. This was with a 850rpm idle. My buddy with the CC306 cam which is way more agressive even got 10-12". Check for vacuum leaks, and make sure you installed your cam correctly (timing gears aligned, opti installed right). Good luck!

 

Could me stock tunning cause me to have low vaccum or is it a strictly mechanical thing?

thanks,
Shawn