Mikey97Z

I just finished my heads/cam install, and I'm having this problem. It seems like a vacuum leak. Datamaster says that during decel (cell 17) and at idle my Right side BLM goes to 160, but Left is OK (at ~128).

I checked for leaks, but didn't find anything. The BLMs only split bad during decel, they're ok the rest of the time. Any ideas where I should look? I'm using a stock throttle body.

Thanks.

CC XE 230/236 cam and Nu-Tek ported heads.

Mtrhds94Z

Just a thought hre but manifold vacuum is also at its maximum during decel, so if it's a small one it may only leak then, during the highest vacuum time?Going to be hard to find that..

Injuneer

Cells 17 and 18 appear to be "calculated" based on data from the other cells. The Cell 17 algorithm would most likely rely more heavilly on the Cell 16 (idle) values than anything else. And, you have the problem at idle, from what you posted, so its not just a "decel" problem.

Have you checked the passenger side header for leaks? Have you tried switching the left and right O2 sensors to see if the problem follows the sensors = sensor problem? Do you have an aftermarket TB - sometimes cause split BLM's at idle? Possibly a misfire on the passenger side? Possibly a misadjusted valve?

All of these things might explain a problem that only shows up at idle.

Mikey97Z

Thanks, Fred! I didn't know cell 17 was calculaterd from 16.

I'll recheck the valve lash. Never thought of that. Also check for misfires. I am obd1 so I guess the water drops on the headers is the best way, huh? I'll give it a shot.

ryaskovic

Mikey97Z, did you ever find your problem? I'm having similar symptoms and can't find anything wrong. However, I also have some stumble that's started showing up so I'm suspecting maybe an ignition problem. I'm having the ignition system scoped at a local shop tomorrow.

Rob
95Z28

Mikey97Z

Well ..... I sorta fixed it.

I had slightly split blms at idle (right side was high). Since then I switched throttle bodies and now my left side is real high. I don't think I have a vacuum leak. I'm going to experiment more with my throttle body to try and even out the blms. They're only split at idle. It may be my ported intake manifold.

ryaskovic

Mine are split at idle as well, with the right side being high. Stock TB. I can't find anything wrong and I've checked: vacuum leaks, exhaust leaks, O2s, compression, leak down, coil, IAC, TPS, ignition module. The only other thing I can think of is the opti since the engine seems to stumble in the idle-2k rpm area. I'm acutally hoping the scope shows an ignition problem, even if it is the opti, so I can be rid of this problem!!

What TB did you end up with? Does it have the correct IAC passage?

Rob
95Z28

Mikey97Z

I put on a AS&M 58mm TB. I had to drill an idle air hole (rather than **** (lol ... ****) the blades open). I also closed up the notches on the backside of the TB so the IAC passage seals against the intake hole ... like the stocker. So my high blms went from the right side to the left.

ryaskovic

Maybe you installed it upside down?

How bad is the split and what are the IAC counts and TPS voltage at idle?

Mikey97Z

155 on left
128 on right

IAC is 50-60
tps is 0

ryaskovic

Any progress Mikey? I haven't had time to fiddle with too many things lately but I haven't been able to find any problems with what I have done. My latest thought is: maybe the intake manifold isn't sealing well to the heads (my heads and block have both been milled). I don't have an external leak that I can find, but maybe it's pulling air from the lifter valley. I'm trying to find a local shop with a smoke machine to check for this or any other leaks I might have. Only other way I know is to pull the manifold and analyze the gaskets.

Rob
95Z28

Mikey97Z

Actually I still have the split blms at idle, which I'm pretty sure is caused by my throttle body. But today I was bangin through the gears on the street and I screwed somethin up. Now my car wants to idle real high ... like 1600 instead of 900rpm. Arrrrrrgh. Might be my throttle body, or my IAC valve.

At this rate I'll never get it to the track!

I was hopin to get there soon, cuz racing in the summer in Florida bites!

ryaskovic

I'm in Florida too so I sure know what you mean! Maybe it's the Florida air that's causing our problems!

Rob
95Z28

Mikey97Z

Talk about PROBLEMS! Hare's what happened to me today!
http://web.camaross.com/forums/showt...5&pagenumber=2

I'm wondering if I have a vacuum leak in the lifter valley. There sure is a lot of oil covering the inside of my intake manifold! It's only 2 months old and it already looks like my old stocker!