LS1LT1 Forum banner

Running lean? rich? Hell I dont know..

6198 Views 8 Replies 4 Participants Last post by  caseycallender
95 Trans am, LT1, Freshly rebuilt with Lunati cam PN# 20089908,
Dur at 050 - 219/219
1.5 rocker ratio
adv dur 270/278
Lyoid Elliot LE2 heads, ported, polished,
Block bored to 355 size,
New pistons etc..

The guy that knew what he was doing with my car left for work, oilfield work which is code for he wont be back for a couple weeks or more.. so im left to finish up my car.. He mentioned it would probably be running lean when it started, which could cause problems.. Was having problems with it overheating today when it fired up, thinking it might be because of it running lean (Headers were red red pretty quick after startup) I dont know if this is rich, lean, or what any of these numbers mean.. Can someone with Datamaster help me out here?

Heres the link to the datamaster data, the DTC is a transmission code I know I know, the motor is hot as a firecracker.. Dont know why, just know I dont want to run a new motor like that..

1 - 9 of 9 Posts
Rich running doesn't cause headers to turn red, unless it's so rich unburned gas is going out the exhaust valve and burning at the header. But if it's running that rich, your probably getting bore washing and the damage that goes with it.

So I would lean towards very lean running. I lean this way because with the heads & cam setup, I believe your stock injectors and pcm tune are not up to the task. Add sluggish o2 sensors to the mix, some vacuum leaks and you have a very lean running condition.

Also beware that running lean enough to cause your headers to turn cherry red at idle, can melt your pistons in short order.

As stated in the other post you have, pm me with your e-mail address and I'll send you the pdf file of "sensor readings and what they mean.

Also since you are using DataMaster, you can upload the scan file to a file sharing site, then link it to a post, where members can review your data log and help you determine the problem.

Your mechanic is right about the mods causing pcm to need a tune. You could get tunercat and learn to tune yourself, but since you don't know what sensor reading mean yet, I suggest sending pcm to a tuner and have him do the job. You will have to fill a form out with your engine mods, he might want to look at a couple of your DataMaster log files also.

Tuners at LT1 PCM Tuning - Welcome!
PCMforless - Home
See less See more
Right off RPM is at 1500 and the desired tune RPM is 600. TPS=0% voltage is .67 which is good, but the IAC is at 0 so the PCM is trying to slow it down but it's still running 900 RPM to fast. Both fans are running and temp is still 241* F . BLM's are not perfect, but not drastically out of whack. Are injectors stock ?? . Is TB stock ?? Up front looks like TB blades are opened to much as AFGS is above 14 so it's getting to much air and running away. Or could be a vacuum leak letting in the air. Also desired idle at 600 seems low for your setup, tune should fix that. FYI DTC 83 83_A.jpg
Throttle body and injectors are still stock.. Would the adjuster screw on the TB to shut the blades help get the AFGS back down where they need to be. I will double check all vacuum system for leaks make sure there no air getting in there, alot of the vacuum system is new too.. With the DTC 83, I read that post and it seems like that is an automatic transmission fault, correct me if im wrong.. Car is an M6, so maybe I have a setting in the new PCM that needs to be changed for this car..
I also have TCC turned off, in the new PCM as well as the TCC/ASR relay in the fusebox under the hood is MIA, has been since I bought the car so I never put one back in it.. Wonder if that could have something to do with the 83 DTC. This is a whole new PCM, I guess I should look at the settings in the switch table and figure out which ones I need and flash them in there..
think that problem is done with now,
In the constant switch table for some reason auto transmission was selected which makes since.
that isn't exactly a gigantic cam you're running there. mine isn't much smaller and it ran fine on the stock tune..

stock injectors should be alright on your build, at least below 6k rpm or something.

i dont like hearing that it's that hot even on the stock tune and bottoming out the IAC trying to hold an idle; something screwy is going on, vac leak or something mechanical.

that car should be driveable on the stock tune with such a mild heads/cam, just a bit rough and lacking power. it should never make your headers glow or be unable to drop to a reasonable idle.

dont try to tune around it until you figure it out...
I'm not an engine I'm really asking this question to some of the experts.. will running an engine at 1500 RPM get it that hot ??

Casey, reason I mentioned tune was that desired RPM in your log is 600, stock A4 is 550 D / 650 P and stock M6 is 800. So the 600 looks like the tune was altered.. If you have a stock TB and injectors then you have something wrong. The LT1 needs most of it's idle air coming from the front port in the intake that is feed by the IAC valve. That port feeds the intake plenum runners that allow the idle air to reach all cylinders evenly. With IAC = 0 that says all air is entering from the TB blades (or a vacuum leak). The TB closed voltage spec is .45 to .75 and you are at .67 which should be good. You can crank the TB stop screw in and close the blades a bit, that will lower the .67 volts and the IAC counts should go up. I like to see IAC counts at idle at 30-40, that gives the PCM room to control idle speed. I still think you have a vacuum leak as your idle is way to far out. Closing the TB may help a little, but not 900 RPM.. just keep an eye on the TB voltage, keep it above .45 . Here is place to download a stock '95 F-Body M6 tune, The Official LTx Tune Database
See less See more
I wonder the same thing, should the engine get that hot at such low RPM's??

That would make since, I ordered the new PCM from Checker auto parts so im pointing the finger... Something weird though, every throttle body I have seen has ports for 2 hoses off the passenger side, one is for coolant, one is for the EGR that plugs into the valve cover.. The one on my car has three ports, I was told the other one might be for vacuum, So I rigged it into the vacuum system, didn't seem right, still doesn't.. Anyone know where the middle port goes to or what it is for?
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.