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Discussion Starter · #1 · (Edited)
I have a 1994 trans am, lt1 motor that was just rebuild. New cam, and headers. Had the computer reprogrammed for all the work that was done. this thing will not idle right, keeps going up and down. All the sensors, and i mean all!, are new, the opti spark is also new. I've attached the data log from a Solus Ultra scanner of it idling. I sure hope someone can look at that log and see what's wrong with it. We are all thinking the shop that built the motor didn't line up the cam and crank right, but before we rip back into the motor I hope someone here can give some advice. thanks for reading, and feel free to ask more questions!
 

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You might want to download the trial version of DataMaster. It logs sensor data to a file that other members can watch in real time on their DataMaster. Trial good for 20 free data logs and unlimited data playback. Get at TunerCat

Then you will need a cable to hook car's dlc to usb port of laptop or notebook. Get it at ALDL OBD1 OBD cable OBDI OBD2 engine codes

When you do a data run, since our forum doesn't recognize the file type to upload, you will have to upload it to a file sharing site and link it back to here.

We also have a free obd1 scan program especially made for 94-95 f-bodies. Created by our member GaryDoug, it scans reads regular codes, and like no other program available, it also reads ABS & SIR codes. Find it in sticky threads of 4th gen section.
 

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Discussion Starter · #3 ·
ok, thanks for the response. But i have $4,000 snap-on scanner, not sure i want to spend another $60 on a usb reader! But i guess if no one can read my log file, i'm on my own!

thanks again.
 

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No one has commented on your data log because there is no data log to view. The reason I recommended DataMaster, the free trial version, is it does something even your $4000 snap on scanner doesn't. It logs and plays back sensor scans in real time, so you or members here, if you post it up via file sharing site, can view you car's data live as it happened. That way we can see how the sensors are interacting with each other, plus monitor fuel trims, short and long term, all on one screen.
 

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there's a bit we can do without a datalog..

here's a start:

-provide specs on the cam you are using
-use your snap-on scanner to check the IAC position while hot idling to see if you're within an acceptable range
-define 'up and down', a bit surge is normal with certain types of cams
-check for vacuum leaks @ the intake using propane or something, it's not hard to mess up the intake gasket or mis-torque it

it's damn hard to put a smallblock chev cam out of time, you'd have to be really retarded not to rotate the crank several times and ensure it's still on the mark. if the shop is that retarded that they'd mis-time a cam, you should redo the entire job
 

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Discussion Starter · #6 ·
I didn't realize my log didn't get attached, but i guess it doesn't matter, cause no one can read it! :D

here's a link to screen shots I took of the logged data:
https://www.dropbox.com/s/1nwtq8vlr1czgqu/scan_log.bmp

I don't know the exact specs of the cam right now, i'm at work. I will get them tonight or tomorrow morning.

we've checked for leaks, none have been found, and looking at the scan log I think it's holding vacum just fine?

and i think the IAC is ok, we did adjust the throttle stop a little after this log, and go the number closer to 30, but it still moves up and down, just like all the other sensors!

you'll see we did step on the gas twice during this log, just to see if the TPS was working.

thanks again for the help.
 

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ah gotcha.

this log is bullshit though, i dont think your scanner is configured for the right ECM type.

that MAP chart is throwing me for a loop, for one.

it says inHG, but it's fluctuating between between 70 and 150.

no engine would ever pull 150 inches of mercury... i'll assume it's actually kpa?

well assuming it's kpa, it's still way the hell out to lunch. 150 kpa? unless you're running this thing like 3km below sea level...

and it has a target idle of 3188?

if those map readings are even remotely correct (verify with a vacuum gauge) something is going on there, that sketchy of a MAP might be tight valves or something, i guess?.. that's where i'd start, maybe someone set your lifters up too tight so they're stuck open...
 

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Discussion Starter · #8 ·
I thought the same thing, there should be a decimal there, it's between 7.2 and 10.2 . That's what it shows while running.
 

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-use your snap-on scanner to check the IAC position while hot idling to see if you're within an acceptable range
OP

don't overlook this. your IAC counts want to be 30-35 at idle with engine at operating temp. Don't f around with the TB stop screw to "trick" it into seeing the right count....that leads to other problems...tranny. Some people slot the TPS screw holes to bring the TPS voltage back to .67 vdc at blades fully closed...again another trick I don't endorse but people do it

do you have a stock Throttle Body?

if you do put the stock one back on and see if you still have high IAC counts

aftermarket TB's can ne made to work with a "drill" mod but first confirm if TB and IAC counts are your issue. If they are OK you could need some tuning adjustments....assumeing there is not a "mechanical" issue on the installed parts.
 

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I went throught the almost exact same issue,took me a week to resolve it, and after everything i tried it turn out to be the damn charcoal canister purge valve being stuck open and not creating vacuum as it should so the idle would stay at 1000rpm( were it is set from tune) for a few seconds then drop to around 600rpm and dance around there after the purge valve was changed it stayed at 1000rpm and has for over a week now
fyi it was the purge valve located behind the drivers rear tire right before the canister youll see it as soon as you take the tire off and remove the access panel
hope this is some help:homer:
 

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Discussion Starter · #12 ·
Original throttle body. Just warmed it up and checked...
IAC 33-61
Every time the rpms start to drop, it revs back up and the iac count goes up. While in the "normal" idle iac stays between 35 and 45. Normal idle is still rough, it was between 495 & 1348 for this test. Stays between 800 & 1000, but then drops real low and immediately revs up. And will eventually die if left running.
 

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Discussion Starter · #13 ·
thanks for the canister tip. I have not checked it, but I did plug the line that goes back there, should that have stopped the problem? Cause it didn't! ;-)
 

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j1

it sounds like the TB is not the source since it does it with the stock one also and IAC counts for that are within range.

if you can get data log and discuss with your tuner hopefully that will point to a direction that resolves this.

any codes being thrown would also point to issues
 

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happened to me, and it was due to tight clearance on the main bearings.... im just throwing this out...
 
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