Caged Monkey

I recently got a cable to start scanning my PCM so I can figure out this hesitation under 2K a lot of us are having and noticed something weird. My spark advance will drop quickly to zero and then after 2K rpm, it jumps back up to where it should be. I searched the forum to see if it had been talked about but I didnt see anything.

Heres some necessary info:
97 Camaro
OBD1 conversion
Using Freescan when the problem was seen

Already replaced front O2's, IAT sensor, coolant temp sensor.

Other things done to the car:
!EGR
!AIR
!Cats
LT's w/ true dual
!rear O2's

It doesnt seem right for the advance to drop that low and I am not pulling any knock retard. It only happens under 2K where the hesitation is. If I can figure out how to record with Datamaster, I will have some logs to look at also but I have some reading up to do with that one.

Thanks for any help given

Caged Monkey

Well, I got a Datamaster log done and every time I step on the gas from a dead stop, the timing drops down to 3 degrees and once it gets up around 2K it jumps right back up. It holds pretty steady at idle and at WOT. I am not getting any spark retard at all but thats about the extent of my knowlege of this stuff. Any help is greatly appreciated.

Buttercup

If you have a datamaster log you can send it to my email address

If there isn't any knock retard pulling the timing down than the ignition tables are set for that much timing It's one or the other and neither is preferred obviously. If you'd like you can send a PCM image from your car with a datamaster log for inspection. To read your PCM use http://carputing.tripod.com/pcmread.exe

I can't imagine someone tuning your PCM to give zero timing advance though

Caged Monkey

I had my PCM programed by Brian @ PCMforless.com. I dont really think it was programed that way - I think something is wrong with a sensor or something long those lines. I had the same PCM in the car and went 14.6 @ 96 mph and a month and a half later, this hesitation started. I dont know how the advance was before the hesitation started but its strange. I will send a image of the PCM and the datamaster log to you so you can look at it and see if you can tell whats up.

Buttercup

I'll keep an eye on my email

I highly doubt someone (especially Bryan) would program such a mistake into the PCM but it certainly can't hurt to take a look. I'll look for anything out of the ordinary in the log file as well.

Send as much related info as possible with the files.

Seal

I dont know anything about this, but i'm getting the same exact prob... i thought i wasnt gettnig the right a/f ratio and bogging or something...

Caged Monkey

Mail sent... thanks for the help

Buttercup

Wasn't sure to reply via email or on here

I see a few strange things happening. Number one, and this is common, I think your TB needs some adjusting. I see a lot of times it is resting at .33 Volts and sometimes at .31 Volts. If it doesn't return to the same position every time the throttle is closed the PCM won't know when to idle. This can cause the car to pull forward at a stop, reduce engine braking, and can also contribute to an unstable idle. You may have to adjust the throttle stop on the TB (you want the throttle stop to stop the blades, not hang them up in the bores), playing with the tension on the throttle cable, and also playing with the linkage on the TB itself (if I'm not mistaken the earlier Holley TB's had problems with the linkage seperating).

Number two, your IAT reading are all over the place. You said it's a new sensor so I would double check the wiring. I would also check ALL grounds. Bad grounds is a common problem on modded cars. I would actually remove many of the grounds, clean the connections thoroughly and resecure them. Make especially sure that the PCM is very well grounded.

Number three, and this could be related to number two. It appears you have a very dirty data line. There is lots of corrupted data coming through. Poor grounds are a typical cause, as are electricallly "dirty" ignitions. Once again I would go through the grounds thoroughly.

Number four, you are running at the limit of your PCM's fuel corrections... on the rich side. Usually I see lean problems caused by ignition faults, vacuum leaks, and/or exhaust leaks. Being so rich is likely just high fuel pressure or fuel injectors that are larger than the programming is aware of. If you can fix the "real" problems I would also fix this as well. Your BLM's in many cases hover very close or at 108 so when you go WOT I would expect you to be running very rich, this can cost power.

This is the stuff that "pops" out at me at first glance.

btw, the igntion advance is doing exactly what it should be doing. In the log you sent me it wasn't sitting at zero but does drop way down at lower RPM and high MAP. I'll email you some more info

Caged Monkey

E-mailed you back...

I will check these things out and pull another log. See if any of it was fixed.

Thanks!

rlf07

this is the same problem, I have 97 firebird m6, how to solve it, please help, I'll go crazy ...

Injuneer

You have posted in two threads indicating you have the “same problem”. One thread is about excessive knock retard below 2,000 RPM:

https://www.camaroz28.com/forums/lt1...-463905/page2/

And this one is about timing dropping to “0” without knock retry

Let's get your earlier problem out of the way - you indicated the PCM would not go into closed loop:

https://www.camaroz28.com/forums/lt1...d-loop-888290/

Did you fix this problem? The data you posted was very confusing, and the follow up didn’t really clear things up.

Neither of the people who posted the original threads you posted on have signed into this site since more than 12 years ago.

Best thing you can do is start a new thread describing your specific problem in detail. Be sure to include a list of all the modifications that may have been done to the engine and PCM.

Fred / Moderator

rlf07

Hi injuneer, I have been following the forum for a long time, I fixed many malfunctions of my car with the information shared by you and shbox.
very very thanks

I can open a new title, but I may not be English enough to describe the problem . The issue related to the software in my old title, the car is locked in an open loop by the old owner willingly. now stock software litle tuning

Injuneer

Do you have the ability/equipment to scan the PCM for sensor and PCM parameter values? A data log might help.

If the PCM has been reprogrammed to run open loop only, who knows what else they did to it. Makes it almost impossible to diagnose a problem.

rlf07

although it was very difficult , in my country, I found someone with dst tuning. he installed standard software, canceled egr-like things. as for the scan program. there is only obd2 bluetooth scanner. it's a simple thing. no gm tech 2: ( but it can show a lot of things, like torquepro. but no knock delay and iat steps. there's no fault code in the car . when idle wot, the advance goes down to zero or even minus sometimes. Up to 2500rpm wot can also break up to 0. 2500rpm after that, it's normal as it should be.

rlf07

video The reason for the advance drop could be things happening in the knock retard episode?