Cam72aro

iTrader: (28)

What fuel system is in the car? How are the lines routed?

tording99Z28

iTrader: (3)

Yes it is a 3 bar SD OS. I don't know for sure how the MAF is failed to be honest. My tuner is Ed Hutchings who is a very popular well known tuner in my area so I am sure he did it the same way he tunes all cars. I can post the tune if you would like. The O2's are about 2 years old but it was an O2 causing the problem I fail to see how putting the external box fan on the passenger side firewall area of the car would correct it. It is the same little black MAP sensor that everyone uses, I don't know how else to identify it. Again on the vacuum leak I don't know how the external fan would correct that problem plus I don't see any drop in vacuum on my gauge or in the scanner. I appreciate the ideas and throwing things out there, keep em coming or if you can think of a reason that one of these things could be it throw it out there.

tording99Z28

iTrader: (3)

-8 feel line - 6 return. Magnafuel pro tuner 750 pump. Magnafuel 8850-B regulator with boot reference. Aeromotive rails. Lines are routed up the passenger side frame rail and then to keep them away from the exhaust I crossed them over at the tranny crossmember to the drive side and then up the frame rail and up under the brake booster to keep them away from heat. They were routed differently before and I thought the fuel was being heated so I installed all new lines and re-routed them and there was no change from any of this. I also changed to the aeromotive rails because I had the cheapy speed inc rails before and thought they were heat soaking the fuel maybe, no change with new rails either.





Here is 3 videos I made yesterday of the problem, watch them in sequence and you will see exactly what I am doing and what is going on.

Video #1

Video #2

Video #3

Cam72aro

iTrader: (28)

I watched the videos and see what you are doing and have to agree that something heat wise is causing the problem. Was the car sitting there idling for 20 minutes or so with the hood open and it did this, or is the hood closed and you drive it around and it does it? Trying to understand the pattern. My car gets super hot under the hood but never have this problem. Its possible that something else is getting cooled indirectly. I know you point it directly at the ecm, but it could be the connector or something in line, or that scotch lock that you have there, jk. I would think that if it does it with a different ecm then its not to blame.

gtamike

Hey. I seem to be having the exact same problem.

I have a aps tt kit on my car and when its hot out, or sitting at idle for a long time the car will lean out like yours and my IATS are in line and not getting heat soaked.. I am running 2 bar speed density open loop.

Afr goes lean up to 16.0-17.0

Ill see if a fan on the pcm clears the issue and ill report back. I will also take temp reading with a ir temp gun.

gtamike

Tording99z28,
Hopefully we can get to the bottom of this. These are my findings.

After engine warmed up hood closed in garage. Open loop 2 bar TEST 1
engine temp: 200*
Iat 98*
Injector pw 2.1ms

After about ten minutes TEST 2
engine temp the same
iat 102*
Inj pw 2.1
But the afr is 2 full points leaner and the motor seems to run rougher.
Pcm case temp 160*

Opened hood applied household fan to pcm area after 5 minutes everything went back to the normal test 1 specs. pcm temp went down to 120*. Iat went from 102 to 98*.

Shut hood. Let car get to test 2 issue.
Opened hood. Running lean.
Pcm temp 160*
Coil packs 250-260*
Iat 102*
Inj pw still 2.1ms

This time I put the fan on the rad support and aimed it at the motor. After 5 minutes the afr was back in line
Pcm temp was still hot. 160*
Coil packs were down to 200*
Iat 98*
Inj pw still 2.1ms

Do you think maybe our coil packs are overheating and causing slight misfires which would read lean on a wideband?

98Camarod

iTrader: (43)

If you want to try and use my coil relocation stuff and see if that fixes it, you're more than welcome to it tyler. Just bring it by one night and we can swap my stuff over and give it a shot.

GMTECH4

I had a similar problem with a yaw rate sensor, stability system would go crazy when hot, but I could move the yaw rate sensor off the hot floor board and it would work fine. Gm sent out a engineer and we found backed out pins n a connector, try thinking outside the box

gtamike

Another update. Not sure if this will help you but I was able to replicate the issue by other means.

This is odd because iats only varied by about 5* in my earlier teating.

I started the car up, warmed it up and pulled the iat out.
I heated the iat up with a hair dryer from a distance. As soon as iat got a little over 100 it started going lean, even though injector pulse width stayed the same. Turned it off and it went back to normal afr. I did this multiple times to make sure.

I was wondering how it leaned out even though injector pulse width stayed the same. I found that IAC counts went from 35-40 to near 60 when temp was increased. This must be adding additional airflow that causes the lean condition. What are your iac counts doing?

There must be some sort of iac airflow adder based on iat?

denmah

iTrader: (2)

i have had this happen only in really hot stop and go traffic in ocean city MD in my turbo truck

code4

iTrader: (30)

As I said before it's your IAT. Some setups I have tuned have iat heat soak issues others don't.

I have had hell trying to tune out this issue and have better luck moving them or running two, one in the bumper & the other where it was using a pressure switch to activate under boost.

tording99Z28

iTrader: (3)

Wow these are some great findings guys and I appreciate all the help with this. I still have to test the IAT theory but I have been having this problem for 8 months or so which goes into last winter and my IAT's in my logs back then were like 60 and 70 degrees and I will having the issue so I don't think that is an IAT heat soak issue at 60-70*?

tording99Z28

iTrader: (3)

Might be worth a shot Rodney and I would appreciate it but I don't think it will make that that far. Once it starts running lean it runs like complete crap and will not accelerate when I hit the throttle. It would definitely start doing it before I got to Chesapeake which would leave my stranded somewhere along the highway until it cooled off some.

tording99Z28

iTrader: (3)

I just looked at a couple logs and it does seem that the lean condition and my IAC counts are related. When the lean condition starts happening the IAC count is considerably higher than when it is not happening. Would be causing this and is there a way to fix it?

gtamike

Toding, i think code4 is correct.

As for the lower temps in winter, not sure how cold it is there is the winter. But if the iat is heat soaked and reading higher then ambient im sure it could cause it.

I have done some reading amd some people upgrade to the gm 4.3 turbo cyclone/typhoon iat as they say it is faster reacting and less prone to heat soak.

As far as the table to adjust, from what i've read we are out of luck with the 99 operating system. The newer OS's have a bias table to adjust but we do not.

Another thing for us to maybe consider would be iat sensor calibration. With the engine cool iat should read ambient temp. If its off by 10-20* it might make a difference and the table we can adjust for this might possibly have a possitive effect.

Ill look into it more after work.

tording99Z28

iTrader: (3)

I will grab a hair dryer and simulate the hot IAT. The other thing then is when I put my box fan on the car and it corrects the problem the fan is no where near the IAT and the IAT temp does not move. For it to correct the problem I would expect the IAT temp to drop when I put the fan on the car.

In fact I just looked at the videos I posted up above in this thread and the third video when the problem lean condition is corrected by the fan the IAT temp is actually warmer at 84* than in the second video when it is is running lean and the IAT temp is 82*.

gtamike

Weird. The fan stopped my issue too but the iat did drop 5* in my case because of the hood being open and probably from the air being sucked in from behind the fan aswell. What was ambieny temp during your testing? Mine was around 75*.

tording99Z28

iTrader: (3)

It was about 78 degrees I believe.

98Camarod

iTrader: (43)

You can come and borrow the coils and wires or my trailer if you need to. Do you have an IR thermometer to see the external temps of things when this happens?

tording99Z28

iTrader: (3)

Sure I could do that, but you wouldn't want to come take a look at the car with me would you since you have experience with turbo cars? Maybe you will see something I am missing? Another set of eye ***** never hurts.


Also I did take the IAT sensor out and heated it up with the hair dryer. It does cause the AFR to lean out into the high 15's or low 16's but that is as high as I could get it to go and the IAT temp was up to 137. I have never had the actual IAT that high and sometimes when my problem is happening I will see 18 or 19 for the AFR.