My LTFTs maxed out at idle!

[johnsZ06]

At idle my LTFTs stay at +25. What would be my first step to bring these down to zero? Multiply the affected VE cells by a percentage greater than 100 and go from there?

RPM is set at 900 and MAP reading is 14.8 inHG.

[Bruce Melton]

My delemma exactly<
My idea is to knock it back in rage with IFR but let's see what the "smart guys" say?

I put mine out by loading +25% onto the IFR going from 28# to SVO 30s. This what I had calculated as the right move anyway.

[Dirk Diggler]

usually +25 is indicative of an exhaust leak on that bank. If both banks then check for any intake leaks behind the MAF

[johnsZ06]

usually +25 is indicative of an exhaust leak on that bank. If both banks then check for any intake leaks behind the MAF

I'm pretty sure I don't have any leaks...I think it's a result of my cam. My left and right bank follow each other pretty close.

[Nick 02 Z06]

This seems to be the norm with the Halltech stinger Intake. I have a basically stock setup with the stinger and have been watching my LTFT's for a couple of months now. I have tightened, loosened, repositioned, etc. to try and get my LTFT's to come down and nothing works. I was told by Jim Hall that GM had the same results when they tested the Halltech stinger and the problem is a leak between the bridge and the smooth coupler. (Let me know if you're interested in the email that he sent me)

I found that by opening the hood, I can cut my LTFT's in half which would indicate a leak caused by the hood touching the intake when closed. Try opening the hood or closing the hood while monitoring your Long terms. I would be interested to hear your results. I'm ready toss my halltech because it won't seal and I'm just about done trying to fix it. Good luck

[Bruce Melton]

[quote="Nick 02 Z06"]This seems to be the norm with the Halltech stinger Intake. I have a basically stock setup with the stinger and have been watching my LTFT's for a couple of months now. I have tightened, loosened, repositioned, etc. to try and get my LTFT's to come down and nothing works. I was told by Jim Hall that GM had the same results when they tested the Halltech stinger and the problem is a leak between the bridge and the smooth coupler. (Let me know if you're interested in the email that he sent me)

I found that by opening the hood, I can cut my LTFT's in half which would indicate a leak caused by the hood touching the intake when closed. Try opening the hood or closing the hood while monitoring your Long terms. I would be interested to hear your results. I'm ready toss my halltech because it won't seal and I'm just about done trying to fix it. Good luck[/quote

Hmmm, I have to force my hood down.

http://sohat.us/engine.jpg

[dfe1]

When you install a cam with a healthy amount of duration, the O2 sensors will see a somewhat erroneous oxygen level because so much of the intake mixture passes right through the combustion chambers and out the exhaust system. When I recalibrate the old mass air systems (1986-89 TPI engines) I found that I always had to bump the injector flow rate by 1.5 to 2 pounds-- that is, if 22 pound injectors were installed, I set the injector constant to 24 pounds. The ECM would then determine that a shorter pulse width was required (because of the "larger injectors". That would get the fuel trims back in range. There's no VE table in these systems, so injector flow rate is the only means available to alter fuel flow. In my opinion, altering injector flow rate should be the first step with an LS1/LS6 system. Then use the VE table just to fine tune. It's really pretty easy with the LS1/LS6 system because you can tune IFR according to manifold pressure.

[johnsZ06]

This seems to be the norm with the Halltech stinger Intake. I have a basically stock setup with the stinger and have been watching my LTFT's for a couple of months now. I have tightened, loosened, repositioned, etc. to try and get my LTFT's to come down and nothing works. I was told by Jim Hall that GM had the same results when they tested the Halltech stinger and the problem is a leak between the bridge and the smooth coupler. (Let me know if you're interested in the email that he sent me)

I found that by opening the hood, I can cut my LTFT's in half which would indicate a leak caused by the hood touching the intake when closed. Try opening the hood or closing the hood while monitoring your Long terms. I would be interested to hear your results. I'm ready toss my halltech because it won't seal and I'm just about done trying to fix it. Good luck

Nick, interesting that you mentioned that. I had the Halltech installed before the cam install and my LTFTs were all over the place, allthough not quite as lean. I've read this before on one of the other forums.

I'll take your advice and try monitoring with hood up. I might also try running the stock bridge. I'll keep you posted.

[johnsZ06]

When you install a cam with a healthy amount of duration, the O2 sensors will see a somewhat erroneous oxygen level because so much of the intake mixture passes right through the combustion chambers and out the exhaust system. When I recalibrate the old mass air systems (1986-89 TPI engines) I found that I always had to bump the injector flow rate by 1.5 to 2 pounds-- that is, if 22 pound injectors were installed, I set the injector constant to 24 pounds. The ECM would then determine that a shorter pulse width was required (because of the "larger injectors". That would get the fuel trims back in range. There's no VE table in these systems, so injector flow rate is the only means available to alter fuel flow. In my opinion, altering injector flow rate should be the first step with an LS1/LS6 system. Then use the VE table just to fine tune. It's really pretty easy with the LS1/LS6 system because you can tune IFR according to manifold pressure.

I'll give that a try. Thanks!

[BigTex]

Just curious, but have you altered any of the typical idle tuning tables? IAC, Idle Airflow, Idle Airflow Parked, Throttle Cracker, etc... Ported TB?

It may just be me, but the more I've had to raise those IAC and idle values, the leaner my idle LTrim values have become at idle / low rpm.

[johnsZ06]

Just curious, but have you altered any of the typical idle tuning tables? IAC, Idle Airflow, Idle Airflow Parked, Throttle Cracker, etc... Ported TB?

It may just be me, but the more I've had to raise those IAC and idle values, the leaner my idle LTrim values have become at idle / low rpm.

I raised the RPM at idle from 800 to 900, but out of necessity!

[johnsZ06]

Update:

Opening the hood didn't make any difference to the STFT. I did however scale IFR back. PCM now thinks I have smaller injectors so is compensating by increasing pulse width. My STFT now at -2 at idle and LTFT down to +5. I'm going to put some more miles on it before I make another adjustment. Now my big problem is hot start. Car wants to die and stumbles terrible until it figures out what to do. Ughh!

[Bruce Melton]

What did you did you do to get from +25 to +5?
- what % IFR? and did you do the whole table?

Thanks
Bruce

[johnsZ06]

What did you did you do to get from +25 to +5?
- what % IFR? and did you do the whole table?

Thanks
Bruce

I scaled the entire table by .93%.

[Bruce Melton]

John,
It worked but I am uncomfortable. I had gone up 25% on the IFR to go from 28s to SVO 30s. Had to kick it back 14% (net +11%) to get anything negative at part throttle and idle is still + 20.
Had you bumped up your injectors?
Our engines seem to be in the same realm.
Thanks for your help,
Bruce

[johnsZ06]

John,
It worked but I am uncomfortable. I had gone up 25% on the IFR to go from 28s to SVO 30s. Had to kick it back 14% (net +11%) to get anything negative at part throttle and idle is still + 20.
Had you bumped up your injectors?
Our engines seem to be in the same realm.
Thanks for your help,
Bruce

My injectors are stock for now. I ordered 32# Delphi which flow 36.5# @ 58psi and would have worked great but I wasn't happy with the way they fit so now I'm looking for another solution.

Short terms are running in the negative now at idle and the throttle response is very crisp. My main problem now is when I shut the engine off and restart it, it will stumble until it catches and then it idles fine. I have no idea what to adjust to fix that..

Try setting your IFR back to stock and see what that does and if your still lean try scaling in the opposite direction. That's all I know how to do for now. :lol: