I'm helping a friend of mine tune his car. It's a 408, with a fairly large cam, and a th400. Long story short, if it's idling and you get into the gas at all, it will just stumble, or die, the rpm's won't raise at all. If you get into it 5-6% it's fine, but anymore than 10-20% it dies, or stumbles horribly. I have a log and the tune attached. The tune is very rough, we're just working on idle, and right off idle stuff. We're working with open headers, so we haven't had a chance to do any driving what so ever. Also does anyone know how to get the pcm to realize if it's in gear/not in gear with a TH400?

http://e-junky.net/Logandtune.zip

Any advice is appreciated.

Thanks guys,

Mike

 

Not sure about the TH400, maybe a manual tune rather than auto would help though.
As for idle, it sounds like a classic case of needing to tune in your running/desired airflow plus maybe follower

 

try adding more timing at idle and throttle tip in

 

I tried adding a few degrees of timing, but we got knock. Any other ideas?

 

try decreasing fuel

 

How much timing did you try? and How much Knock did u see? If not tuned out the stock PCM can pull timing at throttle tip in and it will show up as knock retard on the scan tool.

Also what kind of plugs and what heat range/gap are you using?

Are you running in closed loop?
if so, do u notice it runs better while in open loop? (cold startup)

 

One thing I noticed we didnt change was EGR Correction. Looks like it adds up to 7* part throttle. Any ideas on that? NGK 8 plugs. Seems to run better in open loop.

 

Turn off egr and air, and cot

 

They have been off. The table I'm talking about is under Spark Control>Spark Advance>EGR Correction. Anyone familiar with this table? Looks as if it throws in timing part throttle?

 

Not if your EGR is disabled.

PM me with your email addy, I've got a change in your tune for you...

And with a T400 you'll have to run it as a manual tranny tune, or just change all your in-gear/neutral tables to be identical.

 

I understand my VE Tables aren't perfect yet my LTFT's and STFT's were not terrible. At least not enough to give me that kind of stumble. Also when the RPM's are brought up to avoid stumble it still acts lazy/unresponsive. Any thoughts?

 

Did you drop those changes I sent you in and try it?

 

I didn't use the exact numbers but scaled them all down using your curve. My STFT's immediately shot into -15% and more

 

I was thinking maybe a timing issue with the KR but still the fall on its face still doesn't add up?

 

first step is to get it running. It needs a little drive in order to calm down the LT's after a fresh flash. And you shouldn't even worry about ST's until you're LT's are between 5 to -5.

It's still no good how ya'll have less VE as MAP increases.

 

What is happening to the AFR?

Steve

 

Cameron, I agree with you. I did use your spreedsheet to correct the VE curve and a difference was made. It still has a stumble but like you said maybe I just need more drive time to justify the changes and letthe fuel trims settle. As far as AFR the narrowbands were picking up low to mid 100's. LEAN.
I need to install my wideband I purchased a month ago and get some use out of it. As far as the stumble I've just been going off the narrowband as I know I'm lean. In fact I was watching a recent log and noticed a direct relationship between lean narrowband and knock. I guess I'll drive it more with Camerons VE and post up any change. Thanks again for all of your guys advise.