Idle tuning and exhaust leak
Idle tuning and exhaust leak Sooooo, I've been wrestling with my idle tune, for a while now, trying to figure out why in OL the car idles good but as soon as I put it in CL it starts to surge and the idle becomes more unstable. Even when doing a test run I can feel the surge. Then yesterday while fiddling with it I noticed a slight "tapping" sound. I've heard this sound several times before and knew it was coming from the exhaust but I never really payed to much attention to it because it would fade away. But yesterday it got a little louder so I slid up under the car to check it out and I could feel some exhaust pulses (air) hitting my hand while the car was idling. I have swap headers with slip-on collectors and that's where the leak is coming from.
Sooooo, for any one who may know, would this be the reason (well one reason) why I can't seem to get my idle dialed in? I haven't heard any leaks on the other side but I believe that air may be getting past that collector too.
Sooooo, for any one who may know, would this be the reason (well one reason) why I can't seem to get my idle dialed in? I haven't heard any leaks on the other side but I believe that air may be getting past that collector too.
Last edited by Monte4ever; Jul 27, 2013 at 07:23 AM.
What are your fuel trims doing at idle when it goes into Closed loop? Sounds like a VE problem. Try unplugging your MAF and tuning VE at idle and see if that helps. Unless your leak is really bad, it should not hurt anything.
If its bad enough that you can hear it then you may have a problem. All my connections are tied together with stainless band clamps and I can still feel small puffs of air coming through but not enough to hurt anything.
If its bad enough that you can hear it then you may have a problem. All my connections are tied together with stainless band clamps and I can still feel small puffs of air coming through but not enough to hurt anything.
I'm MAF-less (SD). My VE table looks good (IMO) during CL and OL operation. Both idles a little high at 950-975 (target 850). CL cold startup is VERY SHITTY and is the worst part. It will fire right up but then idle very rough and drift low. Once its warmed up it idles as described above. I can get the idle down to 850-900 by way of the Proportional table but that's when the surging really starts. And yes, the leak is noticable.
Try to open the throttle screw/blade up some when it is cold and start it. Go about a half turn at a time until it fires and idles cold. Sounds like you are fighting the same thing I am. If it idles high hot, then more than likely your IAC counts are at 0.
What do you think my IAC's should be at with KOEO? This particular situation didn't start happening until I adjusted my VE table. My last OL log had my AFR error at +/~ 5% on a 20 minute drive. Before my AFR meter was showing 16-17+ AFR readings.
Last edited by Monte4ever; Jul 27, 2013 at 01:21 PM.
I want to point out that my IAC's are not 60 at idle. My log was showing 30 at hot (target 865 - Idles +/- 50 in each direction) idle. Are these IAC's to low?
Trending Topics
Thank you for this tip. I have an Edlebrock 90mm TB and it has a screw on the top that allows you to adjust the amount of air that enters the TB. Its there so you do not have to drill the TB blade. Well, I went out and started the car and it fired right up but started to idle crazy. So I turned the screw until it idled smoother. Long story short, with a couple of hours adjusting the PID, Base Airflow, and Throttle Follower tables its idling the best its ever idled. The real test will be when I start it up in the morning, but for now I'm happy.
I want to point out that my IAC's are not 60 at idle. My log was showing 30 at hot (target 865 - Idles +/- 50 in each direction) idle. Are these IAC's to low?
I want to point out that my IAC's are not 60 at idle. My log was showing 30 at hot (target 865 - Idles +/- 50 in each direction) idle. Are these IAC's to low?
No it should be fine there, if you opened up the throttle blade, got your counts down to 30, I bet it starts better cold. You are going to get more air for cold start. Its a good idea to use a volt meter to check your TPS voltage so that you can monitor your changes. Just in-case you need to go back. I will see how mine starts in the morning as well. I think my problem was that my VE was too lean in the areas around idle. I straighten out a paper clip and stick it in the blue wire hole in the back of the connector, not in the wire itself.
Be sure to watch your idle air flow, and watch the IAC in the chart, when you start it cold. You will be able to see whats going on.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo No it should be fine there, if you opened up the throttle blade, got your counts down to 30, I bet it starts better cold. You are going to get more air for cold start. Its a good idea to use a volt meter to check your TPS voltage so that you can monitor your changes. Just in-case you need to go back. I will see how mine starts in the morning as well. I think my problem was that my VE was too lean in the areas around idle. I straighten out a paper clip and stick it in the blue wire hole in the back of the connector, not in the wire itself.
Be sure to watch your idle air flow, and watch the IAC in the chart, when you start it cold. You will be able to see whats going on.
Be sure to watch your idle air flow, and watch the IAC in the chart, when you start it cold. You will be able to see whats going on.
I went out and added TPS volts to my log and it was around 40ish. I say "around" because I turned it a little before I logged it. I set it to .45 volts. By the way, I let it cool down for a few hours and started it up and it still idled bad before it reached operating temps. If I would of let it run it would of cut off. 
Lol. I just talked about an air leak in my other thread titled Idle Issues. Today I heard a hissing sound coming from my brand new brake booster. A quick test with a vacuum pump confirmed it. I hope that's the problem.
Last edited by Monte4ever; Jul 29, 2013 at 09:03 PM.
