Rough Idle Only In Park
Rough Idle Only In Park Hello All,
Recently installed stock 243 heads and a mild blower cam on my c5, got the VE + MAF tuned but no matter what I do I cant get it to idle smooth in park or neutral. It feels like a random misfire. Had heads machined, measured preload for new pushrods, new ls7 style lifters, new ngk plugs, new wires, new 02 sensors. Everything was smoke tested for leaks and hooked up a vacuum to exhaust when I was checking the band clamps. Also had the Idle airflow values updated per the idle tuning tutorials. Not sure what else it could be. Attached is one of the logs.
1999 corvette frc ls1: 243 heads, ls6 intake, TB Bypass, SE Longtubes, TI mufflers, ZZP 7.375 Pushrods, ls7 Lifters, PAC 1218, Melling 10295, A+A Blower Cam.
Recently installed stock 243 heads and a mild blower cam on my c5, got the VE + MAF tuned but no matter what I do I cant get it to idle smooth in park or neutral. It feels like a random misfire. Had heads machined, measured preload for new pushrods, new ls7 style lifters, new ngk plugs, new wires, new 02 sensors. Everything was smoke tested for leaks and hooked up a vacuum to exhaust when I was checking the band clamps. Also had the Idle airflow values updated per the idle tuning tutorials. Not sure what else it could be. Attached is one of the logs.
1999 corvette frc ls1: 243 heads, ls6 intake, TB Bypass, SE Longtubes, TI mufflers, ZZP 7.375 Pushrods, ls7 Lifters, PAC 1218, Melling 10295, A+A Blower Cam.
Last edited by cookster489; Oct 13, 2020 at 04:48 PM.
Im open to any ideas? Ive already pulled spark plugs ensured everything was torqued properly. Made sure all plug wires clicked on both the coils and plugs. Also double checked for vacuum leaks with some brake cleaner with no luck. Pulled valve covers and all components are tight, and even went to re-check my pushrod measurements if accurate. Not sure where to go next, if anyone needs me to log anything else I would be glad to? lost at this point what I need to check next...
You are logging a ton of channels....
I am no tuner, but a couple of observations...Your spark is a bit low at idle, your AFR is dancing around a bit, and your throttle is showing at 6.3%. Depending on how your tune is setup, you may not actually be in your idle parameters due to the TPS position of 6.3%. If this is a cable throttle body, that may be your problem.
Cut your channels down, half the crap you are logging is not needed. Log the IAC position from cold start to operating temp. Post your tune as well.
I am no tuner, but a couple of observations...Your spark is a bit low at idle, your AFR is dancing around a bit, and your throttle is showing at 6.3%. Depending on how your tune is setup, you may not actually be in your idle parameters due to the TPS position of 6.3%. If this is a cable throttle body, that may be your problem.
Cut your channels down, half the crap you are logging is not needed. Log the IAC position from cold start to operating temp. Post your tune as well.
Here is a log from cold start to normal operating. Spark was increased from 16 to 18 but any higher the vacuum starts to drop off. Everything I read indicates its best to add spark until vacuum starts to drop off. I will remove more of the channels next time I log, was trying to look at everything initially to see if anything was missed. This scan was cleaned up a little to better identify the idle areas. With a little more spark and cleaning up the airflow tables helped a little but I can still feel an intermittent stutter or what feels like a random misfire. (I ohmed the plug wires last night and they all have good continuity)
Also the TB is a DBW if that makes any difference. Is there a way I can keep the afr more steady?
Also the TB is a DBW if that makes any difference. Is there a way I can keep the afr more steady?
also wanted to add, I was concerned that maybe the head gasket or valves might be the problem because its only apparent at idle so I recently did a compression test and all cylinders are between 150-160psi cold. Going to double check for exhaust leaks again here shortly.
Never so happy to find an exhaust leak. Hooked up the positive side of the vacuum and spray soap water everywhere and found leaks on all ports of the head. This would definately cause the issue Im having. Will keep everyone posted...
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Here is a log from cold start to normal operating. Spark was increased from 16 to 18 but any higher the vacuum starts to drop off. Everything I read indicates its best to add spark until vacuum starts to drop off. I will remove more of the channels next time I log, was trying to look at everything initially to see if anything was missed. This scan was cleaned up a little to better identify the idle areas. With a little more spark and cleaning up the airflow tables helped a little but I can still feel an intermittent stutter or what feels like a random misfire. (I ohmed the plug wires last night and they all have good continuity)
Also the TB is a DBW if that makes any difference. Is there a way I can keep the afr more steady?
Also the TB is a DBW if that makes any difference. Is there a way I can keep the afr more steady?
AFR at idle can be a pain, especially if you have a large overlap cam.
Looking at your tune, your BRAF looks reasonable for what you are running, but your spark for in gear and in park are vastly different. Not that it is necessarily a bad thing, but it could be why you see a difference in feel between park and drive.
Good find on the exhaust leaks.
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Verdad Gallardo So exhaust leaks are all fixed finally but the idle misfire/stumble is still there. Only in park/neutral, I tried increasing spark to match drive and it helped but the problem is still there. attached is the latest log...
Joined: Nov 2003
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From: Wichita KS / Rancho San Diego
I'm not familiar with HPT, nor with tuning DBW, but for LS1's EFILive has separate throttle cracker and base spark tables for park/neutral and in gear. If you have similar tuneability with your system, you may trying increasing airflow and/or spark in the p/n tables.
Your absolutely spot on about what tables to adjust. Problem is neither of those were able to get rid of the misfiring. They both helped once dialed in but did not fix the problem.
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So... drive and reverse is fine/no problem? How are you determining misfire? How does timing and AFR change between neutral and in gear?
I can feel a definite stumble. The cam has a little shake to it but then there is a definite difference between the "shake" and misfire that I intermittently feel. Timing is only a few degrees apart and afr looks the same. And yes drive and reverse feel smooth as butter.