Surge right off idle???
04-01-2008, 02:45 AM
#1
Surge right off idle???
Ever since I ported the heads, and changed to the .96 AR my truck has ben running wierd. When I start it up cold it will surge, and almost die like two or three times. Then runs kind of rough. Once warm it runs better but still isn't right. I have a surge at light throttle right off idle. The thing confusing me is the AFR is 14.5-14.8 the whole time.
If you try and hold a steady 1800-200RPM in park it will surge, and mix up a bit. Could the VE table be off now since I made those changes? Or could it be ignition. Either way I would think the AFR gauge would pick it up. I did have to adjust the WOT fuel curve alot. Most of that was probably due to the meth though. Runs good @ wot tough so I don't think it is ignition, or mechanical. Feels lean to me even though AFR reads good. Could it be fluctuating too fast for the AFR to pick it up? Thank's J
If you try and hold a steady 1800-200RPM in park it will surge, and mix up a bit. Could the VE table be off now since I made those changes? Or could it be ignition. Either way I would think the AFR gauge would pick it up. I did have to adjust the WOT fuel curve alot. Most of that was probably due to the meth though. Runs good @ wot tough so I don't think it is ignition, or mechanical. Feels lean to me even though AFR reads good. Could it be fluctuating too fast for the AFR to pick it up? Thank's J
04-01-2008, 09:30 PM
#3
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I'd scan and log to see what's going on. Are you running SD or MAF with the turbo? More than likely you're running somewhat lean with ported heads and you can correct that fairly easily by increasing the MAF or correcting the VE table for SD. Since the heads have been ported I don't think increasing the idle is going to correct your problem but might helpk some of the surging at idle.
Last edited by WS6Truck; 04-01-2008 at 09:37 PM.
04-02-2008, 03:25 AM
#4
I'd scan and log to see what's going on. Are you running SD or MAF with the turbo? More than likely you're running somewhat lean with ported heads and you can correct that fairly easily by increasing the MAF or correcting the VE table for SD. Since the heads have been ported I don't think increasing the idle is going to correct your problem but might helpk some of the surging at idle.
04-02-2008, 04:43 AM
#6
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The v.e table is only used in transition while running mafed, adjusting the v.e while running the maf will be like chasing a dog, in a maze, at night....
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04-02-2008, 08:37 AM
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I have to agree with Wilde on this one when adjusting the VE table. When I put my new heads on it leaned me out and the MAF wasn't able to correct for it so I had to adjust the MAF table but that was also due to me porting the MAF to 85mm.
If you're using a wideband, you should log in open loop. I'm assuming you are since you're able to read AFR. You don't want fuel trims to interfere with the w/b reading. You want to determine the actual % error between what you're commanding and what the w/b says your tune is actually delivering. When they match +/- 1%, you're done. You can use the MAF histogram in your tuning S/W tuning with a wideband and copy them to the MAF table in your tune and multiply by % until the non-PE portion of the MAF table is within 1-2% rich. The PE portion you want at 0 so that your PE afr is dead on.
If you filter your MAF histogram to ignore afrs greater than 14.5, it'll show you which MAF Hz cells you've zero'd out that you can now multiply by 1.015 to give you a bit of safety in normal use. The trims will zero it out as necessary in closed loop. This is the quickest way for me to get the tune back in line after a head or port job. It's tough to try and tune over the net without actually looking at your tune and vehicle.
If you're using a wideband, you should log in open loop. I'm assuming you are since you're able to read AFR. You don't want fuel trims to interfere with the w/b reading. You want to determine the actual % error between what you're commanding and what the w/b says your tune is actually delivering. When they match +/- 1%, you're done. You can use the MAF histogram in your tuning S/W tuning with a wideband and copy them to the MAF table in your tune and multiply by % until the non-PE portion of the MAF table is within 1-2% rich. The PE portion you want at 0 so that your PE afr is dead on.
If you filter your MAF histogram to ignore afrs greater than 14.5, it'll show you which MAF Hz cells you've zero'd out that you can now multiply by 1.015 to give you a bit of safety in normal use. The trims will zero it out as necessary in closed loop. This is the quickest way for me to get the tune back in line after a head or port job. It's tough to try and tune over the net without actually looking at your tune and vehicle.
04-02-2008, 09:20 AM
#10
Just suprises me that the heads can change things so much. Im sure it is off because it was right on before I did the heads. The gain on the heads was probably massive too. I have gotten an honest 300CFM from a similar set of stock valved 317's. Stock is only mid 240's.