Hello all.
I think this is the first time I have ever had to post anything but I have run into a problem that I cannot figure out. I have used this forum to tune my supercharged Silverado in SD and now I am tuning a 2004 Corvette. My main problems are surging between 1000 and 2000 rpm with light to no throttle, with very light acceleration, and even with deceleration. The idle was hanging up around 1200 rpm as long as the car is rolling. I think this is fixed now by running the idle config again and lowering the values. Also, about 40% of the time when I start the car at full warm but sitting for 10to 15 minutes, it won’t go on the first crank but always on the second. If it does go on the first crank it will hunt for a steady idle. Sometimes it will find the idle point and other times it will die. I have modified every table I can think of and the only change that has made a minor improvement on the surging is increasing the throttle follower decay. I have focused on the surging mainly. I think some cranking fuel table modifications will help start up but I haven’t gone there yet.
What I have tried to fix the surging/bucking:
Injector scaling and min pulses are correct.
Stock idle and low rpm timing, commanding a timing using controls from 15 to 25 degrees, no change.
Open or closed loop makes no difference
It does improve a little when too rich, but I don’t want to drive it like that.
Throttle cracker zeroed or stock, no change
No hole in TB plate. There was one before. No change.
Idle air flow has been done a few times. Cold start up is great. Warm start is good most of the time.
I lowered the o2 switching points
I added rpm in the rolling rpm table, no change.
I have also changed the startup flare cont to pull less timing around the 500 rpm and more timing around the 900 to 1000 rpm. This didn’t help the hunting for idle on start up when it does happen.
This is what the engine does well:
Great throttle response.
468 ftlbs of torque at 4700, Above 350 ftlbs of torque from 2000 rpm to 6500, 500 hp at 6200.
Idles at 900 rpm. It will actually idle at 800 but will die if reved up as it passed 800 when coming down. 900 rpm is good enough.
Engine specs:
SD tune for now, MAF is unplugged, 404ci ls2, 11.5:1, Ported AFR 205 heads, ported fast 92, ported ls2 TB, cam is 239/243 on a 114 + 1 with .624 lift, yella terra rockers, Johnson lifters, kooks headers, no cats, billy boat exhaust, green top injectors.
I have gotten to the point that the level of surging is somewhat acceptable if I sacrifice and run rich, or have higher idle through higher idle airflow numbers I don’t like those compromises either. I have had the car on a dyno with wide band and the VE table is really close to where it needs to be as well as the timing table. LTFTs are -2 to -3.
The attached log was today in the rain so ignore the ltft. They are much better on a warm sunny day. I also put most of the tune back to stock to show the basics of what I have.
I am looking for some suggestion. Thanks
Closed loop is not your friend on that setup. Tuning via fuel trims is unlikely to be accurate. Your exhaust and valve events place the narrowbands outside their designed and intended pressure and temperature range meaning the resultant trims and airflow modelling is likely inaccurate and contributing to the surging. Recommend open loop and without a decent gas analyser or perhaps EGT sensors then just give it what it wants. Same same with timing, find the happy medium and realise sometimes not all reversion especially in a manual is curable.
I know this is an old thread but I found it while searching for some answers of my own. I'm trying to cure the same bucking/surging at cruising you are and tried everything you did. Adjusting end of injector timing helped the most so far. At stock settings the injector finished spraying 84* before the exhaust valve closed, taking a lot of that fuel with it I would imagine. I adjusted EOIT to 16* before the exhaust valve closed and it feels like a different car. Bucking is 10% of what it was before and the increase in torque is easily noticeable. It's been raining so I haven't driven it today but tomorrow I'm going to try adjusting the EOIT again to finish the instant the exhaust valve closes. Here's the thread: http://www.hptuners.com/forum/showth...ereencing-what it also has excel worksheets to calculate everything.
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