OBDI LT1, Tunercat, big cam, right bank running very lean

I've got a local shop tuning my car since I'm clueless about this stuff. They did my machine work for me and have previously tuned anything from boosted Hondas to carb'd big blocks to late model fuel injected stuff- so they definitely have a wide range of experience.

I went to the shop last Friday because I wanted to get in on some of the tuning and maybe learn a thing or two. After messing with the VE tables and getting the car to idle ok (and switching it from speed density back to MAF) we have encountered a problem. It seems that my right bank is running quite a bit leaner than the left. I thought that oxygen sensor might have gotten damaged by a nice coolant spray when I put the motor together (long story) so I went ahead and put a new one in- both oxygen sensors are new GM units.

I don't have the datalog with me right now, but from my memory the left O2 sensor at idle was reading 650-700 Mv, and the right was reading 350-400 Mv.

I could see that the computer was adding more fuel to the right bank trying to compensate, but that side was still reading 350-400 Mv. We probably ran the car for about 25 minutes idling, revving, etc., and there was one point in time for about 30 seconds where both O2s were reading within 40 Mv of eachother which I would be fine with, but then the right one dropped again.

Any help would be appreciated. I need to get a solid base tune on this thing so I can drive it home and pull the transmission. I was going to dynotune it out there, but the trans is slipping so bad it needs to be fixed first. So it's got to be- base tune->pull trans->dynotune, and I have a little less than a month to do this before the track day I need to be at.

Tell us your shop isn't trying to tune your A/F's without using a wideband. You really need to be on a wideband to get the real story. Also, what do your blm's look like and what are you actually trying to tune? Idle, part throttle, WOT?

Ken R.

They're not using a wideband at this point. What we are trying to do is get the idle and some part throttle close so the car can be driven to the dyno and tuned there with a wideband.

Will try to get a datalog posted on here today at some point.

i had the same issue, turned out to be vacuum leaks at the TB. (cracked hoses)

If the Camshaft in your signature is actually in the car then you've got a rough time ahead.First problem is that your camshaft is going to cuase massive idle air distribution issues.Secondly get over the idea of trying to tune the engine in closed loop. Use the AFR 10x table where its AFR vs rpm and KPA to get the desired idle fuel values same for part throttle. Make sure the MAF hasn;t been ported etc if it has i will remind you now ive made 430rwhp on a mustang dyno with a stock 75mm 3 pin if your after MAF airflow buckle down and get a 5pin 2001 up vette MAF and get an SLP 3-5 pin conversion harness and get a MAF table from a vette etc to put in the pcm. Also don't be affriad of the cylinder fuel trims. They can often correct some fiarly large cylinder imbalcnes.the VE table is used for Large Delta events IE opening teh throttle rapidly. If the throttel cuase a lean spot in the engine log the event preceding the lean and after RPM and MAP and goto those areas and add or subtract fuel as needed.

Thats all the free advice your getting.





I've got a local shop tuning my car since I'm clueless about this stuff. They did my machine work for me and have previously tuned anything from boosted Hondas to carb'd big blocks to late model fuel injected stuff- so they definitely have a wide range of experience.

I went to the shop last Friday because I wanted to get in on some of the tuning and maybe learn a thing or two. After messing with the VE tables and getting the car to idle ok (and switching it from speed density back to MAF) we have encountered a problem. It seems that my right bank is running quite a bit leaner than the left. I thought that oxygen sensor might have gotten damaged by a nice coolant spray when I put the motor together (long story) so I went ahead and put a new one in- both oxygen sensors are new GM units.

I don't have the datalog with me right now, but from my memory the left O2 sensor at idle was reading 650-700 Mv, and the right was reading 350-400 Mv.

I could see that the computer was adding more fuel to the right bank trying to compensate, but that side was still reading 350-400 Mv. We probably ran the car for about 25 minutes idling, revving, etc., and there was one point in time for about 30 seconds where both O2s were reading within 40 Mv of eachother which I would be fine with, but then the right one dropped again.

Any help would be appreciated. I need to get a solid base tune on this thing so I can drive it home and pull the transmission. I was going to dynotune it out there, but the trans is slipping so bad it needs to be fixed first. So it's got to be- base tune->pull trans->dynotune, and I have a little less than a month to do this before the track day I need to be at.