Hi Volts Z06

I have (or should say HAD) a LS3 stroker which was built specifically for road racing. The car is NOT street driven so there are no concerns as far that is concerned. Here's my situation:

I built this motor with durability and reliability in mind. The bottom end was all forged and everything was new- nothing rebuilt. The engine builder performed my tune on a dyno- I needed to be within a certain horsepower so his plan was to tune the engine to max power and then use throttle position to back off the HP. This seemed to work well as our max power was 446 HP/ 481 TQ and after back it down we were able to get 400 HP with 461 TQ. The car always seemed to be rich at idle and even at part throttle. (I literally was getting sick from the fumes in the car). Last event (90 degree day) the car started to misfire at WOT as if I lost a plug wire. I pitted and examined everything but couldn't find anything wrong or get any codes. I then pulled all the plugs- white like new out of the box so I knew it was lean. I then noticed the coupler on the air cleaner side of the MAF was partially disconnected so my assumption was simply- Vacuum leak. I put it all back together- but still misfiring (almost randomly- couldn't pinpoint a cylinder by using laser thermometer). Checked fuel pressure- I was getting 60lbs at the fuel rails at idle (although I did notice the needle was kinda jumpy- wasn't my gauge and the owner if it said it always did that). We pulled valve covers to make sure there was no broken springs- nothing. The next day, after exhausting all options we replaced the MAF sensor. This seemed to smooth things out. I was surprised I didn't have any codes. I took the car out for practice and despite being cooler (75 degrees) the car was definitely down on power. I took the car out for qualifying and within a few laps- splashed the engine. Obviously the motor leaned out since I found oil in intake but there is no obvious block damage (externally at least). The engine is effectively junk and I have already purchased a crate motor as I'm done with spending money on "boutique" engine combos. Now to my questions:

In speaking with the tuner- I stated that obviously we had a fuel delivery issue. Regardless of whether the fuel pump is failing or if the MAF sensor was bad- why didn't we throw codes or go into limp home mode? That answer was- your car is tuned in open loop mode. (I realized when I started to tear things down I don't even have O2 sensors). I asked why we did this and I was told because of my cam. (Not a big cam- MTI X-1 that a used to run in my LS-6 motor). Is this typical protocol to tune race motors in this manner? I feel like we set ourselves up for failure by not allowing the computer to do it's job. Before having this new engine tuned I will replace both the MAF and the fuel pump so we start fresh but I've become so paranoid of leaning out another motor that I've purchased a wide band and will export that data to my RLC data system to monitor for a lean condition. Is that overkill? Should I find a new tuner? Does the factory ECU support some kind of ability to monitor for this? Opinions please......

Bad Karma

I'm just getting into tuning on this car (up until buying HO Tuners, I've done everything prior and on other cars with piggy backs), but I would find a new tuner. If the maps were based off what sounds like a possible bad MAF and with a vacuum leak, I wouldn't trust the tune... and to only run in open loop mode seems like a shortcut.

Hi Volts Z06

The tune wasn't done with a bad MAF and vacuum leak- that developed midway through the season. I just don't think that running in open loop only is smart. What failsafe do I have if something causes a fuel delivery problem again?

BmoreRnsDeep

I am definitely no expert but I would guess since you had an intake vacuum leak and when you replaced the maf things smoothed out that maybe the maf was dirty. Try cleaning it and hooking it back up and see what happens.

o1Z0sick

Ill take a stab from my experience.

What happened to your engine and have you done a compression test? Do you think you lost a ring land, did you have spark knock?

If your tuner set you up in open loop then the MAF would have been defaulted to fail either by setting the Hz range high or low or by unplugging the purple or all three MAF wires. The MAF is usually kept in place to retain the IAT sensor.

Im going to assume your tuner used a widenand on the dyno to dial in VE and if using PE that was accordingly without scaling for the injectors but actually using the proper injector data.

The O2s that were gone were they the front or rear set? The rear ones are not needed for non-emessions or catless exhaust but the front ones are needed if your closed loop. The front O2s are turned off in open loop in hp tuners but efilive does have a custom operating system called semi open loop to use the O2 feedback in open loop at part throttle or where ever you want a stoich ratio. They dont have great resolution outside that range to tune WOT air fuel with accuracy. Also at idle they dont work great with higher overlap cams so until about 1500 to 2000 rpm is where they become useable and accurate.

Being this is a bolt on ls3 and if the work was done dialing in VE in open loop then the next step would be to re-enable the MAF and tune air fuel to dial that table in. It is a little more work to get transients in line with MAF enabled but it can be done.

Hope this helps.