When my car was running 8lbs on the vortech, no problems. However, now that I have 12lbs, I can't get the car to tune. I'm working with a local tuner and we are tearing our hair out. Assuming we define a baseline that worked with 10 lbs, the first two gears has the computer adding up to 30% more fuel. When you hit 3rd gear, the system reverses and pulls out 30% more fuel. So, if you tune for the first 2 gears, the top 3 are way above 18:1. If you tune for the top 3 gears, the first two are way below 10:1. We have changed computers. The only other diffference is the blow off valve that was added. However, we have clamped that off and pressure tested the system so no leaks in the intake anywhere. Any ideas would be greatly appreciated.

 

I guess this makes no sense to me. If you add say 10% fuel from TP's 200-650 thats what its going to do. What gear your in should make no difference.I would go back to your 8psi tune and slowly add in fuel as needed.....try to do it in small steps. Is your base tune your 8psi tune with tweaks or a new tune completely? If it is a new tune then something in it is written wrong. Is the blow off valve and ACT in the correct place?Good luck

Adam

 

It makes no sense to us either. I agree, the gear shouldn't matter but it does. We even monitor load thinking that the load change is what the computer is using. We have changed out the computer, the injectors, the MAF, etc... When that gear changes from second to 3rd, manual transmission, the system goes from dumping fuel to pulling fuel. It doesn't matter where we set the MAF, that's what happens.

 

Like i said is this a new tune completely or a tweak of the 8psi tune? I'm thinking something basic got over looked. Have you changed all your injector values, set your MAF transfer function with new MAF and injectors? There are so many things it could be. try emailing or calling sct www.sctflash.com

They also have a place where you can post up your tune for their experts to look at. If your tuner is an authorized SCT dealer he should be able to call them up and get some answers today...good luck and let us know how it goes.

Adam

 

It's a new tune. My tuner has already talked to SCT. They weren't all that that helpful. They thought the computer was bad. We replaced it. No difference. I have spent a lot of hours on the the tune and I would say I probably now know 25% of what I need to know to tune a car from scratch. What I can definitely tell is that the load is probably not the lone deciding factor on the change in tune. The deciding factor is probably speed related but we can run 30mph in 2nd and 30mph in 3-4 and get completely opposite responses by the computer in terms of fuel/air. The computer is also throwing a tire/axle code but it's been doing that for 2 years. I"m 2 inches from either tossing the vortech and starting over with a Kenne Bell or tossing SCT in the garbage and just buying a new fuel management system.

 

Thats a very odd problem. I have never heard of such a thing. Ryan@sct is usually who is pretty helpful. I am thinking if they weren't that helpful then he must not be an SCT dealer/authorized tuner. I don't think the problem is on the software. What happens with the 8psi tune besides it being lean in the top end? If the 8psi tune doesn't do it..your new tune could be corrupted, it happens.

 

We have run the car through 3 chips, 2 computers, and ungodly number of different tunes. My tuner is authorized, SCT just doesn't have an answer. It's not in the tune. For some reason, something in the computer code is reasoning incorrectly and changing the base line for the auto tune. The funny part is, we even tried turning that off and tried eliminating the o2 sensors. None of that makes any difference.

We assumed it might be sensors such as the O2, fuel pressure, etc but we watched all that. In addition, the car is now changed to a return system so we even worked with 97 base line settings.

 

Damn...that sucks. Adaptive learning off? Sounds like you are covering your bases.....

 

Something "obvious" is being overlooked (glad I am not close enough for your to hit me). I would say the problem is not the computer or the tune as you have proved this by swapping everything out.

Could it be as simple as a bad computer ground strap? I have heard of problems like this resulting from a disconnected ground strap on the computer. Something like this could be a common denominator with each chip and ECU.

 

I've never tried to tune a sc car, but I have encountered damaged harnesses that send weird, intermittent jolts through the computer. Wires can get crushed when doing a build - done it, been there, bought the t shirt.

At this point I'd be tempted to check the whole harness from maf to computer.

I just had a pretty crappy day, but I'm glad I'm not you right now...

Best of luck! Maybe we'll both have a better day!

tripleblack

 

We thought through the cable harness and the ground as being issued. I've tested the ground with the car running and not running and it's clean to the computer and the block. As for the harness, we checked for crimping, cuts, etc... everywhere we could. However, the problem seems too consistent to demonstrate an intermittent problem. What makes no sense is why the car under open and close loop acts exactly the opposite one you jump from the 2-3 gear shift.

As for being something obvious, hey, I'm open. Sometimes when you work on a problem too long, you focus too hard and miss something. I don't think this one has an obvious solution however. What I wouldn't give to talk to an engineer who worked on the computer software right now....

 

Wild thought: Try pulling all the fuses you don't have to use to actually run the motor (stereo, lights, power windows, etc). If this fixes the problem, you're in an elimination loop that might get you fixed.

Just trying to come up with a path that doesn't involve getting inside the computer, since you've already swapped that component out.

tripleblack

 

Interesting idea. thanks. I'll take a look at that.