Uprev fuel tables with elevation

TopgunZ

I just moved from Denver at 6000ft elevation to Minneapolis at 800 ft. I am boosted with a sc that seen 9.5psi in Denver. I am expecting to see 12 psi down here at 800ft.

My question is...Is it as easy as just adjusting fuel tables to compensate the lean condition I will see? Or do I need a totall map overhaul?

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RadioFlyer

What are your AFR's telling you? Was there a big difference there? If they're still in the same range, then the ECU is compensating correctly, and you have the fuel for it. But if they're off, you should get a retune. 2.5psi is a pretty significant change.

I only have the tuner version, not the shop version of UpRev, and I have a G37. I'm not sure how the software differs, but I haven't seen an elevation compensation table.

TopgunZ

Is Uprev open or closed loop? Will it attempt to compensate for the elevation?

I cant really tell since its only 30 degrees here. My tires break loose every time I get on it to hit boost. Ill probably not be able to until it warms up in like April.

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RadioFlyer

A good way to think of it is:

Open loop fueling is when the car just runs whatever values you have in the fuel and timing tables. Or, it tries to hit those AFR targets and makes corrections based on the knock detection. This is the mode you're in when you're trying to accelerate more than, say, 50% throttle pedal input.

Closed loop fueling is when the car tries to maintain 14.7 in cruising and light throttle applications. This is your daily driving mode where you're cruising in traffic. Barely touching the gas pedal.

One way to see which mode you're in at the time is to log, or monitor with Cipher, the fuel trims. It doesn't apply the fuel trims (that you can monitor in Cipher) in open loop. When you drive in closed loop, the fuel rims are constantly adjusting. So you'll see the fuel trims go from 108%, 95%, 110%, etc. while you're really light on the throttle just maintaining a cruising rpm. Your AFR's will be reading pretty close to 14.7. But when you tip in on the throttle, and the AFR's drop, you'll see the fuel correction go to exactly 100% and stay there as you sweep through the rpm band. That's an indicator that you're in open loop.

My guess is that your car will be able to make the corrections in closed loop to cruise around at 14.7AFR. But when you get on it, you'll probably be lean since it doesn't apply the same amount of corrections to the fueling in open loop. So if you were tuned to be at 11.5AFR at WOT, with 2.5 more psi, you might be seeing 12.5-13.0 on your gauge, and that would be significantly leaner than you were tuned for. Your motor might be able to handle it, but I'd have them adjust the fuel table to keep you where you were tuned. But it could all be monitored by your gauge. If your AFRs are where they used to be, then the ECU is compensating correctly, and you don't have anything to worry about. If they're leaner, then that's what you need to address with an adjustment in the fuel tables.

TopgunZ

Right on. Thanks RadioFlyer.

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Rusty

Another way to look at it. You're in open loop at cold start up. Closed loop in normal driving. Open loop at WOT.

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JWillis72

We have talked about elevation so many times that I recently noticed IPhone has added it to the compass, my car is being tuned at 10' above sea level

Rusty

You have to be careful with some apps with an altimeter. The altimeter is based on a barometer reading. If the barometer goes down. The altimeter will read higher. If the barometer goes up. The altimeter will read lower.

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JWillis72

Interesting, being from Florida we don't really have altitude.


Sent from my iPhone using Tapatalk

Rusty

Your whole state is 1ft above sea level. So......yea!

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TopgunZ

So would it be as simple as just opening my map and adding some sort of fuel percent across the boards? Any advice on how to compensate for my lean condition would be appreciated. I don't want to spend $450 on a tune because I am going to either swap to cog pullies or a different supercharger this summer some time.

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RadioFlyer

I don't know if I'd recommend doing that, but it might work. First, you'd have to see how far off your AFRs are from target. Then you can correct accordingly. The problem with just adding 10% to all the values is that you're probably off by varying degrees, and thus would be way off by varying degrees if you changed all cells by a percentage. But your could try! Just keep an eye on the AFRs.

TopgunZ

What if I just put my stock exhaust back on to reduce the extra air im getting now? Lol. I'm not going to do that but for the sake of argument...would that work?

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RadioFlyer

You could try any number of things. A different pulley would work to bring your boost down too.

Ultimately, you're just watching your AFRs to see if they are in the ballpark of where they used to be. If they're higher (leaner), you're ECU is probably pulling timing, and you should change the tables to fuel for it. That way, you get the proper fuel and all of your timing.

Think of it this way: air, fuel, spark. If you have a good tune, then the three components are working in harmony, and you're making power safely. If you change one of those three components, the other components need to compensate.

In this case, you changed the air component. ...and possibly fuel quality, but we'll ignore that for now. If you give it more air, you'll need to give it more fuel. The ECU might do that for you, AFR's will tell you if it is. If not, you'll need to get in there and change the tables. If the ECU can't adjust to the fuel demand, it will pull timing (the spark component). If you're running more air with the same fuel, this is most likely what's happening. You don't want to be in this scenario. Pulling timing is the ECU's way of keeping your motor safe. If you're normally running around with your timing pulled, then you're decreasing the threshold of *how much more* timing the ECU can pull. In other words, you're getting closer to running out of the protection that the ECU can do for you.

All of this is playing within the boundaries of what the ECU allows. If you get to the edge of what it allows, you'll get a light, and go in to limp mode. Or you will det, the ECU won't catch it, and you'll hurt your motor. This is a possibility in the lower gears where the RPM's sweep through the rev range very quickly.

But back to basics: air, fuel, spark. You can change one and compensate, or you can change your setup to bring the air component back to where it was when you were tuned. That's what you were asking about with the stock exhaust. If you're going this route, I'd say it would be better to change pulleys back to the PSI you were tuned for, and keep the rest of the car as it was. Hope this helps!