Guess what meter was used? *STOCK* Yes you can tune the stock meter even if it pegs 5.0 volts, Ive been doing it for awhile now,As soon as my gas pedal hits the floor the meter is pegged.And i can take the A/F's down in the 9's if i wanted. Some may say other wise but theproof is in the pudding i mean time slip... JL

 

I think this statement is wrong. The boost bypass allows the air to bypass the supercharger, but it's still going into the engine. The boost bypass is not venting the air previously measured by the MAF.

 

some info is right some is wrong in this thread. First the bypass recirculates into the system, so the metered air does not escape. Thus it's still metered and accouted for. Even aftermarket systems recirculate the air, unless it is a blow thru MAF and the bypass is before the MAF. If it's before the MAF it can vent air to atmosphere because it has not been metered yet. Once metered, it stays in the system.

Yes, you can tune a car with a pegged MAF. Is it a good idea? No. When the meter is not pegged and the car is tuned properly, the engine is able to take the metered air and calculate VE correctly. So as air density changes (with altitute, season, etc), the vehicle can continue to adjust VE and fuel. Some people chose to tune pegged MAF's in the past because they may have believed that there was not a consistantly reliable alternative. There are other aftermarket MAFs out there, but if you search the internet you will see that the results are not anywhere close to 100% repeatable.

When the MAF pegs, it stops reading air. It believes that you are only flowing the same air that you were when the MAF hit 5V, regardless of actual engine airflow. So what a tuner has to do is find a way to dump more fuel in. This is usually done by commanding a richer air/fuel than actual in the open loop fuel table (SCT calls it Base Fuel Table). When you are on the dyno you just dump more fuel in until that air/fuel ratio on the dyno sheet looks good.

But what happens when you roll off the dyno? Let's say that you tuned the car with it was 90 degrees outside. If you take it for a spin when the air is more dense, what happens? I'll tell you. On a colder day or when the air is more dense, the meter does not know it above 5V. So in the critical area where you are making a lot of power, there will be no additional fuel compensation for the additional air volume. When you have more air and less fuel, that means that it will be leaner. Is it lean enough to do damage? Maybe, maybe not. It all depends on the conditions, and how much timing is in the tune to begin with. Many tuners have made pegged MAF's work because they had no other good choice. But if you look historically at all the eaton powered 03-04 cobras and lightnings that have had engine failures in the past, I bet you would find an intresting pattern for those that had pegging stock MAFs.

That's why it's bad. There are a lot of answers to this problem now. SCT has a MAF sensor that has stock repeatability but the transfer function to handle additional power. There are also several MAF extender devices out there that can work behind the hands of the right tuner.

Brian

 

Interesting Brian! So the MAF basically becomes useless when pegged at 5V and maintaining an acceptable AF just becomes a hit-and-miss game on the Dynojet? Sounds like a lot of guesswork involved....

 

And I used to think the good ole days of changing jets and reading plugs was hard!


Rich

 

Below is some information I've gathered through dealing with various tuning tools in the past. The information is purposely rather vague as to not give out anyone's tips and tricks.

There are quite a few ways to tune around the MAF meter. Some work well for racing applications, others are better for daily drivers.

The best solution is to cure the pegging issue with a properly programmed MAF sensor. Therefore, no matter what the conditions, your PCM is always in control. This can be done with an aftermarket MAF sensor or a an inline device, such as the MAFterburner. Both work great as long as you don't degrade the resolution too much. Some rescale the whole curve, others just scale up top.

Other ways around the issue are having the A/F's dive rich right before the MAF sensor pegs and continue richening through the rest of the rpms. Rescaling the motor to allow for more airflow is another way around it.

In the end, it really doesn't matter how you choose to go about "resolving" the problem. The 1/4 mile, HP/Trq, and longevity of the motor tells the tale.

 

so what about this idea of using a stock maf but cutting the voltage in half and using that to tune?

 

Here is a good article concerning the MAF...

http://www.allfordmustangs.com/Detailed/583.shtml

 

Thanks for the explanation Brian.

 

Hey Johnny ! I wonder how much more power you would make if your Meter wasn't pegging ??? If you had say a MAF extender and the CID, Injectors, and MAF transfer function were dialed in to command the exact A/F the Base Fuel Table commanded. If the EEC was back in control of A/F during launch and shift points wouldn't the truck make more power? I don't think it would make less... I was pegging my Cobra's calibrated 92mm Pro-m right at the top of 1/4 mile so I was diving my A/F to compensate. I am testing a MJChip MAF extender and it works great datalogged some runs no pegging. 4.41 volts at 6700 rpm 20.5lbs boost and this was on the lowest scale (5/6) EEC in total control, A/F was being command as long as my BAP and Pumps kept up the Flow of Fuel.

No doubt your truck is making the power !!! But with available options, I think it would make much more given the EEC stayed in control of the A/F instead of the "work around" tuners are performing.