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Originally posted by Chico Stang:
When changing the fuel injectors on a 1999 Mustang GT, do you have to change or recaliber the computer? Or is all I have to do is buy a MAF calibrated for 24lb injectors? Thank you very much, just wondering once I buy the MAF and 24 lb injectors if I have to do anything else.

Josh

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I heard back in '99 that you don't need to calibrate the MAF on a returnless system NA car. Sorry I'm not much help

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Originally posted by Andrew WOT:
Calibrated for injectors MAF is just a band aid and is not the right way to do it. You need to make changes to transfer function in your PCM via chip or computer reflash. Here some details on how all that schit works
http://www.mustangworks.com/articles/electronics/InductionBlues.html

And if you're staying NA there is no need for bigger injectors for your power level.

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Originally posted by Andrew WOT:
And if you're staying NA there is no need for bigger injectors for your power level.

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Originally posted by Chico Stang:

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Originally posted by Andrew WOT:
And if you're staying NA there is no need for bigger injectors for your power level.

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I am staying NA, but how do you even know what my power level is with my car?

Josh

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Originally posted by Andrew WOT:
Calibrated for injectors MAF is just a band aid and is not the right way to do it. You need to make changes to transfer function in your PCM via chip or computer reflash. Here some details on how all that schit works
http://www.mustangworks.com/articles/electronics/InductionBlues.html

And if you're staying NA there is no need for bigger injectors for your power level.

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Read your "link" agian!!..You dont have to recalibrate your computer with aftermarket MAF's...One good point in that link is how most aftermarket MAF's are not that well calibrated..
(I went through 3 Pro-M's)

Like I said before...."All you need is a calibrated MAF to go with your injectors"..Just to answer your original question...


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-SLOWER TRAFFIC KEEP RIGHT-

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Q:

What's wrong with running large injectors and a "calibrated" MAF sensor? I'm running 36lb injectors and 36lb MAF. The car doesn't idle very well and part-throttle performance is down. Why?

A:

A little background:

The ECU is constantly making decisions about how and when to fire the fuel injectors. One of the parameters calculated is "injector duration" or in layman's terms, "how long should I open this injector?". The largest factor contributing to injector duration is the amount of air flowing into the engine. The MAF sensor is responsible for measuring this air. The ECU reads the MAF, calculates injector duration based on the MAF voltage, then fires the injector for the proper length of time.

The aftermarket parts industry found a way to "trick" the ECU into metering the "right" amount of fuel for a particular type of injector. The way they accomplish this is to modify the MAF to report a different amount of air so that the ECU calculates a different injector pulse width. For example, let's say your factory ECU is programmed for 19lb injectors and a factory MAF. You want to run 36lb injectors; twice as large as stock. The solution is to modify the MAF so that it "lies" to the ECU and reports exactly 1/2 the amount of air than what is actually flowing into the engine. The ECU will calculate an injector pulse width 1/2 as long as "stock" and your 36lb injectors will deliver the "correct" amount of fuel. Neat trick....for the most part.

The biggest complaints with this kind of combination is poor idle and sluggish part-throttle response.

Here's why these side effects occur:

1. Poor Idle

Most factory ECUs are programmed to account for a phenomenon called "Injector Slope". A 19lb fuel injector behaves like a 26lb fuel injector at very short durations (at idle). This is called "Injector Slope" and is a characteristic of the size, brand, and model of injector. If you install 36lb injectors and a "calibrated" MAF, the ECU will still be making assumptions about larger flow at idle based on "Slope". 36lb injectors flow like 36lb injectors at idle, but due to the "factory" programming inside the ECU, they will be handled like 49lb injectors . The resulting injector duration at idle is not correct and this will effect idle quality.

The larger the injector, the harder it is to meter small amounts of fuel at idle. It's a bit like trying to fill a water glass with a fire hose without getting the floor wet; difficult but it can be done with careful control of the flow and some attention to detail.

By programming the ECU with the proper slope, proper injector size, and proper MAF curve, the chances for good idle greatly improve. By further fine-tuning the idle mixture in the ECU, good idle will result even with extremely large (70-80lb/hr) injectors.

2. Sluggish part-throttle

Remember how the ECU calculates injector pulse width based on the MAFS input? Well, that's not all it calculates. It also calculates engine load. "Load" is a value used throughout the EEC's programming to determine timing and fuel needs of the engine under different amounts of load. If a "calibrated" MAF under-reports the amount of air entering the engine, the corresponding calculations will skew the load tables in the ECU. ALMOST EVERY POWER-ORIENTED TABLE IN THE ECU IS BASED ON ENGINE LOAD! The larger the MAF "calibration" the worse this problem becomes. A 36lb MAF on a processor intended for a 19lb MAF will cause almost over 90% error in the load computation.

The reason these symptoms are largely eliminated at wide-open throttle is because beyond a certain point, the engine reaches "full timing advance" regardless of load. The problems tend to occur more at part throttle.

These load errors are eliminated as soon as the ECU is reprogrammed for the proper injector size, slope, and MAF curve. Part-throttle performance suddenly wakes up and the car runs like it never has before. This is extremely common.

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Originally posted by Black94 5.0:
-----Andrew WOT: You are right about having your ECC tuned being more accurate than buying an "after-market" MAF....A lot of people have problems when they first get their "Pro-M's" or "C&L's"(Including me)....For the most part, most people can gain up to .1-.3 tenths in the 1/4 with just a MAF change....I've driven a lot of mostly stock and modified 5.0's & 4.6's that have had a stock MAF and switched to a Pro-M or C&L...I noticed a LOT of difference and Its been proven many times at the track and on the dyno...I gained .3 and 2mph in the 1/4 with my '94 with just by adding a 75mm Pro-m...

How much do you think it is to get your ECC tuned?...Isnt it like $300. just for the chip?...Then you have to pay for the tune and the dyno runs on top of that!!....Most "do-it-yourself'ers" dont have the money or the time to get a dyno tune...Its much more easier to just buy a MAF and have it shipped to your house and just bolt it right on....

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