TropicGreen03GT

I have an 03 GT and want to swap from the stock 21.5# injectos to 24#. What do I have to do to make everyhting work together? THIS IS THE BIG QUESTION. Do I need to have my computer reflashed or will just a 24#/hr calibrated MAF (from a 6 pin Cobra or Mach I) and the injectors do the trick? Do I need to get a fuel managementunit from PROM or MSD to control the injectors, rather than a computer flash. Will a hand held unit do the trick. I pose this question because I have the following on the car which causedit to trip the "SES (service engine soon)" light and my OBD II said it was running lean (ie too hot with not enough fuel). What is on the car:BBK CAI, 85mm C&L MAF, 70mm BBK TB, BBK Plenum, Typhoon Manifold. Would also possibly need headers to help the car breathe better? I am looking for advice from anyone who has similar problems/setup.

Please no responses withSPECUALTIONS on what will not work or saying my partsare crapunless the have used them and found them to not work. I am looking for tried and true answers or the direction of a shop/company that can answer these questions.

Thanks, Jonathan

Shawn02GT

why did you get the C&L MAF?

did you get a tune after the larger MAF?

Obsequious1

I'm pretty sure you have to tune your car to a larger MAF. My 03 came with a intake air temp sensor in my MAF. Some older mustangs came with the sensor mounted on the intake tube. My 90mm maf didn't come w/ the sensor built in so I had to order one to mount on my intake tube. I had my car dyno tuned with the 90 maf before I bought the sensor and it still set off the CEL. Code PO113 intake air temp. charge too hot. That screwed up the air/fuel ratio until my sensor arived. And believe it or not, once I put the sensor on and corrected the air/fuel I gained 30 more hp. Thats how bad having a incorrect air/fuel screwed my car up. I think you need a good dyno tune..

03GTVert

Unless there's something wrong with your stock injectors, you're nowhere near maxing them out if you're not running any kind of power adder like N2O or a S/C.

If you didn't get your car tuned or the chip re-flashed when you put the MAF on it, that would definitely cause problems.

tbirdscwd

+1, you need a tune for the larger MAF. That is almost certainly why you are running lean. You can run larger injectors, but there is really no use since you are nowhere near maxing out the 19s. You need to have your car tuned for the MAF or else you will continue to have the CEL and having ****ty overall performance. Basically, your engine is ingesting more air than it "thinks" it is, and is not injecting enough fuel.

lizzyfan

But the stock MAF and injectors back on!

TropicGreen03GT

The C&L came as recommendation. In fact it worked incredibly well the first 100 miles before tripping the CEL. The car acceleratedmore quickly through the first two gears and made the most noticeable gains of allbolt ons. Since then the C&L was removed, stock MAF went back in and the car has been put away for the winter here in Ohio.

No I didn't get it tuned. I wanted to hold off in the assumption I would do heads and then tune it at one time, but if all of these parts would make it deem able for a dyno session, then that is part of my answer.

In my readings I understand I don't necessarily need bigger injectors b/c stock FP is 39-40psi andwith a 21.5# injector w/ a DS of 90% (BSFC of 0.52) I should be able to handle 271 hp at the motor. (That is withthe DS at max flow and a returnless fuel system as found on 99 and newer models.) Now that I have added the larger MAF, TB &Plenum and this is a returnless system with out the ability to adjust fuel pressure (unlike 96-98 GT models) and I am flowing more air in essence I should have exceeded the hp of 271at the motor right? Is this what constitutes the tune b/c I have screwed up the A/F by adding so much more air and I am maxing out my injectors. I cannot add a FMU to correct this so bigger injectors right?

As for the chip re-flash how would that work? Does a company burn anew fuel map into the chip and it is uploaded to the car's computer? Or don't the new cars constantly adjust the A/F ratio as they are driven.

I am not trying with this to act like I am super smart, this is all of the math I have gotten from the web to calculate power and injectors needed. S/Cing is way off for my app., for now, but will be something to consider in the next few years.

Thanks so far guys and/or gals.

TropicGreen03GT

Sorry, I meant to say DC for duty cycle not DS. AlsoI have a Pro Prod fuel rail system and Bosch Pt spark plugs I am looking to put on the car. The car has 36K. What is the max hp for use with 21.5 # injectors, not 19s? I have pink tops.

(Engine hp*BSFC) / (Cylinders*DC)= estimated injector size

so... 260(stock) * 0.50 (according to most websites)=130.0
now divided by 8 cylinders * DC of 0.80(practical maximum injector flow rate) = 130.0/6.4 = 20.3125 for the injector size. This is from http://www.msdignition.com/pdf/fmc.pdf page 3.

So stock andbackcalculating, I can handle 275.2 hp on the motor. Aren't all these mods together greater than 15.2 hp to the motor. Also what if I add Saleen UDPs?

03GTVert

No, you need the tune because the computer thinks it still has a 75mm MAF and it has an 85mm MAF on it. The 85mm MAF may not have gotten you any more power and still may not even after a tune. The problem isn't that it's flowing better, it's that the computer is basing it's decisions on the amount of fuel to send on the incorrect assumption that it still has a 75mm MAF. You don't really even need a "tune" per se. You just need to tell the computer that you have a different MAF so that it can map it properly and give the right amount of fuel. Getting a SCT X3 programmer would probably help out quite a bit and be a lot cheaper than a dyno tune... where you'd have to buy the SCT or diablo or a chip anyway.

03GTVert

Under drive pulleys don't increase power, they just free up power that's being used to spin the accessories. As for the injectors, I have yet to have heard of anyone needing bigger injectors without a power adder of some kind or at least considerable head/cam work.