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EFI Injectors, MAFs and ECU's....

daveSanborn

Active Member
Does anyone have a great link to gain a better understanding of what size/when to change fuel injectors? I'm still using the stock 19lb. injectors on my 347 and have been curious how a step up to 24lb. or 30 lb. injectors would effect the engine. What besides the injectors should also be changed? I assume the MAF? Will the ECU pickup the changes and automatically adjust for the different Air/Fuel delivery rates? Are different spark plugs recommended when changing injectors?

General knowledge like this within a link would be great.

I'd rather not hang around a 5.0 forum to get smart on this subject.....

TIA,
Dave
 
Yes Dave, the injectors must match the mass air flow sensor. I notice you have a stock MAF, so that must be replaced. Some aftermarket MAFs have sample tubes that can be swapped out depending on injector size. Is that a stock throttle body too? Anyway, I don't know what heads and cam you have or the power level you have achieved, but you are most likely above the 19 lb injector. Check out this website with an injector size calculator. For example, 350 HP requires just over 27 lbs, so I'd use a 30 lb injector.

http://www.injector.com/injectorselection.php
 
I agree. My 42lb injectors will allow me to go up to about 550 hp. You have to have a little room for improvement. ;D
 
Is that a stock throttle body too?

The throttle body is a new BBK 70MM unit.

The heads are ported and polished GT-40's.

From my foggy memory, I believe the cam is either a B-303 or E-303. The motor was professionally built by the previous owner and I have the engine build sheet.... somewhere....

So generally speaking, I should focus on upgrading to 30lb. injectors and matching MAF? Will any other components need to be changed? Does the ECU recognize the larger MAF/injectors and make any necessary changes to it's programming?
 
30 lb injectors sound right to me. You only need the injectors and MAF meter. The computer will recognize it (via MAF meter) and give the correct data for the injectors to fire properly. I originally went with a C&L meter because I liked the tubes that can be changed later if you change injectors. My tuner did not have any good things to say about these meters and recommended just about any other one out there over them. I have heard good things about ProM meters though.
 
You only need the injectors and MAF meter

When you say "MAF meter", do you mean the actual housing/tube that the OEM MAF sensor secures to? Or a combination of a larger diameter housing/tube and an aftermarket MAF sensor? In other words, do you use the OEM MAF sensor on a larger diameter housing/tube? Or is the MAF upgrade a combination of two items?

I've been looking at various injectors/MAFs all morning (it's a slow day at the office). One other thing I've noticed and don't understand....

30 lb. injectors are being paired up with anywhere from 70 to 80MM MAFs. Okay, I guess I got this and 76MM seems to be optimum from what I've gathered so far.

And then I see 24 lb. injectors paired up with the same range of MAFs and a comment is made that "the MAF has been calibrated for 24 lb. injectors". How the heck do you "tune" the MAF? It's just a larger dimension tube? Do they mean that the "MAF sensor" has been tuned? I'm confused in this area..... Here's an example of what I'm talking about....

eBay 24lb. Injectors and 75MM MAF


Maybe I'm just confused with some of the terminology being used in a fashion that I'm unfamiliar with.... a MAF Meter would regulate (by it's interior dimension) the amount of air making it to the throttle body. A MAF meter sensor will report to the ECU how much air flow is making it to the throttle body. When used on a larger MAF Meter, why wouldn't the OEM MAF Sensor report the increased airflow through the meter? Why is is necessary to "calibrate" the sensor to the meter?

More learning to do I guess....
 
My understanding of MAf meters is it is the electronics that control it an not really the size itself. The benefit of a larger MAF meter is the amount of air you can run through it. Remember that the system will have restriction at the TB since it is a smaller diameter and will only flow a certain amount of air unless it is force in via blower turbo.

Most MAF meters come pre calibrated and are us consumers are not able to adjust. This creates a potential problem if you want to change injectors again. (i.e. putting that blower on you were looking at this past spring.) The benefit of the C&L system is calibration is easily changed by purchasing a $30 sample tube. Some of the others can be sent back to the factory for reprogramming. My understanding the C&L system would be fine for NA cars but when under boost the signal gets a little funky.

Again I am no expert on this so if I have something wrong someone else please step up and correct me. All my knowledge has come from my own limited experiences and what I have read about.
 
68EFIvert is dead on. What you found on ebay will work, but I would hold out for a 30lb ProM and 30lb injectors. Check on the classifieds at corral.net as they are the 5.0 mega-fieds.
 
Maybe, I'm not familiar with that style MAF meter. It looks to be one for a 4.6 engine. I don't know if it will work with your earlier set-up or if that sensor is compatible with your EEC-IV. Gonna need to do some research on that one. ~???
 
I am running a MAF from a Lightening. In my case I had to use an adapter to connect the MAF to the harness and then later just hardwired in place. I would send a question to the buyer and ask if it would work on an 89-93 Mustang.
 
One last thought I had on this about injector compatibility. EV1 Injectors will fit 86-04 Mustangs except 99-04 Cobra and 03-04 Mach 1. Those models use EV6 injectors. The wiring adapter I referred to about converted a 6 wire MAF into the 4 wire plug we use. If it does have a 6 wire plug it is not a big deal. You can find adapter harness for less than $30.
 
Well, after getting a little bit smarter on the subject, I took the plunge last night and picked up a C&L 73MM MAF with a 30# cal tube and a matching set of 30# injectors.

They'll probably arrive early next week and I should have them installed by next weekend.

Is there anything else I need to do for the EFI system as part of this injector/MAF upgrade? Fuel Pressure? I'm still running a vacuum operated FPR. Is this okay or do I have to run a manually adjusted/set FPR?
 
You should be fine with what you are getting. I am running an adjustable FPR just for tuning reasons. Not needed though. You should see a nice increase in power with the new injectors.
 
i think you'll be just fine Dave, if the maf is matched to the injectors.
back before we had the ability to hack and tune the ecu's, the easiest way to build better breathing and fuel capabilities was to go the "matching" maf and injectors route.
what this did was fool the ecu into thinking you hadn't changed anything.
full range output on a stock maf is 1 to 5 volts.
at 5 volts on a stock maf, this amounts to about 840 kg/hr of air flow.
and stock, most stangs came with 19 lb/hr injectors.
a maf that is "matched" to 38 lb/hr injectors (two x 19) would flow 1680 kg/hr (two x 840) of air at 5 volts.
so the ecu, if seeing let's say, half the range on the maf, will demand half the fuel from the injectors, so the air/fuel ratio stays where it should.
If you were way off on your maf and injectors, the car would run like crap.
Properly hacked, or tuned, you can run any injector/maf combo, so you don't see as much reference to the "matching" requirement.
 
I installed the 30# injectors along with a 73mm C&L MAF (calibrated for the 30# injectors) the weekend before last. The engine seems to have accepted the upgrade without any side effects.

The next upgrade is a set of AFR 185 heads.... one of these days.
 
There was not a dramatic "wow, this a lot quicker" type difference between the 19's and 30's. I'm figuring that the heads are now the limiting factor. I'll keep my eyes and ears out for a "can't refuse" type deal and maybe this Winter change out the heads.
 
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