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post #1 of (permalink) Old 09-17-2002, 01:39 PM
mindbender
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Mustang injectors in a 4.0/4.2

Sometime ago, I read a thread on the Cherokee BBS about the use of Mustang injectors in a 258. With major modifications to the 4.0 head and with a slightly greater lift cam, I want to be prepared to upgrade my injectors if I get too much pinging. Assuming it will start. I have seen several wrecked Mustangs in the junk yards that have injectors.

Will Mustang injectors work in a 4.0 head? If so, 6 or 8 cylinder?I understand that an adjustable fuel pressure gauge is first step, maybe some modification to timing/however setting electronic timing really just means reclocking the camshaft, or increasing the size of injectors.

I assume there is some similarity in logic about carbs that also applies to injectors. That is the injectors are controlled by the computer and therefore the computer sets the length of time the injector is pumping fuel in the intake. To need to increase the size of the injector would mean that the injector size puts a limit on the amount of fuel that can be injected during some maximum time frame established by the computer. I assume that this problem should really just happen at higher RPMs when the demand on the cylinder exceeds what the computer is programmed to do and what the injector can do when maxed out. If this logic is true, I don't understand how changing injectors will do anything, unless the pinging is at high RPMs.

Also, I have the same questions about the adjustable fuel pressure. I can understand that this could be a problem, if the fuel pressure is not delivering enough fuel to the injectors. However, I thought the computer could adjust for this shortage by increasing time for injectors...up to a point. If the pressure gauge is bad, I can understand it creating a pinging at a lower RPM, but if one is using the stock pressure gauge, then the computer should adjust for greater need, unless it is at higher RPMs.

I am back to the issue of timing when it pings at lower or mid RPMs?


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post #2 of (permalink) Old 09-17-2002, 02:21 PM
 
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Re: Mustang injectors in a 4.0/4.2

Yes, the injectors will work in a 4.0L, but they have to be the yellow-top injectors from a 5.0L V-8. They're a direct fit, but they flow more and have a wider spray pattern. The other stuff I don't remember a lot really, in my MJ I used the injectors and built myself an adjustable MAP sensor to change the fuel flow.
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post #3 of (permalink) Old 09-17-2002, 03:24 PM
 
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Re: Mustang injectors in a 4.0/4.2

If you use a 4.0 HO head, you'll need the 24# Mustang injectors which I believe have blue tops. If you use a non-HO head, use the 19# injectors which have an orange top.
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post #4 of (permalink) Old 09-17-2002, 03:28 PM
 
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Re: Mustang injectors in a 4.0/4.2

A few thoughts on the subject:

How are you going to compensate for the presumably increased fuel flow accross the board with these larger injector? They will flow more at idle, cold start, fast idle, open loop, wide open throttle, etc. Where's the tuning? I question the wisdom of tinkering with fuel pressure, as that's doing the same thing, increasing the fuel flow under all conditions, not just where you want it. If you really want to compensate on a speed density system for modifications that improve the volumetric efficiency of the engine, you need to be able to reprogram the computer to deliver more fuel, ie longer pulse lenghts, to the injectors, under the conditions requiring more fuel. The other stuff like altering temperature sensors, fuel pressure, etc is imprecise and alters fuel flow across the board. That's fine if you are tuning it for only one condition, wide open throttle, but I doubt that is the case.

Bigger injectors are needed if the duty cycle of the injectors under peak fuel flow is too high. They should be open no more than about 80% at wot.

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post #5 of (permalink) Old 09-18-2002, 10:20 AM
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Re: Mustang injectors in a 4.0/4.2

The system will always try and maintain a proper fuel mixture. If you have a cam that takes a bigger gulp of air the system will add the appropriate pulse/durations to compensate. The system should be somewhat numb to mods and merely respond to symptomatic conditions created by the mod.

Based on that (..that is, that regardless of the injector rating, it is cycled in either frequency or duration of pulses -or both) the electronics must be indifferent to what size injector is installed. If it were not so ...you would be running at one fuel flow at a given rpm regardless of throttle position. So you don't "get increased fuel flow across the board" ....you only get increased fuel flow "capacity" across the board.

This is much like an enlarged throttle body installation IMHO. It does nothing until you've reached a state that exceeds the flow capacity of the stock unit ....which is typically near or at WOT. I think in a totally stock set up there would be little noticable difference between one size injector or the other ..BUT given the use of larger tires and daily driving (WOT onramp assaults, etc.) you could see REAL performance improvements over the stock units within the limits of those "exceed the supply" conditions -where bigger is truly better. Most here go on an "exceed the need" basis for mods. So if the costs are basically the same, or don't radically alter the numbers, the larger injector installation would be wise for those "fringe" events
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post #6 of (permalink) Old 09-18-2002, 01:54 PM
 
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Re: Mustang injectors in a 4.0/4.2

Lots of people on the Mid Sized board have upgraded to Mustang injectors. Do a search there and you'll find posts that indicate noticable power increases across most RPM ranges, not just in the top end. Remember, 4.0s are tuned lean to begin with.
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post #7 of (permalink) Old 09-18-2002, 02:19 PM
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Re: Mustang injectors in a 4.0/4.2

heres another smalll note.. the OBDII 4.0's use a 22# injector already and it plugs right in... even for my stroker I didnt change injectors...
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post #8 of (permalink) Old 09-18-2002, 02:59 PM
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Re: Mustang injectors in a 4.0/4.2

There is a guy who i would call "EFI Guru", you should ask him....
Go to http://www.customefis.com/ and ask him...
Good luck
post #9 of (permalink) Old 09-18-2002, 08:29 PM
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Re: Mustang injectors in a 4.0/4.2

Mindbender~ I did a search on the Mid-size board and only found 2 articles. One reported a gain of 2-4 mile per gallon. This sounds good to me so if you find out anything else I would be interested and also where do you plan to get the injectors and what year 5.0?
post #10 of (permalink) Old 09-18-2002, 11:24 PM
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Re: Mustang injectors in a 4.0/4.2

Since the computer is monitoring the air/fuel ratio the increased size of the injector, and flow, causes the computer to shorten the open time. Gain = 0. Same AFR.

The claims that it's increased mileage are more than likely perception. When you "think" it does something, it does. The placebo effect.

It's akin to being on a diet of 1000 calories. Serving it on a larger plate doesn't give you any more food.

The best thing, giving the most performance, is getting the injectors matched for flow rate. Then all cylinders get the right amount, rather than some too lean and some too rich. The O2 sensor only "sees" the average. See a speed shop to find out who does it locally. They swap around some of theirs with some of yours to get a matched set. The flow rate itself doesn't matter much (in a closed loop,) as long as they are all the same.


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