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What fuel injectors fit the 3.9 motor?

2K views 5 replies 2 participants last post by  ZMAN24250 
#1 ·
Hi all,
I've been wanting to upgrade my crappy stock single port wonders to something that will atomize the fuel better...however, I don't want to pay $60 per injector to the tune of $360+tax for a "performance set" from autozone. Any suggestions? I think I read somewhere that injectors from an F150 will fit these motors, can anyone back that up?
 
#2 ·
I just got done doing the Ford "19lb" injectors and shes tickin along just fine.

I see you have a 99' as well so as long as you get a set of injectors out anything with a ford 4.6 that is a 1999 or earlier then it will directly fit. I got a set off of a 1999 Ford Expodition from pull-a-part and cleaned them up really good with carb cleaner. Then got a set of O-rings for them and they were all set. I think all in I was somewhere around $60 and for a upgrade that you wont see THAT much improvement I think $60 is worth it. Plus I get to wrench on the car a bit :p.
 
#4 · (Edited)
Just thought I'd update about my injector swap. I just filled up on the way home and it turns out I got 16.7 mpg and I was driving a bit aggresive for the first quater of the tank. Now to put that in perspective, thats the highest I have recorded and the highest I have had since the new year is 16.0.

Now what I dont know is whether the weather warm up or the injector swap is what increased the mpgs (Its warmed up from ~20 to ~40 this week), probably a little bit of both.

Edit: I also sea-foamed the intake side along with a full synthetic oil change just before I filled up for the last mpg run.
Also, Ive been running the new injectors for 300+ miles now so the computer has had time to relearn.
 
#6 · (Edited)
Just thought Id update again for any future viewers looking at this thread for research.

I brought a little scientific reinforcements with me this time because ya know, why not? Before I did the swap I did some acceleration pulls while video taping it so I could get a fairly accurate time by counting the amount of frames it took to accelerate through the rpms. Then after the swap and the computer learned the new injectors, I repeated the same tests. I did three runs of each and found their average.

Here are my results:

----Before (seconds)----| After (seconds) |----% Difference

(1st gear; 3k-4k)
1.06 s______________| 1.19s_________| -12%

(2st gear; 2k-3k)
4.51s ______________| 4.42s_________| 2%

(2st gear; 3k-4k)
4.05s ______________| 4.03s_________| 0.5%

What took from that was that the new injectors don't really help with the higher rpms but more of the lower rpm. i.e. where normal driving range is. This might explain why my mpgs are marginally better.

Id like to mention that the data wasn't taken in the exact same conditions and that I did the best that I could do as far as data recording but I decided to run the numbers anyway. I do also believe that there is a very high error % for the first gear pulls but I have no way of proving that without rerunning that test which I don't care to do at this time.

So, would I do it again? Well in my case if you pull used ones from the boneyard and clean them up, I would say meh, why not. For $60 I can wrench on my car on the weekend and get negligible-ly better performance.

Who says you wont use science in the real world?
 
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