REQ fuel with stock injectors

[MechRick]

I ran into an interesting issue with my '94 over the weekend. I've slowly been putting it back to stock on the off chance I might sell it and upgrade to a 3/4 or 1 ton. Stock cam went in a couple of months ago (fixed an annoying ping when on the throttle). Swapped out the 24 lb-hr injectors for the wimpy 14's, thinking I could just redo the req fuel worksheet and tweak the ve1 bins a bit.

1st problem is the req fuel worksheet would not accept an injector that small. Kept coming up with an 'req fuel cannot be larger than 25.5' although the 14 lb-hr injectors wanted 35.

2nd problem is I could not add enough wide open throttle fuel to keep it from running lean there. Played with it for quite a while before swapping in the stock ecu (runs fine with it, but I want the MS for a backup).

Anyone run into this? It's a MS1 with extra code controlling the stock tfi.

 

[E4ODnut]

I use 6 squirts alternating, 9.2 ms req-fuel, stock injectors. Idles smooth down to about 450 RPM, no problem with WOT mix, but I never go above 3000 RPM.

 

[MechRick]

After reading your post I went back in to the extra manual, and I think the problem arises from the number of squirts I was using. I'll try it again with 6 and see what happens. Thanks for the heads up...

 

[E4ODnut]

I experimented with 6 alt and 2 alt. I had idle problems with 2. I didn't try sim because I didn't want fuel pressure pulsations. I think if you run the calculator it will suggest about 12.7 or so if I recall. The exact number isn't critical as long as your idle PWs aren't too short and duty cycle at full speed and load is about 80% or less.

I'm pretty sure the Ford strategy is 2 alt, don't know why it didn't work for me.

Let me know how you make out.

 

[MechRick]

Do you fudge the injector flow number to account for the fuel pressure difference?

I've been entering 21 lb-hr (40 to 60 psi = 50% increase, 14 lb-hr x 50% = 21 lb-hr).

 

[E4ODnut]

I'm not sure what you are talking about.

I'm using the stock fuel pump and pressure regulator. The regulator is strictly mechanical and is supposed to keep a constant pressure drop across the injectors at any manifold pressure. I doubt that it is perfect, but probably close enough to keep the errors within a reasonable range.

The actual flow rates of the injectors will vary from the published specs somewhat, but it's no problem to tune around it. The numbers are really only a starting point, from then you just tune to what the engine wants.