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Discussion Starter · #1 ·
I'm in the process of upgrading the MPI kit on my 258 w/ 4.0L head. I'm installing Hesco's enlarged throttle body and adjustable fuel pressure regulator, and I would also like to install some larger injectors. Bennie, (@ Hesco) told me that the largest injectors I should go with are 21 lb. (the stock MPI inj's are 19.7 lb.). I've been told that Ford 5.0L inj's are a direct replacement, but I've been unable to confirm this or find any rated for 21 lbs. Does anyone know where I might find specs on fuel injectors so that I can track down a direct replacement for the stock inj's?

Dean

 

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I don't know about injector swaps, but a good guage for determining what your injectors are doing is the learn function in the pcm. With a scanner, there is a function in the pcm that shows it's learn value. The range is from -40 to +40. If your Jeep requires larger injectors, the values will be in the + side, meaning that the pcm is trying to compensate for a lean condition, and more fuel needs to be delivered. You shouldn't have any values much over a +6 or +7. I am running 4.0 that is stroked to about 4.5l, and my stock injectors are giving me values of -2, but I live at high altitude. Also remember that it takes a couble of days, and over 100 miles of driving to get good learn values.

 
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Discussion Starter · #3 ·
Thanks a bunch. That's some very handy info to have that I wasn't aware of. I'll hold off on the injectors for a while until the pcm gets adjusted and I see how this thing does. I'm very interested in hearing the details of your stroker build up. I've been thinking of doing that with my 86 CJ-7. Was yours a kit or DIY, and about how many HP are you pulling out of the motor now?

Dean

 
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Discussion Starter · #4 ·
I run a 4.0 stroker as well. I use stock replacement 4.0 injectors for 94 XJ, and have no lean condition, or excessive injector duty cycle. Running larger injectors will not give you any more power, unless the engine needs it. Often, running too large of an injector can cause problems, especially whena it is not need..ie:a stock engine. The Ford injectors have a wider spray pattern, and may not attomize as well as the stock units. I did not dyno my engine, but it is significantly more powerfull than a stock 4.0. I have a crane cam, mild head work, 94 XJ PCM, bored throttle body...along with a few other things....I get approx 15-17 MPG in my CJ with 999 non-lockup trans, 35 BFGs and 4.10. DIY is the way to go....use 258 crank and rods in 4.0 block. No special machining necessary to the block, early cranks need slight mods to fit late model damper. 96 blocks with main bearing girdles will need a bit of work to get the girdle to clear the crank


 
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