Injector compatibility
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Trailering
Joined: Dec 2023
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Injector compatibility
Hey everyone, I have a 94 F-250 with a rebuilt 351. Truck has speed density system & new custom true dual pipes coming off longtube headers with stock location O2 sensors. Comp cams Ford EFI grind, PROMAXX aluminum heads, stock bottom end, scorpion roller rockers. I am and have been for a while convinced my injectors have been limiting my power due to the fact the truck doesn't rev much past 4,000 rpm. Everything seems fine no misfire just kind of doesn't climb far past that like its being heldback due to a lack of fuel or air.
I am using stock mapping on stock computer with stock 19lb injectors. I would like to get bigger injectors but I am not sure if the computer will compensate for the increase. What size injectors could I use to get the this SBF more fuel.
I am using stock mapping on stock computer with stock 19lb injectors. I would like to get bigger injectors but I am not sure if the computer will compensate for the increase. What size injectors could I use to get the this SBF more fuel.
Hotshot
Joined: Jun 2015
Posts: 12,781
Likes: 2,422
Hey everyone, I have a 94 F-250 with a rebuilt 351. Truck has speed density system & new custom true dual pipes coming off longtube headers with stock location O2 sensors. Comp cams Ford EFI grind…. I am and have been for a while convinced my injectors have been limiting my power….I am using stock mapping on stock computer with stock 19lb injectors. I would like to get bigger injectors but I am not sure if the computer will compensate for the increase. What size injectors could I use to get the this SBF more fuel.
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Trailering
Joined: Dec 2023
Posts: 18
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Oxygen sensors in more than one? The factory EFI system on has one sensor so I’m not sure how you have more than one oxygen sensor. What is an “EFI grind”? What camshaft did you install? It is possible that might have a fuel problem. What fuel pressure do you have with the vacuum hose connected and with it disconnected and plugged? You are correct in that the computer is programmed to work with 19# injectors. The computer has no way to know that you installed larger injectors.
COMP Cams Xtreme Energy Camshafts
CCA-35-349-8
Fuel pressure is consistently in the 30’s stock regulator appears to be fine. Havent tested it since last year; I just remember it was operating as it should. New fuel pumps work fine. Just wondering if it’s worth investing money in larger injectors without tuning this engine.
Hotshot
Joined: Jun 2015
Posts: 12,781
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You’re right one O2 sensor. Comp cams makes a shaft specifically designed for use with small block ford EFI systems.
COMP Cams Xtreme Energy Camshafts
CCA-35-349-8
Fuel pressure is consistently in the 30’s stock regulator appears to be fine. Havent tested it since last year; I just remember it was operating as it should. New fuel pumps work fine. Just wondering if it’s worth investing money in larger injectors without tuning this engine.
COMP Cams Xtreme Energy Camshafts
CCA-35-349-8
Fuel pressure is consistently in the 30’s stock regulator appears to be fine. Havent tested it since last year; I just remember it was operating as it should. New fuel pumps work fine. Just wondering if it’s worth investing money in larger injectors without tuning this engine.
I already answered the last part…
meaning you cannot simply change the injectors and expect the computer to adjust without tuning.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
To know(instead of guessing) how well your truck is doing in terms of supplying the correct quantity of fuel you should add a wideband O2 sensor and an electric fuel pressure gauge, those will come in handy with tuning anyway.
The 4000rpm shift point is part of the factory programing since that was where peak HP occured with a stock motor, but your motor may also run into intake airflow restrictions sooner or later, the lower portion will be where the bottleneck first occurs. There are options to address that, you could have the whole thing ported... Bigdogs porting is one place that seems to specialize in Fords, the other option of course would be to replace the whole intake.
Logistics Pro
Joined: Aug 2014
Posts: 3,551
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Trending Topics
Logistics Pro
Joined: Aug 2014
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If you still have Napa distributor, junk it and put the factory back in.
as in your other post, this appears to be more of a mechanical issue rather than efi issue.
your Napa distributor probably isn’t advancing correctly if at all.
id recheck cam timing.
did you degree the cam? Is it what it is supposed to be?
as in your other post, this appears to be more of a mechanical issue rather than efi issue.
your Napa distributor probably isn’t advancing correctly if at all.
id recheck cam timing.
did you degree the cam? Is it what it is supposed to be?
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Hotshot
Joined: Jun 2015
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I didn’t know there was another thread 🤔
OP must be editing that thread because post #1 states “Aftermarket aluminum heads (promaxx 9175)”
OP must be editing that thread because post #1 states “Aftermarket aluminum heads (promaxx 9175)”
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Trailering
Joined: Dec 2023
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cams installed straight up. stock intake. i dont want to spend money on an ecm and tuning. If it is a fuel restriction, im under the impression the larger injectors would increase fuel regardless of tune. The computer has no way of knowing the injectors are larger but between the speed density system and O2 sensors it should balance AF ratio. This is may not produce peak power but if my stock 19s are maxed at full cycle the increase in fuel per pulse would certainly help (if the problem is indeed a fuel restriction).
Of course the issue could be something else but everything I’ve tried over the last year has brought me back to AF. So perhaps the only answer is to tune but i need to buy injectors either way so I may as well try swapping them first and see how it goes.
Of course could be the intake limiting me. Idk anyone who tunes professionally or if there is an ecm i can tune myself having no experience. In order to tune I’d need to purchase an intake, injectors, and an ecm at least.
Of course the issue could be something else but everything I’ve tried over the last year has brought me back to AF. So perhaps the only answer is to tune but i need to buy injectors either way so I may as well try swapping them first and see how it goes.
Of course could be the intake limiting me. Idk anyone who tunes professionally or if there is an ecm i can tune myself having no experience. In order to tune I’d need to purchase an intake, injectors, and an ecm at least.
Cargo Master
Joined: Mar 2007
Posts: 2,784
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I know my 95 5.8 w/stock injectors does not run out after 4,000 rpm, even with 8psi boost.
If you don't have a wideband, I really suggest you get one. With that sensor, it proves what you are thinking. I have resolved a lot of stock issues with the stock Ford programming with a wideband.
If you don't have a wideband, I really suggest you get one. With that sensor, it proves what you are thinking. I have resolved a lot of stock issues with the stock Ford programming with a wideband.
Lead Driver
Joined: Jan 2019
Posts: 5,066
Likes: 863
From: N.W. Alabama
Adjustable fuel pressure gauge, can fix some lean issues, you could try mustange 21lb injectors, and increasing fuel pressure, but if you look at A/F you will know what to do instead of going down 3 different rabbit holes expecting a different answer, you could find a 7.5L ECM with E4OD, and install 24lb injectors, that run the 7.5L, a couple of members have done that successfully, my 95 will roast the 31's off from a stand still, still using the 19's, and 36-38lb of fuel pressure, with procomp heads(2.02 in)and pulls hard til about 4100-4300 rpm then just looses it, all done.
Logistics Pro
Joined: Aug 2014
Posts: 3,551
Likes: 848
cams installed straight up. stock intake. i dont want to spend money on an ecm and tuning. If it is a fuel restriction, im under the impression the larger injectors would increase fuel regardless of tune. The computer has no way of knowing the injectors are larger but between the speed density system and O2 sensors it should balance AF ratio. This is may not produce peak power but if my stock 19s are maxed at full cycle the increase in fuel per pulse would certainly help (if the problem is indeed a fuel restriction).
What is your AF?
All you need is an ECM and or a piggy back.
Pimpx $$$$$$
Moates Quarterhorse $