fuel injector ?

I have an 87 4.0. The 4th injector is leaking, now my question I have a 94 that I am going to get parts from will the fuel ijectors fit? With no trouble? They are about a year of so old. Thanks

yes the injectors will fit in your 87 Renix fuel rail, keep in mind that the fuel injectors from the 94 are rated at 21 lbs/hr. vs the stock 87 Renix injectors which are rated at 18.6 lbs/hr. that translates into: more gas consumption obviously. how many mods do you have? like: freeflow exhaust, air intake, etc.? the reason i ask is, the H.O. injectors might be a little heavey for a stock 4.0. hope this helps you out.


P.S. we are talking about a 94 4.0, right?

yeah no mods just a k&n air filter. got any recomedations?

for mods: well, if you don't wanna go into the internals, then i would suggest a nice freeflow exhaust (like a catback) and maybe a cone filter (if you have a drop in one currently), a bored out throttle body and spacer. the cone filter and exhaust should even out your rig pretty good for the bigger injectors. there's a guy on Ebay who sells bored out throttle bodies for Renix 4.0's, but i can't think of his name right now. also, i would recomend putting new plugs in after the bigger injectors, if yours have a little age on them. those are the most basic mods that you could do to your 87.

jk333 said:

yes the injectors will fit in your 87 Renix fuel rail, keep in mind that the fuel injectors from the 94 are rated at 21 lbs/hr. vs the stock 87 Renix injectors which are rated at 18.6 lbs/hr. that translates into: more gas consumption obviously. how many mods do you have? like: freeflow exhaust, air intake, etc.? the reason i ask is, the H.O. injectors might be a little heavey for a stock 4.0. hope this helps you out.


P.S. we are talking about a 94 4.0, right?

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Correct - but since the difference is nominal, the RENIX ECU should be able to adapt by shortening the injector "trigger" pulses to tune fuel flow. That's what the oxygen sensor is there for...

5-90 said:

Correct - but since the difference is nominal, the RENIX ECU should be able to adapt by shortening the injector "trigger" pulses to tune fuel flow. That's what the oxygen sensor is there for...

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hmmm, that's news to me. good to know though. :spin1: i was told that, in order for bigger injectors, you should have some performance mods.

jk333 said:

hmmm, that's news to me. good to know though. :spin1:

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That's the difference between "open loop" and "closed loop" operation of fuel injection - in "closed loop," the HEGO input is used to "trim" fuel delivery to get as close to stoichiometric combustion as possible (~14.65-14.7:1 AFR.)

The system will be in "open loop" mode during warmup (about two to five minutes) and at WOT ("best power" mix is around 12.5-13.0:1,) and "closed loop" at all other times.

That was what Rochester was trying to do with the old "Feedback" carburettors (I remember those things...) when they added the HEGO in the late 1970's. Bosch invented the thing - but they used it to help with their fuel injection. Early systems were mechanical, but EFI came around shortly after there was a way to monitor the AFR.

Granted, if you go too far from the stock spec, the ECU won't be able to keep up - even though it will try. However, we're looking at a change of ~10%, so the system should be just fine.

cool so in other words no big deal. no swaping intake exhaust heads and such. Really I'm just to cheap to spend $ on injectors there like 70 or 80 bucks a piece.just want to get it fixed by winter. and free donor even better I'll steal as much as I can and scrap it.

jimmyc751 said:

cool so in other words no big deal. no swaping intake exhaust heads and such. Really I'm just to cheap to spend $ on injectors there like 70 or 80 bucks a piece.just want to get it fixed by winter. and free donor even better I'll steal as much as I can and scrap it.

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that's right you've got a cheap fix. :yelclap: