Do 24 lb injectors work on a 4.0L stock rebuild too?

[Jonner]

First time post here, hi guys!

I came across this website when I blew the headgasket in my Cherokee (by way of Naxja). I haven't decided if I will attempt to build a stroker or just rebuild the motor to a 4.0L. I know that I would like to purchase new injectors during the rebuild and am putting together a parts list.

Golen's website recommends 24 lb injectors for their 4.6L stroker. Will 24 lb injectors be suitable for a mostly stock 4.0L? The price difference for injectors on fiveomotorsports would be zero between a 24 lb injector and a stock replacement injector. I'm ready to improve my fuel economy but still have the option to purchase parts for a stroker if I choose that route.

Thanks in advance,
Jonna

[SilverXJ]

Why would anyone put injectors on an engine larger than it needs? It doesn't improve anything and just makes the PCM unhappy.

[Cheromaniac]

Will 24 lb injectors be suitable for a mostly stock 4.0L?

No. I used them on my original 4.0 when it already had performance mods (CAI, 62mm TB, header, exhaust, ported head) and it ran rich. I managed to correct it with a homebrew MAP adjuster by lowering the MAP voltage to 4.2v.
I kept the same 24lb injectors for my stroker but I now have the MAP adjuster set at 5.3v.

[6TIME]

I ran 24lb injectors on a 4.0 in closed loop (with O2 sensor functioning) and I didn't notice any problems. It seems like the computer just backed them off a bit. This was with OBD I ECU in a 93'. Could be different in a OBD II setup.....

[sly-jeeper]

stock injectors should work just fine...for fuel economy focus on porting, compression, and tuning after it's together...oh and i would put new filters in the injectors

[6TIME]

If you are planning on any type of modifications to your 4.0, you might as well do 24lbers so you have room to grow. Especially if you go the stroker route..... If you are going to run a stock 4.0 get injectors rated close to the factory specs. I noticed no negative affects on mileage when I ran 24's with the 4.0. The plugs all looked fine, no darkies or signs of a rich condition.... Again this was with the stock OBD1 ECU operating with the O2 sensor just like normal.

[SilverXJ]

The plugs all looked fine, no darkies or signs of a rich condition...

Poor way to determine AFR on an EFI vehicle.

[Jonner]

So 24 lb injectors are not useful on a 4.0L build?

If I did a stroker, it would most likely be a 4.2L. I'm trying to keep my options open as I start gathering parts. Not sure if I'll be able to stroke it or keep it stock, but would like to start shipping items for the project where I know shipping charges will be separate from other purchases.

I will most likely be ordering from Five o motorsports unless I hear alternate suggestions that are worth checking out.

[Burnsmacdonald]

Not all Mopar stock OE injectors are the same.
Some came with 21lb injectors, which should fine in a near-stock build

You need to find out what specs your existing injectors are before you start laying out more cash.

[SilverXJ]

His 97 came with 23.2 lb injectors, so the 703s might work on a 4.2l stroker.

[FlyinRyan]

Run the stock injectors.

[jeepxj3]

The difference between the stock 23.2lb injectors and the 703 24lb injectors is so small, like 3.4% bigger. Can't the ecu just change the short and long term trims to still get the required AFR and 14.7? That doesn't seem like that much to have to adjust and is within the limits and capability of the ecu. It will just have to learn and make the adjustments. In open loop it might be slightly more richer on stock engine than stock injectors. Maybe the improved spray pattern of the 703s outweighs the slight richness.

[SilverXJ]

The difference between the stock 23.2lb injectors and the 703 24lb injectors is so small, like 3.4% bigger. Can't the ecu just change the short and long term trims to still get the required AFR and 14.7?

the step from 4.0 to a 4.2L should be covered by the PCM using stock or 703 injectors

Maybe the improved spray pattern of the 703s outweighs the slight richness.

No. The spray pattern of the 703s do nothing over the stock injectors.

[6TIME]

The plugs all looked fine, no darkies or signs of a rich condition...

Poor way to determine AFR on an EFI vehicle.

I guess I should add more for you.... I was merely stating a fact. My fuel mileage did not suffer and afr was not out of range other than near wot when the flow potential of the injectors is realized. I ran them (blue top 24's)simply to test this theory for my own observations. The wide band also confirmed this..