24# injectors on nearly stock 4.0

oldseddie

NAXJA Forum User
Location
Fairview, NC
Has anyone tried running 24# injectors on a stock 4.0?
I have a 91 MJ and it has around 140,000 on original injectors. I have freed up the exhaust and intake a little but otherwise it is stock for now. It feels like it is running a little lean at WOT. I plan on building a proper long rod, stock compression stroker in the near future.
 
oldseddie said:
Has anyone tried running 24# injectors on a stock 4.0?
I have a 91 MJ and it has around 140,000 on original injectors. I have freed up the exhaust and intake a little but otherwise it is stock for now. It feels like it is running a little lean at WOT. I plan on building a proper long rod, stock compression stroker in the near future.
If your gonna build the stroker real soon, go for it, youll need them anyways. You probably wont feel a difference with the stock motor. I think that your stock injectors are 21 lb/hr, so 24 isnt taht far off, the only thing i would suggest is clean them before you install them. if theyre used. :sunshine:
 
These are reconditioned injectors so they should be like new. I just want to iron out the fuel, ignition, and exhaust before I drop a stroker in there so I don't damage the new motor. I'm sure others have done so as I have made that mistake myself on other projects. I heard that the cpu will adjust for the richer injectors and wanted reassurance that it wasn't going to be undriveable.
 
You're likely to run into trouble with running rich (OEM injectors run 19-21#/hour,) and I don't know if the ECU will be able to compensate for the higher flow rate - at least, not without throwing a code. It's worth a shot - and, as has been said, you're going to want them for your stroker engine anyhow.

However, don't waste your time dialling things in on the stocker - you'll have to do it all over again on the stroker. Get the injectors, and just leave them in the box until you do your stroker - it's less work in the long run.
 
Well I decided to put them in anyway. I made sure that the ECM was drained and after a couple of days of relearning, she is running better than ever. I do intend to do the MAP sensor adjustor as soon as the parts arriver from Mouser.com. I'm, sure there is some merit to having adjustability. It has always had a flat spot above 3500rpm but not anymore!
 
well it will only run rich and throw a code if the jeep cant pull enough air in to even it out right?

Im running an AFE intake and 99+ intake on my jeep. they way I under stood it was that as long as the jeep can compensate with the air intake it would calculate and do fine. I know the combustion chamber is still the same bore but wouldnt it be sufficiant.



im kinda talkin out my ass as i dont know much about motors but I thought this was kinda how it worked
 
im kinda talkin out my ass as i dont know much about motors but I thought this was kinda how it worked


yes, you are kinda talking out your ass.

the jeep does not know a lot about what is happening. It knows the amount of vacuum in the manifold, it knows the temperature of the motor, and it knows the amount of o2 leaving the motor. That is about it, everything else is secondary or derived from calculations based on those numbers. And everything from the OAT to the temp of the fuel, to the cleanliness of the combustion chamber can have an effect on how the motor runs.

I was with 5-90 on getting them and leaving them out till you have the stroker. But, since you put them in already, do what you can to get them running correctly. Mainly getting that map sensor in and tuned correctly. I had LT1 25lbers in my stroker and it ran rich until I got the voltage adjusted out correctly. If you have access to a wideband you would be set on dialing it in. If not I would tune as well as you can, then start looking at the exhaust tip and pull spark plugs to see how they look, those can tell you a lot.
 
With the 97+ model year the 4.0 got 23.8# injectors and distributorless ignition, I believe the 96 model year was the start of OBDII. The stock fuel / ignition can be used up to (I think) about 260 horsepower, after that injectors are needed, around 300 and the ignition holds you back some. Good luck getting 300 out of a 4.x without FI
didn't the XJ's have like a 23.8# injector stock one year? I think thats whats in my 98.
 
From Dino's site.

Model Year, ...Part #, ......Colour, .....Fuel Pressure, ...Static Flow,
'87-'90, ........53003956, ...Black, ........39psi, .................18.6lb/hr
'91-'93, ........33007127, ...Brown, .......39psi, .................21.0lb/hr
'94-'95, ........53030343, ...Tan, ...........39psi, .................21.0lb/hr
'96-'99, ........53030778, ...Grey, .........49psi, .................23.2lb/hr
'00-'01, ........04854181, ...Blue tip, .....49psi, .................22.5lb/hr
 
yes, you are kinda talking out your ass.

the jeep does not know a lot about what is happening. It knows the amount of vacuum in the manifold, it knows the temperature of the motor, and it knows the amount of o2 leaving the motor. That is about it, everything else is secondary or derived from calculations based on those numbers. And everything from the OAT to the temp of the fuel, to the cleanliness of the combustion chamber can have an effect on how the motor runs.

I was with 5-90 on getting them and leaving them out till you have the stroker. But, since you put them in already, do what you can to get them running correctly. Mainly getting that map sensor in and tuned correctly. I had LT1 25lbers in my stroker and it ran rich until I got the voltage adjusted out correctly. If you have access to a wideband you would be set on dialing it in. If not I would tune as well as you can, then start looking at the exhaust tip and pull spark plugs to see how they look, those can tell you a lot.


I havent put them in yet. but according to this:

From Dino's site.

Model Year, ...Part #, ......Colour, .....Fuel Pressure, ...Static Flow,
'87-'90, ........53003956, ...Black, ........39psi, .................18.6lb/hr
'91-'93, ........33007127, ...Brown, .......39psi, .................21.0lb/hr
'94-'95, ........53030343, ...Tan, ...........39psi, .................21.0lb/hr
'96-'99, ........53030778, ...Grey, .........49psi, .................23.2lb/hr
'00-'01, ........04854181, ...Blue tip, .....49psi, .................22.5lb/hr


i already run 23# and i believe they only have 1 port in the injector for that gas to go into the cylinder. with the 24# they will have 5 holes on each injector.(i think that is what i read)

does that make a difference.


thanks for helpin me,
 
You may be thinking of the Chevvy LT1 injectors - I believe those are "four-port" jobs, which result in finer atomisation of fuel. Finer atomisation = better combustion ~= more combustion efficiency. Not necessarily enough to really notice in the wallet, but we have to assume Chevvy did it for a reason - drilling one small hole is difficult enough, but drilling four very small holes is a pain!
 
You may be thinking of the Chevvy LT1 injectors - I believe those are "four-port" jobs, which result in finer atomisation of fuel. Finer atomisation = better combustion ~= more combustion efficiency. Not necessarily enough to really notice in the wallet, but we have to assume Chevvy did it for a reason - drilling one small hole is difficult enough, but drilling four very small holes is a pain!


I love the LT1s, I thought they were the best thing I had done other than the stroker. With a set of sonic cleaned, flow matched, new pintl cap and such ford 24lbers it just did not run quite right. Idle was rough, initial power was horrible and it bucked. The first time I switched to the LT1s it was a night and day difference. Idle was silky smooth and the power increase was awesome. Mileage went up too.

While it is possible that I got a set of bum Fords, I will say that I am set on the LT1s. Hell, they were used, We took them right off my buddies race car. I just shook the excess 116octane out of them.
 
I love the LT1s, I thought they were the best thing I had done other than the stroker. With a set of sonic cleaned, flow matched, new pintl cap and such ford 24lbers it just did not run quite right. Idle was rough, initial power was horrible and it bucked. The first time I switched to the LT1s it was a night and day difference. Idle was silky smooth and the power increase was awesome. Mileage went up too.

While it is possible that I got a set of bum Fords, I will say that I am set on the LT1s. Hell, they were used, We took them right off my buddies race car. I just shook the excess 116octane out of them.

are those "plug and play" ? what year lt1?
 
You may be thinking of the Chevvy LT1 injectors - I believe those are "four-port" jobs, which result in finer atomisation of fuel. Finer atomisation = better combustion ~= more combustion efficiency. Not necessarily enough to really notice in the wallet, but we have to assume Chevvy did it for a reason - drilling one small hole is difficult enough, but drilling four very small holes is a pain!


thanks ill do some more research on that. maybe i can find a 23-24# with multi port injectors..

i need new ones anyways thats why i was looking into this.
 
The fords have four holes and the lt1s have six, ftr. My 23.2#ers didn't cut it on my stroker, the lt1s at 25.5# work great.
 
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