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Terrible MPG's

H

HotChiliRam

NAXJA Forum User
Location
Santiago, Chile
I changed my inyectors because I had two that were leaking. I bought 6 Inyectors from FiveO. I have nothing to say about the inyectors, the problem is that after I changed them my MPG's went down drastically. I was getting 15Mpg's and now I can barely get 12 Mpg's. Maybe I did something wrong when installing my inyectors. I really don't know what could be wrong or what is producing this pour milage.
Any help would be greatly appreciate...

Thanks in advance...
 
You don't mention your year, on the newer Jeeps the operating parameters are stored in the computer. I would disconnect the battery for 30 min or so then reconnect it, this will reset the system and force the computer to relearn it's parameters again. I also put the pink injectors in from 50 but that was on a reman jasper engine, my milage stayed the same from the old motor to the new one..
 
The injectors on the Renix engine are smaller. If you put 5.0L Stang injectors in or even Jeep HO ones, the mileage drops BUT power goes way up! (if you only changed 2, then the sensors wouldn't trim the fuel back so extra gas is being dumped in)
My buddy John (@wagoneers.com) learned that the hard way too!
 
I changed all six. So you're saying that with this new inyectors 12MPG's is kind of average?
I don't feel the Jeep with a lot more power, it run's a lot better and push a little better, but I can't say that I won 10hp's..
I bought the inyectors from FiveO, The inyectors are Denso and says "Ford" on it side so I beleive this are the 5.0 inyectors. I read that this inyectors are 19lbs and that the OEM Renix Inyectors are 18.5 or something like that. Does those .5lbs more send your MPG's to the floor?
I know that Cherokee's are not know because of their great gas milage, but 12 MPG's is kinda low. Damn I'm getting the same gas milage that I got with my Ram on 35's. Really I'm not liking this poor gas milage....
 
I have a question that goes along with this thread - i'm also getting PITIFUL gas mileage on my '96.....my O2 sensor is located in the cat converter - is this replaceable without breaking it in the cat? has anyone just unscrewed their O2 sensor and not damaged the hole it goes in?
 
HotChiliRam said:
...
I read that this inyectors are 19lbs and that the OEM Renix Inyectors are 18.5 or something like that. Does those .5lbs more send your MPG's to the floor?....
Click to expand...

I'm no expert, but I have noticed that different companies rate their injectors at different pressure. And obvioulsy your pressure didn't change. Maybe the factory are 18.5lbs at 40psi, but the new ones are 19lbs at 32psi. You'll be running them at 40 which will flow a good bit more gas.

--- Just a guess ---

Even still though, the ECU should trim them down... Physically pulling the power (as mentioned above) for a minute would be a good thing to do if you haven't already.
 
Go to Autozone and they will hook your jeep up to a computer. They don't charge anything for this. Then you will know if your O2 sensor is bad.
 
bacelaw said:
I have a question that goes along with this thread - i'm also getting PITIFUL gas mileage on my '96.....my O2 sensor is located in the cat converter - is this replaceable without breaking it in the cat? has anyone just unscrewed their O2 sensor and not damaged the hole it goes in?
Click to expand...

An O2 sensor in the Cat is only there to check that the Cat is working. There should be one up near the exhaust manifold that the engine computer uses to adjust the mixture.
 
I put ford injectors (bought from 5-O) in my 1990 with 4.0 engine, AW4 transmission and saw no change in milege. I put in the 19 lb injectors, nothing oversize. Works great- 2 years and no complaints yet. When the O2 sensor goes out, gas mileage falls off on mine. I would start checking there.
 
Fozzy nailed it. There is an adapter kit to put an HO throttle body on a Renix intake and power does go up (especially with bigger injectors. Can't recall if fuel economy went up or down tho.
 
HotChiliRam said:
My year is 1990. It's an XJ with 4,56's, 33's, ARB, 4.0L, AW4, NP242.
Sorry....
Click to expand...

I have a similar setup.. 96 XJ 4:56s, 33s, ARB, 4.0, AW4, and 231 t case. But I only get 10 - 11 mpg, with stock injectors. I changed my front O2 sensor and saw no cdifference in mileage. My motor is in real good shape with nothing wrong.

Stock I only saw 12mpg, no idea why it is so low.
 
You have a sensor gone bad or injectors that are leaking to be that low on fuel economy. Heck, I get 15 mpg from my 1 ton '73 Jeep J4000 with a carbed 304, tired TH400, Quadratrac with part time kit and 17% O/D with 3.73 gears (D44 front and D60 rear) on 33" tires! Just slightly less than that with 6500 lbs of concrete on it!
 
My injectors are new, so I don't think they're leaking. Actually I'm getting much better MPG's now, Now I'm at 13MPG's, and I hope it gets better. I'm still checking to see, My plan is change my O2 Sensor first. Haven't done it yet, but I will next week.
 
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