Brian83
TJ Enthusiast
MPG gains have nothing to do with having 12 holes in your injectors. Its from replacing worn leaky injectors with new ones.
Average 8 mpg, need suggested fixes
- Thread starter Clarythedrill
- Start date
MPG gains have nothing to do with having 12 holes in your injectors. Its from replacing worn leaky injectors with new ones.
Brian83
TJ Enthusiast
Several ways to test this. Easiest is intake vacuum. Compare idle reading to reading at 2500 RPM. Should be close to each other and hold steady.
liquidfluidity
TJ Enthusiast
Been there done this when the 4-hole swap first came out. Gained a noticeable smoother idle and that was it. By looking at the o-rings on the original injectors, I can guarantee that I would have achieved the same gains with new o-rings on the old injectors. The only reason I swapped mine was because I already had the 4-hole injectors from another V8 project and one of my original Siemens injectors was cracked. Less that $10 for new o-rings leaves $140 for other mods.
Don't really know what "hand waving"
means. And other than my pointing out his math is as solid as 
I also gave several possible causes for getting below normal MPGs. So I'm guessing you are the hand waver.
That interesting....
So what your saying is the increase in fuel atomization when going from a 1 hole injector to a 12 hole injector has no impact on gas mileage... Does it lower emissions ? Does increase performance ?
I have a friend that is a 25+ year Jeep Technician; he accessed the Adaptive Monitor function of the Jeeps computer before and after the 12 hole injectors were installed. In Closed Loop the before Adaptive Memory Cell Values for C18,19,20 and 21 were +1,+1, +5 and +4; then in Closed Loop the after Cell Values were -5,-8, -10 and -11.
I documented my gas mileage driving 85 miles to his house and my gas mileage was 17 mpg and on the same drive home the gas mileage was 20 mpg. Both of these drives were primarily highway in moderate traffic driving at 60-75 mph.
There are numerous studies where when fuel atomization is enhanced; emissions go down, performance goes up which intern depending upon how you drive... Gas mileage will go up too....
Brian83
TJ Enthusiast
You are comparing rebuilt 12 hole injectors to your stock ones. Until you compare new vs new those numbers mean absolutely nothing. And Im not saying that better atomization doesn't help to a point. But all 12 hole injectors do vs say a 4 hole is lighten your wallet.
Brian83
TJ Enthusiast
Brian83
TJ Enthusiast
Disagree all you want but when the fuel spray becomes so fine that the volume of air trapped in the droplets isnt enough it throws off your air fuel ratio. So yes more holes and the shape of the hole help with atomiziation but once you pass a certain threshold all it does is look cool for a flow test.
liquidfluidity
TJ Enthusiast
Tons of info out there on this...... been dis-proven over and over. As was stated, only a test in a controlled environment with equally new parts will really work. Highway driving doesn't take into effect tail and side winds or drafting behind another vehicle.
Good debate but this has been hashed out in thousands of posts across the internet......
I'd say if the focus is going to come down to injectors, go to NAPA and get some o-rings first and see if there is any improvement. With the amount of additives that are in fuel these days, it's less likely to have an actual dirty injector than ever before.
I think that the focus is deviating and we need an updated rundown of what the OP has tried....
Good debate but this has been hashed out in thousands of posts across the internet......
I'd say if the focus is going to come down to injectors, go to NAPA and get some o-rings first and see if there is any improvement. With the amount of additives that are in fuel these days, it's less likely to have an actual dirty injector than ever before.
I think that the focus is deviating and we need an updated rundown of what the OP has tried....
Steve Rodgers
TJ Enthusiast
If the speedo is not corrected, each rotation of the tires will cover more ground than the stock tire would. The speedo will think the Jeep only traveled the stock distance of each rotation. You will get a pessimistic gas mileage calculation.
I may have missed it if someone already hit on this. The OP @Clarythedrill has a 2001 4.0 with the automatic. Everyone has mentioned tire size gear ratio and speedometer accuracy multiple times. While these do play into figuring out mileage it's not hard to do the math to figure out what percentage off your speedometer is off. Then you have an accurate mileage to compare fuel consumption with. I have done that in many vehicles. One of the biggest problems with automatics, having incorrect gearing and inaccurate speedometers, is your shift points. The trans is designed around shifting at certain rpm vs speed vs torque applied by the engine. If your trans is shifting too early under normal driving conditions (having too tall a gear ratio (taller tires without proper gearing) will do this) your fuel consumption is going to go up because the engine now has to work harder at a lower RPM.. To combat that you press down on the throttle pedal further there by holding the trans in a lower gear longer, also consuming more fuel than what it needs to.
Adjusting the speedometer to read accurate will only solve part of the problem. Re-gearing then adjusting the speedometer calibration is the optimal choice...
Adjusting the speedometer to read accurate will only solve part of the problem. Re-gearing then adjusting the speedometer calibration is the optimal choice...
In the world of troubleshooting the first rule is accurate information and in concept doing the math is fine but with the installation of a $40 part all doubt will be removed.
I do believe I covered that at the end of my comment, but yes a corrected speedometer gear would help.
Edit: the biggest point I was eluding to is the automatic does not know how to shift properly for the bigger tires...
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I don't think you need a corrected speedo gear necessarily, you just need to know how much farther each revolution takes you with bigger tires. In my case, its about 10%. I've confirmed this with GPS and revs/mile rating on stock vs upsized tires. So, I figure my MPG at each fill up in the traditional method then add 10%. Today I filled up after driving mostly 40-55 MPH and got 18 MPG! Previous record was about 16, 13-14 is normal.
Rubicon John
TJ Enthusiast
Is there a write up for correcting the speedometer? I drove past an electronic radar and my speed matched but I’m wondering if there’s a way I can check if it’s been corrected for the 33s I have.
Depending on how fast you were going when you went through the radar (slower speeds are closer to accurate than higher speeds), I'd say if it was saying you were going the same speed as your speedometer, It's a safe bet that it's been done.
Yes it's in the "How to" section.
Here's a link to it.
https://wranglertjforum.com/threads...ometer-after-changing-tire-sizes-or-gears.83/
Rubicon John
TJ Enthusiast
Got a Rubicon. I wonder if the Autel at work has this function hmmm
Terrance802
New Member
Can I just throw it out there. It's a jeep and your expectations on reliability should be high but very low on gas mileage. It's a square vehicle, no matter what you do, your wasting money on trying to get better gas mileage. By 2mpg or so. You wouldn't get your money back by selling or driving the vehicle until maybe 10 years down the road. There is a saying, know where your at and don't make it impossible to get rid of. If you just want to hand out money instead, my hands are out. But I am being honest and saying and trying to save grace and time, their are somethings are not worth it unless money and time is really not an issue with you. It's not going to hurt the unbeatable straight 6. Maybe if you did have a thermostat issue, ok you have a fair point. But I will leave with this, don't over do it or think it analogy
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