05 TJ getting 7 mpg

[Weman823]

I've been lurking on these forums for a long time, but I have a problem I can't find anywhere on here, so I made an account finally and I need some help.

My 2005 Jeep TJR never was good on fuel, I get that. I didn't buy it for fuel efficiency, I bought it for fun. However, on 245/70R16s, the NSG370 6speed, and my 4.0 that has 219,000km on it. I'm getting horrendous fuel efficiency.

I have cleaned the TB sensors, ran seafoam through the gas tank, the brake booster vaccum line, and crank case. I'm running castrol edge high milage full synthetic 10w30. (Will be switching back to 5w30 conventional in the summer, synthetic made my rear main leak like crazy after replacing it).

I replaced both downstream 02 sensors, no change. I replaced the Cold air intake with a stock airbox from same year, with a new filter. I was getting 230km to a tank...
Not being happy with that, I replaced the upstream sensors, and spark plugs with Mopar NGK and NTK sensors and plugs, all checked the gap at 0.035. I took the throttle body apart again and cleaned everything out. Taking each sensor off and cleaned gently, but thoroughly with electric sensor cleaner and a soft bristle brush.

For those who are going to say " Don't drive with such a heavy foot" or "you should of bought a honda". It's not helpful like I've seen on every other thread. A heavy foot doesn't cause a 50% deficit in fuel economy. If anyone else has solved this issue or might know some solutions I would appreciate it.

After replacing the plugs and upstream 02 sensors, I burned through a quarter tank in a 30km round trip.

 

[imahnu]

Welcome to the forum!

The only experience I have with this was on my dads old truck. The fuel filter was pretty clogged and was causing him a serious drop in mpg.

On a TJ it isn't likely that you would have a clogged fuel filter due to the design as I understand it. However it still wouldn't hurt to test out your fuel pressure given all of the stuff you have done to try and remedy the problem.

Hope it helps!

 

[LONGJP2]

For those who are going to say " Don't drive with such a heavy foot" or "you should of bought a honda".

How about this one?
'Are you sure you're calculating your mileage correctly?'

 

[macleanflood]

Exhaust manifold? Mine was cracked. Not all the exhaust was getting to the O2 sensors so they just telling the computer to add more fuel.

Can't see how you wouldn't have checked since you replaced the intake.

Mines a 97.

-Mac

 

[Potomus Pete]

Throttle position sensor could be the culprit. My new one is on it's way now because it's sucking gas. No CEL , but I have been through this before.

 

[Weman823]

How about this one?
'Are you sure you're calculating your mileage correctly?'

I used Google maps to calculate each trip I took in the jeep until it was empty empty. Like, fuel guage dial under the red lol.

My speedo is off because it's a NP231 swap (PO blew up the 241 and swapped it before me). So I haven't been using the odometer.

 

[Weman823]

Throttle position sensor could be the culprit. My new one is on it's way now because it's sucking gas. No CEL , but I have been through this before.

I took it out and cleaned it yesterday, unless it's an actual mechanical failure. It idles around 600rpm which I thought was kinda low, however I know I also have the heat soak problem, the PO also removed the heat sheild under the fuel rail for some reason. Another thing on the endless list to do.

 

[Weman823]

Exhaust manifold? Mine was cracked. Not all the exhaust was getting to the O2 sensors so they just telling the computer to add more fuel.

Can't see how you wouldn't have checked since you replaced the intake.

Mines a 97.

-Mac

I just wanna be clear, I changed the cold air back to stock. I didn't remove the intake manifold. I might try to pressurize the tail pipe and spray the welds with soapy water when cold. That should show any leaks in the exhaust.

 

[Vtx531]

Google maps isn't the usual way people would do it. Normally you would top off the gas tank, reset the odometer to 0.0, drive it, then top off tank again and divide odometer mileage by gallons at the pump.

Could there also be an issue with miles/kilometers and or gallons/liters/imperial gallons?

 

[Weman823]

Google maps isn't the usual way people would do it. Normally you would top off the gas tank, reset the odometer to 0.0, drive it, then top off tank again and divide odometer mileage by gallons at the pump.

Could there also be an issue with miles/kilometers and or gallons/liters/imperial gallons?

The speedometer isn't reading correctly, like I said, it doesn't have the right tooth count so it's off. Hence why I was using Google maps.

 

[JKP]

I took it out and cleaned it yesterday, unless it's an actual mechanical failure. It idles around 600rpm which I thought was kinda low, however I know I also have the heat soak problem, the PO also removed the heat sheild under the fuel rail for some reason. Another thing on the endless list to do.

You can't clean the TPS, its a sealed sensor that attaches to the throttle body shaft.

 

[Trevlaw]

Throttle position sensor could be the culprit. My new one is on it's way now because it's sucking gas. No CEL , but I have been through this before.

Did you test your old one at all? I just tested mine today and the voltage seemed to increase smoothly upwards, but I was only getting 3.78v at WOT, and I think it should be closer 4.6. Hoping that's my culprit, new sensor gets here tomorrow.

 

[JKP]

Do you have a loss of power in addition to the bad gas mileage?

 

[Trevlaw]

Do you have a loss of power in addition to the bad gas mileage?

Not the OP, but I'm also getting 8mpg. It drives normally enough around town, maybe just a bit light on power. It's gutless on any type of incline, pedal to the floor still losing speed. Did a pull on flat ground WOT and maxed at 70mph 3400rpm.

 

[JKP]

Not the OP, but I'm also getting 8mpg. It drives normally enough around town, maybe just a bit light on power. It's gutless on any type of incline, pedal to the floor still losing speed. Did a pull on flat ground WOT and maxed at 70mph 3400rpm.

The usual suspects are the pre cats or the main cat failing and plugging the exhaust. An exhaust shop can check for backpressure, or you can remove the upper O2s and see if it has more pwr.

You can also drop the pre cats down a little and look inside to see if they are melted or blown out.

 

[Trevlaw]

The usual suspects are the pre cats or the main cat failing and plugging the exhaust. An exhaust shop can check for backpressure, or you can remove the upper O2s and see if it has more pwr.

You can also drop the pre cats down a little and look inside to see if they are melted or blown out.

Precats are less than a year old. Just had them off last week and they're clean. I also just swapped out my 4.0 with a lower miles one. Old motor had a cracked head, and pieces of something in the pan. New motor has 150psi compression across the board. All gaskets and seals are good, new injector o rings, clean intake and exhaust runners, O2 sensors are new and functioning, new cam and crank sensors(Mopar), cam signal sync is good, no vacuum leaks, cleaned IAC, no exhaust leaks, axle gearing is correct, and TV cable adjusted correctly.

Not much left it could be I hope lol

 

[Potomus Pete]

Did you test your old one at all? I just tested mine today and the voltage seemed to increase smoothly upwards, but I was only getting 3.78v at WOT, and I think it should be closer 4.6. Hoping that's my culprit, new sensor gets here tomorrow.

Mine feels like it's running out of gas. I throttle back, and it catches up. Plus terrible gas milage. Idle can be off at times, but not always. I have not checked it with a multi meter, but I had this happen on both of my other vehicles that are both twenty, and thirty years old. New fuel pump just installed. I may be wrong and will let it be known tomorrow. Hopefully the little screws will come out. just sprayed them today. If this is not the problem then oxygen sensors. Nothing has been changed on this jeep since new so not really a waste

 

[dracotonisamond]

i am in a similar boat, i actually saw this is my fill up logs.
over 3 months i lost 6 mpg.

i never could figure it out, ive replaced almost every sensor on the engine, new cats, cleaned injectors, leakdown tests on about everything i could think of. i even changed every fluid and measured the current consumption of the electrical system, nothing fixed it or stood out as abnormal.

the odd part is the plugs are normal and it doesnt smoke, i even looked for gas leaks since gas doesnt just disapear.

ill be keeping an eye on this thread i guess.

 

[Weman823]

Google maps isn't the usual way people would do it. Normally you would top off the gas tank, reset the odometer to 0.0, drive it, then top off tank again and divide odometer mileage by gallons at the pump.

Could there also be an issue with miles/kilometers and or gallons/liters/imperial gallons?

Also with the conversations, I've done them right on paper. I just used mpg because I know most of you are yanks and I didn't want any confusion, but I think I may of made it more confusing haha.

You can't clean the TPS, its a sealed sensor that attaches to the throttle body shaft.

Maybe you have a different throttle body than me? Mine unbolted with two machine screws and came off. Opposite of the throttle cables.

Do you have a loss of power in addition to the bad gas mileage

 

[Weman823]

I haven't noticed a loss of power, I actually thought it seemed more responsive after the plugs. But could just be me