05 TJ getting 7 mpg

[tr21triton]

No it’s not calibrated. I’ve only been going off of the dial for logging my distance travelled.

just a rough guess because I was running 32's and mine was off 10%. dropped to 31's and it's closer to 5%. so I'm guessing your off about 25% which should have your actual mpg about 12. so that would mean when your running 40mph on speedo your true speed is 50mph. if you have a gps you can verify that....i know you can also use google maps to show speed

 

[MikeE024]

I believe I’m off by about 10 mph once I’m up around 50 or so mph.

I checked to see if my mileage gauge was accurate many months ago and it was pretty much dead on —>however I was driving pretty slow which would explain the accuracy. I was not mindful like I should have been.

This is super helpful thanks for helping me understand my errors.

 

[MikeE024]

just a rough guess because I was running 32's and mine was off 10%. dropped to 31's and it's closer to 5%. so I'm guessing your off about 25% which should have your actual mpg about 12. so that would mean when your running 40mph on speedo your true speed is 50mph. if you have a gps you can verify that....i know you can also use google maps to show speed

I run the Torque Pro app on my head unit running gauges for the GPS speed right next to the speed gauge reported by the Jeep. Makes it pretty easy to track.

90%+ of my driving is on local roads at 45 mph or less.

 

[tr21triton]

dont know if ya'll have those portable radar trailers that the police put out showing your actual speed in AZ. or maybe a friend who's a cop that can shoot ya. but you can get it damn near dead nuts on by running 40 on your speedo and seeing your true speed. but if your speedo is off by "x" % so is your odometer, your speed wont change the percentage.

 

[tr21triton]

I run the Torque Pro app on my head unit running gauges for the GPS speed right next to the speed gauge reported by the Jeep. Makes it pretty easy to track.

90%+ of my driving is on local roads at 45 mph or less.

next time your out drive 40mph on your speedometer and check it to whats showing on the app. i'm just guessing on the 25%. figure out your % and multiply your miles x percentage / gallons and you'll be real close. bet you will be happier and your mpg will get better when you regear

 

[MikeE024]

next time your out drive 40mph on your speedometer and check it to whats showing on the app. i'm just guessing on the 25%. figure out your % and multiply your miles x percentage / gallons and you'll be real close. bet you will be happier and your mpg will get better when you regear

My gps reading lags but I believe the Speedo might be off by about 14%.

I’ll check again when I’m able to properly maintain a steady speed.

 

[tr21triton]

My gps reading lags but I believe the Speedo might be off by about 14%.

I’ll check again when I’m able to properly maintain a steady speed.

no need to check. I forgot about the old apple PIE=3.14. orig tires were 29. your speedo is off 20.7% .my maff teachers from over 40yrs ago would be proud DAMN i got a headache !

 

[MikeE024]

no need to check. I forgot about the old apple PIE=3.14. orig tires were 29. your speedo is off 20.7% .my maff teachers from over 40yrs ago would be proud DAMN i got a headache !

I believe the original tires were 30.5”

 

[tr21triton]

I believe the original tires were 30.5”

if so your off 15%

 

[Weman823]

well its easy enough to get a rough calculation of how fur it's off. get on a highway with mile markers. reset your odometer to 0. drive preferably until it shows 10 miles. and check compared to the MM's . if you've gone 11 miles your off about 10%. then when you go to calculate use mileage + 10% divided by gallons. also then if your speedo is at 60mph your real speed is about 66mph.

Yup! Haha I've been doing this. It's increased by 1.35. I set the odometer and when it runs out, ill just multiply it by 1.35

 

[Weman823]

Fun little update to today. Was driving it to work this morning. It lost all power around 10 mins into my ride and threw a code. Stalled out on the road but I was able to limp it the rest of the way. P0340 and P0129.

Speedo is off by about 1.35% and a few posts on here have mentioned that being an issue sometimes.

I'm getting really sick of constantly breaking down, I've had lots of 4.0s before but I think this one is cursed. I've had nothing but problems with it. P0340 is the Cam position sensor and P0129 is Baromatic pressure low.

 

[Fishtaco]

Fun little update to today. Was driving it to work this morning. It lost all power around 10 mins into my ride and threw a code. Stalled out on the road but I was able to limp it the rest of the way. P0340 and P0129.

Speedo is off by about 1.35% and a few posts on here have mentioned that being an issue sometimes.

I'm getting really sick of constantly breaking down, I've had lots of 4.0s before but I think this one is cursed. I've had nothing but problems with it. P0340 is the Cam position sensor and P0129 is Baromatic pressure low.

Not any help but I speak metric as my native language lol my 2006 6 speed is getting a constant 6.5km,s per litre around town and I get around 110 -120km,s from the full - 3/4 tank mark. 18 litres per 1/4 tank it has a 72 litre capacity so if you are not smelling petrol, blowing thick black smoke and kangarooing down the road or have an obvious leak in your fuel system its probably impossible to get less than 2km,s per litre, it just wouldn't run your cylinders could not handle that much wet fuel without the plugs fouling wet and your injectors couldnt atomize that much fuel plus your exhaust would eventually explode full of unburnt fuel.

You have to fill your tank full to the top run it to 3/4 and re fill calculating kms travelled per litre used then do it a few times.
Use a GPS sat nav to see your true speed on your wheels/tyre set up against what the speedo is showing. Buy a Garmin and you wont need to change your speedo gear.

On a recent longer trip I got over 8km,s per litre in 6th at 100 -110kph almost all the way.

 

[MikeE024]

if so your off 15%

Makes sense. I came to 14.xx% and rounded it down to help ensure I don't overestimate. (I believe I'm getting around 10.5 mpg)

 

[MikeE024]

Fun little update to today. Was driving it to work this morning. It lost all power around 10 mins into my ride and threw a code. Stalled out on the road but I was able to limp it the rest of the way. P0340 and P0129.

Speedo is off by about 1.35% and a few posts on here have mentioned that being an issue sometimes.

I'm getting really sick of constantly breaking down, I've had lots of 4.0s before but I think this one is cursed. I've had nothing but problems with it. P0340 is the Cam position sensor and P0129 is Baromatic pressure low.

In case this helps:

My previous jeep (1999) cut on me after I had the exhaust manifold replaced by a local shop. I drove the jeep away and it died (cut off) about a mile down the road. Supposedly, the shop found the wiring to the crankshaft position sensor touching the manifold, which caused the problem. They replaced the part and things were just fine up until I sold the jeep for my current vehicle.

Also, I've self-adjusted my camshaft position sensor location because the OPDA was accidentally spun by the shop that replaced my freeze plugs when they struggled/failed to get my engine back in (I ended up installing the engine myself at their shop so I could get it the hell out of there). I was able to get the CPS aligned pretty easily and experimented by moving it until it cut off.

Also, if your camshaft position sensor is going bad you can use the Napa Echelon series sensor to replace it without any issues (based on others' opinions here and my own experience). I pulled my OEM CPS when changing the OPDA just to see if the Napa part would work okay. It worked great, so I left it installed and keep my stock CPS as my spare (since they are a unicorn nowadays). The Napa part has been running fine for 7 months. Note: For other engine-related sensors, I buy OEM via Rockauto or Amazon.

 

[Trevlaw]

@Weman823 have you checked your cats to see if they are plugged yet? Just got my problem figured out the other day, my two upstream cats were fine, but my 1 year old third cat was plugged up.

If you can find a long stretch of flat road you can try doing a top speed test. Just do a full throttle pull and see how fast it'll go. Mine wouldn't go higher than 70mph around 3400rpm. After gutting the third cat I can hit 95mph no problem.

 

[Weman823]

@Weman823 have you checked your cats to see if they are plugged yet? Just got my problem figured out the other day, my two upstream cats were fine, but my 1 year old third cat was plugged up.

If you can find a long stretch of flat road you can try doing a top speed test. Just do a full throttle pull and see how fast it'll go. Mine wouldn't go higher than 70mph around 3400rpm. After gutting the third cat I can hit 95mph no problem.

Previous owner gutter both cats, I've got extensions on the lower 02 sensors so they don't trip CELs. All 4 new 02 sensors, proper parts numbers for all. The last cat still has its internals so I might gut that one too as it's kinda pointless at this point.

Fuel milage is still garbage, so I'm thinking it might be the TPS as some here have suggested, or an exhaust leak but I haven't been able to find anything.

Parts are scarce right now because of covid, so getting OEM replacement are near impossible where I am. Might have to go with Dorman exhaust manifolds and replace the gasket.

On Monday my jeep went Into limp mode on the way to work. Threw a p0340 p0344 and p0129 codes. Would crank but no start. I unplugged the VSS (which is the wrong tooth) and the jeep fired right up. But fuel economy is still garbage. 30kms went through the top quarter of a tank.

My course of action is going to be putting 33s on it to match the 4.10s better, replace the TPS with OEM, exhaust and intake gasket, exhaust manifold, proper speedo gear and replace the VSS, and gut that last cat and see if that does anything. Anyone else have any suggestions?

I don't have any power loss that I can notice, doesn't lag. Just burns a ton of fuel and smells rich, however the smell is prob from the lack of cats.

 

[Trevlaw]

Previous owner gutter both cats, I've got extensions on the lower 02 sensors so they don't trip CELs. All 4 new 02 sensors, proper parts numbers for all. The last cat still has its internals so I might gut that one too as it's kinda pointless at this point.

Fuel milage is still garbage, so I'm thinking it might be the TPS as some here have suggested, or an exhaust leak but I haven't been able to find anything.

Parts are scarce right now because of covid, so getting OEM replacement are near impossible where I am. Might have to go with Dorman exhaust manifolds and replace the gasket.

On Monday my jeep went Into limp mode on the way to work. Threw a p0340 p0344 and p0129 codes. Would crank but no start. I unplugged the VSS (which is the wrong tooth) and the jeep fired right up. But fuel economy is still garbage. 30kms went through the top quarter of a tank.

My course of action is going to be putting 33s on it to match the 4.10s better, replace the TPS with OEM, exhaust and intake gasket, exhaust manifold, proper speedo gear and replace the VSS, and gut that last cat and see if that does anything. Anyone else have any suggestions?

I don't have any power loss that I can notice, doesn't lag. Just burns a ton of fuel and smells rich, however the smell is prob from the lack of cats.

If you have the access to a scanner that can show you fuel trims that would tell you if it's rich.

Before you spend any money on all that stuff, I'd get a replacement for the two cats on the side of the motor, those being missing is a big red flag for your awful mileage. The motor doesn't necessarily need the third downstream, but it certainly needs the uppers to run correctly in a stock configuration

 

[Weman823]

If you have the access to a scanner that can show you fuel trims that would tell you if it's rich.

Before you spend any money on all that stuff, I'd get a replacement for the two cats on the side of the motor, those being missing is a big red flag for your awful mileage. The motor doesn't necessarily need the third downstream, but it certainly needs the uppers to run correctly in a stock configuration

Lots of guys on here all say they aren't nessicary as the downstream 02 sensors don't sctually do anything other than monitor the condition of the Cats. Only the upstream 02s adjust fuel trim. @Jerry Bransford.

I have bung extensions that pull the 02s out of the stream of exhaust to give it a leaner reading, tricking the computer into thinking that the cats are working efficiently.

I get the proper fix would be to replace the exhaust all together. However I'm on a very tight budget and saving for a TDI swap. Sensors (though they add up) are relatively cheap compared to a $1000 cad cat system.

 

[Trevlaw]

Lots of guys on here all say they aren't nessicary as the downstream 02 sensors don't sctually do anything other than monitor the condition of the Cats. Only the upstream 02s adjust fuel trim. @Jerry Bransford.

I have bung extensions that pull the 02s out of the stream of exhaust to give it a leaner reading, tricking the computer into thinking that the cats are working efficiently.

I get the proper fix would be to replace the exhaust all together. However I'm on a very tight budget and saving for a TDI swap. Sensors (though they add up) are relatively cheap compared to a $1000 cad cat system.

This is from the FSM for a WJ, which uses the same 4.0 and catalytic converter configuration as a TJ. I don't have a TJ FSM handy, but I'd imagine they probably function the same

It's easy enough to test the back pressure in your exhaust. Get an O2 sensor bung plug, drill and tap it for a 1/8" npt barbed fitting. Get a low pressure air gauge, 30psi max, connect the two with some air hose, screw the plug into an O2 sensor bung and see how much psi you have around 3000k rpm. Anything more than about 2 psi is a problem, mine had 20psi at 3k rpm.

If your cat is plugged that extra load fighting the engine will cause your pcm to switch into Open Loop-Drive earlier than it's supposed to, probably anytime your around 55-60mph depending on how plugged it is. That will make your engine run richer than it should

 

[Weman823]

This is from the FSM for a WJ, which uses the same 4.0 and catalytic converter configuration as a TJ. I don't have a TJ FSM handy, but I'd imagine they probably function the same

View attachment 310805

It's easy enough to test the back pressure in your exhaust. Get an O2 sensor bung plug, drill and tap it for a 1/8" npt barbed fitting. Get a low pressure air gauge, 30psi max, connect the two with some air hose, screw the plug into an O2 sensor bung and see how much psi you have around 3000k rpm. Anything more than about 2 psi is a problem, mine had 20psi at 3k rpm.

If your cat is plugged that extra load fighting the engine will cause your pcm to switch into Open Loop-Drive earlier than it's supposed to, probably anytime your around 55-60mph depending on how plugged it is. That will make your engine run richer than it should

I checked the FSM for the TJ. You're totally right.

I'll have to check my 02 readings. But as of writing this. All three cats are empty now so there should be no blockage whatsoever.

Does anyone know the parameters I should be looking for for a healthy fuel trim? I have a half decent scanner that does live data.

I really didn't want to spend the money on a new exhaust, with a swap in the books, but I think I'll have to