MPG suffering after repair

[jlwf4matt]

Hello!

Recently I had a few issues come up that were repaired under warranty. One was a new wiring harness (due to a damaged wire) that was making the engine run rich, a small oil leak that leaked onto the O2 sensor causing it to throw an engine light, and a rear differential sensor replacement.

The Jeep is mostly back to its former glory EXCEPT that the MPG is still suffering significantly. Where I used to drive it conservatively and get 17+, I am now sitting at 14.5. There’s also a somewhat noticeable humming like noise produced when I take my pedal off the gas. If I throw it into neutral and let it coast, I still hear it (so not thinking it’s engine or tire related).

I’m thinking the noise and MPG issue may be related and have something to do with the differential. Would replacing the diff sensor cause an adjustment to be made that would cause it to be tight or misaligned in some way? Would it be worth taking to a differential shop? The dealership is writing it off as “road noise” ?

Thanks.

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[2nd 392]

Did he explain how “road noise” could cause an ~2.5 mpg decrease ? If not, ask him to. ?

 

[Pig-Pen]

Have you crawled under there to take a look? See if anything looks out of place? Thats really odd.

 

[jlwf4matt]

Did he explain how “road noise” could cause an ~2.5 mpg decrease ? If not, ask him to. ?

I haven’t returned to that dealership since the wire repair, but wherever I go I plan to request a technician to drive with me so I can point out the noise. At the time they wrote off the MPG issue as part of the wiring / computer communication / engine running rich issue. I’ve driven a few hundred miles and the noise + MPG issues persist.

 

[jlwf4matt]

Have you crawled under there to take a look? See if anything looks out of place? Thats really odd.

Yes, nothing looks unusual

 

[2nd 392]

I haven’t returned to that dealership since the wire repair, but wherever I go I plan to request a technician to drive with me so I can point out the noise. At the time they wrote off the MPG issue as part of the wiring / computer communication / engine running rich issue. I’ve driven a few hundred miles and the noise + MPG issues persist.

Do it— my new 95 Ram became gutless under throttle. Even with equipment hooked all over Can not duplicate, second trip Can not duplicate. I told him get it and take a ride . Mashed the throttle and it stopped accelerating in a couple seconds….. He had a new fuel pump installed.

 

[richk225]

Jeep service tech; Avoid working on any Jeep or replacing parts, just say you couldn’t find any problems
Don`t forget to walk around like you hate your job

Jeep Service Manager; It’s a Jeep thing and don’t listen to the customer, and sorry I can’t go for a ride along with you

 

[richk225]

Do you have the stock tires on? Have you done anything with a Tazer or Jscan? Possibly the dealer may have reset tire size etc. back to stock.
Where do you think the humming might be coming from? Maybe jack up the back end and see how the tires rotate and maybe you could pin point the noise.
I have not done a rear diff sensor but can it be set in too deep and make contact with the internals of the diff?
Do you feel any type of drag when let off the gas or park on a incline to see if it rolls freely

 

[jlwf4matt]

Do you have the stock tires on? Have you done anything with a Tazer or Jscan? Possibly the dealer may have reset tire size etc. back to stock.
Where do you think the humming might be coming from? Maybe jack up the back end and see how the tires rotate and maybe you could pin point the noise.
I have not done a rear diff sensor but can it be set in too deep and make contact with the internals of the diff?
Do you feel any type of drag when let off the gas or park on a incline to see if it rolls freely

Yeah, I have a Tazer properly programmed to the correct tire size and gear ratio.

I’m not sure where it’s coming from, but it’s more prominent when coasting down a small hill when I let off the gas. It goes away almost completely when I lightly press the throttle to match the speed and comes back when I take my foot off the throttle. It’s not the engine because I still hear it while coasting in neutral. It’s not the tires because I don’t hear it at all when lightly pressing the throttle. Imagine the humming of an engine brake rev, but a bit quieter and it’s not coming from the engine.

I’m not entirely sure if I feel drag or if it’s just in my head because I’m watching my MPGs constantly. That’s a good suggestion- maybe I’ll put it on jack stands and try pinpointing it while it’s spinning. If anything, I can record a video in case the shop won’t go for a ride along. Thanks

 

[JL ME]

Yeah, I have a Tazer properly programmed to the correct tire size and gear ratio.

I’m not sure where it’s coming from, but it’s more prominent when coasting down a small hill when I let off the gas. It goes away almost completely when I lightly press the throttle to match the speed and comes back when I take my foot off the throttle. It’s not the engine because I still hear it while coasting in neutral. It’s not the tires because I don’t hear it at all when lightly pressing the throttle. Imagine the humming of an engine brake rev, but a bit quieter and it’s not coming from the engine.

I’m not entirely sure if I feel drag or if it’s just in my head because I’m watching my MPGs constantly. That’s a good suggestion- maybe I’ll put it on jack stands and try pinpointing it while it’s spinning. If anything, I can record a video in case the shop won’t go for a ride along. Thanks

Sounds like differential gear noise. probably replaced the sensor and never put gear oil in it.

 

[richk225]

Yeah, I have a Tazer properly programmed to the correct tire size and gear ratio.

I’m not sure where it’s coming from, but it’s more prominent when coasting down a small hill when I let off the gas. It goes away almost completely when I lightly press the throttle to match the speed and comes back when I take my foot off the throttle. It’s not the engine because I still hear it while coasting in neutral. It’s not the tires because I don’t hear it at all when lightly pressing the throttle. Imagine the humming of an engine brake rev, but a bit quieter and it’s not coming from the engine.

I’m not entirely sure if I feel drag or if it’s just in my head because I’m watching my MPGs constantly. That’s a good suggestion- maybe I’ll put it on jack stands and try pinpointing it while it’s spinning. If anything, I can record a video in case the shop won’t go for a ride along. Thanks

Just out of curiosity have you tried it in 4 hi or 4 low not sure what transfer case you have ?
Have you thought about disconnecting the battery and then see what the mpg`s are after that?
I wonder if one of your E brakes is hanging up, I would set it up on jack stands and check it out and at least rock both wheels back and forth to see it they both feel the same. Like I mentioned I'm not sure about the sensor but I would check it for sure. I`m going to educate myself on how to change one today. I know the feeling of bringing it in for one thing and then having something else go wrong while it's in their possession.
Do you have E lockers or a LSD ?

 

[tinymay]

........ I know the feeling of bringing it in for one thing and then having something else go wrong while it's in their possession.

After many dealer trips over the years, my opinion is THAT is how they make more money. No one knows but things just happen.

 

[richk225]

After many dealer trips over the years, my opinion is THAT is how they make more money. No one knows but things just happen.

OHHHH SO TRUE

 

[SargeDiesel]

Yeah, I have a Tazer properly programmed to the correct tire size and gear ratio.

I’m not sure where it’s coming from, but it’s more prominent when coasting down a small hill when I let off the gas. It goes away almost completely when I lightly press the throttle to match the speed and comes back when I take my foot off the throttle. It’s not the engine because I still hear it while coasting in neutral. It’s not the tires because I don’t hear it at all when lightly pressing the throttle. Imagine the humming of an engine brake rev, but a bit quieter and it’s not coming from the engine.

I’m not entirely sure if I feel drag or if it’s just in my head because I’m watching my MPGs constantly. That’s a good suggestion- maybe I’ll put it on jack stands and try pinpointing it while it’s spinning. If anything, I can record a video in case the shop won’t go for a ride along. Thanks

Use about a three foot piece of garden hose, hold it up to your ear and use the other end to search for the noise, when you find it, it will jump out at you. Good luck.

 

[Paluss]

Sounds like differential gear noise. probably replaced the sensor and never put gear oil in it.

seriously, I would check the fluid level

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