Gas mileage has tanked (1 Viewer)

[flintknapper]

I don't know if it's been covered but:
1) does your EGR system work?
2) does an OBD-II scan indicate EGR is functional
3) are you sluggishly accelerating and have you considered an exhaust restriction?

Re: the point on RPMs at 60-65mph, what is normal for stock gearing and stockish tires on flat road?
I have to keep somewhere around 2150rpm to keep at 65mph.

^^^^^

That's about what mine runs at (on 33's)

 

[bigakguy]

The only thing high in that pic is your fuel gauge.

It looks like you're still running stock 4.11:1 gears and probably 33" tires (285/75-16)

I think the poor mileage is O2 sensor and temp sensor related.

One affects the other.

Literally laughed out loud at this. Will keep on with getting the second O2 sensor replaced and temp sensor. And yes stock gears on 33s.

1) does your EGR system work?
2) does an OBD-II scan indicate EGR is functional
3) are you sluggishly accelerating and have you considered an exhaust restriction?

Re: the point on RPMs at 60-65mph, what is normal for stock gearing and stockish tires on flat road?
I have to keep somewhere around 2150rpm to keep at 65mph.

Would a standard scan gauge/ ultra gauge be able to determine this? Or are we talking some level more of a scanner? I don’t think it’s terribly sluggish. But I’ve never driven another 80, other than one with a manual in it. I’ve considered the exhaust restriction, not sure how to diagnose that though. Thought about doing the magnaflow high flow cats, because it’s something I’d like to do anyways, but just a spendy “maybe this will work”.

 

[jatree]

^^^^^

That's about what mine runs at (on 33's)

Thanks flint - I'm running 265/70r17 KO2's which are about 31.6" so pretty close. I'm just undertaking my first longer trips at speed so didn't know what to expect. On the plus side, mpg is up to 15 after fixing recent issues. On the negative, I hate my muffler/exhaust sound and will be looking into that next!

 

[jatree]

Would a standard scan gauge/ ultra gauge be able to determine this? Or are we talking some level more of a scanner? I don’t think it’s terribly sluggish. But I’ve never driven another 80, other than one with a manual in it. I’ve considered the exhaust restriction, not sure how to diagnose that though. Thought about doing the magnaflow high flow cats, because it’s something I’d like to do anyways, but just a spendy “maybe this will work”.

Yes I have a cheap HF scan gauge - as long as you can check pending or stored codes and whether the computer feels the egr/catalyst monitor (can't remember the name) drive cycle is complete.

I know sluggishness is subjective and hard to determine. But reason I ask about the restriction is that my front cat was toast and it took me a year to figure it out. I also had a non-functional EGR VSV. Fixing those two issues (I did use a single Magnaflow cat) brought my mpg back up to normal. I kept my existing O2 sensors (which are only a few years old) and verified the readings with said cheap obd reader.

On the exhaust restriction, there's multiple ways to diagnose. I went to a muffler shop and they did it for free so I of course gave him actual business later. He just drilled a small hole just before Cat-1 and stuck a probe in to read back pressure. It becomes pretty obvious if anything is keeping the exhaust from flowing.

 

[bigakguy]

Yes I have a cheap HF scan gauge - as long as you can check pending or stored codes and whether the computer feels the egr/catalyst monitor (can't remember the name) drive cycle is complete.

I know sluggishness is subjective and hard to determine. But reason I ask about the restriction is that my front cat was toast and it took me a year to figure it out. I also had a non-functional EGR VSV. Fixing those two issues (I did use a single Magnaflow cat) brought my mpg back up to normal. I kept my existing O2 sensors (which are only a few years old) and verified the readings with said cheap obd reader.

On the exhaust restriction, there's multiple ways to diagnose. I went to a muffler shop and they did it for free so I of course gave him actual business later. He just drilled a small hole just before Cat-1 and stuck a probe in to read back pressure. It becomes pretty obvious if anything is keeping the exhaust from flowing.

Gotcha. I’ll have to look into that. I wouldn’t expect it to be an issue. One of them was replaced right before I bought it, was stolen off the truck, but exhaust is on my list any ways so that should be done.
I have the ultra gauge. I can check and clear codes. But I’m not getting any codes other than the occasional recurring P0170. And not sure if this thing can check function of the EGR

 

[bigakguy]

Happy to say my mileage is back to where it was! 14 mpg on my last highway cruise additionally I have gone through a few tanks of fuel and not one p0170 code, which I was getting every 50 miles or so. In all I replaced spark plugs, o2 sensors! And a couple vacuum lines to the charcoal canister all with OEM stuff. Thanks for everyone’s help!

 

[338Lapua]

Happy to say my mileage is back to where it was! 14 mpg on my last highway cruise additionally I have gone through a few tanks of fuel and not one p0170 code, which I was getting every 50 miles or so. In all I replaced spark plugs, o2 sensors! And a couple vacuum lines to the charcoal canister all with OEM stuff. Thanks for everyone’s help!

Man what I would do for 14mpg!!

 

[bigakguy]

Man what I would do for 14mpg!!

It was down hill both ways with a tailwind...while on a flat bed truck. Hahaha