Effect of tires on mileage?

[DenLip]

Ok sorry, just finally got a chance to check the responses.

Ok. I have '01 4.0 AW4. DIY K&N, DIY IAT relocate to intake tube, Poweraid TBS (yes it does help), Borla cat-back, hollowed primary cat, 180F thermostat, [...] Bad bearings in the front; they make a lot of noise, but I can't see them affecting mileage that much.

The bearings are probably a contributor. The 180F thermostat could be a contributor (making it run in "cold start" mode all the time). I'm stunned that a hollowed-out cat isn't affecting an '01. I wouldn't think the computer would approve of those sorts of shenanigans. (I don't!)

Aggressive tires will certainly hurt mileage. My old Stratus used to get 33mpg highway on it's good tires (Michelin MXV4 Energy), but about 30 on the snows.

All of the intake/exhaust mods you've done CAN, in theory, help gas mileage by making the engine breathe freer. By contrast, if you ARE a leadfoot, they WILL make the mileage go DOWN. The added power has to come from somewhere.

My stock '00 got about 19-20 mpg around town on the stock 225 Wrangler RT/S tires (nickname: slick!)... it's down to a pretty steady 18 with the 235 Pirelli Scorpion AT's.

Den

 

[DenLip]

Yeah, I have a REALLY hard time going "easy" in-town, which is primarily where most of my driving occurs, but I don't think I drive anywhere near hard, by any means.

Alignment is good. Tires look fine. I still have a hard time believing that bad front bearings would make a 25-33% difference in mileage, but I don't doubt they affect it maybe 5-10%.

If you're driving mostly IN TOWN... then mileage down in the 15mpg range probably isn't unexpected.

 

[langer1]

I fixed by buddies Power/Compfort switch a couple of weeks ago. It broke and he hard wired it to Power mode.
His mileage was 16-18 and now with the switch working in Compfort mode his mileage is 21-23 mpg.

 

[DenLip]

Oh yeah, I forgot to mention that the coolant is definately not operating in "open-loop". I have hood vents that help to evacuate a great deal of heat, and even in ambient temps of around 75-80*F, I am able to maintain a constant (assuming I am in constant motion) 180*F on the thermostat. The "open-loop" is certainly not an issue, especially with high 30s this morning.

You're misunderstanding. "Open loop" mode is when the engine control computer IGNORES most of the sensors on the engine, and runs via a slightly-rich set of predetermined numbers for the fuel injection.

The purpose is (a) to let the sensors warm up to operating temperature, and (b) run the engine a bit rich until it gets up to operating temperature.

"Operating temperature" for the 4.0 in a late-model Cherokee is anywhere between 190 and 230. If your 'stat is never letting the engine get UP TO 190, it may never "warm up" as far as the computer is concerned. This would be made WORSE by the hood vents, and the cool air temps outside. And if the engine never "warms up", if will never get out of that overliy-rich warm-up mode. The O2 sensors are not registering a fault because they are being ignored by the computer.

I'm also doubly concerned by your comment that it "never smells like it's running terribly rich". How terrible is terrible? A modern car should not smell like hydrocarbons AT ALL, EVER... except for maybe a couple of minutes on a cold start.

Den

 

[grahamtwatson]

Is there an easy way to tell if I'm running open loop or not? (90 XJ 4.0 Ltd Auto). When running open loop does it ignore specifi sensors or just the "out of range" ones? I've checked the sensors as best I can, but I'm still visiting my local gas stations far too frequently.

 

[krakhedd]

To answer everybody's questions:

There are not O2 sensors post-cat (there are 2 pre-cats right in the headers that I didn't touch....yet), so that's why there's no code being thrown. I really don't care about what the law says, I'm hunting for mileage, and I suspect that, due to the large increase in backpressures, you're only marginally better off, in terms ot NOx emissions/etc., running a cat. No offense. (I tend to support measures to reduce emissions, only via improved efficiency, not putting a "band-aid" on the problem) Also, with all these computers and such nowadays, there's absolutely no reason a motor cannot run, w/o a cat, and meet emissions restrictions. "But I digress......."

By terribly rich, I mean, for a minute or so at startup. Nothing out of the ordinary. I question (not doubt, just question) whether this "open-loop" thing was ever an issue though, because I've been running the 180* for over a year now, and never smelled rich exhaust except when I'd expect to (cold start-up, for example).

I decided there was enough substance to the theory, and put in a 195* t-stat today. I'll report any increase/decrease in mileage from that. If that does little/nothing, the bearings come next. About time to relpace them anyway, since winter is around the corner, and I don't want to be sitting in an unheated garage wrenching on my ride.

If replacing the bearings still doesn't help much/any, then I would be resigned to the idea that it is, indeed, simply overly-aggressive driving that is causing my horrible mileage.

On any given tank, I do about 60/40 or 65/35 city/highway driving, but included in that city driving is 45MPH speed limits (I usually do about 5-7 over). That's about the sweet-spot, according to my brother's '99 w/trip computer, for mileage.

 

[Craig]

I would agree on the thermostat issue. My '00 Sport runs 210* whether I'm driving through a snow storm in OH or I'm stuck in traffic down here in FL.

If you think its your bearings or brakes dragging, then something has to be making some heat to slow you down. After a good drive on the highway, are your hubs or wheels (at the lug nuts) too hot to touch? They should be quite warm to somewhat hot, but if they burn ya, you should take a look at everything before you blow a tire.

Otherwise, it could be that some of your mods aren't agreeing with each other.

 

[yardape]

To answer everybody's questions:

There are not O2 sensors post-cat (there are 2 pre-cats right in the headers that I didn't touch....yet), so that's why there's no code being thrown. I really don't care about what the law says, I'm hunting for mileage, and I suspect that, due to the large increase in backpressures, you're only marginally better off, in terms ot NOx emissions/etc., running a cat. No offense. (I tend to support measures to reduce emissions, only via improved efficiency, not putting a "band-aid" on the problem) Also, with all these computers and such nowadays, there's absolutely no reason a motor cannot run, w/o a cat, and meet emissions restrictions. "But I digress......."

By terribly rich, I mean, for a minute or so at startup. Nothing out of the ordinary. I question (not doubt, just question) whether this "open-loop" thing was ever an issue though, because I've been running the 180* for over a year now, and never smelled rich exhaust except when I'd expect to (cold start-up, for example).

I decided there was enough substance to the theory, and put in a 195* t-stat today. I'll report any increase/decrease in mileage from that. If that does little/nothing, the bearings come next. About time to relpace them anyway, since winter is around the corner, and I don't want to be sitting in an unheated garage wrenching on my ride.

If replacing the bearings still doesn't help much/any, then I would be resigned to the idea that it is, indeed, simply overly-aggressive driving that is causing my horrible mileage.

On any given tank, I do about 60/40 or 65/35 city/highway driving, but included in that city driving is 45MPH speed limits (I usually do about 5-7 over). That's about the sweet-spot, according to my brother's '99 w/trip computer, for mileage.

Are you saying that a catalytic convertor is a bandaid?

 

[DenLip]

If replacing the bearings still doesn't help much/any, then I would be resigned to the idea that it is, indeed, simply overly-aggressive driving that is causing my horrible mileage.

On any given tank, I do about 60/40 or 65/35 city/highway driving, but included in that city driving is 45MPH speed limits (I usually do about 5-7 over). That's about the sweet-spot, according to my brother's '99 w/trip computer, for mileage.

With a more-city-than-highway mix, I wouldn't expect to get any more than 16-17mpg out of my Jeep. In the wintertime, I get down near there already... and it's mostly highway (plus a fair amount of idling).

Since you're "resigned" to the fact that over-aggressive driving is causing it, might I suggest that ... well... that would require no wrenching to fix! :roll:

Den

 

[krakhedd]

Yes, catalytic converters are band-aids. If motors were designed and constructed properly, there would be no need for them. Granted, this would take a little dough, but the net result would be much cleaner, more efficient motors.

I think I need to take a wrench to my leg to fix this issue, still getting trash mileage. It's so hard not to use that damned right pedal......

 

[yardape]

Yes, catalytic converters are band-aids. If motors were designed and constructed properly, there would be no need for them. Granted, this would take a little dough, but the net result would be much cleaner, more efficient motors.

I think I need to take a wrench to my leg to fix this issue, still getting trash mileage. It's so hard not to use that damned right pedal......

Given that motors are not designed to your specifications please consider the following: I recently failed an emissions test with a Nitrous Oxide reading of around 3.5 GPM. The state limit here is 2.6 GPM. I installed a new high flow cat as my other one was toast. The follow-up reading was .20 GPM. Catalytic convertors DO work and the impact on performance of a high-flow is miniscule. Despite your defiance of the law and responsibility as a driver, catalytic convertors do what they are supposed to and there is no reason for anyone not to have one on their Jeep or any other vehicle for that matter.

 

[krakhedd]

I didn't say they don't work.

As far as designed to my specifications, all I want out of my motor is something that runs well, with minimal parasitic loss (within reasonable parameters).

 

[treedoc]

As far as designed to my specifications, all I want out of my motor is something that runs well, with minimal parasitic loss (within reasonable parameters).

i thought you were concerned with fuel economy. bad wheel bearings seem pretty parasitic to me. an engine that is running in warm up mode is not efficient. the 4 cylinder in the corolla runs very well AND gets good milage, even with the cat.

so you would dump the cheap, simple cat in favor of more complex and expensive "computers and such" to get the same net result?

 

[krakhedd]

If the cat were a high-flow unit, that barely impeded fuel economy, I would have no problem with it, however, I have seen the difference firsthand between a high-flow unit and an OEM one, and OEM obviously gave no consideration to fuel economy.

I am going to replace my wheel bearings, ASAP. Other than my mods not going well with each other - which I cannot accept, since they mostly revolve around restoring HP lost parasitically - I cannot think of anything else that could be affecting my mileage that much. I am in the midst of a c.12-13 MPG tank right now (I fill in 5-gallon increments, so it's very easy to accurately estimate mileage).

More to follow-up later.....let you guys know how right you all have been about the wheel bearings being the root of my problem

 

[krakhedd]

Ok, I think somebody said something about check my brakes, and I should have. I purchased a new bearing & power steering pump (mine makes a LOT of noise, sounds like a freaking blower!). Anyway, I didn't know until I got down to the bearing assembly, that it is pressed in, and needs to be pressed out (un-pressed?). I noticed when I removed my caliper assembly and disk that the pads and disk looked virtually un-used. During my inspection about 1 month ago, the dealership told me my right-front brake was almost gone (but still passed inspection), so I thought it weird that my left-front was so fresh.

Anyway, while I had the caliper assembly off, I hopped in and hit the brakes, to make sure it wasn't frozen. The caliper worked, so I used a piece of wood and a C-clamp to retract it. Point being, since then, I have been getting 2-4MPG better per tank (I fill up with 5 gallons every time) than before, yet I changed nothing else. So I guess that brake was sticking, or at the very least, not fully retracting. I would expect this to cause the brake to wear unnecessarily, so I'm not sure why it was barely used. But whatever.

I never felt a pulling to one side or the other when I'd brake, either, nor do I now, which confuses me. I cannot come up with any other explanation as to why my fuel economy has improved so much. The wheels never became too hot to touch either, another symptom I'd expect with a brake issue (and something somebody pointed out prior in this thread as a symptom of a failing bearing). Oh well, I finally am getting c.16MPG mixed, which was really good considering how much I was romping on the gas for that tank. Apparently my leadfoot is not quite as detrimental as I had thought prior! :d

Ok, enough of that, time for another question while I have everybody's attention. How much of a loss might I be getting from my power steering pump? Is there a way to adjust the amount of compensation it provides? My steering definitely requires far less effort than my brother's 99, so I wonder if the whining noise could simply be indicitive of the pump providing too much assist.

Thanks guys!

 

[XplodJeepster]

my friends 88 has a worn out PS pump and yes - it does create that whining noise.

REPLACE IT before you lose all your power steering.

 

[krakhedd]

I'm not worried about losing the power steering, I'm just worried about the impact a bad pump could have on my mileage. I can handle the thing w/o power steering - kinda hard, yes, but I can do it. It's gotta be a great upper-body workout, too

I have been getting 12-14MPG for some time now, and since a few days ago, as per my last post, am only getting still around 16-17, mixed driving. This number is getting to where I want it to be (18-20 mixed), and I'm just trying to chase down any remaining phantoms.

 

[fordtech]

: I recently failed an emissions test with a Nitrous Oxide reading of around 3.5 GPM. .

your jeep makes nitrous!! awsome!!! you should plumb that back in to the intake, or a tank!!!!


just ribbin' ya!
NOx is actually nitrogen oxide.....so you were close.

please resume your regularly scheduled thread.

 

[yardape]

your jeep makes nitrous!! awsome!!! you should plumb that back in to the intake, or a tank!!!!


just ribbin' ya!
NOx is actually nitrogen oxide.....so you were close.

please resume your regularly scheduled thread.

You got me. Thankyou. :laugh3:

 

[Ecomike]

Rather than a straight failure, the O2 sensor's output starts to drift out of tolerance, it still works, but gives an inacurate reading. In this situation, you get no code.

How would one test for this problem???

Any idea what would cause that problem?