The jeep that keeps holding back...

[alwaysxj]

So in oct I took the jeep and the family to Moab, round trip was about 800 miles, jeep ran great the whole time with no breakage..... Here is my jeep on fins and things. a fun little trail that is not to hard. :rolleye0012:
http://i873.photobucket.com/albums/ab298/alwaysxj/297522_2210424015451_1093002121_32059355_22387718_ n.jpg

well now since I got back my jeep seems to be holding back when I am coasting like my brakes are being applied, even when they are not... I can be at 50ish and let off and with in a city block the jeep will slow down to about 20. If there are no cars behind me and I have time to let it cost it will about come to a stop:confused: now what I don't under stand is when I am on the free way I still have plenty of power and power when every I need it.

I use my jeep daily as well as delivery pizza for a second job. my gas mileage in the last couple of months has gone from 14is in town to 10 if I am lucky. With that much of a loss I am not making any money from the second job since I am always at the pump....:mad0090:

I have no idea what this could be. I have done a visual exception of the brakes since that was my first guess but they seem to be fine and not rubbing. Could this be a o2 sensor or, map sensor? but would those make the jeep feel like it is holding back? it would explain the sudden drop in fuel economy I guess.

Let me give you a feel for my jeep so you can better help me diagnose.
2001, auto, about 8 inches of of lift, long arms, 285/75R16, locked in the rear, stock 3.55 gears (I know I need to regear) custom made heavy duty front and rear bumpers,sliders, spare full size tire with tools all the time.
I know I am pretty heavy, and I should probably take some of it out. But even with it I was still getting about 14 around town, and I would like it back.
thanks for any help in advance
sorry for the long post.:D

[4.3LXJ]

Steve

When was the last time you replaced your O2 sensor? They wear out over time and do not sent as much of a signal to the ECM as they should and cause the ECM to signal the injectors to squirt more fuel thus causing the engine to run rich and drop the milage. They won't throw a code unless the heater in them quits working. I realize the 01s have four of them, but they do have to be replaced periodically.

[alwaysxj]

Steve

When was the last time you replaced your O2 sensor? They wear out over time and do not sent as much of a signal to the ECM as they should and cause the ECM to signal the injectors to squirt more fuel thus causing the engine to run rich and drop the milage. They won't throw a code unless the heater in them quits working. I realize the 01s have four of them, but they do have to be replaced periodically.
I have had the jeep for about two years and have yet to replace anything. not sure on the past owner:stars:
would the O2 sensor make it slow down like it is? also do I need to replace all 4:banghead:

[4.3LXJ]

I would say you are definitely over due. Expensive I know, but those sensors are considered a consumable part just the same as spark plugs

[alwaysxj]

Thanks Steve I will try to get some soon. any idea why it will not coast?

[4.3LXJ]

No ideas on that. See what happens when the motor is running right first.

[bigjim350]

If you were having any issues with the o2 sensors it would throw a code and tell you which one it is. Is the "check engine" light on?

[cantab27]

just been through the same kinda thing...hesitation, bad fuel consumption... did the 02 thingy like steve said,,,,, heaps better.....had no codes come up ..tis a 95..

[XJ Wheeler]

A couple things come to mind.

(1) I don't know how to check it but a clog in the catalytic converter MIGHT cause this. Once upon a time we were riding in my moms zj and it wouldn't go faster than about 25 mph. The problem-clogged cat.

(2) Check your wheel bearings, they could hold it back and if the motors fighting them all the time your mileage would be cut down.

(3) Just to be sure with the brakes after driving for a while stop to see if any of the wheels are hot (be careful not to get burnt), bad wheel bearings could also cause this.

[alwaysxj]

If you were having any issues with the o2 sensors it would throw a code and tell you which one it is. Is the "check engine" light on?
Jim I got no codes coming up so i am puzzled.:confused:

[Mudderoy]

If I'm understanding it correctly NOTHING other than brakes are going to slow you down that fast. Well I guess if you had it in a low gear it could explain it, but I'm sure you'd know if you did.

To rule out the drive train do the same coasting experiment, but this time put the transmission in neutral.

Also check to see if you have one wheel (or more) that are much hotter than the others.

A video of the test would be helpful to get an idea of how fast it is slowing down, the next best thing would be to time it say from 50 mph to 30 mph, or 0 mph. Then we could do some comparisons.

[4.3LXJ]

The only thing an ECM can measure is whether or not it gets any voltage at all from the O2 sensor and whether or not the heater in it is working. But a malfunctioning sensor that is wearing out will not show a code. That is because there is no way for the ECM to evaluate that. After all, it is depending on the sensor for that information in the first place. They wear out just like solar panels do and loose their ability to generate current at capacity.

[cantab27]

is the problem there straight away...of after you have driven it for a bit....

[steph74]

(remember crappy gas in the winter....) we always have seen a serious decrease in gas mileage during winter months since we moved in Logan ;)

[steph74]

(remember crappy gas in the winter....) we always have seen a serious decrease in gas mileage during winter months since we moved in Logan ;)

PS. Do I have to order a pizza to get to see you and talk jeep ? lol

[alwaysxj]

PS. Do I have to order a pizza to get to see you and talk jeep ? lol
No Steph we still need to have a beer or two. I don't work all that much now that the wife got a new job. just let me know when and where or we can go shoot when i get some shells. :drinking:

[alwaysxj]

is the problem there straight away...of after you have driven it for a bit....
seems worse in the cold mornings, also don't know if this is related but lately my belt and pulley have been squealling like crazy in the morning or when I start the jeep when it has been sitting.

[bigjim350]

As mentioned checking for a clogged cat would be a good idea too. It could slow you down that fast if it was clogged. It would be acting as an exhaust brake.

Sent from my VM670

[Mudderoy]

As mentioned checking for a clogged cat would be a good idea too. It could slow you down that fast if it was clogged. It would be acting as an exhaust brake.

Sent from my VM670

How would you know? :sniper:

[prerunner1982]

To rule out the drive train do the same coasting experiment, but this time put the transmission in neutral.

Also check to see if you have one wheel (or more) that are much hotter than the others.

I was thinking this as well. My first thought if it wasn't the brakes that it was something in the trans. Almost like the torque converter was not releasing, or staying locked up.

Is it like when driving a manual trans and you let off the gas without pushing the clutch?

I have also had a brake dragging and boy you can definitely tell which one it is. I didn't have to get that close to it to feel the heat radiating off of it.

[alwaysxj]

Is it like when driving a manual trans and you let off the gas without pushing the clutch?

Yes john that is exactly how it feels...

so I did some testing today on the way home from work.
I would like to see if anyone can do this same thing and report back to me to compare. :pray::pray::pray::pray::pray::pray:
so I got the jeep up to 55MPH with it in drive and reset my trip to zero just as I let off. The jeep coasted for .4 of a mile to get down to 20 MPH (I had a car behind me or I would of kept going)

Test # two, Tony mentioned if it was a difference if the tranny was in neutral and I let off.
so same thing got up to 55 MPH and reset the trip. now this is where I am stumped :spongebob::crazy::D ( I love the spong bob)
when I let off it took .2 of a mile to get down to 20 MPH in neutral.

I am not sure what is going on with it. I can touch the hole rime on all four tires and they are cold not hot at all so i don't think it is a brake issue.

they keep saying it could be a clogged cat how do I check this?
thanks.

[prerunner1982]

Yes john that is exactly how it feels...

so I did some testing today on the way home from work.
I would like to see if anyone can do this same thing and report back to me to compare. :pray::pray::pray::pray::pray::pray:
so I got the jeep up to 55MPH with it in drive and reset my trip to zero just as I let off. The jeep coasted for .4 of a mile to get down to 20 MPH (I had a car behind me or I would of kept going)

Test # two, Tony mentioned if it was a difference if the tranny was in neutral and I let off.
so same thing got up to 55 MPH and reset the trip. now this is where I am stumped :spongebob::crazy::D ( I love the spong bob)
when I let off it took .2 of a mile to get down to 20 MPH in neutral.

I am not sure what is going on with it. I can touch the hole rime on all four tires and they are cold not hot at all so i don't think it is a brake issue.

they keep saying it could be a clogged cat how do I check this?
thanks.

Hmm.. the trans in gear takes longer to slow than the trans out of gear... :out:

As far as the clogged cat.. if the trans is not in gear any restriction on the cat converter or engine would/should not have any effect on the speed/deceleration of the vehicle... since they are no longer engaged.

If I can remember.. I will try the deceleration test on the way home tonight. Granted I have a manual trans, but in Neutral it should not matter what type of trans, right?

[alwaysxj]

Thanks john

[4.3LXJ]

I was thinking this as well. My first thought if it wasn't the brakes that it was something in the trans. Almost like the torque converter was not releasing, or staying locked up.

Is it like when driving a manual trans and you let off the gas without pushing the clutch?

I have also had a brake dragging and boy you can definitely tell which one it is. I didn't have to get that close to it to feel the heat radiating off of it.

Nearly a half mile to slow 35 mph is not dragging. The difference you are seeing when in gear is due to the engine at idle pushing the Jeep. I really don't think there is anything wrong with the drive train or brakes.

[alwaysxj]

Nearly a half mile to slow 35 mph is not dragging. The difference you are seeing when in gear is due to the engine at idle pushing the Jeep. I really don't think there is anything wrong with the drive train or brakes.

Maybe I just have not noticed it then, but it still seams weird to me. I would like to see if someone with a auto could do the test to see if there is a difference.

[prerunner1982]

Nearly a half mile to slow 35 mph is not dragging. The difference you are seeing when in gear is due to the engine at idle pushing the Jeep. I really don't think there is anything wrong with the drive train or brakes.

I know in a manual that is the case, but his is an auto there should not be as much "engine braking" on an auto.... from my experience.

And now that you say it, you are right that 35mpg in almost 1/2 mile does not seem bad... however out of gear he dropped 35mph in .2 miles. Why when no engine braking the XJ stops quicker?

[4.3LXJ]

I know in a manual that is the case, but his is an auto there should not be as much "engine braking" on an auto.... from my experience.

And now that you say it, you are right that 35mpg in almost 1/2 mile does not seem bad... however out of gear he dropped 35mph in .2 miles. Why when no engine braking the XJ stops quicker?

An auto, particularly late model ones will push a vehicle by staying in gear at idle. You don't notice it, but it does happen and this little test is proof of it. It doesn't operate the same as a standard tranny

[XJ Wheeler]

Because the engine is still pushing even with no throttle being applied, think about when your idling in gear with no brakes. The vehicle moves just not fast because there's not many rpm's. And when its in neutral you don't have that idling power pushing.



Edit: looks like you beat me Steve.:driving:

[prerunner1982]

Well then my data is pointless...

In neutral 55-20 in .6 miles.
In gear 50-25 in .3 miles. Could not get to 55 due to speed limit..and had to pull out at 25 to keep engine from dying.

[alwaysxj]

I guess I just never noticed it slow me down that much.
now I need to get some o2 sensors to see how my gas mileage improves.

[cantab27]

do what i do steve.... park next to a buddys xj and swap sensors to it run rights , then go and buy that said sensor...... saves cash..........my was running like shit until i put a new o2 in the front...only needed the one as i dont run a pussy.....

[bigjim350]

any decent exhaust shop should be able to test for a bad or clogged cat.

[alwaysxj]

do what i do steve.... park next to a buddys xj and swap sensors to it run rights , then go and buy that said sensor...... saves cash..........my was running like shit until i put a new o2 in the front...only needed the one as i dont run a pussy.....
That would work wayne if I knew some one with a 01 that was close. :bang: