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very poor fuel mileage

Re: very poor fuel milage

I'm with ya ruger81...

My mileage has gone f/18-20mpg City/Hwy driving about 1 year back to most recently 11-12mpg. My tune-up is spot on, but I think I've either developed a header gasket leak or had my O2 Sensor get bad. I've currently got 247K miles on my '96 4.0 Auto 4x4. Runs like a top, but burns the gas like crazy!!

My exhaust leak and O2 sensor could be effecting each other obviously... but we'll see.

If you found your culprit its always nice to hear the results.
 
Re: very poor fuel milage

cruiser54 said:
With a bad MAP, it would run pig rich and idle very poorly, if at all.
Click to expand...
i tested it with a volt meter everything seems to be fine. it idles way rich i think, it smells of fuel. also when i go up in the mountains it will idle like crap sometimes right after start up for a few, then it cleans up.
 
Re: very poor fuel milage

In order, the most likely sensors to cause rich running are:
MAP-whether in open or closed loop
CTS-whether in open or closed loop
O2 sensor-in closed loop only
 
Re: very poor fuel milage

Hmm, I would have listed the O2 sensor first and the MAP last, at least for a Renix Era MAP. I almost never hear of a bad MAP, and a working O2 should compensate in closed loop.
 
Re: very poor fuel milage

could someone tell me how to check my o2 sensor. i dont have any trouble codes now and my last tank i got 10.6 per gal..
 
Re: very poor fuel milage

Ecomike said:
Hmm, I would have listed the O2 sensor first and the MAP last, at least for a Renix Era MAP. I almost never hear of a bad MAP, and a working O2 should compensate in closed loop.
Click to expand...

Being that his symptoms are in open loop as well as closed loop, the MAP and CTS are on my list before the O2 sensor which only comes into play in closed loop.
 
Re: very poor fuel milage

tonight i replaced the o2 sen. i will drive another tank or two and report back. i also bought a new map sen as well so we will see what one it is.

( the body of the new one was twice as big around as the old one also the new one is bosch and the old is some weard brand)
 
Re: very poor fuel milage

ruger81 said:
tonight i replaced the o2 sen. i will drive another tank or two and report back. i also bought a new map sen as well so we will see what one it is.

( the body of the new one was twice as big around as the old one also the new one is bosch and the old is some weard brand)
Click to expand...

Only replace one at a time so you will know which one it was.

I'm having very similar issues with my 90. Fuel mileage tanked out, went from 300 miles on a tank to 175. I also smell fuel near the rear of the Jeep but I have no fuel leaks anywhere so Its coming from the exhaust. I replaced all of my sensors and output devices 4 years ago when I installed my rebuilt original engine. I'm suspecting the MAP on this one because the idle is very rough at times.
 
Re: very poor fuel milage

xjtrailrider said:
Only replace one at a time so you will know which one it was.

I'm having very similar issues with my 90. Fuel mileage tanked out, went from 300 miles on a tank to 175. I also smell fuel near the rear of the Jeep but I have no fuel leaks anywhere so Its coming from the exhaust. I replaced all of my sensors and output devices 4 years ago when I installed my rebuilt original engine. I'm suspecting the MAP on this one because the idle is very rough at times.
Click to expand...

Check the integrity of the vac line from the TB to the MAP. Also make sure the harness connector to the MAP is clean and secure.
 
For those that like spending money and randomly throwing new parts at a jeep to fix it, do not read the rest of this post.

For the others, who prefer to test parts to see what is bad and what is not before parting with their money, here is a link to a thread I wrote up a while back on how to test Jeep oxygen sensors, O2 heater relay and wiring with a multi meter (volts and ohms):

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test+renix
 
cruiser54 said:
Check the integrity of the vac line from the TB to the MAP. Also make sure the harness connector to the MAP is clean and secure.
Click to expand...

I have good voltage at the MAP, The original line had been repaired by me a few times since 1990 so I popped the $20 for a new one at the dealer last week. I'm going to test the MAP and O2 today to see which one it is.

Ecomike said:
For those that like spending money and randomly throwing new parts at a jeep to fix it, do not read the rest of this post.

For the others, who prefer to test parts to see what is bad and what is not before parting with their money, here is a link to a thread I wrote up a while back on how to test Jeep oxygen sensors, O2 heater relay and wiring with a multi meter (volts and ohms):

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test+renix
Click to expand...

With ya Mike, test before you buy!
 
87 aw4 4.0 31s 3.55s was getting 20 last fall lugging in OD at 45-55 going up into the mountains. Broke on the way back and just started driving it again after a good bit of upgardes was getting like 10, CTS tested bad now getting 14.5 on a 120 mile trip to pick up a t case the other day drving into some gnarly wind and haulin balls on the way back. Gonna check the O2 tommarow. Hopin thats it but if so damn some luck to lose both at once.
 
Ecomike said:
For those that like spending money and randomly throwing new parts at a jeep to fix it, do not read the rest of this post.

For the others, who prefer to test parts to see what is bad and what is not before parting with their money, here is a link to a thread I wrote up a while back on how to test Jeep oxygen sensors, O2 heater relay and wiring with a multi meter (volts and ohms):

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test+renix
Click to expand...

maybe you should read the entire post again i have tested every part.. you have good advice all the way up to your comment about throwing parts at a jeep to fix it... we all do that in one way or the other. thats one of the more ignorant things to say. feel free to post productive reply's in this post other wise dont. (n)
 
ruger81 said:
maybe you should read the entire post again i have tested every part.. you have good advice all the way up to your comment about throwing parts at a jeep to fix it... we all do that in one way or the other. thats one of the more ignorant things to say. feel free to post productive reply's in this post other wise dont. (n)
Click to expand...

Hmm, I think you kicked over the wrong rock here sir!

YOU asked how to test an O2 sensor in this thread a day ago. Your very next post in this thread said you replaced the O2 sensor, with no mention by you of having tested it first. There are also others that have jumped into this thread with posts, that I was also addressing my "test first, and how to test an O2 sensor" comment to.

If you wish, I will glad to avoid answering any further posts or questions you post asking for help. Sorry to have waisted your time and rattled your cage with my "ignorant" post. LOL
 
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