Running Rich

[BlackYJ]

Well my mpg in my YJ has been sucking some ballz lately so I took it into the shop and they said my engine was running rich and I probably needed a new O2 sensor.  Okay no big deal but I replaced it back in early spring, so I am kind of surprise this went bad already.  It was a bosch O2 sensor.

So my question is, is there really anyway to correct how the engine is running or is it self adjusting?  I am not running a cat and have not been for years, so I know this is not a problem.  Also when I did the engine swap, they mechanic did not put back all the emission stuff like the charcol box or whatever it is, would this make a difference.  I did the swap back in June and it was running great until september then my mpg took a huge nose dive.  I went from 425 km per tank to about 285-300 km per tank.

[BUKI]

hey dude, hopefully I can help.  your O2 could definetly be an issue. but your Map sensor as well, and your coolant temp sensor could be telling your engine it is always running in the cold mode. have you checked your plugs, wires, cap, rotor and coil as well. any fault in any of these could result in a drop of mpg.  also check your timing in third year I learned your timing is always overlooked in a tuneup.

Mike

[Gearhead]

Timing is not adjustable ,  also , it would be nice to read the data stream and look at actual sensor values

[BlackYJ]

hey dude, hopefully I can help.  your O2 could definetly be an issue. but your Map sensor as well, and your coolant temp sensor could be telling your engine it is always running in the cold mode. have you checked your plugs, wires, cap, rotor and coil as well. any fault in any of these could result in a drop of mpg.  also check your timing in third year I learned your timing is always overlooked in a tuneup.

Mike

The cap, rotor, wires, plugs, etc are all recently new.  Just a question though, if the coolant temp sensor was telling the engine it was cold, it would probably run leaner because oxygen burns hotter than gas.  I think I will take it back and tell them to check some of the sensors.  Anyone have any other ideas

[Gearhead]

You have it reversed , if the eng. temp. sensor is sending  the ecm  a value that shows a lower temp than what is the actual value , the ecm will throw more fuel in , as though it were still warming up . This is where reading / viewing the data stream , and interpreting that data will help.

[Dragonmaster]

You have it reversed , if the eng. temp. sensor is sending  the ecm  a value that shows a lower temp than what is the actual value , the ecm will throw more fuel in , as though it were still warming up . This is where reading / viewing the data stream , and interpreting that data will help.

What he said.

[BUKI]

ok, so if you losen the bolt on the distributer, and twist the distributer, what are you adjusting??? :?  And if it was OBDII you could read the data stream with a scantool, I have a Snap-on one.  Old but still very usefull.
definetly worth the money.

[Gearhead]

ok, so if you losen the bolt on the distributer, and twist the distributer, what are you adjusting??? :?  And if it was OBDII you could read the data stream with a scantool, I have a Snap-on one.  Old but still very usefull.
definetly worth the money.

The distributor body is indexed by the hold down bolt and can't be rotated.

I use an OTC enhanced 4000 monitor , an oldie too , but it works well on both of my OBD 1 Jeeps , reads data , codes , erases them , tests relays , tests injectors , tests the fuel pump and more. With this scan tool and an infra red thermometer , a guy could check the CTS  easily.