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General Forums => The Mess Hall => Topic started by: spoonman on September 11, 2009, 05:54:42 PM
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i did the 4.0 swap. there's plenty of power now for me. my problem is i'm now getting 14.5 mpg and it's running rich. i was getting 21 mpg + and expected a slight drop, not this much. i can't make my 100 mile commutes in the jeep getting 14.5 mpg. i'll give it another week and see what happens. i have put 500 miles on it this week. the computer should be adjusted by now and i also disconnected the battery when i swapped. ugh i don't really want to put the stock tb back on but might have to.
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When you disconnected the battery, did you touch the positive and negative clamps together to drain the capacitors holding the ECM's memory?
It may take 50 warm-up cycles for the computer to completely adjust.
Your mileage shouldn't have changed that much, something is going on. I get 15mpg but that's with 35" tires and 5.38 gears.
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When you disconnected the battery, did you touch the positive and negative clamps together to drain the capacitors holding the ECM's memory?
It may take 50 warm-up cycles for the computer to completely adjust.
Your mileage shouldn't have changed that much, something is going on. I get 15mpg but that's with 35" tires and 5.38 gears.
maybe he didn't change the tps, not sure how you end up richer otherwise
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You might want to investigate the sensors that affect the fuel to air mix (e.g., coolant temp. O2).
Also, you may have the wrong gear ratio for maximum fuel efficiency with the 4.0. The recommended ratio for 35s on a 4.0 liter DD rig is 4.56 (as per Jim Allen).
Give it some time for the computer to adjust, then look at your sensors. Just curious, what's you axle ratio and tire size?
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You might want to investigate the sensors that affect the fuel to air mix (e.g., coolant temp. O2).
Also, you may have the wrong gear ratio for maximum fuel efficiency with the 4.0. The recommended ratio for 35s on a 4.0 liter DD rig is 4.56 (as per Jim Allen).
Give it some time for the computer to adjust, then look at your sensors. Just curious, what's you axle ratio and tire size?
he swapped the t/b and his mpg dropped to 14.5 from 21 - there is no way the difference is that big due to the computer using wide fuel trims (and since it is supposed to be a larger t/b it would be leaner and not richer). I'd say swap back and see if you're back at 21 - then your focus is on the t/b and the only thing that is on there which is tps - if it's still at 14.5 or close then look as see like VA_YJ said one of the sensors (maybe you unplugged something by accident when you swapped the t/b). btw, how did you determine it is richer?
EDIT: all this of course assuming that the mpg was calculated at the same speed on the hwy - if you had 21 at 55mph and 14.5 at 80mph then it's normal to have less mpg even at that difference
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the tires are stock. gears are 4.10. my guess it's running rich is that i get black smoke now when i wind out 1st and 2nd. it now has strong exhaust fumes and it didn't before. my guess is i just disconnected the positive and didn't touch the 2 together, or i screwed up and put the wrong map back on. not sure how the wrong tps would affect it. as soon as i did the swap the jeep no longer tries to die on the first startup of the day. i'll redo the battery cables. i'm also going alot easier on it now. i was wringing it out before. i also wasn't going 55mph on the highway at anytime. i go 65 and was still getting 21mph.
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Since your swap the biggest thing I would look for if the map sensor is getting proper vacuum the hose is not cracked or loose and the fitting on the TB housing has no leaks
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the tires are stock. gears are 4.10. my guess it's running rich is that i get black smoke now when i wind out 1st and 2nd. it now has strong exhaust fumes and it didn't before. my guess is i just disconnected the positive and didn't touch the 2 together, or i screwed up and put the wrong map back on. not sure how the wrong tps would affect it. as soon as i did the swap the jeep no longer tries to die on the first startup of the day. i'll redo the battery cables. i'm also going alot easier on it now. i was wringing it out before. i also wasn't going 55mph on the highway at anytime. i go 65 and was still getting 21mph.
the map should be the same (i think, for the 91-95 they are the same for sure), however the tps will make a big difference so if you did not use the one off the 2.5l one you should put it on, that could be your "rich" problem and that also explains why is not dieing when cold (check the p/n on the 2 of them, you'll see they are different, you can check the ones on the map sensors as well but those should be the same). the reason it dies when cold could be the temp sensor for the pcm/ecu and it sounds that it is your problem by what you describe. the 55mph was just an example - when you compare mpg you should do it at the same constant hwy speed, the faster you go the less mpg and it can get a big difference especially if you put the pedal to the floor or the moment you're out of the closed loop to be more specific (so even if you have pedal left but your pcm is not using o2 for adjusting the air/fuel ratio).
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thanks for the help like always. the jeep is in the garage for a few days. i'm painting the work car today. i'll check the sensors tomorrow. i have some amber hellas to put on the jeep this week, so i'll have the jeep out soon.
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i'm taking the 4.0 tb off. i reset the pooter yesterday while i put on the hellas. same gas mileage. ugh i did make sure all the 2.5 parts made it on. i did leave all the 4.0 pigtails on the 4.0 sensors. so i didn't screw that up. i have no clue why this killed gas mileage this much.