Topic: anyone think this is odd?

[stan98tj]

I dont want to add to yet another mpg thread but i do want to throw out a few specs and see if anyone finds this odd.
thus far i have added an AEM cold air intake, 62mm TB and spacer (im going to bore it out soon-havent had the time) banks header and exhaust.  With all this my average mpgs are around 12mpg. The AEM actually helped, i was originally at about 9mpgs. Im only running 31s and i have a 3spd auto (that was recently rebuilt). I know the jeep isnt a fuel efficient vehicle, i know it's not a hybrid....but isnt this sort of low?? I dont drive it hard, dont floor it, i average 60-65mph. Over really long hauls on the interstate, my mpgs may climb to about 14, maybe 15.

So, here is the question, if you think this is prob not normal, where do i start looking? Could my injectors be shot? Fuel sender/pump. Maybe fuel filter is shot? what about the computer? am i missing anything?

oh and HOW THE HELL are you guys with 35s getting over 20mpgs???!!! (as per the official mpg thread) 

[sharpxmen]

I dont want to add to yet another mpg thread but i do want to throw out a few specs and see if anyone finds this odd.
thus far i have added an AEM cold air intake, 62mm TB and spacer (im going to bore it out soon-havent had the time) banks header and exhaust.  With all this my average mpgs are around 12mpg. The AEM actually helped, i was originally at about 9mpgs. Im only running 31s and i have a 3spd auto (that was recently rebuilt). I know the jeep isnt a fuel efficient vehicle, i know it's not a hybrid....but isnt this sort of low?? I dont drive it hard, dont floor it, i average 60-65mph. Over really long hauls on the interstate, my mpgs may climb to about 14, maybe 15.

So, here is the question, if you think this is prob not normal, where do i start looking? Could my injectors be shot? Fuel sender/pump. Maybe fuel filter is shot? what about the computer? am i missing anything?

oh and HOW THE HELL are you guys with 35s getting over 20mpgs???!!! (as per the official mpg thread) 

if you don't floor it i'd say it's too low - my mpg is around 13 with 33x12.5 tires and pedal to the floor in 4th gear on the hwy. It gets better if i watch my afr gauge to make sure i keep it in closed loop but i yet to have the patience to calculate that (I do some fuel savings but then i get carried away and go wot since everyone else is passing me and 80 yo women are giving me the finger for driving too slow).

not sure how much of a difference the auto would make, i have a manual.

i'd say to see if the o2 sensor is in good condition and if your cat is good (aside of the other things that make for a good tuneup). Also keep in mind that if you didn't change your speedo gear you also need the account for the error in miles displayed by your odometer (from stock tires to 31s) - that would make some difference, about 10% in your case i believe - so in fact would be 13.2 mpg if that's the case.

Dunno about the guys getting 20mpg with 35s, i'd be interested in finding that out too.

[aw12345]

Stock 4cyl rarely gets 20 mpg. Still mine on the highway will get 17-18 mpg and not much worse with mixed driving. Something like 16-17 mpg so not bad on 35" tires, quite happy with the current setup. Stan you might want to check that the torque converter clutch engages while driving, could be more of a reason for the poor milage than anything else. If the engine runs good when started/ doesn't run rough or like it chokes you can pretty much figure the injectors are good. If you had no cat failures or a check engine light on then most likely the whole feed back system is ok. Would not hurt to hook it up to a scan tool and look at O2 sensor toggle and fuel trim, but I still think the converter clutch not engaging is your most likely culprit

[stan98tj]

Stock 4cyl rarely gets 20 mpg. Still mine on the highway will get 17-18 mpg and not much worse with mixed driving. Something like 16-17 mpg so not bad on 35" tires, quite happy with the current setup. Stan you might want to check that the torque converter clutch engages while driving, could be more of a reason for the poor milage than anything else. If the engine runs good when started/ doesn't run rough or like it chokes you can pretty much figure the injectors are good. If you had no cat failures or a check engine light on then most likely the whole feed back system is ok. Would not hurt to hook it up to a scan tool and look at O2 sensor toggle and fuel trim, but I still think the converter clutch not engaging is your most likely culprit

how would i find out if the converter clutch is engaging or not. torque converter blowing up was the reason i had to get the tranny rebuilt to begin with. id like to think they rebuilt it pretty well...the lags between shifts are now gone. A cat failure would throw a code as would an O2 sensor failure correct?

[sharpxmen]

how would i find out if the converter clutch is engaging or not. torque converter blowing up was the reason i had to get the tranny rebuilt to begin with. id like to think they rebuilt it pretty well...the lags between shifts are now gone. A cat failure would throw a code as would an O2 sensor failure correct?

o2 failure would, not sure about the cat in your case (i don't think it would if it gets plugged, but i dunno to be honest).

[stan98tj]

o2 failure would, not sure about the cat in your case (i don't think it would if it gets plugged, but i dunno to be honest).

so if my O2 hasnt thrown a code, then it should be functioning correctly. how can i make sure?
oh, and i think my speedo is still accurate. my gps tells me when i get up over 55mph so i checked it against my speedo...lit up right as the needle passed 55mph.

[Sine Deviance]

One thing is manual vs. automatic. I'd assume that the majority of the posters here are running manuals because they seem to be less rare. Automatics use more gas than manuals for two reasons, one is because the gearing is different all around, and two is the automatic transmission itself is not as efficient as a manual because of the torque converter. Still, an automatic will usually only lose a couple mpg compared to a manual in the same vehicle.

[radark1]

The Jeeps I run with .... two  (1992 and 1995) are the 4 bangers and one is a 6 cylinder (1987 w/ Fuel injection) ...the 4 bangers ... both have 4.88 gears, 3" lifts, running 33" tires. Lockers front and rear. The 4 bangers are getting about 13-14 MPG....and the 6 cylinder is getting around 15 MPG.

I find it very hard to believe that anyone is getting 20+mpg.

[stan98tj]

im thinkin my injectors may be bad. i had them out once and checked the stream, it seems to just piss fuel in a straight line. have any of you checked ur injector stream? or know what it's supposed to look like? i know its a simple injector and wont atomize into a mist or anything, but shouldnt there be some type of spray pattern rather then a straight line?

[sharpxmen]

im thinkin my injectors may be bad. i had them out once and checked the stream, it seems to just piss fuel in a straight line. have any of you checked ur injector stream? or know what it's supposed to look like? i know its a simple injector and wont atomize into a mist or anything, but shouldnt there be some type of spray pattern rather then a straight line?

on the pintle design should atomize a fine mist in a cone pattern - did you check them at the stock fuel pressure (49 psi in your case)? if the pressure is too low it won't atomize.

[stan98tj]

on the pintle design should atomize a fine mist in a cone pattern - did you check them at the stock fuel pressure (49 psi in your case)? if the pressure is too low it won't atomize.

i dont know. i just popped them out and activated them-the stream came out strong, but didnt mist or make any type of spray pattern.

[sharpxmen]

i dont know. i just popped them out and activated them-the stream came out strong, but didnt mist or make any type of spray pattern.

did you jump the fuel pump during that time? if you didn't the pressure goes away really quick

[aw12345]

I guess the easiest way to check converter clutch engagement is at about45 mph steady speed in 3 th gear keep the gas steady and lightly apply the brakes to the point that the brake lights come on and see what the tach does. If the rpm goes up a bit doing this the clutch was applied before you hit the brakes, if it makes no difference it wasn't

[stan98tj]

did you jump the fuel pump during that time? if you didn't the pressure goes away really quick

no i didnt think to. should there be enough pressure in there to make a spray pattern on the first activation? because it shot straight stream the entire time.

[sharpxmen]

no i didnt think to. should there be enough pressure in there to make a spray pattern on the first activation? because it shot straight stream the entire time.

it's not enough pressure - it's a liquid (so not like an air compressor tank or a gas bottle) and the pressure will drop right down significantly the moment you open the injector (since liquids won't compress) - whatever pressure it was there was stored mechanically in the lines deforming slightly. for a test to be relevant you should have the pump running the entire time when you test the injectors.