post #1 of Old 01-22-2013, 09:58 PM Thread Starter
kgb_m3
Registered User
1989 YJ Wrangler 
 
Join Date: Dec 2011
Location: San Diego
Posts: 1,026
Poor gas mileage

Hey guys, I'm a bit confused as to what is going on with my gas mileage lately. I have been working on the jeep for the past year or so and have replaced just about everything under the hood.

I've been getting around 18 to 20mpg until recently. Bought a hard top and had my mc2150 tuned to eliminate rough idle and slight misfire. Since then, the Jeep runs a lot better but uses up a lot more gas. I would say I'm down to 12mpg or so.

Would the hard top and properly tuned carb really cause this much of a drop? What else should I consider looking into?


89 YJ 4.2L http://www.jeepforum.com/forum/f12/kgb-89-yj-storyline-build-thread-1520814/
96 XJ 4.0L http://www.jeepforum.com/forum/f177/600-96-xj-budget-daily-overland-build-1855418/
http://www.jeepsunclassified.com
kgb_m3 is offline  
post #2 of Old 01-23-2013, 05:49 AM
Mark05059
Registered User
1989 YJ Wrangler 
 
Join Date: Mar 2009
Location: quechee Vermont
Posts: 4,687
lots of drag/extra weight with that hard top. If the tune of the carb added fuel to the mix then yeah you would loose some efficency there too. Just throwing things out there. Take the hard top back off and see what happens with it.

1998 ZJ 5.2 Auto

1989 Wrangler Black Bone Stock 2.5l 5spd
/l , [____],
|---L--[]lllllll[]-
()_) ()_)==O=)_)
Mark05059 is offline  
post #3 of Old 01-23-2013, 06:14 AM
EABiker
Registered User
1989 YJ Wrangler 
 
Join Date: Dec 2004
Location: Frederick, MD
Posts: 1,715
If your carb was running a bit too lean before the tuneup, you may have been on the edge of the balance between running lean with good efficiency, and not quite enough fuel to keep away the misfire. After the tune, the F/A ratio was probably fattened up a bit more than needed to eliminate the poor running, and caused a drop in MPG.

Of course, your mileage may vary!
EABiker is offline  
post #4 of Old 01-23-2013, 06:31 AM
Rufe
Registered User
1994 YJ Wrangler 
 
Join Date: Aug 2011
Location: Hamer
Posts: 29
I lose about two miles per gallon when I switch from a safari to to hardtop, but my hardtop has a roof rack on it. I suspect that the roof rack is the main offender. Roof rack was installed by previous owner and I would be afraid to put more than a fifty pound load on it.
Rufe is offline  
post #5 of Old 01-23-2013, 06:57 AM
EABiker
Registered User
1989 YJ Wrangler 
 
Join Date: Dec 2004
Location: Frederick, MD
Posts: 1,715
Your hard top weighs less than a normal passenger; do you see the same drop with 2 in the Jeep? Also, the aerodynamics of a Jeep are so bad anyway I cannot see that the minor change in the top shape would make such a big difference. The outdoor temperature change when running a soft/no top versus a hard top, (colder out), probably has alot more to do with the MPG losses than the aerodynamics. My bet is still on the carb.
EABiker is offline  
post #6 of Old 01-23-2013, 09:01 AM
Beachcruiser
Registered User
1987 YJ Wrangler 
 
Join Date: Feb 2008
Location: Raleigh, NC
Posts: 419
What's your setup on the MC carb?

IOW, do you know what was changed?

They are VERY easy to tune yourself......

probably out breaking stuff.
Beachcruiser is offline  
post #7 of Old 01-23-2013, 11:22 AM
Rproject
Registered User
1987 YJ Wrangler 
 
Join Date: Aug 2008
Location: Sandwich, IL
Posts: 2,759
I had the same problem when we did the nutter bypass. Since it's winter, and the Wrangler doesn't get driven much this time of year, I'm holding off until spring to really dig into it.

1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
Rproject is offline  
post #8 of Old 01-23-2013, 02:42 PM Thread Starter
kgb_m3
Registered User
1989 YJ Wrangler 
 
Join Date: Dec 2011
Location: San Diego
Posts: 1,026
Thanks for ideas guys. The carb was bought from the "famous" ebay guy as a "pre-tuned, plug and play" setup. I installed the carb, nuttered the jeep and the gas mileage has been great. However, the choke was set around 1200rpm on cold start and at warm the idle jumped from 450-600rpm barely keeping the jeep running. Since I have never owned a carbed vehicle, I took it to a shop for them to tune the 2150 months after running it with ebay guy settings.

I picked up the Jeep and couldn't believe how nice they got it running. Smooth idle, healthy sound, in Park around 900rpm and when drop it in Drive 650 -700 or so. Cold start choke is much higher close to 1800rpm. I have electric choke.

89 YJ 4.2L http://www.jeepforum.com/forum/f12/kgb-89-yj-storyline-build-thread-1520814/
96 XJ 4.0L http://www.jeepforum.com/forum/f177/600-96-xj-budget-daily-overland-build-1855418/
http://www.jeepsunclassified.com
kgb_m3 is offline  
post #9 of Old 01-23-2013, 04:27 PM
Rproject
Registered User
1987 YJ Wrangler 
 
Join Date: Aug 2008
Location: Sandwich, IL
Posts: 2,759
Quote:
Originally Posted by kgb_m3 View Post
Smooth idle, healthy sound, in Park around 900rpm and when drop it in Drive 650 -700 or so. Cold start choke is much higher close to 1800rpm. I have electric choke.
Those sound dead on for factory idle settings.

Mine was adjusted about a month or two ago to those specs and that's when I saw my fuel economy plummet as well.

1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
Rproject is offline  
post #10 of Old 01-23-2013, 07:27 PM Thread Starter
kgb_m3
Registered User
1989 YJ Wrangler 
 
Join Date: Dec 2011
Location: San Diego
Posts: 1,026
Quote:
Originally Posted by Rproject View Post
Those sound dead on for factory idle settings.

Mine was adjusted about a month or two ago to those specs and that's when I saw my fuel economy plummet as well.
Makes sense then. I would rather waste more gas and have the jeep run the way it does now over how it ran before. I couldn't even go through a trail without killing my battery. The idle speed was so low and due to slight misfire, the alternator wasn't spinning enough to keep everything at 14V.

I'm going to replace the fuel filter, clean my K&N air filter (haven't done so in about a year now with over 15 offroad trips), check my alignment (toe will kill your gas mileage if it's off).

89 YJ 4.2L http://www.jeepforum.com/forum/f12/kgb-89-yj-storyline-build-thread-1520814/
96 XJ 4.0L http://www.jeepforum.com/forum/f177/600-96-xj-budget-daily-overland-build-1855418/
http://www.jeepsunclassified.com
kgb_m3 is offline  
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome