Knucklehead97 Posted August 2, 2013 Share Posted August 2, 2013 Okay guys I've recently been noticing that I've really got bad gas mileage. I had 160 miles on the trip when I added 15 gallons to it yesterday. I think I fixed the rough idle, need to get some vacuum line bushings though. I shift at 2300 rpms (to high? To low?) I'm running 30x9.50 mud tires on stock gears, could this result in anything? Ive got idle adjusted to about 800 rpms. Ive got new muffler with no cat on stock pipes. But a small exhaust leak hole (waiting till I repipe to 2.5" before I fix that) and Ive still got my bad rms leak. 4.0/ba10/4x4 with 224k miles. Please give me every little thing that could be causing this because I can't afford the gas. Should I readjust the TPS? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 And wheres places that gas leaks often appear? I don't smell anything but it may have one when running, who knows Link to comment Share on other sites More sharing options...
nitroxsteve Posted August 2, 2013 Share Posted August 2, 2013 Do you still have vacuum leaks? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 Not from what I could tell. I had to tape up the connection to the MAP sensor because it was so rotted. The only other bad one I can find is the oil return line (I think?) Does anyone have a diagram of the complete vacuum line harness? I think I may actually be missing a line from the air box... Link to comment Share on other sites More sharing options...
nitroxsteve Posted August 2, 2013 Share Posted August 2, 2013 I don't think your ever going to get maximum MPG as long as you have vacuum leaks. I am sure someone can help with diagrams. Is it the 89 4.0? Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 Yep. Original Renix. Itd be greatly appreciated if someone had a diagram. I need to check under the hood of my friends 88 XJ and compare >.> Link to comment Share on other sites More sharing options...
fiatslug87 Posted August 2, 2013 Share Posted August 2, 2013 The three vacuum harness lines are Dorman PN 46003, 46004 and 46005. Link to comment Share on other sites More sharing options...
Eagle Posted August 2, 2013 Share Posted August 2, 2013 A bad or failing oxygen sensor results in poor fuel mileage because the engine is always running rich. Same thing can happen if you run a cold (or no) thermostat, or if the coolant sensor (the one on the side of the block, that sends data to the ECU) is bad. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 I am deffinetely missing a couple lines... need to see it on an actual engine to be sure. And how do I check the o2 sensor? Link to comment Share on other sites More sharing options...
Oddmodman Posted August 2, 2013 Share Posted August 2, 2013 Don't forget that at that mileage you may simply be losing efficiency due to loss of compression. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 But down to 160 miles a tank? Seems a little drastic honestly. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 2, 2013 Share Posted August 2, 2013 MAP line taped? Not good. If you've never replaced your oxygen sensor, do it. Adjusted your idle? Not good. And, you're shifting at way too low an RPM, Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 So i should do what? Adjust the tps again? And what rpm should I? And how do I change the oxygen sensor? This all explains alot. Where can I get the new map sensor connection? Its not the line I taped, just the rotten end at the MAP sensor. Thanks. Link to comment Share on other sites More sharing options...
Eagle Posted August 2, 2013 Share Posted August 2, 2013 nd, you're shifting at way too low an RPM, No he's not. It's a Renix, not an HO. I have always shifted at 2200 RPM. My '88 XJ (287,000 miles) still gets 20 MPG, and the '88 MJ (125,000 miles) gets 18 to 19 MPG. Link to comment Share on other sites More sharing options...
ParadiseMJ Posted August 2, 2013 Share Posted August 2, 2013 MAP line taped? Not good. X2 on this. Vacuum lines are MUCH cheaper than gas. Get the proper, or at least SOUND vacuum tubing. One whole solid piece, not repaired...replaced. You can even get a MAP sensor at the junkyard for a song.You should be getting at least 250 miles on a tank IMHO. I see tons of sketchy and missing vacuum configurations in the junkyards. Buy the correct harnesses where you need to, and the rest of the vac lines can be just bulk line...like 75 cents or $1 a foot. Taped up and/or spliced lines are invitations for leaks, ergo poor performance...and bad mpg. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 2, 2013 Author Share Posted August 2, 2013 Is there like a package I can buy that has all the vacuum lines? Like a harness or something? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 2, 2013 Share Posted August 2, 2013 nd, you're shifting at way too low an RPM, No he's not. It's a Renix, not an HO. I have always shifted at 2200 RPM. My '88 XJ (287,000 miles) still gets 20 MPG, and the '88 MJ (125,000 miles) gets 18 to 19 MPG. Geez. I've only shifted at higher RPMs since these were new in 1987 and never had mileage issues. HO stands for Highly Overrated anyway. That's lugging it. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 2, 2013 Share Posted August 2, 2013 So i should do what? Adjust the tps again? And what rpm should I? And how do I change the oxygen sensor? This all explains alot. Where can I get the new map sensor connection? Its not the line I taped, just the rotten end at the MAP sensor. Thanks. I want to know how YOU adjusted the idle. Link to comment Share on other sites More sharing options...
Keyav8r Posted August 2, 2013 Share Posted August 2, 2013 89 with a BA10 transmission? I thought they were AX-15 after 88. Maybe an early 89? Link to comment Share on other sites More sharing options...
fiatslug87 Posted August 3, 2013 Share Posted August 3, 2013 Is there like a package I can buy that has all the vacuum lines? Like a harness or something? I listed the part numbers of the three main vac lines you need, search any auto parts site. They are very simple to install. The last one would be the MAP line, do what has been posted, buy bulk vac line and replace it.This is what the 003 & 004 parts look like: And on the engine: Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 3, 2013 Share Posted August 3, 2013 HO stands for Highly Overrated anyway. That's lugging it. Uncalled for ignoramus maximus statement that does nothing to answer the OP's question. Link to comment Share on other sites More sharing options...
Eagle Posted August 3, 2013 Share Posted August 3, 2013 89 with a BA10 transmission? I thought they were AX-15 after 88. Maybe an early 89? Correct. The change to the AX-15 was a mid-year change in the 1989 model run. Around the same time was when the C101 firewall wiring harness connector went away. Link to comment Share on other sites More sharing options...
Eagle Posted August 3, 2013 Share Posted August 3, 2013 Geez. I've only shifted at higher RPMs since these were new in 1987 and never had mileage issues. HO stands for Highly Overrated anyway. That's lugging it. Shifting at 2200 RPM is lugging it? Not hardly. With the automatic and stock tires, 2200 RPM is about 68 MPH in overdrive. I don't think comes anywhere near ANY definition of "lugging it." Link to comment Share on other sites More sharing options...
cruiser54 Posted August 3, 2013 Share Posted August 3, 2013 HO stands for Highly Overrated anyway. That's lugging it. Uncalled for ignoramus maximus statement that does nothing to answer the OP's question. Point being that HO or Renix, short shifting at low RPMs does not guarantee better mileage figures. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted August 3, 2013 Author Share Posted August 3, 2013 I simply adjusted it by screwing that allen wrench screw off the TB. I'm guessing now that that was a bad idea and shall do everything according to what you recommend. And thank you for the pictures. How many lines come off the air intake box? And the BA10 was in them till about mid 89. Mine was made in febuary. Hence the ba10 Link to comment Share on other sites More sharing options...
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