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Poor gas mileage, exhaust fumes burns eyes.

M

MaxxXJ

NAXJA Forum User
Location
Bakersfield CA
I'm assuming I'm burning rich, my question is what do I need to check?
Ok I have an 89 renix with a 4.0 and 255k miles on it so no OBD, i average 12mpg in town driving easy in 3rd with 31" tires and stock 3.55's. last night I changed the coil/cap/rotor, changed the plugs 2 months ago and taylor wires aRe on order, also changed O2 sensor but didnt help. Its got a new muffler so stocks off, I've tried Z-max oil treatment but it didnt do much for me lol.

Reason for the coil/cap/rotor bug was it got cold recently and my jeep would take forever to start, just cranked and cranked, I thought it was fuel but my pressure was low but good,cranking was near 38-40 but at idle it was about 30-32 lbs, once it started it was fine, since the change it fires right up, now I'd like to fix my to rich issue... What else can I look at? All my vac lines look old and brittle, but don't think there is any leaks. It's not a carbed Chevy 350 so I'm kind of lost, any help would be great.
 
Does it smell like it's burning rich? It could be a number of things from old, tired sensors to stuck injectors. Since you messed with the exhaust, you could have an exhaust leak throwing off your O2 sensor. Those tires on 3.55s aren't helping your cause either. I'd do the basics such as finishing those plugs, checking exhaust for leaks and compression test. Then I'd move to replacing sensors such as MAP and coolant temperature sensors.
 
Check the vacuum line from your throttle body to MAP sensor on the firewall. If it leaks at all, the MAP thinks youve got your foot into the accelerator and richens up the mixture.

Also, the sensors cannot give the eCU good info if they have poor grounds. This needs to be done to eliminate it as a possibility:
Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 12-04-2012
 
cruiser54 said:
Check the vacuum line from your throttle body to MAP sensor on the firewall. If it leaks at all, the MAP thinks youve got your foot into the accelerator and richens up the mixture.

Also, the sensors cannot give the eCU good info if they have poor grounds. This needs to be done to eliminate it as a possibility:
Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 12-04-2012
Click to expand...

That's a great idea, that will be my friday task. Also you said map sensor leaking is bad, the 1hose/2 plug fitting that goes into the throttle body is pretty loose, it's popped out on a few situations, also, someone has broke that little plastic hose at the throttle body end where it bends so it only has a nub sticking in that rubber boot... Guess ill source out one of those this weekend at the JY.

Thanks guys.
 
If you have not read my old thread"The RenX Files" do so. Also read my "Testing Oxygen Sensors" thread. It will give you live data, and tell you what the O2 is sensor is seeing and trying to do!!!

My 87 had several problems causing bad gas mileage when I bought it, but the oddest one no one ever talked about was that the back side of the TPS was bad (I was testing the front side per the 87 FSM). It was shifting up to the next gear ar 1200 to 1300 rpm, and at about 1600 to 1800 at WOT!!!! Took forever to get up to speed. NEW TPS bought me an increase from 8-10 mpg to 12-14 mpg. New O2 sensor with a good 12-14 volts from the O2 heater relay got me up to 18 mph on the first highway test drive.

There must be a dozen other things that cause low mileage too.

http://www.naxja.org/forum/showthread.php?t=1012701&page=5

http://www.naxja.org/forum/showthread.php?t=905849
 
If you have the old OEM fuel injectors get rid of them, they leak at the middle casing joint and they are a fire hazard.
 
Also pull the vacuum line to the fuel pressure regulator, on the front of the fuel injector fuel rail, to see if there is any gasoline there. If there is, it is defective, a leaking diaphragm, making it run rich (ECU can not turn off the fuel leak).
 
MaxxXJ said:
That's a great idea, that will be my friday task. Also you said map sensor leaking is bad, the 1hose/2 plug fitting that goes into the throttle body is pretty loose, it's popped out on a few situations, also, someone has broke that little plastic hose at the throttle body end where it bends so it only has a nub sticking in that rubber boot... Guess ill source out one of those this weekend at the JY.

Thanks guys.
Click to expand...

The MAP sensor vacuum source falling out of the throttle body needs to be addressed first.
 
MaxxXJ said:
What else can I look at? All my vac lines look old and brittle, but don't think there is any leaks. It's not a carbed Chevy 350 so I'm kind of lost, any help would be great.
Click to expand...

You DON"T THINK they're leaking ? ? ? Do you smell gas ? ? ? I'd say :
  • you're smelling gas fumes from a poorly operating vacuum system venting your gas tank. If the hoses to/from your tank are crusty, rotting or cracked I'd be checking there first...OR
  • You're not smelling gas fumes, you're smelling exhaust fumes...possibly from a cracked manifold or exhaust donut gasket leak.
  • You could have leaking injector. Watch the engine and the o-rings around them while it's running. A leaky injector can cause quite a bit of fume action when it runs down on to the ex. manifold...then it all evaporates before you actually look at it. Also a major fire hazard, just sayin'
  • Wait, RENIX, go back. It's the tank venting...I'm sure it's gas fumes from the charcoal cannister lines. Those vacuum lines are suuuuper cheap, just regular bulk hose. Just replace them. <$5!!
  • On a related note it could be a broken nipple on the tank rollover valve(s)...further investigation necessary.
 
Last edited:
Ok, I went to the JY today and picked up 2 map sensors and one of those vacuum hoses, changed my battery to block ground from a 6ga to 4ga, cleaned all the grounds with carb cleaner and rag back to shiny metal. Cleaned my battery posts, then changed that crappy flat ground from block/firewall with a 4ga wire...seems like it picked up some pep at idle I also put mid grade in it this morning as well. Ill see if she picked up any mpg and go from there, injectors will be next on my list
 
I can't say how good this is but one way fighting the harsh wind And rain and a few 6% grades i got 14.4 mpg, on the way back I got 16.4 with no wind. Doing 60-65 in 3rd gear between 2500-2900 rpm's (I heard that's the sweet spot on these motors)

Idk how good that is with 3.55 gears, pro comp mud terrains with a 6x4 roof rack, winch bumper up front and swing away on back... I guess I'm not very aerodynamic anymore... Might remove the roof rack until I actually need to use it...
 
I only know one other person that claimed to get their best gas mileage in third gear (or a lower gear that OD), at that high of an rpm, it was 5-90, Renix 5 speed IIRC, with big tires. I tried it on mine and it was terrible.

Most of us with AW4s get peak mileage at 2000 rpm TC locked, in OD, 4th gear. But I am not sure how a 6% grade figures into that. Not sure I would know a 6% grade when I saw one.
 
Ecomike said:
I only know one other person that claimed to get their best gas mileage in third gear (or a lower gear that OD), at that high of an rpm, it was 5-90, Renix 5 speed IIRC, with big tires. I tried it on mine and it was terrible.

Most of us with AW4s get peak mileage at 2000 rpm TC locked, in OD, 4th gear. But I am not sure how a 6% grade figures into that. Not sure I would know a 6% grade when I saw one.
Click to expand...

So with that in mind... I will have to further investigate lower rpm's and mileage, since I read about driving in 3rd that's what I've done instead of keeping it in low rpm's. my Hondas on the other hand, her sweet spot is at 2800-3000(70mph) I get 40mpg(38 average) with her on a good day
 
Ecomike said:
Not sure I would know a 6% grade when I saw one.
Click to expand...

6% doees not seem like such a big number...on paper.:lecture: 6 ft. down (or up) for every 100 ft. forward. 100 yds. = 6 yds. 18 ft.

In 5280 ft.(mile)the road climbs (or drops) about 318 feet. As a point of perspective the Golden Gate bridge is only 282 feet at mean tide from the road to the water. So in 5 miles the road would drop/climb ~1600 feet. The World Trade Center towers were 1775 feet tall.

That will make all the difference where the snow line is, whether your ears pop, etc, etc. Our local "7% grade" is nine miles long. 3330 ft. change in elevation. Raining at the bottom, blowing snow and icy at the top today. In the summer the difference is about 10-15 deg. F from top to bottom.

6% on the road going UP is hard on any engine with a load on. 6% going DOWN towing a trailer, with just OK brakes, with an automatic looks alot like this :wow: or :scared:.
 
ParadiseXJ said:
6% doees not seem like such a big number...on paper.:lecture: 6 ft. down (or up) for every 100 ft. forward. 100 yds. = 6 yds. 18 ft.

In 5280 ft.(mile)the road climbs (or drops) about 318 feet. As a point of perspective the Golden Gate bridge is only 282 feet at mean tide from the road to the water. So in 5 miles the road would drop/climb ~1600 feet. The World Trade Center towers were 1775 feet tall.

That will make all the difference where the snow line is, whether your ears pop, etc, etc. Our local "7% grade" is nine miles long. 3330 ft. change in elevation. Raining at the bottom, blowing snow and icy at the top today. In the summer the difference is about 10-15 deg. F from top to bottom.

6% on the road going UP is hard on any engine with a load on. 6% going DOWN towing a trailer, with just OK brakes, with an automatic looks alot like this :wow: or :scared:.
Click to expand...

I am still not sure I would know (unless it was labeled) a 6% grade when I saw one, as my eye balls and buttometer are not calibrated that way, LMAO!!
 
ParadiseXJ said:
6% doees not seem like such a big number...on paper.:lecture: 6 ft. down (or up) for every 100 ft. forward. 100 yds. = 6 yds. 18 ft.

In 5280 ft.(mile)the road climbs (or drops) about 318 feet. As a point of perspective the Golden Gate bridge is only 282 feet at mean tide from the road to the water. So in 5 miles the road would drop/climb ~1600 feet. The World Trade Center towers were 1775 feet tall.

That will make all the difference where the snow line is, whether your ears pop, etc, etc. Our local "7% grade" is nine miles long. 3330 ft. change in elevation. Raining at the bottom, blowing snow and icy at the top today. In the summer the difference is about 10-15 deg. F from top to bottom.

6% on the road going UP is hard on any engine with a load on. 6% going DOWN towing a trailer, with just OK brakes, with an automatic looks alot like this :wow: or :scared:.
Click to expand...


Yeah lol well to give ya an idea of where I drove was from Bakersfield to morro bay taking hwy 46, it's up and down thru mountains, what's just as bad is going to mojave taking hwy 58, or the grapevine is another bad one... Thinking about it anywhere I go has a horrible grade! No wonder I can't get good mpg I live in a giant hole!!
 
MaxxXJ said:
Yeah lol well to give ya an idea of where I drove was from Bakersfield to morro bay taking hwy 46, it's up and down thru mountains, what's just as bad is going to mojave taking hwy 58, or the grapevine is another bad one... Thinking about it anywhere I go has a horrible grade! No wonder I can't get good mpg I live in a giant hole!!
Click to expand...

Well, lots of steep hill driving probably is better in 3rd gear.
 
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