5 mpg & black smoke from 4 cyl - JeepForum.com

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post #1 of 27 Old 11-12-2011, 03:37 PM Thread Starter
87milton
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5 mpg & black smoke from 4 cyl

i got an 87 2.5L 5 speed. the motor is rebuilt with about 3k on it and new gas tank fuel pump filter and injector. it also has new EGR valve MAP sensor and oxygen sensor. the throttle body was also rebuilt. new plugs wire cap rotor ignition coil and air filter. the cat has been gutted. im running 32X11.50s with stock gears with about 40 psi in the tires. i heard the fuel pressure regulator but wouldnt that be included in a throttle body rebuild? any suggestions on what could be causing this bad mileage? this is my daily driver and im living pay check to pay check just feeding it


4 in a row makes it slow
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post #2 of 27 Old 11-12-2011, 03:39 PM Thread Starter
87milton
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thanks in advance guys

4 in a row makes it slow
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post #3 of 27 Old 11-12-2011, 03:45 PM
88Jeff94
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A heavy right foot or a leaky fuel line.

But really that's hard to diagnose over the internet. It could be any number of things.

How long have you had the jeep?
Is this the first time you got 5 mpg?
What was your average before?
Did the spedo gear get changed?(could cause mpg calculations to be off)
City or hwy driving?

I'm not sure what could be causing the black smoke but start with basics, see if anything is leaking, do a compression test, or take it to a mechanic. We need to know more.
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post #4 of 27 Old 11-12-2011, 05:19 PM
oldtime_ironman
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Fuel pressure regulator OR a piched off return line. Either way you should test and see because its obviously *way* too rich. I didn't know the 4-banger could get that bad of a MPG.
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post #5 of 27 Old 11-12-2011, 05:22 PM
UltimatE
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On a side note, 40psi in the tires is WAY too high. You should probably be at 30psi or below. With 40psi you're probably gonna need new tires way too soon.

-Matt

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post #6 of 27 Old 11-12-2011, 08:09 PM Thread Starter
87milton
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no the spedo is the same, i have had the jeep for about a year and it was in the shop for about 5 months lol its mostly city but i take the high way to work 15 min away this is constant since i got it rebuilt i never bothered to check before i got it rebuilt and i usually shift at 3k unless im on the highway or i gotta poop lol but do people usually replace the fuel pressure regulator when they rebuild a throttle body? also are there any other sensors that could be telling the computer to dump more fuel? i replaced the thermostat it had in it while the motor was braking in it was a 180 so it was running rich and flooding while it was breaking in if that has anything to do with it

4 in a row makes it slow
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post #7 of 27 Old 11-12-2011, 08:33 PM
oldtime_ironman
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Quote:
Originally Posted by 87milton View Post
no the spedo is the same, i have had the jeep for about a year and it was in the shop for about 5 months lol its mostly city but i take the high way to work 15 min away this is constant since i got it rebuilt i never bothered to check before i got it rebuilt and i usually shift at 3k unless im on the highway or i gotta poop lol but do people usually replace the fuel pressure regulator when they rebuild a throttle body? also are there any other sensors that could be telling the computer to dump more fuel? i replaced the thermostat it had in it while the motor was braking in it was a 180 so it was running rich and flooding while it was breaking in if that has anything to do with it
Yeah the O2 sensor would do it too, but that much? Wow.
.
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post #8 of 27 Old 11-12-2011, 08:53 PM
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3000k is low, the engine is just beginning to make its power around there. It will cruise at 3500rpm all day long without a hitch (when it's tuned up).

My suggestion is to go through all of the sensors and DOUBLE check to make sure everything is working properly before you begin messing with fuel pressure regs.

All about that unibody life.
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post #9 of 27 Old 11-12-2011, 08:54 PM
superj
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Temp sensor too

I don't feel like working on anything, at this time.
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post #10 of 27 Old 11-12-2011, 10:17 PM Thread Starter
87milton
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the 02 sensor is new and if the temperature sensor was bad wouldnt that make it run below operating temp? it warms up to right about 210 on the gauge. im about to just go to a mechanic but i would rather do it myself and save $300

4 in a row makes it slow
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post #11 of 27 Old 11-12-2011, 10:54 PM
oldtime_ironman
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There's more than one temp sensor on these IIRC one of them is for the gauge the other one is for the computer.
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post #12 of 27 Old 11-12-2011, 10:58 PM
oldtime_ironman
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One other thing, an exhaust leak can really throw off the O2 sensor, give it a bum reading. Since the signs are really obvious and you just had the motor done, I would go over it all with a fine-tooth comb and start looking for the small simple things.
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post #13 of 27 Old 11-13-2011, 08:05 AM Thread Starter
87milton
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i do have atleast one exhaust leak its a small hole where the cat bolts up to the down pipe could this be it you think?

4 in a row makes it slow
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post #14 of 27 Old 11-13-2011, 08:35 AM
oldtime_ironman
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Originally Posted by 87milton View Post
i do have atleast one exhaust leak its a small hole where the cat bolts up to the down pipe could this be it you think?
At least partly anyway. Any leaks upstream from the O2 sensor will for sure do it too. Might want to check all of the exhaust maniold bolts where it goes into the head, they are famous for going loose.
.
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post #15 of 27 Old 11-13-2011, 02:54 PM Thread Starter
87milton
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will do, also what is the exact name of the temperature sensor? is it called the coolant temprature sensor?

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