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Old 02-17-2015, 06:06 PM   #1
Drake
 
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Unhappy Poor gas mileage:(

I'll try to be brief and specific, here it goes.
I purchased a 86.5 4x4 D21 SE V6 and noticed it had really poor compression in two of the cylinders and a clogged radiator but operated fairly well under the circumstances. I was hoping to avoid many more problems so I purchased a new V6 3.0 re-manufactured long block motor from S&J motor out of Spokane Washington. I re-utilized my old intake but had to clean out the ports that were clogged leading to the EGR valve. I have put a new radiator, thermostat, plugs, dist. cap, dist. rotor, plug wires, fuel filter, air filter, battery, alternator, muffler and rear tail pipe, all vacuum hoses and all rubber fuel line excluding the two short pieces that attach to the gas tank.
I seemed to be stopping at the gas station more than I would have likes so I started noting the exact mpg that I appeared to be getting. I am only getting about 10 mpg and I would think I should be getting closer to 15mpg. I have about 1000 miles (normal daily driving) on this new motor but am getting the same mileage. I live 25 miles from the nearest town so most of this mileage is freeway driving. Any suggestions regarding the poor mileage would be greatly appreciated???? Please send me any of your thoughts. I am looking forward to receiving all your wisdom.
Thank you all in advance.
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Old 02-17-2015, 06:17 PM   #2
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I am not much of a help but overall, does the truck run okay, have you put larger tires on it? Anything changed from the factory? Not sure if the 86.5 had lights on the ECU to check for any codes. What speeds are you doing on the freeway.

I am shooting from the hip but maybe I spark a question or two from others.
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Old 02-17-2015, 06:52 PM   #3
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After all that work, I assume something is compensating for all the work that you did. Pulling the intake and cleaning everything out just opened a whole can of worms down stream.

I look at it like this-starting from the fuel to the exhaust-

Fuel:
1. You changed most of the fuel lines, are they leaking?
2. Fuel filter, same thing, leaking?
3. Intake, if you cleaned all that out, I suppose you fiddled with injectors. Are they seated properly?

Air:
1. Everything that was changed was rechecked for being properly seated? (i doubt it have anything to do with it though).

Vacuum lines / EGR:

1. Since most/all has been changed have you rechecked all the connections?

Fire:

1. Spark plugs/Distro/Wires, again all seated correctly.
2. Did you make sure the distro was put in correctly, if its off a little it can throw everything off.

Exhaust.

1. Did you fool with any O2 sensors? Might need to be changed.
2. Cut the cat out?

I'm not the best at this either, I'm a KA24 / 4's guy, not much help with the VGs / 6's nor anything predating 92-91, but its just some ideas I'm throwing out to get more info back.

Let me ask this too, do you smell fuel in the cabin at any time? Id do like scoob said and check for lights too.
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Old 02-17-2015, 07:11 PM   #4
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My first question anytime fuel mileage is mentioned is what is the timing set to?
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Old 02-17-2015, 08:02 PM   #5
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86.5 V6 4x4 owner here. Definitely check the timing. Makes a big difference in how it runs and what your mileage is. Also, check your brakes. Both of my front brakes had a seized piston that I was constantly fighting against while driving, costing me gas mileage.

EDIT: FYI I almost always get 15.8mpg in the city (downtown city driving, rarely getting past 3rd gear) and around 19-21 on the highway.
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Old 02-18-2015, 12:38 PM   #6
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How fast do you drive (these trucks were designed when the speed limit was 55), and what size tires are on the truck?
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Old 02-18-2015, 07:19 PM   #7
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Thanks for all the feedback. I will attempt to answer all the questions.
*My tires are also new Cooper AT3 30x9.5/15LT. I put new front brakes on but not the rear yet (I think I need to change them as well soon). If I jack the front off the ground I am able to free spin the tires without the brakes dragging.
*I have noticed I have been driving between 70-75mph on the freeway. Freeway seems to be the only time I put it in 5th gear. In the city I have never gotten out of 3rd gear. Shifts smoothly however, when cold takes a bit to warm up trans gear oil. I'm thinking of changing trans oil to synthetic and see how that goes. Has anyone noticed a difference with the synthetic oil vs regular gear oil in the trans?
*I haven't noticed any fuel leaks at all (that is what is really puzzling me). I have two more shorter pieces of rubber fuel line that attach directly to the gas tank that I will be changing just because they look old. I have not been smelling fuel (like a rich smell). All in all everything appears to be seating. I will say though that intake was massively clogged to the point that I wonder how the EGR system was even functioning. Another wonder I have is when I cleaned that intake and now it has full circulation how that affected everything else (ECU, EGR, ect.)? I was also wondering about the O2 sensor? The only connections I bothered were to remove the plug in side off the top end and I made sure to get them tightly back on with there clips and everything.
*Distributor, plugs and wires all seem tight and are not shifty.
*All in all the truck runs smoothly (weird I know):/
*I have not read any of the computer codes yet and this I plan to do.
*Few things it looks like I need to do: 1) Replace rear brakes and check for drag. 2) Check O2 sensor or replace. 3) Change all rubber fuel line and check all fuel line for any leaks (pressurize fuel system lines). 4) Change trans gear oil to synthetic. 5)Give you all an update when completed!!!
Again thanks a ton guys you are all awesome!!!
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Old 02-18-2015, 10:47 PM   #8
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What's the timing set to?
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Old 02-19-2015, 09:50 PM   #9
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Alabama, how often (noobie question) does the timing need to be checked or adjusted? 192,00 miles and counting....
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Old 02-19-2015, 09:58 PM   #10
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It should be checked every 191,000 miles.

Every


Time
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