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Discussion Starter · #1 ·
I picked up a cheap Trooper 5spd. Runs OK 160K on odometer. I'm half way through my first tank of gas, at least according to fuel guage, and I'm sitting at 100 miles on half a tank?! There are no hills here and I drive slow and easy. I read some people said to try a fuel injector cleaner, but will this work on the 1991 2.8 tbi (I don't know much about engines)?

Are there any other options to check regarding fuel consumption? The engine runs smooth so I don't think it needs a tune up. It doesn't appear to be burning oil, but does have an exhaust leak.

I'm new to Isuzu, so any information is appreciated
 

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It certainly won't hurt. Over the next couple of fill-ups, put a bottle of Chevron Techron or a comparable product in with the fuel. It'll help clean things out, especially if the truck sat for a while before you bought it.

You - should - be getting about 16-18mpg highway and if your really lucky, close to 19.

The Trooper has a 21.9 Gallon fuel tank so at optimum conditions, you should be getting close to 360-380 miles to the tank. I have been - very - lucky a few times and squeezed out 400 miles before filling up - but I was sweating whether I would be coasting into the gas station :lol:

What size tires are on your truck? Stock size was 235/75R15 which is a tire diameter around 29-29.5" If the tires are the wrong size, that can screw the mileage up too.

Air filter clean?

Exhaust system in good shape?

Documentation on oil changes, spark plug changes, O2 sensor changes, air filter changes? Tire pressure?

Cheers,
 

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I'm currently fighting with a 1992 Rodeo for better mileage. My first tank only got me 175 miles :shock: The truck has the big tire package but I can't see them costing me that much gas...
I've done a lot of small things but no huge difference yet.
I'm planning on swapping the clutch fan with an electric one soon.
I'm keeping a log and I'll post what made the biggest difference when I'm satisfied.

I've thinking about installing a multiport FI system from a early 90's 2.8/3.1/3.4 GM product . Someone please tell me if the fuel savings is going to be worth all the work.

Will

BTW: major tune up already done.
 

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Discussion Starter · #4 ·
right now the trooper has 255/75R, but they're almost bald so I'm going to go with the 235s soon. The oil was recently changed and the old oil was in good shape. As of now, it burns no oil that I've noticed. The airfilter was 'OK', but I'll replace it to be safe. From what I've read, the Chevron is the way to go and the local parts store carries it. I wasn't sure if it would hurt the tbfi or not, so I thought better to ask. Tire pressure is dead on. Other than an exhaust leak near the manifold, the exhaust system seems to be tip-top. I have no idea about the O2 sensor, but from what I've been reading, it can make a bigger difference than what I would have thought, I'll check into that as well. I get paid tomorrow and I'm off to the parts store. I'll post back about any progress.

Thanks for the info on teh tbfi!
 

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fast.asleep said:
My first tank only got me 175 miles :shock:
Yep, that does indeed suck :(

You should be getting at a minimum 300 miles to the tank.

The truck has the big tire package but I can't see them costing me that much gas...
Is this the 'snowflake' option with the 31" tires? You are correct thought that this shouldn't affect your gas mileage as long as the pressure is good. You might even run a lb or two higher, might increase the tire wear a bit, but will also reduce friction as well, thereby making it easier on the engine.

Does your truck have AutoHubs? Have they ever been serviced?

If the Autohubs are locked/frozen active then when you drive, it's dragging the entire front diff system even though the x-fer case is in neutral - something definitely to look at, all other mechanical issues being ruled out.

I've thinking about installing a multiport FI system from a early 90's 2.8/3.1/3.4 GM product . Someone please tell me if the fuel savings is going to be worth all the work
Other than the kewlness factor (and there isn't much of it, unfortunately), it will not improve mileage enough to make it worth the $ and effort.

Cheers,
 

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You - can - try a couple of things like moving over to a K&N non-disposable air filter. I've had one now for probably 5 years. It's advertised to be 'less restrictive' thereby promoting more airflow.

Who knows :?

The other thing you can do is flip the aircleaner lid thereby allowing a full 360 of exposure to the filter. Now this 'poor-man's turbo' mod does help a bit.

The other option is to replace the exhaust system with a less restrictive system including a more modern 'free-flow' cat and a less restrictive muffler. I went with a Dynomax cat and a Flowmaster 40 muffler (although in retrospect, I wish I hadn't and I will replace it with a quieter, more conservative muffler eventually)

The guys replaced the pipes from the manifolds back with 2 1/4" ID piping all the way back. Total cost for this mod - pipes, cat, and muffler was about $366

With the K&N, flipped lid, new exhaust system, I was getting right about 400 miles to the tank straight highway with stock tires, so I really couldn't complain.

Cheers,
 

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LTC Don said:
Is this the 'snowflake' option with the 31" tires?
Yup, max tire pressure for these tires is 50 psi. I'm running 46psi. I'll pump em up a few

Does your truck have AutoHubs?
yup but thankfully not the hub flanges. The cv's shouldn't be turning but I don't know for sure. I'll add it to the list

Have they ever been serviced?
not that I know of. (I've only owned the truck for a month and it was sitting for aprox a year before that)
-I'm getting to it. I still have to do a compression test on the cylinders. (forgot when changing the plugs :oops: )

I might be replacing the engine after all :lol:

Other than the kewlness factor (and there isn't much of it, unfortunately), it will not improve mileage enough to make it worth the $ and effort.
darn. I was hoping multiport would be the holy grail of fuel economy. If I find a cheap one at the wrecker I might do it anyway just for giggles

Will
 

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holy grail of fuel economy
=

DIESEL!!!!1 :lol:

and betta yet, with the veggie oil conversion kit:

http://www.greasel.com :lol:

TIRES: If you have the 31s, they are LT grade, meaning 6-ply. A definite plus would be to scruff up some stock rims and put P grade tires on for commuting because they are 4-ply and thus lighter in weight so the engine doesn't work as hard to 'push' them and keep inertia. Keep the snowflakes with the heavier 31s for wheeling events. OR, if you know that you aren't going to use those larger tires but very rarely for wheeling, dump the LT grade 31s for P grade 31s.

Yep, bump up to at least the max PSI. If they are the stock size for those rims, which are 7.5" wide and your tires are 10.5" wide, then you 'should' be able to run at max pressure with undo tire wear.

Another option is to move from an AT tire to an efficient highway-only rated tire to maximize fuel efficiency. I plan on doing this very shortly since my Troop will once again become a daily driver and the 32's suck fuel like an oil tanker........

If the truck sat for a year, I'd definitely consider several oil changes alternating between 5W and 0W in short intervals to help clean up any gunkiness and even using Sea Foam as well as perhaps a seal conditioner. The 3.1 is a fairly stout engine with good care although you may be looking at a water pump or alternator soon.

All other fluids should be changed including radiator, oil, front and rear diff fluid, power steering, transmission (manual is no big deal, auto is another matter - could open a can of worms), clutch (flush), and brake (flush) to "0-Time" all the fluids so you physically know exactly where they all stand irregardless of what the prior owner documented/said.

Service Manual: http://www.helminc.com

Cheers,
 

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Something else to check, jack the front up and spin the front tires. They should spin freely. If not you need to repack the bearings. If they are dry they will cause you to have undue resistance.
 

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Discussion Starter · #11 ·
I replaced the PCV valve, put in a new airfilter and ran a tank of gas with Chevron's fuel injector cleaner and my mileage jumped to 16mpg for my 1991 2.8 with 160K, which isn't bad considering 90% of my driving is stop-and-go with A/C running. It also seems as if the engine has more pep, but that may just be my excitement about better gas mileage :D

Thank you for the suggestions!
 

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16mpg for my 1991 2.8 with 160K, which isn't bad considering 90% of my driving is stop-and-go with A/C running
Ahh, yes, you are well within the norms for an SUV in city driving then. And actually, 16mph is pretty darn good. Is your Trooper auto or manual?

What's so sad about this is your Tired Old Trooper gets better gas mileage than most - new - mid sized SUVs :roll: So, like me, it's not worth it to get rid of the Trooper.

Cheers,
 

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Discussion Starter · #13 ·
LTC Don said:
Ahh, yes, you are well within the norms for an SUV in city driving then. And actually, 16mph is pretty darn good. Is your Trooper auto or manual?

What's so sad about this is your Tired Old Trooper gets better gas mileage than most - new - mid sized SUVs :roll: So, like me, it's not worth it to get rid of the Trooper.
Mine is the 5spd. My reason for getting the 91 Trooper, as crazy as it sounds, I prefer the styling of the 1st generation Troopers. The Utilitarian Box - I love it! Once I get it running a little quieter (exhaust leak near head) and get the A/C blowing cold rather than cool, I plan on driving it another 10 years. I had been wanting one a long time and now I'm like a kid on Christmas morning.
 

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LTC Don said:
16mpg for my 1991 2.8 with 160K, which isn't bad considering 90% of my driving is stop-and-go with A/C running
Ahh, yes, you are well within the norms for an SUV in city driving then. And actually, 16mph is pretty darn good. Is your Trooper auto or manual?

What's so sad about this is your Tired Old Trooper gets better gas mileage than most - new - mid sized SUVs :roll: So, like me, it's not worth it to get rid of the Trooper.

Cheers,
The best mileage I've had out of an Isuzu was with my RS. 4cyl, 4.77s, 31" tires, automatic (deep overdrive) and highway driving. I've seen 22mpg, and the city driving wasn't bad at all. My dad always got 19-20 city/highway in his 5-speed 88, but I almost never saw it quite that good in my 88 5-speed. Must have had something to do with the 5,xxxlb weight, oversize tires, roof rack and larger alternator.

The VX got 20.5mpg in our last stretch of driving home from Oregon - 65mph with about 5 stops. I've been getting in the 16-17 range in my city driving, which is still better than the lifted Trooper (with larger tires and a rack). I just have to keep my foot out of it otherwise the mileage drops to about 13 :shock:

-Tad
 

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Jacked up the truck and spun the front wheel. It barely rotated half a turn before grinding to a halt. I just fell back and started laughing.
Boy, do I feel dumb... :oops:

Well it turns out both front bearings need to be replaced - BADLY.
I'll probably be replacing both calipers as well. I won't know for sure until I get the wheels off. While I'm there I'll throw new pads on.
It seems the things I didn't look at when I bought the truck are all crap. Oh well at least it's minor.

Now I'm afraid to look at the back wheels... :roll:

Will
 

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WAIT

Do you have manual hubs on the front wheels?

If not, the wheel will never turn freely because you are rotating the CVs, the halfshaft, and part of the diff. Of course it's going to stop right away.

When you grabbed it at the 6 and 12, and pulled back and forth was there any play?
 

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WAIT

Do you have manual hubs on the front wheels?

If not, the wheel will never turn freely because you are rotating the CVs, the halfshaft, and part of the diff. Of course it's going to stop right away.

When you grabbed it at the 6 and 12, and pulled back and forth was there any play?
 

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auto hubs but not hub flanges so the cv's should not be turning. When I spun the wheel it made a grinding sound that reminded me of a stuck caliper.

...Unless the hubs are not fully disengaging. When disengaged should the cv be able to make a full revolution with the wheel stopped? ie I turn the cv shaft while the truck is on the ground - should it spin? (it seems free but does not spin a full 360 degree revolution)

BTW - when I grabbed at 6 and 12... Oh yeah - about 1/4 of an inch play

and there was a popping sound (one pop) when I backed up to disengage 4wd. Normal??
 

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fast.asleep said:
auto hubs but not hub flanges so the cv's should not be turning. When I spun the wheel it made a grinding sound that reminded me of a stuck caliper.
That has the sound of a bad auto hub
...Unless the hubs are not fully disengaging. When disengaged should the cv be able to make a full revolution with the wheel stopped? ie I turn the cv shaft while the truck is on the ground - should it spin? (it seems free but does not spin a full 360 degree revolution)
It should make a partial revolution. It takes about 1 full revolution to get it to engage (in either direction) so you can only turn the half shaft that far before it will start turning the tire as well
BTW - when I grabbed at 6 and 12... Oh yeah - about 1/4 of an inch play
Yea, that's bad. You can start off by removing the auto hub and try again with the spin test, but the hub won't cause the wheel to have 1/4" of play.
and there was a popping sound (one pop) when I backed up to disengage
4wd. Normal??
Sound normal to me. Mine used to go click-click as they disengaged. If I heard only one click, one side was still locked.

-Tad
 

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Tad said:
That has the sound of a bad auto hub
I hope not. I think I saw a set of manual hubs at teh junkyard...

Yea, that's bad. You can start off by removing the auto hub and try again with the spin test, but the hub won't cause the wheel to have 1/4" of play.
I was thinking the bearings were the cause. What else would cause that?

Will
 
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