Long story short, have a 89 4runner SR5 with a rebuilt 3.0, new: injectors, plugs, wires, fuel filter, air filter, battery, etc. & rerman: alternator, power steering pump, starter, etc. Roughly $4500 spent in new stuff(all engine related ).... been driving it for a while now 2900 miles... Im only getting 11 mpg mostly back highway driving @55 & 2400 ish rpm. (Rairlley on the freeway, but thats 70mph @ 3000 rpm's) Even took off the AC belt & that uped it from 10 to 11 mpg.
I need it to get better MPG!

I mostly daily drive it. would like to start off roading it weekend outings, camping, etc. (but not @ this lousy of mpg)

has 4:10 gears, manual trans, manual front locking hubs (so I can have it freewheel when on road), 31x10.5 R15 tires (like to keep the tire size, as they have 75% tread) @ 40 LBS. pressure.

Ive tried the jumper wire & never seen any blinking lights.... took out the cat thinking it may have been clogged, but that made no difference. Re checked the timing & its just above 10 degrees... so Im kind of @ a loss...

Also put on a new turbo muffler & 2" tail pipe.... & a bout 2 weeks ago the muffler cracked open(about a 5" x 3" + shaped crack .. someone said it was possibly a back pressure issue?

Anyone have any ideas????

 

You need to find someone with an old Snap On MT 2500 or similar scanner that can read and troubleshoot Toyota OBD-1 and find out if you are getting into closed loop or not and what the outputs of your various sensors are.

Most sensors can be tested with a VOM and a consult with the FSM, but one of the old professional high dollar scanners is the real deal. A toyota factory scan box would be the ultimate rig, but even the dealers don't seem to have those around any more.

One good guess might be that a faulty engine temp sensor is keeping it in open loop.

Your truck is a good looker.

With your tires and gears, it should be getting 18+ MPG the way you are driving it.

 

Im looking... but have not found anyone with one yet.

 

Have you changed your fuel filter & cat? Also, what octane are you filling it up with?

 

mid grade non ethanal gas, yes changed the fuel filter.

Oh & with the muffler issue, I welded the crack up... 2 days later it cracked open & now have a 3.5" chunk of the muffler missing . WTF???
think Im going to get a flowmaster & see if it will hold up.

 

I think you are just fighting the bad DNA in the ECU. I would very seriously consider the DIY ECU. Oh and lose the tires, get back to the stock 225/75R15's and you mpg's will get better. enough to pay for the tires.

You have a sweet looking truck!

 

What is this DIY ECU you speak of? I want one already.

OP, I was going to ask if you're remembering to calculate the MPGs based on the larger than stock tire size, that would be a couple MPGs right there. There are codes related to coolant temp sensor but it is worth checking, and also picking up a cheap analog voltmeter and testing your oxygen sensor function.

Elsewise, you can make sure you're running thinner, synthetic fluids - 5w-30 or even 0w-30 depending on temps there, 75w gl4 in the trans, possibly 75w gl5 in the diffs as well but I don't know about that. You can advance your timing to 15* although some have gone much higher, and also consider the AFM mod described here Running leaner will boost MPGs at the possible expense of shortening engine life somewhat.

 

11mpg is terrible. Make sure your taking into account the larger tires as jbtvt mentioned. I consistently get in the low to mid 18's with my 89 3.0 auto. Low to mid 17's if I run the a/c.
You could always ditch the 3.0 and put in a 7mge I get 25 on the highway with 33's and 4:10's in my pick up.

 

I think you need to look at how you are calculating the mileage .

I also wonder are you getting much black smoke out the exhaust ??

The fact your muffler cracked either a defect from new then your welding onto metal that expands and contracts .