4runrjunkie

Hey guys,

I am hoping the gurus can give me some advice on possible issues to track down that might be causing my horrible gas mileage. I am currently getting about 4km/L, which equals about 8 mpg. I have no stored CEL codes. It has been getting poor gas mileage, not great power output, and slow throttle response since I bought it a year ago (i knew coming in that it was 3vze so I wasnt expecting spectacular mpg's, but this is a little insane). Since then, I have replaced the timing belt, wires, plugs, alternator, water pump, thermostat, dist cap and rotor, and the o2 sensor.

I have read a bunch of threads on these kind of issues, but all of the ones that talk about fuel mileage that is this bad are usually getting a code that gives them an idea of where to start. I know it could be caused by a lot of things, so here is my list so far of things to look into:

Updated:

-Check Compression Cyl#1:182, Cyl#2:160, Cyl#3:182, Cyl#4:179, Cyl#5:183, Cyl#6:170

-Check Timing Set to 12* jumpered
-Replace Fuel Filter Replaced
-Check AFM (All pins within spec when resting. Will take the afm out on the weekend so I can move the vane and check the resistances when the vane is open)
-Check Fuel pressure Sitting within Spec
-Check Fuel Injectors to see if they are leaking
-Check cold start injector (Seems ok. Resistance is dead on for spec, and no leaking when the fuel pump is on)
-Check CSI time switch sensor (Resistance within spec for warm engine)
-Check ECT (Resistance within spec for estimated engine temp)
-Check to see if the cat is clogged Removed cat when exhaust was replaced
-Replace exhaust since it is currently very rusted and definitely has some leaks in it Replaced with new 2.25 piping from the oxygen sensor back to a magnaflow muffler and then out behind the rear wheel
-Check that new O2 sensor is working properly (Resistance between B+ and HT pins measured at 7.0 ohms. According to the fsm that is a little high, but the engine was still warm so I am hoping that when it cools down to the 20 degrees that the fsm asks for, it will fall back into spec)
-Check EGR system (Both tests that I could find for the EGR system have good results: Checked EGR vacuum modulator by plugging ports P and R and blowing into Q, the air flow was as good as expected with such a tiny diameter tube; EGR diaphram checked by applying vacuum to the line that runs into the top of the valve while the engine was running, with vacuum applied the engine wants to stall out)
-Check fan clutch Replaced, hopefully this will make a difference
-Check ADD system VSV on ADD system is dead, causing my front differential to stay engaged even when the transfer case is in 2wd. I am now on the hunt for a new vsv so I can correct this issue. Now corrected with new vsv

My question for you is, is there anything specific you can think of that would cause this bad of gas mileage? Anywhere I should specifically start on that list? Could the leaking exhaust cause that much of a significant drop in mileage? and finally, is there any reason I am not getting a code considering how much fuel is being dumped in with minimal power output?

Thanks for any help you can offer

92 TOY

does the engine light, light up at all? I had a friend who bought a truck and it ran like hell and found out the bulb had been disconnected.

otherwise I am no help. a pre-cat (pre O2 sensor) exhaust leak cost us about 2 or 4mpg until it was fixed.

BamaYota1

1. Check bulb on cel, or check codes with test light.
2. If truck is 4x4, make sure hubs are disengaging.
3. Check afm, tps, csi, and o2 per FSM.
4. Fix exhaust.
5. Report back.


http://personal.utulsa.edu/~nathan-b...fsm/index.html

bone collector

manual or auto tranny???
gears and tire size??
any vacuum leaks??
egr system in proper order?
what is your timing set at??
what fuel grade you using?
is it burning oil??

4runrjunkie

It is a 4x4. I am fairly sure the hubs are disengaging. The 4x4 light goes out, and I notice a bit more power to the wheels when I disengage. Is there any other to check to make sure?

I do need to check the afm. The tps was checked when I took the plenum off for the timing belt replacement. The o2 is a brand new denso. I also need to check the cold start injector.

Thanks for your input

4runrjunkie

-Manual Tranny
-All Vacuum lines were replaced during the timing belt replacement.
-I am not sure how to test the egr system, can anyone point me in the right direction?
-I will be checking timing as soon as I find a timing light from a friend
-I am burning 87 octane fuel
-Oil levels are staying constant and no blue smoke, so I am pretty sure its not burning oil

thanks

bone collector

Here is what I would do so take it with a grain of salt. set the timing to 15 degrees and open the afm up and adjust the fuel wheel 2 clicks lean. should drive like a champ and get 15-18 mpg.

https://www.yotatech.com/forums/f116...stment-203287/

also do you have manual hubs or auto hubs?? if auto...if you switch to manual you will save about 1-2 mpg's also what size tire you running??

4runrjunkie

The hubs are whatever came stock haha. And the tires are 31's.

bone collector

is there a dial on the hub??

4runrjunkie

No ... so they would be auto.

Co_94_PU

iTrader: (-1)

You didn't not confirm the the CEL/MIL lamp is functional, it should turn on when you switch the ignition to ON or flash constantly when the diag terminal is jumpered.

You didn't say what gears you have, these are listed on the door placard/tag they are the first part of the ATM section.

A malfunctioning/dirty PCV will also cause you to loose power/mpg. Aswell a malfunction in the EGR or PAIR. Finally, just because the o2 sensor is new doesn't mean it is functioning correctly there may be issues with it's wiring also. All of these are listed in the engine section of the FSM, linked above, You'll need to look in the 22re section for the oxygen sensor tests.

Just a quick note, the o2 sensor error codes only trigger if,1) it stops sending any signals for a full half second, 2) it sends maximum lean/rich continuous for 90 seconds, 3)it sends an errornous reading atleast 20% over what the computer is trimed for 60 seconds. IE. if it sends a signal at least once a second that signal could be completely wrong so long as it's between max lean/rich and not over 20% atleast once every minute or so.

4runrjunkie

hey sorry, thanks for keeping me on track with the questions.

The CEL light is definitely operational. When I jump TE1 and E1 to check for codes, the CEL light just flashes constantly. So I know for sure that there are no codes stored.

The placard on my door shows A/TM G254, so I have 4.56 gears.

The PCV was replaced at the same time as the timing belt. Sorry I forgot to mention that.

Any idea how I would check the EGR and PAIR systems are working correctly, without having to simply replace them and find out.

I'll check the the o2 sensor to make sure the new one falls into spec.

Thanks for the help

4runrjunkie

UPDATED the list in the OP

4runrjunkie

I think one of my problems may be the fan clutch. If I am current, the way to test it is while the engine is off and cold, try and spin the fan. If it is working properly, there will be minimal resistance, and if it is not working well then it will not spin freely? Can someone confirm that for me? I couldnt find anything about it in the fsm.

If that is correct, then my fan clutch is definitely not working properly. With a cold engine, it is still hard to spin. When you start the car the fan start blowing air immediately, even if it is a cold engine.

BamaYota1

To see if your diff is unlocking, have someone watch your front driveshaft while the truck is moving. If it is spinning, the differential is not unlocking, and you are basically driving around in four wheel drive. Obviously, this kills fuel mileage, and will wear out everything in your front end quickly.

4runrjunkie

Thanks for the tip, I will get a buddy to do that for me next time I get a chance

4runrjunkie

Fan clutch has been replaced, seems to have made a difference but it may be a placebo effect. I have to wait till I fill up my tank again to check the gas mileage.

I also changed my fuel filter (screw you Toyota for putting the fuel filter there), again it may have made a difference but I really cant tell. Once i fill up again ill be able to track the mileage I am getting.

Innocent Fool

Timing belt might have jumped a tooth.
Check that BOTH cams and the crank line up correctly...

maachine

i was thinking timing belt (as mentioned above). do you know the fuel mileage before you changed the belt?

i'm also thinking vacuum leak.

you can also check your front diff....instead of using a buddy, i drove over my cell phone while it was recording video.

scope103

Did you ever check the ignition timing? Pretty basic, and a whole lot easier to do than most of the other suggestions. Same with compression.