jereli

I am not sure what else to do I am getting 7-8 mpg on my 91 4runner 4x4 auto 3vze. Completely stock except for 265/70 r16 tires. I know these trucks get poor mileage but 8mpg on street and maybe 10 on highway? Something must be wrong. I don't drive it aggressively.

Things I recently did:
Timing belt/water pump
Oil change/filter
Spark plugs, cap, rotor
Valve adjustment
Passed smog no problems
Fuel filter
O2 sensor/cat/muffler
Air intake temp sensor(replaced with used one)
Cleaned throttle body

Only code I get is no starter signal which I don't believe has anything to do with the performance of the vehicle. Any ideas what I can do next or check? 8mpg can't possibly be normal for stock truck..and it use to get the same before I changed the wheels and tires. I might have seen in increase in mileage of about 2mpg more since all that I've done.

RJR

It is puzzling to get that poor of gas mileage while still passing smog. All that extra fuel has to go somewhere, and usually it would show up as excess unburned hydrocarbons in the emissions test.
Some questions to dig deeper:
- How long have you had the vehicle? Has it ever gotten better mileage?
- How's the power? Does it run smoothly and accelerate well? (At least, as well as expected for a 3vze auto)
- What rear-end ratio do you have? I think 4.30 is stock for an auto with stock 31 inch tires. (Your tires calculate out at 30.6 inches, which is about the same.)
- Is your speedometer accurate?
- What rpm do you run at 70mph in overdrive?
- Have you checked timing? Retarded timing can really rob power and mileage.
- Do you have the numbers from your latest smog test? They might give some clues if you posted them here.
- Warm up the engine well and then measure VF1 in the diag connector with a multimeter while running the engine at around 2500 rpm. It should be around 2.5 volts. If it's pegged at 0V, the ECU thinks you are running rich and is trying its best to lean things out.
- Do the same thing with TE1 shorted to E1. You should see the voltage switch back and forth about once/second between 0V and 5V. That will tell you the O2 sensor is working.

rworegon

A neighbor 'borrowing' some fuel?
A leaky fuel line?
Leaky gas tank?

JasonYota

iTrader: (1)

Did the mileage just drop one day? Mileage has been the same since you bought it?
How far is your commute? Stop and go?

jereli

have had it for about 4-5months and yes has always gotten poor gas mileage. it got better after the work I did that I mentioned above.


power feels fines as well as acceleration. accelerates fairly smooth and decent nothing out of the ordinary.


gear ratio is stock so I am assuming its what you mentioned 4.30


speedometer just started to act up a bit getting stuck for a couple seconds and then working fine. I go on off road trips with my brother and i compare the mileage we drove and its pretty much the same maybe off be a couple miles. his is a Tacoma on same tire size as me.


70 mph my RPMS are at 2400 in overdrive. at 60mph my rpms are at 2000.


Timing is at 10BTDC


VF1 at idle I was getting 3.5v...VF1 at 2500rmps I was getting 1.1V


VF1 with TE1 and E1 shorted it does jump from 0V to about 4.9V


daily commute to work and back is about 5 miles round trip.

jereli

here is my smog results

jereli

he better not be barrowing any gas lol...no leaks that I can see..


one thing I notice though was after driving I opened my hood and I heard some noise coming for that evap canister? normal?

JasonYota

iTrader: (1)

5 mile daily commute. That's the reason.

RJR

Sounds like in general the truck is pretty well tuned up. Since your commute is so short, it could be that you're using an abnormal amount of fuel when the engine is cold. Possibly your cold start injector is staying open too long, or something similar.

skypilot

iTrader: (1)

I think you really need to upgrade the ECU, with a DIY or Mega squirt. The factory ECU is really leaves much to be desired. Poor MPG is just one of many issues.

jereli

Now my VF1 was not at 2.5v like stated above at 2500rpms...I was getting 1.1v..is that something to be concerned about?

Now if my injectors were bad, clogged, or just not functioning the way they should...would it show in my smog results that there's an issue somewhere related to injectors? Could the injectors cause really poor mileage?

I will research the diy ecu upgrade as I never heard of it.

Thanks

RJR

I really don't think an after market ECU is the solution. He's got an essentially stock vehicle getting about 1/2 the mileage he should be getting. There's something more fundamentally wrong.

Jereli, your smog numbers indicate things are working pretty well when the ECU is running closed loop. Your 1.1V VF1 number also indicates that the ECU can control the mixture properly in closed loop mode, but the open loop tendency is toward rich. Not all that bad, though. Keep in mind, however, that smog measurements are made with the engine fully warmed up.

I suspect your problem is a combination of your short commute, meaning most of the time your engine is cold, and something not right in your cold-engine operation. When the engine is cold, it runs open loop; the oxygen sensor is ignored and the ECU estimates fuel mixture from the coolant temp, air temp, VAFM, and the TPS. If one of those sensors is giving bad data during cold operation, you could be running quite rich. Also check out the cold-start injector as I mentioned before.

It might be interesting to fill your tank and then take the vehicle on a 100 mile highway trip at moderate speeds. When you return, fill it again and calculate your mileage. If it's significantly better, it would indeed point to a problem when the engine is cold.

skypilot

iTrader: (1)

I had a 3.0 engine and that's about the right MPG for that engine. You are correct its cold temperature operation stinks, and that the temp sensor on the back of the block may be giving bad information.

But when all is said and done, the ECU remains the skeleton in the closet. its just got rotten programming.

Another way to test it, is to let it warm up for a few minutes before leaving. Could also be the thermostat is stuck open. It should be hot by 8 miles and some of the time closed loop.

There really cannot be too much wrong with it since it does pass smog, so any improvement might be marginal.

RJR

8 mpg is not the right mpg for that engine. Mine routinely got about 19.5 mpg in stock configuration. With the 33" tires it's dropped to about 18.5. Of course that's with a manual, but most folks on this board with an auto report between 14 and 16, depending on driving styles and tuneup status.

There could be a problem with auto tranny shift points as well.

jereli

Well my thermostat is new so I think I can rule that out of being stuck open. Now i found a lengthy write up on testing the TPS that i dont really understand but i will look into it..and i didnt really find anything on how to test coolant temp, air temp, VAFM. I found videos on air temp and vafm but doesn't really say how to test it.
My haynes manual doesn't show how to test that stuff.

rworegon

Take a look at the manual link in my sig....you may find something helpful.