efxjay

Hi all,

New to the forum here - hoping to get some ideas about what's up with my 95 4-Runner. The low-down:

Been getting loss of power and crappy gas mileage for many years now, sort of attributed it to having 245K miles and the engine just getting old, but I don't think that's it.

General symptoms > upon accelerating sounds like a lot of air being consumed through the intake, but no power or get-up-and go. Suspecting a bad vacuum, but don't know where to start or how to test. Been through the mass O2 unit, new plugs, new fuel filter. No noticeable air leaks around intake - with the exception of the Mass O2 unit sounds like it has a sucking air leak coming from the throat of the mass O2 unit, but I can't pinpoint anything. acts the same with the air filter on or off. All hoses/hose connections are tight and look good.

This problem doesn't happen consistently but seems to vary with load and power demands. Like going up a grade or needing to accelerate getting onto a highway etc. Wondering if the whole Mass O2 unit is bad somehow? Or I have a critical vacuum or two that are not working properly.

Any suggestions would be greatly appreciated - Thanks!

j2the-e

Have you checked for trouble codes? Have you checked the basics, like compression, timing, plugs and wires, etc...?

efxjay

If I have no engine light on would, it still spit out codes? Have not checked compression, or timing, wires all appear OK on visual inspect, just put new plugs in it. Is there a way to check compression without taking to a shop? Thanks.

scope103

http://www.harborfreight.com/compres...kit-66216.html - compression
http://www.harborfreight.com/xenon-t...ight-3343.html - timing
http://personal.utulsa.edu/~nathan-buchanan/93fsm/ - "The Good Book"

First things first: you don't have a Mass O2 unit. You have a Vane Air Flow meter (VAF). Different principle.

While "looking" at hoses is an important first step, you need to carefully describe your problem. Starting with: "crappy" gas mileage. If you're getting 20mpg on the hwy, 15 in town, you're not getting crappy gas mileage.

The best way to find an intake leak is with an unlit propane torch with a piece of hose on the tip. The idle (or engine speed) will increase with propane enrichment when you hit the leak. You can also do this with carb cleaner IF YOU HAVE A FIRE EXTINGUISHER RIGHT THERE.

If you don't feel like investing in a few simple tools and reading up a bit, there's no shame in having a professional do it for you.

efxjay

Thanks for the info and the links - definitely will bone-up and see what I can detect.

Thanks for clarifying the VAF vs. the mass O2 - I do have the VAF and there is a way to test the resistance on the vane. Recently had that all apart and cleaned the inside - apparently these should run silent, but mine is not.

Will try the propane for testing air leakage. Gas mileage has been between 12-13 mpg on the highway and less around town.

Thanks again!

j2the-e

Yes, you will sometimes get codes even though the check engine light is not on. Not too keen on just replacing parts, but in this case, I would start with a new Oxygen sensor if it hasn't been done recently. Its easy and cheap enough. If you'r running that rich, and not setting a check engine light, the sensor may be reading incorrectly.
Get a cheap denso brand sensor at rockauto.com

Gamefreakgc

Those Harbor Freight compression check kits can be misleading, so instead of looking for exact readings (170 range according to FSM I think) look for uniformity. It might be off by as much as 30 PSI but as long as they are all the same, you're good. A shop did a compression check for free for me. I have a good relationship with the manager so he cuts me deals all the time for jobs I can't handle on my own.

I also own a high mileage Toyota. I received it with 268k miles and it got around 14 MPG highway/city mix. I had several sensors that were failing including the Throttle Position Sensor, Engine Coolant Sensor, and Cold Start Injector Switch. I also had an exhaust valve stuck open (had to do valve adjustment). All that to say fixing up your 4Runner will be a process. Maybe you have a vacuum leak, runs a little better after fixing it. Then you find a failed sensor, replace and runs a little bit better. You'll gradually claw back some of those lost MPG's and HP's until its in good shape for its age. It'll take some patience (and a multimeter) but it's very doable.

One last thing you didn't share with us, what size are your tires? If you're running something crazy like 35's you're mileage will appear to be awful (but in reality not as bad as it looks), unless you've changed the gear ratios.