toyotalytrevor

hi, i was hoping some of you might be able to help me out.

bare with me, as i have a few questions and im a desiel mechanic, not to informed on gas engines.

Vehicle: 1990 4 runner with a 22re and 5spd 470,000km
just bought the truck.

problem i am having it is running lean and i cant figure out why. I know that it is running lean by looking at my "aircare" results. NoX are high, and everything thing is low/zero.

I have replaced the tps, distributor, plugs, cap, rotor, wires. tried another computer, tested egr valve tried another afm new 02 sensor.

the engine has 19pounds of vaccum at idle. compression is 160, 130, 160, 160.

i have checked all the vaccum hoses and they seem ok.

what am i missing?

84sr5yoty

Something isn't right about that one cylinder being 130. Check the valve clearance on that cylinder and see if it goes up a bit. Valve clearances that are too tight or loose will cause a low compression reading.

toyotalytrevor

valve clearence is fine, forgot to mention i did that. Im more concerned with why its running lean. then i'll deal with the head....

myyota

Im just throwing out ideas here, what about the fuel pump or fuel presure regulator ?, also, when was the last time the fuel filter was replaced ?. any one of those being bad could cause the problems your having.

dcg9381

I'm not entirely sure that high NOX is an indication of a lean motor... You're passing emissions or not?

To confirm that you're lean, look at the plugs.. Post a photo if necessary.

Does the motor run bad to you? These motors aren't powerful - but if really lean, they'll lack power big time and probably buck or pop.

Lets confirm that you're lean - but if you ARE lean and you're lean all the time, I'd suspect low fuel pressure (unlikely) or clogged injector(s) - also not that likely....

Condition of the plugs would help.
Additional confirmation would be to get the voltage from the 02 sensor under no-load cruise. We can provide more information on how to measure - but under operating temperature, no-load cruise, you should go into closed loop and dither (quickly) from rich to lean / rich to lean...

84sr5yoty

Well, it can get tricky. Here's the story to my "lean" issue.

Replaced the plenum, lower intake, and throttle body gaskets. Help some.

Had the fuel injectors ultrasonically cleaned and rebuilt. Smoother idle, eliminated the low RPM misfire I was having (1,200 RPM's).

Cleaned EGR valve, didn't make a difference. Completely bypassed the EGR valve. Made a WORLD of difference!!! Idle vacuum went from 17 hg to 22 hg.

Replaced coolant temp sensor even though it tested out per factor service manual. Idled better, slight pinging I had from bypassing the EGR almost eliminated.

Check every single vacuum hose for leaks. Most leaks rear their head from the rubber intake boots. Spray starting fluid around all vacuum hoses and intake gaskets. It works effectively.

The PCV hose usually develops cracks and can suck additional air in.

toyotalytrevor

its not passing due to high NoX on driving test. 3 mechanics that i know, i showed them the paper..... and their first reaction was "wow, your running lean"


im gonna do some more work to it tomorow.

Dare44

idk just throwing out an idea, could ur timing be off?

Kiroshu

You may have worn piston seal rings. that can casue oil to seep in and thus fire in the cylinder.
____________________________________
95 Toyota 4runner SR5 V6 3.0 Automatic 150,000 Miles

dcg9381

You might want to "filter" the advice you get on this forum and other forums.
If you're leaking oil into the cylinder, that's likely to show up as hydrocarbons... Also, the 22R series is more likely to have bad rings in my experience than worn valve seals.. Anyway..

High NOX does indicated high cylinder temps. Typical issues are EGR blockage and catalytic converter problems. Start with the EGR first... These are old motors and it's easy to clog up EGR passages.

The other thing that can cause high cylinder temps is incorrect timing, but you've already checked that.. Just remember that the TPS and timing go hand in hand. Google "4crawler TPS" if you have questions about setting the TPS and timing. If you replaced the TPS, you need to adjust it. Replacing it could cause timing problems (and associated high combustion temps)...