94 FZJ code 26 running too rich

[BlackLS1]

hello guys, just wanted to get some ideas or opinions from the great folks on this board. 94 with obd 1, car begins to run rough from the moment it starts. o2 sensors were replaced about 6 months ago with NTK replacements, I did use my multi meter to get some readings from the diagnostic connecter for both o2 sensors, it seems to be having a very hard time staying in closed loop. when it does switch to closed loop the voltage is around 1 volt! wayy to rich! when I unplug the vane air flow meter the car immediately dies and will not restart which is another indication that its in open loop (unless this is normal operation for this engine to rely on the VAF) I also checked my fuel pressure regulator visually and there is no leak in the diaphragm. I have not confirmed if I have a leaking injector or not yet as I have not removed plugs. I am going to remove the VAF sensor and get some more resistance readings from it. I checked the resistance of a few terminals according to FSM but seemed to be fine, I did not get a chance to check resistance with moving the internal flap. anybody ever dealt with this code before? car has a rough idle and is a slug until about 2000 rpm then feels normal after that. I am trying not to run the car as im afraid damage to the catalyst will occur. can anybody confirm if unplugging the VAF meter will immediately kill the engine? I will be checking the VAF and removing spark plugs tomorrow. hopefully will have it fixed in time for the camping trip in 2 weeks. thanks for the help guys.

 

[Timpanogos Slim]

The engine does rely on the VAF. I think dying when it's disconnected is normal. The injection system is just toyota's version of bosch l-jetronic so the VAF is a thoroughly critical component.

when testing the VAF be aware that the 2nd page of the FSM section on it has an incorrect diagram. Refer to the first page.

The annoying thing about 93-94 cruisers and the too rich / too lean codes is that they can also be caused by a rough idle, according to the FSM.

And rough idle can be caused by vacuum leaks, and unmetered air.

Check the air inlet hose for cracks. Also, I found that the clamps on my inlet hose had worn grooves so deep in the rubber that they could no longer get a good seal. I switched to t-bolt band clamps and got a good seal. Since the diameter is so large (almost 3") a worm gear clamp probably works too.

Use an unlit propane torch or a spray can of carburetor cleaner or something to check for vacuum leaks. There is about 7 feet of vacuum line on this engine. Refer to the vacuum diagram on the sticker on the inside of the hood. Or just buy 7 or 8 feet of 1/8" vacuum line and replace every stinking line like i did.

I still have low idle sometimes, but it's low and smooth. I suspect that my IAC valve needs cleaning, but my experiments have confirmed the FSM assertion that the throttle body should be removed before the IAC can be removed.

 

[BlackLS1]

Thanks for the reply, normally I would suspect a vacuum issue but this all happened immediately one morning. I'm going to try the propane enrichment to see if it will respond to that. I also have access to a 5 gas analyzer so that might help me further to see how much hc and O2, and CO is coming out the tailpipe. I have a feeling it's the VAF for some
Reason and my stomach cringed when I saw the price of $700 from Toyota, ouch. I will let you guys know what I find out tomorrow. It would have been nice to have a lab scope to back probe the injector and get its pulse width

 

[Timpanogos Slim]

Near as i can tell the leading cause of VAF damage is people removing the two screws on either side of the cable connector and pulling on the cable.

You can get a good used VAF for less than $200 from cruiserparts, cruiseryard, etc.

But i doubt it's the VAF.

Certainly bench test it. Remove no screws!

When testing for propane enrichment due to vacuum leak, remember that there is an unholy mess of vacuum solenoids between the throttle body and the intake manifold. There is still at least one original vacuum line on my rig in there, and it will stay there until i take the plenum off to do the valve cover gasket.

 

[BlackLS1]

did a little deeper diagnosis on the VAF and according to the FSM I guess its fine. the resistance for the flap while I was moving it was not a constant increase, the resistance would go up and down as the flap began to open. I guess the FSM says the flap operates in a waveform so it should be correct. however to my surprise after messing with the VAF then putting it back on the rig, I started the engine and it seemed to run perfectly fine. I don't get it, could the flap have been binding maybe? I even drove it around it seems to be running perfectly normal now.

 

[BlackLS1]

Near as i can tell the leading cause of VAF damage is people removing the two screws on either side of the cable connector and pulling on the cable.

You can get a good used VAF for less than $200 from cruiserparts, cruiseryard, etc.

But i doubt it's the VAF.

Certainly bench test it. Remove no screws!

When testing for propane enrichment due to vacuum leak, remember that there is an unholy mess of vacuum solenoids between the throttle body and the intake manifold. There is still at least one original vacuum line on my rig in there, and it will stay there until i take the plenum off to do the valve cover gasket.

im not sure what the FSM says but the plenum wont need to be removed to access the valve cover. it should be removable with just the throttle body out. I would also recommend you clean the egr passage way while your In there.

 

[jason5208]

What's that box under the hood between the air duct hose and the air filter? I'm drawing a blank at the moment but I had your same issues in my 94 and after replacing the O2 sensors and other parts I spoke with Roman at cruiserparts in new Hampshire and he diagnosed it on the phone and sold me a used unit which solved my problem immediately

 

[BlackLS1]

That is the vane air flow meter I have been trying to diagnose mine. It's good to hear that your problem got resolved with a replacement unit. Im suspecting mine now mainly because after messing with it out of the car and putting it back on the engine now seems to run perfectly fine. Thanks for your input

 

[toyotaspeed90]

I refer to the meters as AFM (air flow meter, and no - these aren't an MAF)- as that's what the FSM refers to them as.... in any event, the fuel pump will only run when the engine is first primed (first probably couple hundred cycles at most) and then when the air flow meter is 'open'.... it's Toyota's failsafe to shut the pump off in the event of an accident and the engine shuts off. So unplugging the AFM should cause the engine to die, as there won't be any fuel. You should have also gotten several more CEL codes kicked if you were running and unplugged the AFM (rich, lean, incorrect IAT value, and probably more).

An o2 sensor reading lean or rich is pretty normal, even one reading really rich.... it's also normal that when o2 sensors age/"wear" out that the system will purposely run rich .... it's a failsafe as well... it's safer for engine longevity to run rich than lean (though, running rich can cause problems in the long term as well). However an o2 reading rich wouldn't cause a really rough idle. If it were purely an o2 issue, try (from idle) to go wide open throttle - as 02's are ignored at WOT. The roughness probably won't go away.

A simple way to check the injectors, and this is by no means a 'calibrated' method, but is to use a simple mechanics stethoscope.... you should hear them clicking pretty darn rythmically to one another. A leaking injector will leak the pressure from the lines from the last time it ran - which if the engine hasn't been run in a few hours could cause a longer crank to start (as in - where fuel pressure needs to build back up in the rail) and/or if it tries to start immediately after being off for only a few minutes, could start significantly faster than normal, and have black smoke out the tailpipe. I would have to look and see where the injectors in a 1FZ enter the manifold/chamber, but usually if an injector is leaking the fuel will leak onto the cylinder, past the rings, and you can smell gas in the oil.

Is 26 the only code you're getting?

 

[jason5208]

I was getting both 25 and 26 codes - lean and rich - and spent hours after a full tuneup and O2 sensor replacement trying to chase down phantom vacuum leaks. Even more time reading through the different threads on this site . Talk about information overload...Turned out to be the air flow meter. I can't overemphasize how helpful cruiserparts in New Hampshire was over the phone. Roman over there knew right away what it was. I was so confused and desperate that I took a chance on his diagnosis and he was right. It's worth giving those guys a call. Plus they stock both new and used parts

 

[BlackLS1]

Thanks for the replys fellas. Ok code 26 was the only code. And o2 sensors were ruled out from the beginning because this problem begins to happen during open loop operation. However I just came back from a 200 mile trip with the landcruiser and its running great. However a replacement air flow meter is going to be ordered because I suspect a intermittent fault with mine. As for the moment tho it's running good. Thanks again for the help everybody.

 

[BlackLS1]

damn I got the code again! anybody ever dealt with just code 26? I guess a replacement VAF is still in order. im hoping its the VAF but I hate to throw parts at it and be unsure before replacing things. im going to get the kit and copper washers to check the fuel pressure. any help from fellow mud members would be really appreciated. thanks everyone.

 

[landtank]

since removing the VAF seemed to make a difference and you are getting both a 25 and 26 I would inspect the air tube for cracks. This is the black tube that goes from the VAF to the throttle body.

 

[landtoy80]

Unplug the O2 sensors and driver. If problem goes away, its your O2 sensors. Look at the plugs for corrosion too. They will cause a 25 26 code.

My 94 likes to dirty up the O2's unless I drive all hwy miles. Any city driving I get either code 25 26 or both. When my O2's start to make the motor run real rough, I just unplug them and drive unplugged for months. I will plug them in again and depending on my driving they will either work or make the motor run rough.

I have drove for over a year at a time with them unplugged. I see no difference in performance and mileage when unplugged. Only reason I have them plugged in now is I live in emission testing area.

Also, if you start the motor and it dies right away, that means the O2 is dead. Unplug them and keep driving. I babied a set of O2 for over a year running them plugged in and unplugged till one of them died. Then drove another year with them unplugged.

 

[Brentbba]

Gotta agree with Landtank on the big intake tube. In the OP's original post - you said it ran rough until you got up to about 2000 RPM and it ran fine. My educated guess is that you've got a crack in that intake tube and once the engine vacuum is up at speed the vacuum closes the crack just enough to allow the engine to run smoothly. Inspect/replace that tube. IIRC the last one I purchased was less than $100 from CDAN. While '94's are notorious for ruining O2 sensors and you've replaced those and elimiated the MAF, inspect the intake tube.

 

[BlackLS1]

Thank you guys for the thoughts. The intake tube Dident cross my mind haha. I
Will Defiantly Have a look at that
Tomorrow, I hope it's just that. I'm ordering up a replacement vaf. I
Would like to confirm that I was only
Getting code 26 for running too rich, however when I add propane through the intake the idle begins to smoothen out and run better indicating it actually running lean. I got some new plugs ready to go in as well.

 

[BlackLS1]

Hey guys back again with this F$&kin problem. Ok so i just got a new air filter from Toyota and replacement VAF from the classifieds, I thought it fixed the problem, I drove it to work today and as soon as I got there I felt the little shaking start. It was shaking but not as bad this time. I hooked up a 5 gas analyzer. here are the readings I got
8:52 am
HC 89 ppm
CO 0.05 %
Co2 14.4 %
O2 0 %
NOx % 0 ppm

I don't like the amount of HC I'm seeing, possibly running on the rich side or cat is weak. I noticed HC begin to rise here is next set of numbers
8:57 AM
HC 131 ppm
CO 0.15%
Co2 14.3%
O2 0.2 %
NOx 17ppm
At the time of these numbers the engine was shaking but nothing crazy like a misfire but very noticeable, these numbers seem to show a slight lean misfire? Although o2 is only 0.2% it should be zero.

Next I disconnected Fuel pressure regulator and HC climbed a bit higher to around 175ppm. The same style of shaking still continued.
After reconnecting the regulator, I did zero the gas analyzer and shut the engine off around 9:05 am, I restarted the engine at 9 :17 am, I began the analyzer and now I set the hand throttle at 2400 rpm here are the readings
9:18 am

HC 15 ppm
CO 0.01%
Co2 13.2 %
O2 2.0 %
NOx 192ppm

Ok, it's possible the cat cooled down some, at this time of testing the engine was running Normal and there was no stumble. The Cat is either too cold or engine is running too lean, I'm not happy with the CO being that low.

Ok next I disconnected both o2 sensors while rpm is at 2400. (9:18 until next readings rpm remained at 2,400)

9:22 am
HC 10 ppm
CO 0.01 %
Co2 14.4 %
o2 0.3%
NOx 535 ppm

Still looks a little lean. I'm going to try and change the plugs this Saturday and see try to run it on the analyzer again. Sorry for the long and boring/confusing post Thanks for everybody's help.

 

[Brentbba]

You didn't mention whether you replaced the intake tube???

 

[BlackLS1]

Sorry, I removed the intake tube and after looking at it for 10
Minutes I could not find any cracks or tears on it. The boot is old and hard but if it has no leaks I think it should be ok. I'm going to try and monitor the o2 sensors With my meter again and check for vacuum leaks.

 

[Timpanogos Slim]

Sorry to hear that it is still an issue.

My rig started idling rough again the other day. Haven't investigated yet.

Sent from my SCH-I545