plattey

Update: Replaced the o2 sensor (bosch brand) before heading up to MN and back to SW wisconsin. On the interstate it averaged 19mpg and on the hwy 21mph.

Gamefreakgc

@ plattey: Wow, 21 is pretty good! I'm hoping when I've got this all fixed I'll get an improvement.

Update on the sensor fix:

Couldn't get the ECT sensor out so I took it to a shop. Turns out, it's not an ECT! The busted part was a Cold Start Injector Valve Sensor, that costs $200 bucks from the dealer... gonna hit up the the junkyard this weekend. Oh, and the connector was shot, it had fused with the sensor so had to cut it off. Took one off a 93 4runner and sautered it on myself. Be careful though, apparently the ECT and the Cold Start sensor both have the same connector!

This would make sense, since it only runs rich when it's cold as though the engine isn't getting the right reading as far as temperature goes. I heard a faint whistling sound the last time I was adjusting the idle speed, I think I might have a small leak somewhere as well in all those vacuum hoses.

So the saga continues...

Gamefreakgc

Ok, final post! I found a Fuel Injector (EFI) Cold Start Switch on a 91 4Runner for $7.49. $192.51 savings! Also bought a new dashpot while I was there (Camrys and Corollas have the same kind as well). Since I had the coolant drained I decided to check the Engine Coolant Temperature (ECT) sensor as well. I go to take the connector off and the thing falls apart. It was corroded all the way through! Luckily, I still had the new ECT and popped it right in. From there, I put in the Cold Start Switch after coating both sensors in silicon at the top (to prevent leaks) and anti-seize on the threads. I tested both before installing as well with my ohm meter.

Did the diagnostic check for code 25/26 from the FSM with TE2 and E1 jumped and has a clean bill of health! Finally, I think the issue is solved. Now to fix the vacuum leak I heard with the engine running and the squeaky belt...

Gamefreakgc

Well, it's not looking too good. I thought I had it all figured out but turns out I've still got the CEL on with the code 25. I'm going to check for vacuum leaks one more time, but I think they would be so small and minor that it wouldn't trip the CEL.

Upon the recommendations of a recent thread, I'm going to check my o2 sensor gasket and the welds around it. I'm wondering if when they did the cat-back they were not too careful and broke a weld somewhere along the exhaust. I've never had the code until the day they finished it. In my mind, that either means the increased airflow exposed a leak (more vacuum bringing in more unmetered air) OR they broke a weld further up the system above the o2 sensor. Gonna go at it tonight.

Gamefreakgc

Last ditch effort...

I sealed the o2 gasket because it was leaking. Now it throws code 25 more consistently (every two star-ups compared to every 5-6). I'm thinking my o2 sensor is bad, even though it is only 3 months old.

I have a far-fetched idea. I live in California, and apparently (unconfirmed) 1991 Toyota pickups in Cali have two oxygen sensors. Mine only has one BUT the CEL turned on the day I got it back from the muffler shop. There's no oxygen sensor downstream of the cat, should there be? Would they be so dumb as to rip it out with the old piping and not put another in? Is there any way to check if my truck was made for Cali emissions by having two o2 sensors?

Any other ideas on what might be wrong? Here's a recap of what's been done:

• replaced o2 gasket
• sealed space between o2 gasket
• replaced bad ECT sensor
• checked vacuum hoses for leaks w/ carb cleaner
• checked AFM per FSM specs
• cleaned TB
• New TPS and set to FSM specs
• adjusted idle speed to ~800 RPM
• replaced Cold Start Injector Switch (was damaged)
• ran injector cleaners (in case of clogged injector)

Any help would be appreciated on either the two o2 sensor issue or any idea on what else it could be. Tried using www.toyodiy.com to check what parts I should have but my VIN keeps coming up as a 4Runner.

Kiroshu

Buy a "DENSO" brand oxygen sensor if that doesnt cure your code then possible cold start injector stuck open and or leaking.

Gamefreakgc

Well, the saga is still ongoing. New DENSO oxygen sensor and the light came back on .

When addressing and exhaust leak, I found a vacuum leak under the intake manifold that only made a noise at higher RPM's. See my post here and earlier posts:

https://www.yotatech.com/forums/f116...l#post52015365

Hopefully this will be the end of it. I'll have a chance to check the injectors as well while I'm in there so I'll have checked every single possible issue for a code 25. Hopefully this can be a resource for others with the same issue.

Huckm80

"I should say that cylinder 6 has bad compression (110 compared to 160~ on the rest), common 3VZ-E issue. I could see how that could possibly bring unburned gas into the exhaust but doesn't explain why it's running rich in the first place. ________________"


Well, I think this is your problem. Your number 6 cylinder has low compression. Coincidentally, mine does as well. A gas engine needs the basics to run correctly: Air, Gas, Spark, and Compression. Yes if your engine does not have high enough compression it will not completely burn the air fuel mixture, and the o2 sensor will pick this up as a lean condition, relaying to the ECU to add more gas to the mixture. At what point is not enough compression to completely burn all the gas, IDK.

Have you checked your valve clearances lately? If not, you probably have a a valve that is not seating all the way, thus not producing the full compression you need to completely ignite your air/gas mixture. Do a leak down test on that #6 to see if your valves are sealing properly.

Gamefreakgc

Well, I think this is your problem. Your number 6 cylinder has low compression. Coincidentally, mine does as well. A gas engine needs the basics to run correctly: Air, Gas, Spark, and Compression. Yes if your engine does not have high enough compression it will not completely burn the air fuel mixture, and the o2 sensor will pick this up as a lean condition, relaying to the ECU to add more gas to the mixture. At what point is not enough compression to completely burn all the gas, IDK.

Have you checked your valve clearances lately? If not, you probably have a a valve that is not seating all the way, thus not producing the full compression you need to completely ignite your air/gas mixture. Do a leak down test on that #6 to see if your valves are sealing properly. [/quote]

I did a valve adjustment over the weekend and it did turn out that cylinder 3 had an exhaust valve that was stuck open. I adjusted it to spec and not only does it run better, but no CEL yet. I think that might have been my issue, time will tell for sure.

As a fail-safe, I also had my injectors tested and cleaned to ensure it was not a bad injector causting the issue. I also replaced all gaskets along the way (EGR, Air Intake Chamber, Throttle Body, etc.) to be completely sure it wasn't my issue.

So if anyone else has a code 25 pop up, check the easy things first. O2 sensor, vacuum leaks, those sorts of things. Then check more expensive/complicated thing such as the VAFM, throttle body and TPS, exhaust leaks, then valve clearance as a last resort. In my case, I knew they were bad since my engine would wobble read bad, especially at low RPMs (tell tale sign of misfiring and low compression).

Gamefreakgc

Not trying to perpetuate the thread but posting the final entry.

The code 25 and bad gas mileage was due to the exhaust valve on cylinder 3 being open during combustion. This allowed oxygen to escape to the O2 sensor and cause a lean air/fuel ratio. After the valve adjustment and going from a 3.00 mm shim to a 2.55 mm shim, it works just fine. No codes after 2 weeks and my gas mileage has increase by at least 20%.

Hope this thread helps. I had issues every step of the way so my recommendation is to start with the easy ones and work your way up.

Thanks to all that helped. I learned so much through the whole process from going from a complete novice when it came to engines up to an informed novice who at least knows his way around his truck!

thezman007

First off, thank you VERY much gamefreak for chronicling your struggle with this problem and even more so for actually returning to the thread to tell us what happened! I had the code 25 problem as well. After clearing the code, sometimes it would come back right away, sometimes it would take a week or more. After seeing that doing "the big 3" can fix a lot of issues I decided to start planning out how and where I would run the wires. As I planned this I noticed that someone had broken BOTH the clips off of my VAFM wire!!! After clearing the code I used some thin utility wire in place of the clips. It's been 2 days and no CEL so far. I will update whether or not this is my fix as well. Here's hopin'!