Code 25 and 26 (1 Viewer)

[mattbeck180]

Just to give a description of what’s going on rough idea, wants to shake at lower rpm’s while driving 1800-2300ish, just very sluggish and almost like it’s not running on all cylinders. Clears up mostly at higher rpm’s. Iv had this issue for probably 6 months but seemed much worse yesterday.


I have a 1994 and I’m getting codes 25 and 26. I have had o2 sensors ordered for months. I pulled all 6 spark plugs yesterday. Cylinders 1-3 looked great. Cylinder 4 was very wet and cylinders 5-6 was very lean. Can o2 sensors cause this much trouble? I’m starting to think I may have some bad injectors possibly? Also done a compression test all 6 cylinders was 120-123psi. Any help would be appreciated. Really don’t want to wait on o2 sensors just for that not to be the problem

 

[Fj80oregon]

For Sale - San Diego: NGK NTK 24044 Oxygen O2 Sensor

NGK NTK 24044 O2 sensor. Made in Japan. New unused. I opened one box just for photos. $150 each, two available.

forum.ih8mud.com

 

[Fj80oregon]

You can test your o2 sensors. If they have never been replaced sounds like a good idea. but I don’t believe they are your issue. I would start with the wiring harness where it passes the egr pipe. Second if you already know you have an issue with fueling make sure each injector is cycling you can hear them tick with a mechanical stethoscope cheep tool. Also vacuum leaks can cause lots of issues also causing a rich condition by letting in unmetered air so the engine adds fuel. Egr could also be an issue easily tested. If you don’t have a FSM download one for free in the resources section and go through the engine troubleshooting and start testing systems. The reason there are check engine lights and codes is to point you to an issue and diagnose not throw parts at it. Code 26 is reading rich so investigate why it’s running rich? Stuck open injector possibly? Good luck!

 

[mattbeck180]

Thank you. Po deleted the egr. Also harness is new not saying that’s not the problem it has crossed my mind.

 

[jonheld]

25/26 screams O2 sensors or associated wiring. Start with the low hanging fruit.

 

[OffRoadScott]

You can test your o2 sensors. If they have never been replaced sounds like a good idea. but I don’t believe they are your issue. I would start with the wiring harness where it passes the egr pipe. Second if you already know you have an issue with fueling make sure each injector is cycling you can hear them tick with a mechanical stethoscope cheep tool. Also vacuum leaks can cause lots of issues also causing a rich condition by letting in unmetered air so the engine adds fuel. Egr could also be an issue easily tested. If you don’t have a FSM download one for free in the resources section and go through the engine troubleshooting and start testing systems. The reason there are check engine lights and codes is to point you to an issue and diagnose not throw parts at it. Code 26 is reading rich so investigate why it’s running rich? Stuck open injector possibly? Good luck!

I skimmed over this thread and it sounds like the same issues I was having. My harness near the EGR looked good to the naked eye but when it was running and you moved the harness the LC idled differently. I was also having an issue passing emissions due to high HC/CO, per the FSM the resistance on the O2 sensors should be 5.5-6 ohms mine were double that. Cleaned up my HC/CO issues and was able to pass emissions. Also check your VAF too.

 

[mattbeck180]

Tested vaf seems fine. Was reading and it said to test ox1 on the diagnosis for voltage. I’m getting around .5-.8. Doesn’t change with rpm’s. That means the o2 sensors are not reading correct?

 

[Rifleman]

Below you'll find a link that will answer all you're questions about what's the correct voltage readings for your O2 sensors, ,5 to ,8 volts means your engine is running rich, 1,25 volts is slightly rich, 2,50 volts is considered optimal, and 3,75 is slightly lean, but as long as you're within 1,25 to 3,75 volts you're good to go,

Vf1 voltage

Vf voltage information about Oxygen Sensor

alflash.com.ua

 

[ZackR]

How does it run with the 02 sensors disconnected to troubleshoot? When mine failed I tried this and it ran a lot better, albeit pretty rich.

In your case with a wet cylinder 4 it sounds more like an injector issue (wiring or otherwise).

There's the possibility that the 02 sensor codes are just a symptom of another problem in the fuel system.

 

[mattbeck180]

How does it run with the 02 sensors disconnected to troubleshoot? When mine failed I tried this and it ran a lot better, albeit pretty rich.

In your case with a wet cylinder 4 it sounds more like an injector issue (wiring or otherwise).

There's the possibility that the 02 sensor codes are just a symptom of another problem in the fuel system.

Doesn’t change at all when there unplugged. All the injectors sound fine. I’m not going to start pulling injectors yet.