STUMPED- codes 25, 26, 71. Help please? (1 Viewer)

[jordancollard97]

Hello all. Continuing in my 80 series resto-
Have codes 25, 26, and 71.

Running lean, running rich, and EGR System.

It’s worth noting the vehicle is running fine over all- no noticeable issues.

Any advice on where to start?

 

[CharlieS]

O2 sensors.

 

[LandLocked93]

Disable EGR, delete the PAIR, and disconnect battery to reset codes.

Oh wait, you're OBD2 and doomed to an everlasting CEL.

"Oh Lord receive this 80 into your good graces..."



Lol nah. Just try to keep your hair while resolving.

 

[jonheld]

Any advice on where to start?

How about some basic information like what engine/year.

 

[OffRoadScott]

Check the resistance of your O2 sensors, the FSM calls for 5.5-6 OHMS if they are not replace both.

With not knowing the year of your rig, if you have an OBD LC finding factory O2 sensors is hard to do but there are other options out there. I used Bosch and have used them for a year without issues.

And your EGR might be as simple as a plugged EGR, or EGR solenoid.

 

[jordancollard97]

How about some basic information like what engine/year.

1994. 4.5.

 

[ZackR]

Code 71 is for the EGR, I'd just disable it (short the temp sensor connection together) and leave the equipment in place.

Codes 25 and 26 (lean and rich) could be a lot of things. I'd start with checking for vacuum leaks and replace the 02 sensors.

 

[landtank]

on newer trucks the first place to start is the intake tube, look for cracks

 

[TheGrrrrr]

Code 71 is for the EGR, I'd just disable it (short the temp sensor connection together) and leave the equipment in place.

Codes 25 and 26 (lean and rich) could be a lot of things. I'd start with checking for vacuum leaks and replace the 02 sensors.

View attachment 3442433

Would this chart mean that if you are getting both the 25 and 26 codes then it wouldn't likely be VAF, PAIR, O2, Ignition System, ECT or Compression pressure, because those trouble areas aren't listed for both codes? Unless you have two separate issues?

I only have 25 and 26. Was having rough idling and replaced VAF yesterday and idling is very much improved, but didn't have a code for that anyway. Still have 25/26 and the truck runs great. Fuel pump, igniter, coil are all new as well. No other symptoms that would indicate engine ground bolt is loose.

Just ordered some new O2 sensors just to give that a shot. I'm not going to worry about the CEL too much since its running fine, but my curiosity is getting the best of me.

 

[boobaa]

I have the same codes on my 92' 3FE engine. There is a check for the O2 sensors on pg FI-27 byresetting the CEL by pulling the EGR fuse for 10 seconds, revving up the rpms 3x's to 4,000 then keep rpms at 2,000 for 2 minutes, etc......The second part is FI-28 that may be an injector problem - short, leak, blockage, etc.

Did you ever get the problem solved?

 

[DamoFZJ80]

Code 71 is for the EGR, I'd just disable it (short the temp sensor connection together) and leave the equipment in place.

Codes 25 and 26 (lean and rich) could be a lot of things. I'd start with checking for vacuum leaks and replace the 02 sensors.

View attachment 3442433

Hello all. Continuing in my 80 series resto-
Have codes 25, 26, and 71.

Running lean, running rich, and EGR System.

It’s worth noting the vehicle is running fine over all- no noticeable issues.

Any advice on where to start?

I had a few of these codes in the last few months (1994). What solved it for me:

Code 26 ( I did not get 25)
1) O2 Sensors (I did the Pair Delete and placed the O2 sensors on the manifold). I went on a wild goose chase trying to find O2 sensors. I ended up using the Universal ones from Bosch (15728) and splicing the old connectors from the original O2 sensors. If anyone has long tail OEM ones (NTK), I will pay a small premium for them!!! DM me. lol.



2) Mass Air Flow Sensor. I am currently using a cheap knock off until mine gets rebuilt (hopefully get it back in a few weeks). It works ok.

Code 71
1) EGR Disabled

My vehicle was pretty much baselined before these codes. When I had Code 26, my idle was all over the place sometimes. It would run great a lot of the time though. The start up produced some smoke and gradually got worse over time. Since I changed the O2 sensors, it is night and day on start up. Barely any smoke and consistent idle/performance.

 

[TheGrrrrr]

New O2 sensors went in mine today. No relief. Still 25 & 26.

 

[ZackR]

New O2 sensors went in mine today. No relief. Still 25 & 26.

Did you reset the codes (pull the ECU fuse)? They won't just go away on their own.

 

[TheGrrrrr]

Did you reset the codes (pull the ECU fuse)? They won't just go away on their own.

It actually did go away on its own (as it often does in this case) and then two trips later it came back on. I'll disconnect the battery to reset and do a few more trips before I move onto the next troubleshooting steps.

 

[TheGrrrrr]

If anyone has long tail OEM ones (NTK), I will pay a small premium for them!!! DM me. lol.

You don't need long tail. The OEM 89465-69115 reached just fine in both locations despite being short and they are NTK.

 

[TheGrrrrr]

I disconnected the battery for about 45 minutes yesterday. Have driven about 30 miles over 5 trips since then and the CEL was off the whole time until a quarter mile from home just now. I’m all out of ideas.

 

[Timpanogos Slim]

My interpretation of 25 and 26 together, based on the troubleshooting information in the manual. is that all the ecu is telling me is that the truck is idling rough.

Which is frustrating because i know it is idling rough i am driving it. My other vehicles are newer vw/audi vehicles and i have the same kind of diagnostic interface that independent euro shops use, and it isn't even funny how much more information i get from a 15 year old ECU than i do from a 30 year old ECU.

It's often down to intermittent unmetered air.

I did replace both the o2 sensors and the o2 sensor wire harnesses because the connectors were badly degraded and i had o2 sensor codes. Actually the inner o2 sensor harness had already been repaired by a ham-fisted ape with no understanding of electricity so i just corrected the work. Dumb tech shorted the shield to the signal wire on the one shielded wire.

I replaced all of the vacuum lines. I used blue silicone tubing so that it would be obvious which ones haven't been changed yet and it was a process over a few weekends. Most of it is the same size but not all of it.

I replaced the idle air control valve on the throttle body with one i pulled off of a junkyard truck but this was 11 years ago when that was possible. Some people have said that they just cleaned it, and made sure the IAC channel on the throttle body is clear.

Some people have found that one or more vacuum solenoid valves under the throttle body have failed. They can generally be replaced with aftermarket parts just fine. All of mine were working. They are easy to test.

Some people have reported clogged hard vacuum lines. The thin little tubes attached to the head. They can be cleaned out with a guitar string. I don't know if this would contribute to your condition.

A crack in the air duct between the VAF and TB will 100% cause this problem and you may have to take it off and clean it to inspect it close enough to be sure. My duct has no cracks but i did find that the wire-type clamps at the ends had worn deep enough grooves into the rubber that i couldn't get a good seal anymore, so i replaced them with t-bolt band clamps.

Aside from that, you can use a spray can of starter fluid or really anything that is flammable to check for vacuum leaks. An unlit propane torch for example. If the engine races when you introduce a fuel source near some vacuum lines, something is leaking vacuum.

And i assured that the egr system was in good shape. I didn't need to replace anything but i understand that there's a foam pad inside one of those things that sometimes needs to be replaced.

I did not have any luck disabling EGR by installing a resistor or whatever the trick was.

After all that, i haven't had any codes in 10 years.

 

[TheGrrrrr]

Seem to be down to just an intermittent 25 now. No 26.