Misfire and code 25/26 - need help

[gorbilax]

Hello Mud - need some help with my 94 FZJ80. This truck came to me from a family friend who moved out of state. Before I got it, it sat for several years and wasn't driven. When originally parked, it was running fine, but I just got it back on the road a few weeks ago and it has a bad miss under acceleration. I also have a code 25 and 26.

I've replaced plugs, wires, cap, rotor, and changed the air filter, with no change. I also did a compression test (but having trouble tightening the hose on the tester in the deep spark plug tubes, so I don't know how accurate it is). There's no noticeable drop on any of the cylinders. They're all around 170. The p/o replaced the intake plenum a couple of years before the truck came to me, and I just checked it again and it's in good shape with no cracks or leaks. The gas light was on when I got it, and I've since added ~19 gal of fresh gas on top of the little bit of old gas. I've been reading too many posts and pretty sure I'm overthinking everything, talking myself in circles around what to test, and not getting anywhere. Where should I go from here? What's the best thing to test next?

 

[Red Merle]

O2 sensors

 

[bigredmachine]

25/26 codes are rich/lean code and they are related to the o2 sensors. youll want to replace them with either denso or ngk sensors. also check the connectors for corrosion as that can also give poor readings from the sensors

 

[Red Merle]

25/26 codes are rich/lean code and they are related to the o2 sensors. youll want to replace them with either denso or ngk sensors. also check the connectors for corrosion as that can also give poor readings from the sensors

Code 26 could also be the ECT sensor which is worth swapping out. It's an $80 item, but at this age and the way Mr. T is dropping parts from stock, I would toss one in and test and keep the old one if it's still functional.

But yeah, probably O2 sensors or burned wires by the EGR. Or the ECU. Probably be good to source one of those too, just in case you need a Code Red back-up since those are NLA.

 

[bigredmachine]

Code 26 could also be the ECT sensor which is worth swapping out. It's an $80 item, but at this age and the way Mr. T is dropping parts from stock, I would toss one in and test and keep the old one if it's still functional.

when I was chasing down a similar issue I found the coolant temp sensor for around 10 on rock auto, it was a beck arnley so it was at least a good aftermarket brand. it is easy enough to change and could cause a fueling issue due to incorrect temp readings

 

[Red Merle]

when I was chasing down a similar issue I found the coolant temp sensor for around 10 on rock auto, it was a beck arnley so it was at least a good aftermarket brand. it is easy enough to change and could cause a fueling issue due to incorrect temp readings

Did it plug right in? That was my concern so I just went the Mr. T route but in retrospect it does seem like a pretty simple part that could be a good candidate for an aftermarket unit, especially at those prices.

 

[bigredmachine]

yep dropped right in and had the correct connector, the tip in the coolant jacket was even brass

 

[Red Merle]

yep dropped right in and had the correct connector, the tip in the coolant jacket was even brass

Well, there you go. I probably wasted $70.

At any rate, I did think it was worth doing although my issue did end up being a slightly corroded O2 sensor fitting. I sprayed a little vinegar in the fitting and cleaned it with a brass brush and blew it out with air and electrical fitting cleaner. She purrs again.

 

[bigredmachine]

I figured that for the 10 or so it was worth just replacing it. I tested the old one and it tested fine but it was easy enough to change anyways. mine was also corroded o2 sensor connectors as well as poor wire repair farther up the harness and the sensors were shot.

 

[gorbilax]

Forgot to mention in my laundry list of past repairs - one of my o2 sensors had a connector corroded so badly that one of the wires fell out. I replaced the sensor with a new NTK 24044, took apart the connector from the harness, cleaned each contact with contact cleaner, and reassembled it a few months ago. I never replaced the other sensor, so I will check the connection out on that one as well and replace it to match the first one.

I've been thinking about doing a PAIR delete for awhile now, so this might be a good opportunity to kill two birds with one stone - buy that second o2 sensor, remove PAIR, move both the sensors up to the manifolds, and be done with it. Getting the rusted nuts off the inner sensor is going to suck anyway, so I'd rather just leave the old one hanging there as a block off and install the new one up top.

I already ordered the block off plates for the YR vans that C Dan mentioned in previous posts, so I'll just block off the outer O2 bung down below with one of those and call it a day. Second new NTK 24044 is now on the way.

 

[gorbilax]

My parts showed up today. I removed the PAIR system, capped the vac line and the air box, moved my one good O2 to one of the PAIR ports, and installed the brand new O2 in the other PAIR port. I reset the computer and took a couple of test drives for the computer to relearn the idle. My code 25/26 are gone and haven't come back but my misfire under acceleration is still there. It seems to get worse as the engine gets warmer, but maybe that's in my head. I have the Toyocom app and the bluetooth dongle and verified that my O2 sensor readings both look good. Where should I go from here?

 

[BreckCruiser42]

Throw the same codes in my 94, I was leaning towards it being a fuel injector issue. Was planning to pull them and have them cleaned

 

[ZackR]

Did you clear the codes and see if they came back? I like to do this first to make sure its an actual issue vs a one time thing.

 

[gorbilax]

I cleared the codes and test drove for about half an hour. Codes did not come back. Took it for a test drive a little later for a few minutes and still no codes. I do think I definitely had a bad O2 sensor, but replacing it has only solved the problem with the codes, NOT the problem with the misfire under load. Still don't know what the cause of that is.

 

[bigredmachine]

some times that's just the joys of owning an obd 1 truck, there a misfire with no codes so the only thing to check is everything. when it misfires under load is it all the time or when its at operating temp?

I had a misfire at idle and fortunately it just went away as mysteriously as it came, itll be frustrating tracking it down but do it systematically and youll find someething

 

[gorbilax]

Short lived victory with 25/26. Both codes are now back. @bigredmachine agreed... I know I need to check everything. Just overwhelmed with where to look next. I guess I'll start looking at the fuel system.

 

[bigredmachine]

get an fsm, figure out when the misfire happens more specifically and start with the basics of fuel, spark, air.

 

[ZackR]

Double check the wiring harness the EGR as well.

 

[gorbilax]

Took the hood off today to get a better look at things. The harness seemed to be laying against the egr tube, but there wasn't any visible damage. I moved it out of the way. Started her up and unplugged one plug wire at a time. The miss got worse on every plug except 6. Went through them twice and my wife and I both agree no change on 6, but all the rest made a worse miss. Checked the #6 injector wiring. Good continuity and no resistance back to the ecm and to the battery. Listened to the injector with a stethoscope per the FSM, and it sounds the same as the others... I'm at a loss again... Might need to cut into the harness wrap by the egr to see if anything is melted in there, but since the wiring seemed good to the injector, I'm not sure.

 

[Red Merle]

Took the hood off today to get a better look at things. The harness seemed to be laying against the egr tube, but there wasn't any visible damage. I moved it out of the way. Started her up and unplugged one plug wire at a time. The miss got worse on every plug except 6. Went through them twice and my wife and I both agree no change on 6, but all the rest made a worse miss. Checked the #6 injector wiring. Good continuity and no resistance back to the ecm and to the battery. Listened to the injector with a stethoscope per the FSM, and it sounds the same as the others... I'm at a loss again... Might need to cut into the harness wrap by the egr to see if anything is melted in there, but since the wiring seemed good to the injector, I'm not sure.

Did you ever test the ECT sensor? That is one of the things that Code 26 points to according to my info.