Garage Maintenance Reassurance '94 80 Series

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DeliBoyCreates

DeliBoyCreates

Joined
May 29, 2024
Threads
1
Messages
17
Location
West Virginia
A little over a year ago I resorted to some older threads about CEL codes 21, 26, and 28 for my '94 80 series. Gained knowledge on those codes and I spoke to a few folks and came to the conclusion I needed new O2 sensors which I put in. Codes cleared and truck ran without issue. As of 3 days ago the same codes came back with the same side effects as before (rough idle, terrible mpg, sluggish acceleration which all slightly become less noticeable the more warmed up the vehicle gets but are still prevalent). I jumped under the truck today with time to tinker and did the following:

Disconnected both O2 sensors and inspected both male and female ends (Note: I did not unbolt and remove the sensors entirely, just disconnected the wiring plugin/harness). Driver side sensor appeared perfectly fine with no debris or corrosion on the male and female ends. Passenger side plugin had a bit of debris/corrosion on 2 of the prongs which I cleaned as best I could before reconnecting. I turned on the vehicle and codes still appeared and vehicle ran with above mentioned side effects. Turned vehicle off.

I then disconnected the battery for about a minute or two and then reconnected the battery. I turned the vehicle back on and the CEL continuously flashed but all the side effects went away and the truck ran perfectly fine. I drove it around the block a couple times and the CEL continued to flash but the truck ran perfectly fine. Excellent idle and great acceleration. TBD on mpg.

I guess my question/concern/reassurance would be if my vehicle is running as it should with no issue (CEL still flashing), should I just continue to drive it per usual and keep an eye out for side effects creeping back. Or do any of you with more experience have recommendations for me before I start driving it as normal again?

It's been a pleasure to learn and perform my own maintenance so very appreciative of any advice/tips/recommendations!!!
 
DeliBoyCreates said:
A little over a year ago I resorted to some older threads about CEL codes 21, 26, and 28 for my '94 80 series. Gained knowledge on those codes and I spoke to a few folks and came to the conclusion I needed new O2 sensors which I put in. Codes cleared and truck ran without issue. As of 3 days ago the same codes came back with the same side effects as before (rough idle, terrible mpg, sluggish acceleration which all slightly become less noticeable the more warmed up the vehicle gets but are still prevalent). I jumped under the truck today with time to tinker and did the following:

Disconnected both O2 sensors and inspected both male and female ends (Note: I did not unbolt and remove the sensors entirely, just disconnected the wiring plugin/harness). Driver side sensor appeared perfectly fine with no debris or corrosion on the male and female ends. Passenger side plugin had a bit of debris/corrosion on 2 of the prongs which I cleaned as best I could before reconnecting. I turned on the vehicle and codes still appeared and vehicle ran with above mentioned side effects. Turned vehicle off.

I then disconnected the battery for about a minute or two and then reconnected the battery. I turned the vehicle back on and the CEL continuously flashed but all the side effects went away and the truck ran perfectly fine. I drove it around the block a couple times and the CEL continued to flash but the truck ran perfectly fine. Excellent idle and great acceleration. TBD on mpg.

I guess my question/concern/reassurance would be if my vehicle is running as it should with no issue (CEL still flashing), should I just continue to drive it per usual and keep an eye out for side effects creeping back. Or do any of you with more experience have recommendations for me before I start driving it as normal again?

It's been a pleasure to learn and perform my own maintenance so very appreciative of any advice/tips/recommendations!!!
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I had a heck of time with the same things (same year 80 as yours). Ended up moving the O2 censors to the exhaust manifold - leaving the bungs from the old censors in place to keep the mounting points sealed. You'll need to de-smog your rig to do that, which isn't too much work on a '94. The short of it is, no more codes or CEL.

Also, you can use the one OEM O2 censor that's still available from Toyota... it reaches to both manifold points with no problems.
 
Old Nick said:
I had a heck of time with the same things (same year 80 as yours). Ended up moving the O2 censors to the exhaust manifold - leaving the bungs from the old censors in place to keep the mounting points sealed. You'll need to de-smog your rig to do that, which isn't too much work on a '94. The short of it is, no more codes or CEL.

Also, you can use the one OEM O2 censor that's still available from Toyota... it reaches to both manifold points with no problems.
Click to expand...
Sounds like a good route to go, that'll be my next deep dive. Thanks for the insight!
 
Malleus said:
Rapidly flashing MIL indicates the ECM is in check mode. Turning the ignition off resets the ECM to normal mode. Read the diagnostic procedure in the FSM, starting on page EG-216. If you don't have a copy, download one for free from the Resources forum section, 80 series area.
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This was from a couple years ago but Malleus is the man. As a side note, the 94 won't retain codes unless they are active.
 
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DeliBoyCreates said:
Just went out and turned it on and took it around the block. No CEL light anymore and ran perfect.
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Just as an FYI, removing the 15 amp EFI fuse in the relay box on the left fender is a less invasive way to reset the ECU than removing battery terminals.

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*Update*

As of today during a 4hr round trip the CEL came back on after 2.5 hours of highway driving. Checked codes once I stopped and it threw 21 and 28. Vehicle showed no difference in performance. Normal idle, normal acceleration, normal mpg. I am going to continue driving as normal and order a new O2 sensor for safe keeping and monitor performance.
 
Brindleboxer said:
This was from a couple years ago but Malleus is the man. As a side note, the 94 won't retain codes unless they are active.
Click to expand...
And they reset/clear themselves when they are resolved. At least according to the service manual.
 
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