Hey everyone!
So this issue has been stumping me for quite awhile, but it's not frequent enough for me to really dig into the issue.
The issue:
Occasionally, and seemingly at random, when either close to idle or at idle, the Air to fuel ratio (AFR for short) gets pretty rich without the ECU actually adding any fuel (fuel trims near 0), around 10-12 AFR. Eventually the ECU starts pulling a ton of fuel to get it back to normal around 14.7 AFR (I have a gauge). It can pull up to almost -30 in very rare occasions, but typically pulls the standard "maximum" of -20 in both LTFT and STFT. If I leave it idle for a little bit, all of a sudden the AFR swings back lean due to the ECU command pulling fuel, and will sometimes stall the truck, this is due to AFRs being near 19.0 AFR. This doesn't always stall the truck, but usually results in rough-ish running very shortly before the ECU starts to add fuel again and return to 0 LTFT and STFT and all is good again.
Now if I start to drive during this condition, the fuel trims instantly go back to normal and I have no problems throughout the rest of the fuel map it seems, it's only at idle/low rpm (sub 1000 RPM) that this happens. When driving around, then going back to the low RPM condition, it continues to give me issues, so it's very much within that range.
A few observations: this usually happens after long drives at similar RPM, so like road trips, or on hotter days so I THINK this is heat related, but I'm not entirely sure, I will find out this winter most likely.
I think this issue may have been happening for quite awhile, but I have only recently (within the last year or so) been monitoring fuel trims and AFR at the same time, so it's way more noticable now. I vaguely remember this being a problem right before the full rebuild, but I chalked it up to the head gasket causing issues before it let go.
Some background info:
My 80 has been pretty extensively rebuilt about 40k miles ago, with nearly everything new. New engine harness, new upstream O2, new sensors on the block, new vacuum lines, new cooling system entirely, new distributor cap and rotor, new wires (original ignitor and ignitor module though), new short block, literally almost a brand new 80 powertrain wise. My 80 is also now turbocharged, with a Walbro 255 pump (I also swapped pumps to ensure it wasn't a delivery issue, also this pump is hard wired to the battery), new OEM fuel injectors, colder Toyota plugs, aeromotive FPR with a gauge for monitoring fuel pressure directly, ARP head studs, cosmetic MLS head gasket that's a little bit thicker than OEM, etc.
I have no EGR, as that was deleted on rebuild (sorry CA residents
), so I don't have the engine harness melting on the EGR pipe, as the pipe is removed entirely.
My observations:
I don't ever get a CEL from this issue, except for one time. I got a system too rich bank 1 (expected), and a very peculiar P0125, which I think is a major clue into what's going on.
After I got that code I was monitoring the upstream O2 voltages, and they were pretty far outside the normal operating range of 0.400-0.800V during the condition, I would say between 0.250-0.975V. After the ECU started adding fuel again, the O2 voltages came back within the expected range. I've been through 1 new denso O2 and currently I have an OEM Toyota O2 on the truck due to thinking maybe I got a bad denso sensor. I use all OEM parts, or direct from the manufacturer parts if OEM is NLA.
This is very hard to test, because it seems every time this happens, I'm not really in a position to pull the truck apart and dig into a proper diagnosis. Literally every single time I'm on the way home, it fixes itself before I pull in the driveway
.
I will have some tools available to me soon, most importantly my multimeter, but if I really need to, I have an ocilloscope I can bring out, I just don't know what to look for on an 80 with it regarding this issue.
My gut is leaning towards maybe a bad ECU, but I don't really want to throw too many parts before I can rule out everything else, mostly because now I'm just curious and it's got me interested.
I bring this issue to mud for 2 reasons:
1) If anyone else is having the same issue, maybe this will help if I ever find an answer.
2) There are plenty of people on here with much more experience with 80s than myself, so I am most likely overlooking something.
What do you think Mud? Am I missing something? Any leads I can chase down?
Thanks all!
So this issue has been stumping me for quite awhile, but it's not frequent enough for me to really dig into the issue.
The issue:
Occasionally, and seemingly at random, when either close to idle or at idle, the Air to fuel ratio (AFR for short) gets pretty rich without the ECU actually adding any fuel (fuel trims near 0), around 10-12 AFR. Eventually the ECU starts pulling a ton of fuel to get it back to normal around 14.7 AFR (I have a gauge). It can pull up to almost -30 in very rare occasions, but typically pulls the standard "maximum" of -20 in both LTFT and STFT. If I leave it idle for a little bit, all of a sudden the AFR swings back lean due to the ECU command pulling fuel, and will sometimes stall the truck, this is due to AFRs being near 19.0 AFR. This doesn't always stall the truck, but usually results in rough-ish running very shortly before the ECU starts to add fuel again and return to 0 LTFT and STFT and all is good again.
Now if I start to drive during this condition, the fuel trims instantly go back to normal and I have no problems throughout the rest of the fuel map it seems, it's only at idle/low rpm (sub 1000 RPM) that this happens. When driving around, then going back to the low RPM condition, it continues to give me issues, so it's very much within that range.
A few observations: this usually happens after long drives at similar RPM, so like road trips, or on hotter days so I THINK this is heat related, but I'm not entirely sure, I will find out this winter most likely.
I think this issue may have been happening for quite awhile, but I have only recently (within the last year or so) been monitoring fuel trims and AFR at the same time, so it's way more noticable now. I vaguely remember this being a problem right before the full rebuild, but I chalked it up to the head gasket causing issues before it let go.
Some background info:
My 80 has been pretty extensively rebuilt about 40k miles ago, with nearly everything new. New engine harness, new upstream O2, new sensors on the block, new vacuum lines, new cooling system entirely, new distributor cap and rotor, new wires (original ignitor and ignitor module though), new short block, literally almost a brand new 80 powertrain wise. My 80 is also now turbocharged, with a Walbro 255 pump (I also swapped pumps to ensure it wasn't a delivery issue, also this pump is hard wired to the battery), new OEM fuel injectors, colder Toyota plugs, aeromotive FPR with a gauge for monitoring fuel pressure directly, ARP head studs, cosmetic MLS head gasket that's a little bit thicker than OEM, etc.
I have no EGR, as that was deleted on rebuild (sorry CA residents
), so I don't have the engine harness melting on the EGR pipe, as the pipe is removed entirely.My observations:
I don't ever get a CEL from this issue, except for one time. I got a system too rich bank 1 (expected), and a very peculiar P0125, which I think is a major clue into what's going on.
After I got that code I was monitoring the upstream O2 voltages, and they were pretty far outside the normal operating range of 0.400-0.800V during the condition, I would say between 0.250-0.975V. After the ECU started adding fuel again, the O2 voltages came back within the expected range. I've been through 1 new denso O2 and currently I have an OEM Toyota O2 on the truck due to thinking maybe I got a bad denso sensor. I use all OEM parts, or direct from the manufacturer parts if OEM is NLA.
This is very hard to test, because it seems every time this happens, I'm not really in a position to pull the truck apart and dig into a proper diagnosis. Literally every single time I'm on the way home, it fixes itself before I pull in the driveway
. I will have some tools available to me soon, most importantly my multimeter, but if I really need to, I have an ocilloscope I can bring out, I just don't know what to look for on an 80 with it regarding this issue.
My gut is leaning towards maybe a bad ECU, but I don't really want to throw too many parts before I can rule out everything else, mostly because now I'm just curious and it's got me interested
.I bring this issue to mud for 2 reasons:
1) If anyone else is having the same issue, maybe this will help if I ever find an answer.
2) There are plenty of people on here with much more experience with 80s than myself, so I am most likely overlooking something.
What do you think Mud? Am I missing something? Any leads I can chase down?
Thanks all!
