Ecu misfire?

[TTO5]

So I went out to the truck after it sat for 6 hours or so after the mechanic checked it out. It started right up and I drove it around for about 5 miles letting it get warmed up. Engine light was off when I started it and stayed off with no codes pending. I then parked it for about an hour then drove it home 20 miles mixed 80 mph highway and low speed in town driving. Light stayed off no codes. I asked the mechanic if he unplugged and reconnected the computer when he parked it earlier today and he said no he didn't. Anyway let it sit for about 30 minutes then started it and let it idle. Light came on and blinking. Weird thing is as it's doing this my scanguage says no active codes but there is a engine p0300 but no 304 or 307. This has me completely confused. Mechanic has no idea what to do next and the original installer of the engine (independent store not the toyota dealer where i work) still holds his statement that we need to change the computer. Aye yay yay

Most recent video

 

[TTO5]

Anyone know if it is normal for the truck to go from open to closed loop under different conditions when driving?

 

[TTO5]

For those still reading here's a little recap of what I'm dealing with


Truck Sat for a few hours

Key on engine off no active dtc
P0300 in pending

Started engine

Check engine light not on
No active dtc
No pending dtc

Drove about 8 miles engine fully warmed up
Pulled into parking lot
Code p0300 in pending
let idle for 30 seconds or so, engine light came on flashing
Codes p0300
P0304 and p0307 displayed in active codes
P0300 still in pending.
Turned truck off
Disconnected wire harness from computer for 30 seconds.
Plugged in, turned ignition on without starting truck,
Codes p0300, 304,307 still in active
P0300 still in pending
Restarted engine
Idled smoothly with engine light on not flashing
After about 20 seconds or so light began flashing and protection mode on
Cleared Codes while engine was running
Active codes gone, pending shows p0300, 304 and 307
Light still flashing and protection mode on

Shut truck off for a few minutes. Restarted engine, check engine light NOT on
Shut engine off read codes ignition on engine off. No active codes po300,304,307 still in pending.

Started back up ok no light for 30 seconds or so the light came on flashing. P0300 304,307 in active codes, 300, 304, 307 in pending


Turned truck off for about 10 min.
Restart engine light on solid
Drove 8 miles to home (highway speeds) light on solid whole time no flashing.
Pulled in driveway let idle for about 30 seconds , light starts flashing and protection mode engaged

Truck Sat overnight. Started this morning engine light on solid. Drove 20 miles to work. Light started flashing when I got to work and went into protection mode. This occurred when I Idled the truck (20 seconds after idling)

 

[NikP]

One easier thing you haven't listed or tried is swapping fuel injectors between cylinders. Even the service manual focuses on injectors way before it jumps to the conclusion of ecu. What's stopping you from this simple test? Misfire is typically spark or fuel related and you've swapped the spark side already.

 

[TTO5]

One easier thing you haven't listed or tried is swapping fuel injectors between cylinders. Even the service manual focuses on injectors way before it jumps to the conclusion of ecu. What's stopping you from this simple test? Misfire is typically spark or fuel related and you've swapped the spark side already.

I'll ask the toyota tech that's working on it to try that

 

[njbrain]

As a Toyota Master tech I have never seen an ECU failure cause a misfire. In fact I have never even seen a Toyota ECU fail aside from physical damage. From the fuel trims and conditions it sounds like fuel injectors to me.

 

[TTO5]

As a Toyota Master tech I have never seen an ECU failure cause a misfire. In fact I have never even seen a Toyota ECU fail aside from physical damage. From the fuel trims and conditions it sounds like fuel injectors to me.

Funny, one of our master techs predicts the same thing. He thinks the fact it only trips the light on at idle points to a flow issue and it doesn't happen at higher engine speed because there is more flow which might overcome the issue. This might help explain why I can drive 20 miles from a cold start and it only occurs once I get to my destination and allow it to idle for some time. Let's hope this is what it is. I'm becoming a big fan of the 2024 tacoma 4x4 turbo I have as a loaner car. So much so I'm considering selling the lx570 once it's fixed to buy one.

 

[TTO5]

What do you think about pulling the vacuum line off the fuel press reg to raise fuel pressure? My thinking says with more pressure it won't misfire due to cyl 4 and 7 injectors getting more pressure (like how it seems it only goes into misfire mode at idle/lower pressure). Might be easier than moving injectors. Just spit balling here

 

[bloc]

What do you think about pulling the vacuum line off the fuel press reg to raise fuel pressure? My thinking says with more pressure it won't misfire due to cyl 4 and 7 injectors getting more pressure (like how it seems it only goes into misfire mode at idle/lower pressure). Might be easier than moving injectors. Just spit balling here

From memory the ECU doesn’t monitor fuel pressure, so it won’t know to reduce injector duty cycle. Meaning it’ll start running rich as soon as you do that.

 

[TeCKis300]

What do you think about pulling the vacuum line off the fuel press reg to raise fuel pressure? My thinking says with more pressure it won't misfire due to cyl 4 and 7 injectors getting more pressure (like how it seems it only goes into misfire mode at idle/lower pressure). Might be easier than moving injectors. Just spit balling here

Can't hurt and worth digging into fueling as a culprit. There's definitely a possiblity as they swapped the motors, that contamination got into the fuel lines.

Following symptoms, you had checked out fuel trims earlier and showed that they were mostly on point in each bank. That to me would eliminate the fuel pump or fuel ECU. But it could still be individual injectors as 1 out of 4 (in each bank) may not affect trims enough to show there.

 

[yOHda]

As a Toyota Master tech I have never seen an ECU failure cause a misfire. In fact I have never even seen a Toyota ECU fail aside from physical damage. From the fuel trims and conditions it sounds like fuel injectors to me.

You’ve never worked on the 90s-00s era of cars. Their ecu’s have leaking capacitors that caused all sorts of crazy issues. Uz,jz engines and some other ones.

 

[njbrain]

You’ve never worked on the 90s-00s era of cars. Their ecu’s have leaking capacitors that caused all sorts of crazy issues. Uz,jz engines and some other ones.

You are mostly right. I have been in the dealer for 11 years, so I have worked on very few 90's cars.

 

[TTO5]

Sorry haven't updated this post in a few days. Waiting on our mechanic to continue testing. I'll update as soon as I have more info

 

[TTO5]

Update. Mechanic installed a new fuel injector in cylinder 4 and it did not fix the truck. Code came right back. So far we have moved coil, replaced spark plugs, compression and leakdown test, scoped injector and coil wires/harness, replaced crank sensor. This is insane

 

[TTO5]

I notice cat temp of 1 of the cats is double what the other cat temp is. Can someone with a scangauge please compare these temp differences between cat 1 and cat 2 with their own please?

 

[NikP]

Update. Mechanic installed a new fuel injector in cylinder 4 and it did not fix the truck. Code came right back. So far we have moved coil, replaced spark plugs, compression and leakdown test, scoped injector and coil wires/harness, replaced crank sensor. This is insane

Well that sucks. Time to test wire continuity from each cylinder to the ECU to make sure the wiring is good and consistent between cylinders. Another guy in the Tundra forums found a broken exhaust valve spring.

 

[TTO5]

Well that sucks. Time to test wire continuity from each cylinder to the ECU to make sure the wiring is good and consistent between cylinders. Another guy in the Tundra forums found a broken exhaust valve spring.

Yes continuity has been checked. Leak down and compression test have been done and passed. Will a broken valve spring allow those tests to pass?

 

[TTO5]

Well that sucks. Time to test wire continuity from each cylinder to the ECU to make sure the wiring is good and consistent between cylinders. Another guy in the Tundra forums found a broken exhaust valve spring.

Yes continuity has been checked. Leak down and compression test have been done and passed. Will a broken valve spring allow those tests to pass?

 

[liv2bike]

Man you need to get this donor warrantied. I wouldn’t mess with it anymore. My donor came with a 90 day warranty.

 

[rexington14]

Man you need to get this donor warrantied. I wouldn’t mess with it anymore. My donor came with a 90 day warranty.

Agreed. Sounds like this has been a massive headache since the beginning.
Hopefully at the least you can get a refund of the engine. Then I'd be considering other options like cutting losses and moving on considering the truck is 15 years old w/ 235k. Plenty of other ways to spend more money.