Persistent P0305/P0308 under load | 2002 LX470 (238k miles)

[JThomas]

Hi there, I just bought my first 100-series two weeks ago and am having some issues.

I’m trying to fix a CEL that comes on (and sometimes flashes) at about 75mph or under heavy load. The truck feels smooth and I don't feel any power loss. It idles normally, and the only vibration on the road is what I believe to be a tire alignment issue around 55mph. I don't drive on the interstate often where I live, but when I hopped on this past week, I turned around quickly when the CEL began to flash. The flashing stopped around 55mph, then came back and flashed again at about 65mph as I merged off. I pulled into an AutoZone and scanned three pending codes: P0300, P0305, and P0308. Prior to this, I had been driving around town at normal speeds peaking around 65mph and had no issues with power, knocking, or vibrating.

I parked the truck and just started working on it today. My dad has a scanner, so we cleared the codes to diagnose the issue. We started by recreating the conditions (load, AC, etc.) to trip the code, then we swapped the plugs and coils for 5 and 8, but the codes remained. Next, we swapped injectors 6 and 8 as they were easier to access, but the issue stayed the same.

Since it appears to be isolated to cylinders 5 and 8 and doesn't follow the parts, I’m looking for next steps. Has anyone dealt with this specific misfire on 5 and 8?

Thanks!

 

[AARONTLC]

Hi there, I just bought my first 100-series two weeks ago and am having some issues.

I’m trying to fix a CEL that comes on (and sometimes flashes) at about 75mph or under heavy load. The truck feels smooth and I don't feel any power loss. It idles normally, and the only vibration on the road is what I believe to be a tire alignment issue around 55mph. I don't drive on the interstate often where I live, but when I hopped on this past week, I turned around quickly when the CEL began to flash. The flashing stopped around 55mph, then came back and flashed again at about 65mph as I merged off. I pulled into an AutoZone and scanned three pending codes: P0300, P0305, and P0308. Prior to this, I had been driving around town at normal speeds peaking around 65mph and had no issues with power, knocking, or vibrating.

I parked the truck and just started working on it today. My dad has a scanner, so we cleared the codes to diagnose the issue. We started by recreating the conditions (load, AC, etc.) to trip the code, then we swapped the plugs and coils for 5 and 8, but the codes remained. Next, we swapped injectors 6 and 8 as they were easier to access, but the issue stayed the same.

Since it appears to be isolated to cylinders 5 and 8 and doesn't follow the parts, I’m looking for next steps. Has anyone dealt with this specific misfire on 5

Compression check? Hopefully when compression checks out you are probably wanting to investigate your injector pulse and coil circuits for those 2 cylinders. Download the Electrical Wiring Diagrams EWD from the resources section. Good luck and hoping for good news!

 

[Dirt J]

The diagnostic procedure is found in DI-64 of the FSM.

The first couple of checks the FSM recommends, which seem logical especially with in your example, is to check the wiring to the coils and injectors and then the condition of the spark plugs (and type). My bet is its one of these.

But the FSM then says to: check voltage of ECM terminal for injector of failed cylinder; Check resistance of injector of misfiring cylinder; check fuel pressure; check injector injection; check MAF and ECT sensors; and finally, check compression, valve clearance, and timing.

What's your year and mileage?

Did you clear the codes between each parts swap around?

 

[JThomas]

Compression check? Hopefully when compression checks out you are probably wanting to investigate your injector pulse and coil circuits for those 2 cylinders. Download the Electrical Wiring Diagrams EWD from the resources section. Good luck and hoping for good news!

Here’s my results:
Passenger side (front to back)
1: 170
3: 155
5: 168
7: 181

Driver side (ftb)
2: 168
4: 180
6: 175
8: 172

So all between 150-180… not all 10 within?
So wiring might be the thing to check? (Where is the resource section?

 

[JThomas]

The diagnostic procedure is found in DI-64 of the FSM.

View attachment 4140841

The first couple of checks the FSM recommends, which seem logical especially with in your example, is to check the wiring to the coils and injectors and then the condition of the spark plugs (and type). My bet is its one of these.

But the FSM then says to: check voltage of ECM terminal for injector of failed cylinder; Check resistance of injector of misfiring cylinder; check fuel pressure; check injector injection; check MAF and ECT sensors; and finally, check compression, valve clearance, and timing.

What's your year and mileage?

Did you clear the codes between each parts swap around?

Checked all the spark plugs and coils, all look good and normal. Mixed them around and still tripping just 5 and 8.
Voltage on the injectors looked normal with a meter.
Also changed the injectors around on driver side since it was easier and code stayed on 8…
Just did a compression test on all. I posted right before this the results.

Valve clearance and timing is out of my wheelhouse…

And yes been clearing all codes each time

 

[JThomas]

The diagnostic procedure is found in DI-64 of the FSM.

View attachment 4140841

The first couple of checks the FSM recommends, which seem logical especially with in your example, is to check the wiring to the coils and injectors and then the condition of the spark plugs (and type). My bet is its one of these.

But the FSM then says to: check voltage of ECM terminal for injector of failed cylinder; Check resistance of injector of misfiring cylinder; check fuel pressure; check injector injection; check MAF and ECT sensors; and finally, check compression, valve clearance, and timing.

What's your year and mileage?

Did you clear the codes between each parts swap around?

2002
238,000

 

[Dirt J]

FSM
EWD

Sounds like you've narrowed it down. I'm leaning toward a wiring issue, like a frayed/gnawed wire to the coils. It's interesting that it's just those two cylinders and they are different banks...

 

[JThomas]

FSM
EWD

Sounds like you've narrowed it down. I'm leaning toward a wiring issue, like a frayed/gnawed wire to the coils. It's interesting that it's just those two cylinders and they are different banks...

 

[JThomas]

Latest: After compression test and reseating all the plugs and coils mixing them up to see if the code followed a part, Truck ran great 75-80 mph for half an hour or so sustained and then popped up randomly after that. Still not shake or knock when it happened. Just flashing light and tripped code.

Im leaning towards wiring now and especially because I see signs of an old nest under the top to the engine. I traced wires and dont see any of the coils or injectors leading under that, but there is one wire I see under the upper intake manifold that goes into a sensor on that spot. Any tips for removing this/getting better vantage access under that to clear the nest and inspect wiring?

Trying to do as much as I can before throwing money at it to identify the issue.

 

[Dirt J]

There are two knocks sensors under the intake plus the starter IIRC. Maybe more.

I think you are on the right track.

Needs pics!

 

[JThomas]

There are two knocks sensors under the intake plus the starter IIRC. Maybe more.

I think you are on the right track.

Needs pics!

Hard to focus, but the wire I am able to see only has one coming out? I’m going to borrow a camera this weekend and see if I can get in there.

 

[Dirt J]

Yes, there are two knocks sensors under the intake. They both have only a single-wire connector. Bank 1 has a white wire. Bank 2 has a black wire. Are one of those damaged?

 

[Mchodl]

Double check all engine bay grounds. Look carefully, does anything look clean and new? Could have had a repair prior to sale and something was left loose. Can you provide fuel injector resistance numbers? Also, freeze frame data stored when fault code sets sometimes helps. My initial thought was failing crank sensor but I don't want you to start throwing parts.

Edit: The fact the cel flashing but the engine is not actually misfiring (if true) is what is leading to suspect the crank sensor.

Edit 2: Crank sensor wiring too. What is the mileage on that timing belt sticker? Just done or been a while?

 

[Sh1tboxhundy]

Any updates @JThomas?
I recently tripped codes for P0300, P0302, P0305, P0307 and am just starting my diagnostic journey.
1999 Landcruiser with 334k miles. New to me in last month with largely unknown maintenance history.