I need some help diagnosing this CEL

[Wasatch Rebel]

Last year my CEL came on (2000 is my year of vehicle). I went and got the codes at Autozone. They looked something like this or at least as far as I can remember:

P0301 Cylinder 1 misfire detected
P0300 Multiple Cylinder Misfire detected
P0303 Cylinder 3 Misfire detected
P0300 Multiple Cylinder Misfire detected

I took it to my mechanic who has been marvelous for many years. He could find no misfiring at all, then cleared the light. It came back on the next day. I took it back in and he said that he looked all over the internet to try and figure out this problem, but could only figure out that it might be the fuel injectors so he replaced those.
Meanwhile I did some research on my own, and found out that it was likely the coil packs, but to start with plugs and wires. I ended up replacing the coil packs, wires, and plugs. Then I drove it around a while but it didn't clear the light. I took of the negative battery cable which cleared it, but it came on again about a week later. I went back to Autozone and had them run the codes and they were still the same.
I would love to solve this problem once and for all. Any suggestions?

 

[CdaleR4000si]

These codes could be attributed to all sorts of things, as you've mentioned already... Plugs, wires, injectors, coil packs, head gasket.
Seems like lately I've been seeing lots of posts about these P0300 through P0306. Last year I had the 300 and 304, which was missing on 4, but it was so severe that it was causing a misfire on an adjacent cylinder (can't remember which one).
I tried everything that you did. Mine turned out to be 1 bad injector on #4. When you replaced the injectors, do you know if your mechanic used OEM? I have read many stories on here where people have used parts store/ non-oem injectors, only to have continued misfires. I went a slightly different route, I bought a used set of injectors and sent them off to Witchhunter to be serviced. Then I was able to just swap them out with minimal downtime (took about 2 hours to install them). Given that your codes are on #1 and #3, you can actually get a meter on those without removing the intake plenum. You can check the resistance, which if I recall, should be around 14 ohms.

TL;DR, I would have your mechanic check the resistance of the 1 and 3 injectors.

 

[Wasatch Rebel]

TL;DR, I would have your mechanic check the resistance of the 1 and 3 injectors.

Thanks for the tip. I'm probably not going to get it in to him until August because I'm going on vacation soon and need to get the other vehicle that we'll be traveling in serviced--and I just don't have time to get both done. I will report back.

 

[jgue467]

Have you run any fuel system cleaner/decarbonizer thru your rig? You know like Seafoam, Startron, royal purple, all kinds out there. I run startron (get it at walmart, online or lawn mower shops). It will improve the intake/fuel/cyclinder carbon in about 3-4 tanks fuls, faster if your run it at 'double strength' and its cheaper than the rest. Luck. :cowboy:

http://www.starbrite.com/startron

 

[octanejunkie]

Cylinder misfire codes (p0300-p0306) can be attributed to several factors, as has been said.

Plugs, wires, coils, are the most likely culprits, but there are lots of other factors that can attribute to this code being generated. The P0300 is a general misfire, meaning something affecting all cylinders/entire system. Could be air, could be fuel-related.

Start with the basics. Clean/replace your air filter and clean your MAF sensor. Use MAF sensor cleaner, not brake cleaner on the MAF sensor, it's delicate. Clean out the airbox if it's dusty. Remove the airbox and tubing, Inspect for cracks/leaks and clean inside and out.

Inspect the throttle body for proper function, make sure it's not dripping with sludge. Don't spray cleaner into it on the car, take it off if you have to "deep clean" it. If you remove the throttle body be mindful of all hose and cables and the gasket and note orientation of all parts/connections.

With the airbox and intake tubing off you can access the passenger side plugs and ignition coils. Inspect wires for cracks/wear and age, replace if age unknown. Make sure all boots are fully seated on plugs. Denso 671-6182 Spark Plug Wire Set (Genuine Toyota black) or NGK (4412) TE66 Wire Set (blue).

Inspect spark plugs. Vacuum out spark plug tubes before removing plugs (keeps debris in tubes from falling into cylinder heads) - I like to blow them out with compressed air, then hit them with a vacuum. Wear your safety glasses when working wtih compressed air.

If you remove plugs, have a new set handy to install. Get the correct plugs, should be dual electrode. I used NGK (3967) BKR5EKB-11 which came pre-gapped, install and torque correctly, about 8 foot pounds.

To get to the plugs you have to remove the coil packs on the passenger side. Inspect them well and pay attention to the boots and springs on the bottom. These often wear out, springs get corroded, etc. I replaced ONE of my coil packs due to a misfire code/condition. I isolated it to the coil by swapping coils and observed the "problem" follow the coil. Once replaced, all good. Only use Denso 673-1201 Ignition Coil.

Put it all back together and if your valve covers are oily, or covered in dirt and oil, you will likely want to consider replacing the valve cover gaskets, not because they affect ignition, but you are already 1/3rd of the way there having removed the TB, coils and wires lol

Other conditions that can contribute to PO30X codes, but usually come tih other codes
fuel system issues, pressure, filter, injectors
exhaust system issues, specifically o2 sensors
throttle position sensor issue

Start with the basics and work down the list. The nice thing about PO30X codes is they will often clear themselves when the condition is resolved, so you don't need to clear them manually and wait for the computer to conduct 2 full drive cycles and complete all tests

Drive Cycles
If you do clear the codes, some folks have reported completing a drive cycle in 20 mins. Here are a few links
https://axleaddict.com/auto-repair/Toyota-Drive-Cycle-Readiness-Monitors-for-Emissions
Toyota/Lexus OBD-II Drive Cycles | Car OBD Diagnostics, ECU Chip Tuning & Auto Repair Support

Keep in mind, turning the key off and opening the door are monitored by the computer and are considered part of a complete drive cycle. If you don't have and OBD-II sensor or similar, consider getting one or get a BT OBD-II reader and use Torque Pro app on your android phone (sorry no iPhone app)

Good luck

 

[BoomSticks]

Ok, for a cylinder to fire it needs air, fuel, spark, and compression.

The usual problems are spark and fuel.

Since you've addressed your injectors, start working back in the fuel system. Next up is fuel filter, then fuel pump.

You've addressed spark.

Also remember that all those elements above have to be done at the right time during the cycle, so if your timing is off, the cylinders won't fire properly.

At some point make sure to double check that your timing belt isn't off by one or two teeth.

 

[Wasatch Rebel]

Have you run any fuel system cleaner/decarbonizer thru your rig? You know like Seafoam, Startron, royal purple, all kinds out there. I run startron (get it at walmart, online or lawn mower shops). It will improve the intake/fuel/cyclinder carbon in about 3-4 tanks fuls, faster if your run it at 'double strength' and its cheaper than the rest. Luck. :cowboy:

Star Tron Enzyme Fuel Treatment

I ran some fuel injector cleaners through it when the problem originally happened.
I will try some of those you suggested. About how often should I do this? I only drive it about 8000 miles per year.

 

[Wasatch Rebel]

Cylinder misfire codes (p0300-p0306) can be attributed to several factors, as has been said.

Plugs, wires, coils, are the most likely culprits, but there are lots of other factors that can attribute to this code being generated. The P0300 is a general misfire, meaning something affecting all cylinders/entire system. Could be air, could be fuel-related.

Start with the basics. Clean/replace your air filter and clean your MAF sensor. Use MAF sensor cleaner, not brake cleaner on the MAF sensor, it's delicate. Clean out the airbox if it's dusty. Remove the airbox and tubing, Inspect for cracks/leaks and clean inside and out.

Inspect the throttle body for proper function, make sure it's not dripping with sludge. Don't spray cleaner into it on the car, take it off if you have to "deep clean" it. If you remove the throttle body be mindful of all hose and cables and the gasket and note orientation of all parts/connections.

With the airbox and intake tubing off you can access the passenger side plugs and ignition coils. Inspect wires for cracks/wear and age, replace if age unknown. Make sure all boots are fully seated on plugs. Denso 671-6182 Spark Plug Wire Set (Genuine Toyota black) or NGK (4412) TE66 Wire Set (blue).

Inspect spark plugs. Vacuum out spark plug tubes before removing plugs (keeps debris in tubes from falling into cylinder heads) - I like to blow them out with compressed air, then hit them with a vacuum. Wear your safety glasses when working wtih compressed air.

If you remove plugs, have a new set handy to install. Get the correct plugs, should be dual electrode. I used NGK (3967) BKR5EKB-11 which came pre-gapped, install and torque correctly, about 8 foot pounds.

To get to the plugs you have to remove the coil packs on the passenger side. Inspect them well and pay attention to the boots and springs on the bottom. These often wear out, springs get corroded, etc. I replaced ONE of my coil packs due to a misfire code/condition. I isolated it to the coil by swapping coils and observed the "problem" follow the coil. Once replaced, all good. Only use Denso 673-1201 Ignition Coil.

Put it all back together and if your valve covers are oily, or covered in dirt and oil, you will likely want to consider replacing the valve cover gaskets, not because they affect ignition, but you are already 1/3rd of the way there having removed the TB, coils and wires lol

Other conditions that can contribute to PO30X codes, but usually come tih other codes
fuel system issues, pressure, filter, injectors
exhaust system issues, specifically o2 sensors
throttle position sensor issue

Start with the basics and work down the list. The nice thing about PO30X codes is they will often clear themselves when the condition is resolved, so you don't need to clear them manually and wait for the computer to conduct 2 full drive cycles and complete all tests

Drive Cycles
If you do clear the codes, some folks have reported completing a drive cycle in 20 mins. Here are a few links
https://axleaddict.com/auto-repair/Toyota-Drive-Cycle-Readiness-Monitors-for-Emissions
Toyota/Lexus OBD-II Drive Cycles | Car OBD Diagnostics, ECU Chip Tuning & Auto Repair Support

Keep in mind, turning the key off and opening the door are monitored by the computer and are considered part of a complete drive cycle. If you don't have and OBD-II sensor or similar, consider getting one or get a BT OBD-II reader and use Torque Pro app on your android phone (sorry no iPhone app)

Good luck

Thanks. I have already done the plugs, wires, and coil packs, and my mechanic did the fuel injectors. I will work on checking the other things you mentioned. I have a small crack in my air hose that goes from the resonator to the engine (the hose goes that far, not the crack!). The crack is right where the clamp is, and I'm not sure that the clamp is keeping it from leaking. Could that possibly be the culprit?

 

[octanejunkie]

Thanks. I have already done the plugs, wires, and coil packs, and my mechanic did the fuel injectors. I will work on checking the other things you mentioned. I have a small crack in my air hose that goes from the resonator to the engine (the hose goes that far, not the crack!). The crack is right where the clamp is, and I'm not sure that the clamp is keeping it from leaking. Could that possibly be the culprit?

I doubt it, but one way to find out!

Sent from my Pixel XL using Tapatalk

 

[Wasatch Rebel]

I doubt it, but one way to find out!

Sent from my Pixel XL using Tapatalk

:thanks: