Misfire mystery

[I_bRAD]

Sorry, no update in a while.

I got a scanner. Haven't had time or inclination to figure it out fully yet but freeze frame data shows low stft (~-4%) The action apparently happens ~60kms/hr and ~2000 rpm.

If I record starting at DTC STFT oscillates between positive and negative every second or so.

Still drives fine. Still planning to take it camping this weekend.

 

[thegipper]

This may not be your problem but let me share my random P0300/P0301 pending codes story I was getting.

I'm trying to solve a transmission issue and one of the possible things that was making the tranny act up (stuck in 1st while cold) was the ECM. Around the same time I was getting the random misfire codes but the truck was running absolutely perfect. No stumbles, random dying or loss of power, nothing.

I replaced the ECM with a junkyard one and while it did not fix my tranny issue, I have not got a single misfire code since. When you look at the possible reasons for a misfire code, the very last thing on the list is the ECM. In my case, it was the ECM. I doubt it is common that the ECM acts up and probably isn't your cause of misfire codes but keep it in mind if all else fails.

My local junkyard lady had no clue what I was buying (ECM, MAF, TPS) and asked if "5 bucks" was a fair price for the three items. I gladly accepted.

 

[octanejunkie]

My local junkyard lady had no clue what I was buying (ECM, MAF, TPS) and asked if "5 bucks" was a fair price for the three items. I gladly accepted.

:wow2: Awesome AF!

Could have gone the other way easily too. We have a lady cashier at a local yard that charges insanely high prices. She would have asked for a grand, probably. You did good.

 

[I_bRAD]

This may not be your problem but let me share my random P0300/P0301 pending codes story I was getting.

I'm trying to solve a transmission issue and one of the possible things that was making the tranny act up (stuck in 1st while cold) was the ECM. Around the same time I was getting the random misfire codes but the truck was running absolutely perfect. No stumbles, random dying or loss of power, nothing.

I replaced the ECM with a junkyard one and while it did not fix my tranny issue, I have not got a single misfire code since. When you look at the possible reasons for a misfire code, the very last thing on the list is the ECM. In my case, it was the ECM. I doubt it is common that the ECM acts up and probably isn't your cause of misfire codes but keep it in mind if all else fails.

My local junkyard lady had no clue what I was buying (ECM, MAF, TPS) and asked if "5 bucks" was a fair price for the three items. I gladly accepted.

Where is the ECM located? We were having some pretty wet weather when the problem started. Leaning towards ground problem but this might be worth investigating too.

 

[thegipper]

Where is the ECM located? We were having some pretty wet weather when the problem started. Leaning towards ground problem but this might be worth investigating too.

The ECM is behind the glove box. Drop the glove box out of the way (squeeze in the sides of it so it can drop down all the way) then remove the three 10mm bolts on the black plastic panel above the box. One screw is in the center of the panel and one on each side.

You will then see the ECM. Two screws secure the ECM in place then unplug each of the four connectors.

There have been reports of water leaking through the windshield glass seal onto the ECM and it causing some issues. You can also remove the four screws on the ECM cover and take a look inside for anything obviously wrong (leaking caps or corrosion). Mine looked brand new still though and couldn't find anything wrong with it visually.

 

[I_bRAD]

The ECM is behind the glove box. Drop the glove box out of the way (squeeze in the sides of it so it can drop down all the way) then remove the three 10mm bolts on the black plastic panel above the box. One screw is in the center of the panel and one on each side.

You will then see the ECM. Two screws secure the ECM in place then unplug each of the four connectors.

There have been reports of water leaking through the windshield glass seal onto the ECM and it causing some issues. You can also remove the four screws on the ECM cover and take a look inside for anything obviously wrong (leaking caps or corrosion). Mine looked brand new still though and couldn't find anything wrong with it visually.

Thanks. Will check it out if I can't find any bad grounds. My windshield definitely leaks, but its more on the driver's side.

 

[Buckaroo]

Thanks. Will check it out if I can't find any bad grounds. My windshield definitely leaks, but its more on the driver's side.

FYI....ECM is absolutely the last place you should look....so many more likely causes for a misfire.....thoughts:

1. If your total fuel trim is running -4% and your short term fuel trim is moving back and forth across the neutral line, my opinion is that you seem to be in pretty good shape there. Rule of thumb is total fuel trim less than 10% is not an issue. You could check resistance on the fuel pump (spec is 0.2 - 3.0 ohms) and I think you can check it easily by unplugging the relay and probing at that point.

2. You seem to have covered the spark question with the replacement of all three coils, wires and plugs. Given the P0301 DTC, you might swap the coils on #1 & #3 and the plugs on #1 & #5 just to see if the problem moves. Also, make sure your spark plug wire routing is correct

3. I did not see that you mentioned anything about the MAF. This could cause a non-cylinder specific DTC (P0300). As you likely know, this is a common problem area - clean it at least.

4. Given the age and mileage of your T4R, I would not be surprised if you had an injector issue. They can fail intermittently when hot if coil related. When you are having the cylinder specific issue again, use a long screw driver, place on top of the injector and listen for regular clicking - check other cylinder for comparison. No click = non-functioning injector. If you want to make sure, pull the fuel rail, inspect and swap the injector

5. Don't assume you just have one problem.....


Buckaroo

 

[thegipper]

I tend to agree but in my case, it was the ECM.

 

[Buckaroo]

I tend to agree but in my case, it was the ECM.

I get it but one should be very sure they have checked everything else before they go to the ECM. It is always at the end of every troubleshooting fault tree as it is the cause of last resort....

Buckaroo

 

[I_bRAD]

FYI....ECM is absolutely the last place you should look....so many more likely causes for a misfire.....thoughts:

1. If your total fuel trim is running -4% and your short term fuel trim is moving back and forth across the neutral line, my opinion is that you seem to be in pretty good shape there. You could check resistance on the fuel pump (spec is 0.2 - 3.0 ohms) and I think you can check it easily by unplugging the relay and probing at that point.

2. You seem to have covered the spark question with the replacement of all three coils, wires and plugs. Given the P0301 DTC, you might swap the coils on #1 & #3 and the plugs on #1 & #5 just to see if the problem moves. Also, make sure your spark plug wire routing is correct

3. I did not see that you mentioned anything about the MAF. This could cause a non-cylinder specific DTC (P0300). As you likely know, this is a common problem area - clean it at least.

4. Given the age and mileage of your T4R, I would not be surprised if you had an injector issue. They can fail intermittently when hot if coil related. When you are having the cylinder specific issue again, use a long screw driver, place on top of the injector and listen for regular clicking - check other cylinder for comparison. No click = non-functioning injector. If you want to make sure, pull the fuel rail, inspect and swap the injector

5. Don't assume you just have one problem.....


Buckaroo

Agreed on the ECM. Just covering all the bases.
I've had misfire codes on all cylinders, not just 1.
Wires are in the correct orientation and I cleaned the MAF when I pulled the plugs to check them.

Leaning towards ground problem. BUT it's all just speculation until I have more time to get back to it!

 

[Buckaroo]

Agreed on the ECM. Just covering all the bases.
I've had misfire codes on all cylinders, not just 1.
Wires are in the correct orientation and I cleaned the MAF when I pulled the plugs to check them.

Leaning towards ground problem. BUT it's all just speculation until I have more time to get back to it!

Sorry to ask but when you cleaned the MAF, did you make sure you cleaned the right thing? That temperature sensing bulb is front and center but the hot wire is around the corner.....made that mistake myself the first time.....

see post #33 in this thread by TheDurk.....
http://www.toyota-4runner.org/3rd-gen-t4rs/86675-help-p0171-3.html

Buckaroo

 

[I_bRAD]

Sorry to ask but when you cleaned the MAF, did you make sure you cleaned the right thing? That temperature sensing bulb is front and center but the hot wire is around the corner.....made that mistake myself the first time.....

see post #33 in this thread by TheDurk.....
http://www.toyota-4runner.org/3rd-gen-t4rs/86675-help-p0171-3.html

Buckaroo

I don't think it's MAF but I also don't think I cleaned it properly. I didn't notice that mine could come out of the tube like that, but to be honest I just cleaned in on a whim while I had the intake tube off so I didn't pay a lot of attention to what I was doing.

 

[I_bRAD]

Update

Problem solved, and not what I was expecting at all.

I did find a small leak in the vacuum hose for the fuel pressure regulator and I thought I'd had it solved but it came back again. Continued to drive it with no ill effects other than the CEL:

Here were the final symptoms:

• Always P0300,1,2 or 3 (random misfire, or misfire on 1,2 or 3)
• Always low load, low RPM. Around 2000. Usually crusing at 60km/hr or so in 5th
• After reset, CEL would basically come on as soon as the monitors were set (within a day or so)
• No driveability issues at all, just a CEL. Definitely did not feel like a misfire.

And the culprit was:

ALTERNATOR!

I'm not sure why it would throw a misfire code, but my alternator recently went south (without a battery light BTW) and after replacing it I haven't had the issue since (several tanks of gas with no trouble). The bearings were gone and it would charge enough to run (~13.8V) at 80kms/hr or so but would drop to 12.5 at lower speeds. I'm not sure if the misfire code is monitored by voltage or something but that seems to have solved the problem.

Hope this helps someone in the future.