cylinder #2 misfire

[neilr]

Hi, I'm hoping someone can help me out:

2000 4runner SR5 V6, stick shift, about 200K miles.

I've replaced all plugs, wires, coils, and all 6 injectors.

compression test: all cylinders good

both O2 sensors replaced

still getting #2 misfire.

could it be the wire from #2 injector back to the ECM?

how likely it's the ECM?

thanks Neil

 

[TFJ-4runner]

Have you tried swapping between other cylinders to see if it changes at all.

 

[neilr]

No haven't swapped injectors or coils but they are all brand new; I replaced everything and it still misfires #2.

Plugs, wires, coils, injectors have all been replaced in the last 3 weeks

There's definitely a spark getting to the plug. There don't appear to be any vacuum leaks.

It started after the O2 sensors were replaced. What if Napa gave us cali spec O2 sensors (this is a non cali truck) by mistake. Could that cause the misfire?

thanks

 

[LittleCaesar]

Denso or OEM is what everyone uses for o2 replacement. Autos can be picky on their sensors but a misfire from a O2 sensor is new to me.

Crawl under and see which ones were sold to you (or if you still have the box).

Ever cleaned your MAF?

 

[neilr]

ok, checked the O2 sensors and they are the right ones.

Haven't cleaned the MAF lately but will this morning. It's not throwing a MAF code though and if it was the MAF wouldn't it misfire on different cylinders and not just #2?

 

[TheDurk]

It started after the O2 sensors were replaced. What if Napa gave us cali spec O2 sensors (this is a non cali truck) by mistake. Could that cause the misfire?

thanks

The Cali. sensors have a different plug so I doubt this happened (unless you swapped plugs and got the 'universal' type).

But if they sold you anything but Denso's, THAT could be the problem.

 

[neilr]

It turned out to be the MAF.
Replaced the MAF and truck runs smooth with no misfires.

My questions are:

Why didn't it throw a MAF code?

And given that the MAF is in the airflow to all cylinders, why did it only show a cylinder 2 misfire and not multiple cylinders?

Either of the above could have saved me from replacing injectors.

 

[LittleCaesar]

Neilr,

I am glad you found the culprit. I threw out the MAF as a possibility only because you covered all the basics for tracking down a PO302 (I take it that was a code). Plus another member here earlier this year had a misfire, cleaned the MAF after everything else, it cleared the code for some time but it came back so he ultimately replaced it.

 

[neilr]

OK, the celebration was a bit premature.

When the old MAF was disconnected there were no misfires after the ecm went to default settings.

when the new MAF was installed it ran smooth. truck was driven 20miles at different speeds and no codes.

truck was let sit for a few hours and when I started driving the engine light came back on and the engine ran very rough.

I don't know what's left to check/change????? the ECM? But I don't think they fail very often.

Any ideas??

 

[TheDurk]

At some point, you have to consider a compression check to rule out a valve or ring problem on #2.

So what are you going to do with six good used injectors? I'd ship them to Witchhunter and then eBay them.

 

[neilr]

I did a compression test on all 6 cylinders before changing the injectors.

Compression is good on all 6

 

[Tee Jay]

Did you find a solution yet? I'm having the same exact problem :redbrick:. I have a '99 with 178k miles though, only difference.

 

[neilr]

I "think" I've fixed it.

The first change was replacing the o2 sensors. The truck had been running fine, I just changed the sensors based on mileage. My mechanic got them from NAPA and they were NGKs. I figured NGK and Denso were the usual go to parts for Japanese vehicles, so I didn't question it. SHortly after, I started getting the cylinder 2 misfires.

That was what sent me in the wrong direction; I kept trying to figure out what was wrong with cylinder 2. There were no vacuum leaks. So, plugs (also NGK), wires, 3 coils, MAF, 6 fuel injectors later......I had the nagging feeling it was the NGK O2 sensors.

I sourced Denso O2 sensors and Denso double ground plugs and changed the NGK sensors and plugs with the Densos. So far so good no misfires or check engine light. Hopefully, problem solved.

 

[neilr]

When I ran the scanner in real time with the NGK O2 sensors the L T fuel trim was VERY lean.

Now with the Denso O2 sensors the L T fuel trim is right on.

 

[LittleCaesar]

Neilr,

I am glad to hear that you found the problem. A scanner that has real live data is an invaluable tool when it comes to diagnosing problems.

With time I have found out that autos can be anywhere from sort of picky to extremely picky when it comes to both the spark plugs and sensors used in them. That is why I try to replace them with OEM, or at least the manufacturer of those parts. Such is not always the case, but a general guideline I like to follow.

 

[neilr]

This was an interesting, albeit expensive, "who dunnit" mystery. I believe NGK is a quality product so I didn't think of the NGK O2 sensors at first.

After asking around, I've heard stories of sveral different makes of vehicles being very sensitive to the brand of O2 sensors.

Tee Jay what solutions have you tried so far?

By the way, it might have been an interesting problem to solve but I could have saved a bunch of money and a lot of frustration and stress if I'd put Denso in in the first place.