I have a 2000 toyota 4-runner and it has been misfiring off and on for a while now. here is the story

When it first started misfiring I did the following

1.Changed the plugs with NGK plugs(I found that one of the plugs was finger tight when I was changing them.)
2. Changed the plug wires to NGK wires.
3. Cleaned the injectors with a pro. style pressure pot injector cleaning system.
4. Changed the fuel filter.

at this point it was running pretty good. but it only lasted a few months. It was missing again and was giving a cyl 3 misfire code. so I swapped coilpacks around to see if the problem moved and it did. so i changed out the bad coilpack and it ran really good.

that lasted about 4 months. It is currently missing again really bad. it is the worst at about 1500 RPM under load. it seems to smooth out at higher RPM but it could just be because it is at a higher RPM.

So far tonight I have done the following.
1. Changed the plugs to toyota factory plugs.
2.changed the wires to new toyota factory wires.
3. replaced the other 2 coilpacks (all 3 are new now)
4. Cleaned the MAF
5. Cleaned the throttle body where the butterfly valve is.
6. currently running some injector cleaner throught the tank
I am kinda stuck on what to try now. I think it may be the injectors because if it has been misfiring because of lack of spark mabee they are plugged now and is missing because the injector is plugged?

Any Ideas?

Thanks
Tim

 

Check the oil and coolant for any milkshake - probably not, but easy to check.

Have you been having to add any coolant?

When you say Toyota factory plugs, what brand are they? - Our engines come w/ NGK # BKR5EKB-11 on one side and Denso #K16TR11 on the other (either of these in all 6 cylinders is fine).

Did you use MAF cleaner to clean the MAF?

 

i had this issue. for me it was a simple coil wire set install.

lucky.

my pops always said you need air, fuel and fire to run an engine. maybe a weird air leak somewhere? cracked valve? idk but good luck! keep us posted

 

oil and coolant look good, I used gas and Q-tip to clean the MAF. I got the Denso plugs from the dealer. It has about 136,000 miles on it.

Thanks
Tim

 

Could it be a cam position sensor?

 

it misses when it is cold and warm

 

You aren't supposed to touch the wires on the MAF anything (especially a Q-tip which leaves fibers behind) and you're definitely not supposed to use gasoline to clean it. Your MAF was probably getting dirty and then you damaged it. Have it tested at a shop, I would be really surprised if that's not it.

 

OH CRAP!! Well that makes sense. after I got done working on it last night it was running worse than when I started. I will try and reclean it with some MAF cleaner and hopefully it will be ok. If not Hopefully a new MAF is not to spendy$$ is there a way I can test the MAF?

Thanks

Tim

 

Yes, a shop should be able to test the MAF and see if the voltage is within specs. New ones aren't cheap (if I remember right) they run about $700 from Toyota. Hope you can still clean yours.

 

I recleaned the MAF and it is running better. like it was before I started working on it last night but it is still misfiring. The check engine light came on and it was giving a multiple cyl misfire and a cyl 6 misfire. it runs smooth and misses randomly. I am think it may be the injectors.? I still need to test the MAF but I think it is OK.

Any ideas?

Thanks again for all the help

Tim

 

After driving the 4-runner tonight it seems to mis alot more when it is cold and smooths out a bit when it is warm. But it is still missing when it is warm.

 

Compression tests when cold?

 

OK... so I ran it some more tonight and it was missing really bad, I think it was only running on 4 cyl. so just for the heck of it I tried pulling plug wires to make sure I was getting spark. and one of the cyl was dead at the plug and the coilpack. so I swapped it with one of the packs I had just replaced and now it runs perfectly.

the coilpack that was bad this time was the first one I replaced in the past. and it was a aftermarket non oem pack. and I did notice that when I pulled it out the boot seperated from the pack. kinda weird. these 4 runners sure do seem picky.

so hopefully this is it and I won't have to mess with it anymore

thanks again for all your help. this forum is great!!

Tim

 

I went through simular issues with my 1991 3.0 4runner and it turned out to be the engine harness. It was my number 4 injector would missfire at times and then same issue started with #3 injector. When we figured out it was a short in the harness by pressing on the harness in a certain spot and have the missfire go away for a couple days then we zipped tied the harness in this spot and that lasted a few weeks so we opened the harness to find crispy wires, replaced the harness and she runs perfect now for about 25000 mi now. Good luck.