Too many fixes for one cylinder misfire

I have a 2000 4Runner Limited with 250,000 miles. It's a one owner, and now I'm the second. Originally from California, now in Colorado. I first noticed it ran rough after driving it for 20 mins+, turning it off then restarting. I began by checking engine codes when the light came on. They were P0171 system too lean (bank 1) P0141 O2 heater circuit (bank 1 sensor 2) and P1130 a/f sensor circuit range/performance malfunction (bank 1 sensor 1). I know the front O2 sensor was replaced about 1 mo. before so I fixed a vacuum leak, cleaned the mapp sensor and ran lucas in my fuel. This led to the light going off for a short period of time. then it came back on with the same P0171 and P0141 codes and P1135 a/f sensor heated circuit malfunction(bank 1 sensor 1) and again I put lucas in my fuel and again the light went out. then it came back and with a P0300 random engine misfire. very confusing but I did a tune up with new plugs and wires and fresh oil. this didn't help and the miss got worse so i reset all codes and when the light came back it was P0301 misfire cyl 1. I switched spark plugs no change changed wires (boots) nothing coil packs still cyl 1. I removed the sparkplugs again and while the other 5 show regular wear the one in cyl 1 looks brand new. I don't know what to do next but it seems to be a fuel injector issue. any advice about how to procede would be appreciated I am not sure how to check the injector without replacing it

 

Swap the injector with another one like from cylinder 2 and run the car and see what happens. If cylinder 2 now misfires...bad injector.

If that is the case...either get a new injector or may be worth just going with a cleaned and tested set...

Something like this.

https://www.lceperformance.com/5VZ-V6-Equalized-Fuel-Injector-Set-99-04-p/1062211.htm

I see people buying really cheap injectors off from ebay and having issues. Ask the previous owner if he ever changed the injectors.

If Cylinder 1 is still new...then you have another issue in the fuel line. Doubt its a head gasket failure as cyl 1 would be fouled. Don't think it's a smoked valve but a leakdown test would not be a bad thing to do on this engine...she's got the miles.

I do think you may be chasing multiple problems...but...focus on that misfire FIRST. It will lead to other downstream issues.

 

Thanks for your reply, I will change places with 2 of the injectors if it comes to that. I am going to put a new fuel filter and would like to know how to check the wiring to the injectors (I visually inspected the plug) do you know how to test the voltage or resistance to the injector plug and what are the proper values? any help on this would be greatly appreciated.

 

I don't know the values. You can google it like I would have to

But yes, the wiring could be an issue and worth checking. You'll find the plastic wiring harness protector on top of the engine but under the intake will be brittle as all hell. If it's all busted up...then someone has already been in there to do something.

 

Multimeter and its around 13.8 ohms. Good resistance doesn't mean the internal filter isn't clogged though. Its pretty rare for an injector to actually be bad but it probably happens, and the symptoms do make sense.



Injectors are actually really easy to get to. Just remove the plenum.

 

I appreciate the replies. I have had 2 other issues with my 4Runner since my last post, first the left headlight went out (so I replaced it) then two days later the right one went out too (another trip to the parts store). Then I noticed a new vibration that wasn't due to the cylinder misfiring. Turns out the front u-joint was going bad. So my new question is whether to replace just the front one or do both so I wont have to pull the drive shaft twice. Any feedback would be appreciated thanks

 

Do both, it'll save you trouble later, and get ones with zerk fittings. I just did mine with Moog 285s. You'll need to rent a u-joint press from auto parts store. Hopefully you don't have to grind your old ones out like I did

 

I don’t know how many miles are on it, but personally I would do both.

 

I did replace both. I used a vise but it was still a pain in the a$$. I started this thread because of my engine misfire (error code P0301) and I have now fixed that problem too. I checked the resistance to the injector and it was only 12.4 ohms. So I replaced the injector and the fuel filter and now it runs better than it did when I bought it. Thanks for all the help and I hope maybe this helps someone else figure out their engine issues.