Hello .I have a 99 tacoma 3.4 ltr. Getting random misfire code. I've done a fair bit of research on this sight and others,what I've checked so far:
Plugs all good,coil packs tested, plug leads new, Efi main relay tested,head gasket not blown, Pulled plugs tested in coil packs there getting spark It looks maybe a bit week though ,not realy sure but sparking. visual on all plugs some are dark suty, some are wet with fuel. Pinched fuel return line and idle still missing. Checked for vacum leaks and gasket leaks with stethascope. Tested camshaft sensor it's good. Next on my list is testing mass airflow sensor,Crankshaft position sensor. Any input would be greatly appreciated.

 

possibly a loose crank pulley. What are your fuel trims? That can tell you if you have a lean miss fire or rich. What spark plugs are you running?

 

Thanks for the reply.. I will check the crank pulley, The plugs are toyota denso dual electrode,newly installed a month and a half ago.
I havent checked the fuel trim ,I just had a look at the code reader I borrowed and it looks like it has that function so I'll try to get that info today.
It looks to me like it's running rich due to the wet fuel on 3 of the plugs after running, At one point It smelled like something was burning,I thought maybe fuel igniting in the cat converter. I'm no expert mechanic just a do it you're self hack. thanks again.

 

Do you think it's worth checking the crankshaft sensor?

 

Another point I dident mention; A month and a half ago I could hear a vacuum leak ,turned out to be bad o rings on one of the injectors.Replaced the o rings on the bad one and all the other injectors . While I had them all out I bench tested them, forced CARB cleaner through them while taping wire to 12v battery. When I was done they were all spraying really well. Could I have messed the injectors up by using carb cleaner vs injector cleaner ?

 

I would highly suspect you have a fuel injector(s) taking a crap. This summer seems to have been the expiration date of injectors for many members, myself included.

They exhibited p0300 and sometimes specific cylinder misfires. Randomly occurring. Usually more likely after heat soak. Hundreds of dollars misspent on MAF, TPS, o2, etc sensors only to still have the problem. A few guys even did tear downs after getting misguided advice thinking it was a head gasket.

 

Yea, Fuel injectors have been at the top of the list in my mind after researching p0300. I had them all out and cleaned them a month and a half ago ,resulting with nice clean spray pattern. Because of that I've been checking the other posabilities first.The more things I rule out the more it's pointing to injectors, The truck has 230.000km on it and original injectors so that's another strike against them I geuss. I've just rented a fuel pressure testing tool,If the pressure is good then I think I'm going to order some injectors from rock auto. Any sudgestions as to which brand of injector ?
Thanks very much for you're input.

 

The issue with the recent injector failure is they die when they get hot. Most rehabbers work on the injectors at room temperature. They sonic clean them, replace the screen and tip, and check pattern. Then they return them to the owner.

 

Due to the fact that I cleaned them myself with carb cleaner probably doesent help. Although after the cleaning and reassembly the truck ran better than ever before,very quick and smooth throttle response until now .

the fuel pressure tester I rented will not work, there's not enough room at the end of the fuel rail to attach the unit with it's longer banjo bolt.
Hesitant to spend 500 plus bucks on injectors without knowing the fuel pressure is good, Hmmm

 

Tried to figure out the fuel trim stuff on the code reader. At idle short term trim is all over the place from 0 to 7.0 bouncing around all numbers in between
. long term is sitting steady at 0.8.
Would this mean that injectors are getting fuel intermittently rather than a steady flow?
It also read ,fuel system 1 OL. maybe online ?

 

I picked up a set of injectors off eBay for like $60. 2 of the replacements were bad and they sent me 2 replacements.

 

STFT will bounce around. LTFT is what you're most interested in and .8% is fantastic. Means motors in good health too. So that mean you don't have a vacuum leak. the p300 is a general misfire code, so look into crank sensor, loose crank bolt (if timing belt has be re-done recently especially), and MAF sensor. Possible bad plug wires if they are not NGK or Denso. Maybe look into ignitor testing too but generally those are fail free. Make sure all your ground are good/intact- battery to block, battery to fender, cylinder head to firewall, and ground group by the diagnostic port by intake plenum.

How does it run? How's the power? Possible the timing belt is off a tooth due to a weak tensioner?

Bad injetors will usually throw a cylinder specific code. But i suppose it's possible.

 

Thanks for the fuel trim explanation,helps to know the motor is in good shape.Given those fuel trim numbers would it be safe to say I don't need to do a fuel pressure test? or is that still worth doing? Crank bolt is tight. MAF to be tested. Crank sensor will check that tomorrow. Plugs,coil packs,plug leads all tested and good,camshaft sensor tested and good. All ground conections good thanks to you pointing out where they are !

I'm still not sure that it's not a fuel supply problem ,weak fuel pump,fuel pressure regulator. what do you think?
I had erased the p0300 code twice and it came back,yesterday I erased again and it came back missfire cyl 1 p0301. When I checked all the plugs
cyl 1 was very wet with fuel as compared with the others . I had a vacum leak a month and a half ago ,it was the o rings on one of the injectors,so I replaced them plus the o rings on all the other injectors. At the same time I bench tested all the injectors and flushed carb cleaner through them while tapping them to power supply.When done they were all spraying really nice. After that the truck ran better then it has ever before. Could CARB cleaner rather than injector cleaner have messed them up ? I appreciate you're help.

 

Forgot to add how it runs. Very rough idle rpms up down all over the place. Driving it wants to stumble .jerky .shakey when starting out from dead stop,
driving at higher rpms seems to smooth out a fair bit. coming up a hill I've heard a sound that sounds like a rock coming out of the tread hitting the fender wall. same sound coming up same hill 3 times now. power seems ok but only at high rpm. I looked at the timing belt cause I wanted a visual of the camshaft sensor,it was replaced couple yrs ago ,I checked the tension and it appeared to be very tight.

 

open loop means the computer is in the default mode where it uses whats in the memory for that particular rpm/etc. Closed loop is when the computer uses input from all the sensors to determine the proper air fuel ratio. You want to know what its doing in closed loop.

 

could anyone please tell me if the 2 wires feeding the CRANK position sensor are supposed to have voltage to them when the key is in the on position (not running) . Resistance on the sensor is within spec, just not sure about the leads coming into it. thanks

 

Voltage will be very minimal. The ECU only monitors it's wave pattern and that won't be detectable without an oscilloscope. I have personally had a crank sensor cause p300 misfires and still be within factory ohm spec. Oh and there was one time where I dropped a timing cover bolt all the way down to the crank ring gear thing that the crank sensor picks up on. It broke nearly all the teeth on the crank gear ring. But to me, kinda sounds like your MAF is whack.

 

Thanks for you're responce. I've meter tested the maf sensor and checked readings while blowing air through it and it is working according to toyota spec manual. I would like to check fuel pressure ,rented a pressure tool,not correct fittings, So booked it in for pressure test. It is the only thing left that I havent tested. If fuel pressure, is good That leaves the injectors as the culprit. In my opinion.....

 

Here is an eBay listing for injectors. I think this is the guy I got mine from.

http://m.ebay.com/itm/6-Fuel-Injectors-Denso-toyota-4Runner-T100-Camry-1992-98-3VZ-3-0-5VZ-3-4-REMAN-/272217792115?nav=SEARCH
Even though 2 of the replacements were bad, which he replaced, I ended up with enough to swap around and eliminate my miss.