Random Misfire

I changed the spark plugs in my 2003 3.4L Tacoma, because the truck seemed that it was running sluggish. Now that I have changed them, the problem is gradually getting worse. My mechanic hooked up to the truck and his computer showed that plug 3 and 5 were misfiring. I come back two days later and he does it again and the computer says all plugs are randomly misfiring. There is no pattern to it whatsoever. But im on the interstate pulling hills in 4th gear and the truck is losing speed down to 68 and will hold right there until topping the hill. Does anyone have any suggestions or advice for me

 

First off, gotta cover the basics first, what kind of plugs did you use? Hopefully you went with OEM Denso or NGK, I use the

$6 NGK BKR5EKB-11 NGK Spark Plug Stock # 3967

NGK BKR5EKB-11.

When's the last time you changed your plug wires, and you may want to get new coil pack insulators, the replaceable rubber boot that's on the bottom of each coil pack that sits on the plugs over the passenger side of the engine. If either of those is bad it may be arcing to the plug tubes. Also a good idea to coat the very end of the plug boots in dielectric grease, keeps it from arcing and can prevent the boot from adhering itself to the hot metal on the head.

Had you seen a check engine light? Was the check engine light on when your mechanic tested it, if so what was the code? Any noises accompanying this, engine knock, etc? Is the acceleration sputtery, surging or stalling or a constant loss of power?

Most helpful thing would be to know what code it threw if it did, unless I'm mistaken, if it's a misfire it usually doesn't say it's a plug doing it, just the cylinder. Sometimes when it's a specific cylinder it can be a coil pack going bad or a bad fuel injector, but those are isolated to a specific cylinder and can be determined by swapping things to a new cylinder, like taking the #1 coil pack and swapping it with the #3 coil pack, and vice verse with a bad injector. Once swapped it will move the problem to the new cylinder associated with the bad coil pack or injector.

Might wanna try these cause they're simple and should be done if you haven't:

clean mass air flow sensor
clean throttle body
clean idle air control valve on throttle body, the flapper can get stuck and cause issues
change fuel filter
new air filter if it's dirty

 

what's your fuel trims showing?

 

plug wires....... Toyota made them too thin with too fragile inner conductor, if throwing codes it'll pop up as random misfire, forget the no# tho'....

 

Cylinders 3 and 5 have no wires. They're coil on plug. Make sure knock sensor isnt lose or dirty inside the threads. It still could be the wires as well. each coil has a wire going to the other side of the engine. The wires connected to 3 and 5 may be shorting somewhere. Were the pkugs gapped properly? Or are they the dual electrode plugs that don't need gapping?

 

3.4 dual DENSO OEM

 

The plugs I used were the NGK double electrodes. The wires have been changed not even six months ago and I double checked to make sure they were installed correctly and they were. I'm thinking it might be the coils. The check engine light is not on, i think it may be disconnected or something. I havent had the truck for very long, so im still learning about little stuff about it. Like the check engine light not being connected. I was going to take it to my local toyota dealership and let them hook it up to their computer and find the code for the issue. But they want so much just to do that. I find it crazy to spend a lot of money just to find the issue and then spend even more money to fix it. But anyways, I think it might be the coil packs.

Also I did replace the boots and that didn't fix it.

 

I'd almost try another battery for shits and giggles.

 

Dude most any parts store these days will read your codes for free and there are a plethora of code readers you can buy and do it yourself! Scan and ultra guages are super sweet to own not only are they code readers but are moniterable real time guage readers for anything the ecu reads, all kinds of things, 30 plus different readouts for just about anything your trucks ecu monitors. Reguardless if your cel light is burnt out the codes will still be present and readable... they cant be unhooked, the po either took the bulb out of its burnt out. When you start your truck all the lights on the dash will illuminate for a short time. Does the cel come on when you start up?? Thatll let you know if it still functions/illuminates.

 

Your coil pack(s) might be going bad. Pull one out at a time and see if your engine idle changes. The one you pull out and doesn't cause a change in idle is the bad coil pack.

 

I agree, either take it to a part store to have them check the code, they'll do it for free, OR for the price of the dealer doing it you could go buy a decent obd2 scanner, and from what I know if you get one that shows live data you can check the fuel trims, though I know nothing about that stuff honestly. I'd suggest you at least get one that reads codes, all cars made after 1996 use this code reader so it's a valuable tool to own.

Checking the coils would be a good start, but you need a code reader.

First you need to verify there is a code, and if so on what cylinder.

Second you need to take the coil pack from that cylinder and swap it to another, clear the codes and see if the code moves with it.

Like I said above, you can rule out coil packs if the misfire stays at a particular cylinder, and you can try swapping injectors next, just be sure to replace the o-ring on the injectors you pull.

You never mentioned how it was running, is it surging, stalling, just dogging out, sputtering?

It's possible your fuel pump might be dying if it's surging or stalling or if the flow is getting weak and it's starving for gas. It can cause a misfire as well.

You might try this.

Try to listen to hear if you fuel pump is buzzing in your gas tank while turning the ignition on but not turning the engine over. If you hear it that means it's still functioning at least somewhat, but it may still be going out.

 

buy an elm 327 and the torque app

 

That is awesome, I'll have to check that out.

 

I just picked up a 1st gens 3.4 a couple months back and ran across the same problem.
Mine was like that from the start though & my Engine light was disconnected as well.

I am changing the knock sensors & Timing belt tonight. (Wiring harness & Valve Gasket Cover)

Are there any recommendations on other parts to change out while having the motor half tore apart.
Ex. Water pump?

The truck has 190k on it and I doubt any new parts from previous owner at all.

Parts that I have changed within the last month are:
Plugs(Bosch Iridium) plug wire, Fuel, Air & transmission Filters.

Thanks

 

idler, tensioner and pulley for the timing belt. that's all there really is aside from the peripheral belts.

 

Reseal the front end of the "coolant bypass tube" under the intake, yellow arrow in the stolen pic below.
2 bolts, 10 minutes and a smear of RTV. No gasket or o-ring.

 

Thank you guys...
what about any unforeseen gaskets?

I am going to replace valve gasket covers and any gaskets that are on pulleys.
Thanks again

 

get some extra o-rings jsut in case you somehow disconnect the power steering pump?

and if you wanna add a side job, put a universal hydraulic filter on the return side of your power steering pump. cant remember if it's 3/8 or 5/16 line. I just zip tied it to the reservoir and added more line to the return nipple.

 

This. Very good suggestion if you're gonna be in there doing knock sensor harnesses. Often the source of a mysterious coolant leak, total bitch to diagnose, usually only leaks from a plate at the back of the engine when the engine is off and the metal parts contract during cooling and starts to leak, usually don't see it with engine running or right after you turn off the truck. If you're in there, DEFINITELY do this now. Just cost a friend $1000 bucks for a shop to do it, you can do it yourself for $150 in parts including new wire harnesses for knock sensors, the fipg required for the coolant bypass pipe and new OEM intake manifold gaskets.

Good thread with part numbers

 

I dove in and changed the knock sensors, wiring harness & timing belt kit on my 3.4 this past weekend. It was a pain in the ass but I got it done. I had to soak my intake over night due to it being so dirty from the PO.
You can definitely feel a huge change in the motor performance wise. Still not 100% fixed though, I am losing power on top end, as in its hard to maintain speed around 65, 70mph

I feel as if the timing is almost off or it maybe slightly missing (as in the motor is out of rhythm).
I did line the timing up right with the marked pulleys and had a second opinion from a tech.

Is there a procedure that needs to be taken after changing the Knock sensors or Timing Belt?

Im going to run another Diagnostic on it and probably go ahead and change the Cat on it.

Any and All advice is welcomed. I am about stumped on this.

Thanks in advance