Backfire/Studder under acceleration

[T4RFool]

I'm having a problem Identify the cause of a rather annoying and potentially dangerous problem. about a week ago my 4runner had a spuddering problem whenever i went up hills slowly(5-10mph). i figured it was most likely caused by bad fuel and didnt think much of it. about a week later i took it out on the interstate and all was fine until i hit the gas to get up a hill(70MPH), it didnt like that and began to studder and backfire rather badly. the strange thing was that it only happens under heavy acceleration or use of the throttle. I was able to drive at 70MPH under normal acceleration without problems, it only occurred if i accelerated to aggressively. i have been worried to use it since. i did a little reading and thought maybe it was a spark plug that is the problem. i have the E3 spark plugs in my truck here is a picture of them:

after looking at them its hard to determine if they are truly at fault here. i have heard numerous things of praise in favor of the plugs and many that wont go near them. these plugs are only a year old, along with the plug wires and a new fuel filter and pump. the interesting thing is that after i took the plugs out and cleaned them up a bit and put them back in, the problem seems to have gotten worse. wont go past 2500RPM's without spuddering pretty bad, whereas as before it was closer to 4000RPM's before it started

After some more reading i came across this thread here . specifically post #26. now that scares me a bit cause i recently had my Tbelt, Waterpump, and Tensioner pulleys replaced back in december.

Anyway, any words of wisdom or helpful advice would be much appreciated. Oh yeah, its a '02 SR5 4x4 with 140K.

 

[4-Ripcord]

Definitely start with getting rid of those awful plugs. My money says thats the problem.

 

[T4RFool]

my bet is that its also these garbage plugs too but i wanted to post an ask and see if others could offer a different perspective since im not a motor expert. i had the NGK G power platinums in before i got these and i never had a problem with them so i'll probably just buy a set of those.

 

[DeTwizzle]

Could it be a bad injector? Im guessing that the check engine light didnt come on since you never mentioned it.

 

[T4RFool]

Im guessing that the check engine light didnt come on since you never mentioned it.

the CEL didnt come on and stay on. it flashed a few times but went away. unfortunately i dont have anything to check codes with out and i live an hour away from anywhere so getting stuff done is slow going sometimes. i had considered it might be an injector but after i took the plugs out and put them back in and the problem got worse it seemed that it was most likely the plugs. i hope its not an injector. if it is, it could be awhile before i get it fixed.

 

[PitbullRescuer]

If it's breaking up under load, I'm inclined to think it's either wires or a coil. Especially if taking the plugs in and out seems to have effected it.

 

[T4RFool]

i know its not the coils, i took a good look at them today and am fairly confident that its not them. im also less inclined to think that its not the plug wires because i replaced those about a year ago as well. i'll probably start with replacing the plugs next time i get to the city and if its not that then i'll change to wires. i really hope its not related to the crank bolt.

 

[PitbullRescuer]

There's nothing visible on the coils that would show them going bad. I do think it's spark related though. Try plugs first I guess but be prepared to replace other things too.

 

[T4RFool]

boy i hope its not the coils cause those things are expensive

 

[jonwilly2]

mine use to do that and would get passed by scooters and 90 something year old fossils. I changed out the MAF and CEL went away and ran like new.

 

[BFEATHER2008]

I am a toyota mechanic and id say get ride of those crappy plugs i stick with oem plugs and wires. I had aftermarket plugs and wires in it when i bought the teuck and it misfired and studdered on acceleration. I replaced plugs and wires and bam its fixed. Then it stated misfireing again later down the rode and had to replace a coil. Id would say start with new plugs oem preferred but if not get only denso or ngk plugs due to the fact they are what comes from factory from toyota. And with the CEL flashing then going off is overheating the convertor. If you drive it drive it easy cause you can melt your CAT and if you do that OEM CAT is 1600 bucks. So just beware and drive with ease. Like i said start with new plugs first if its still there replace wires if its still there which i doubt it will be it would be coils. I really doubt it has anything to do with fuel injectors. I have never replaced any fuel injectors. My dad is also a toyota mechanic of 32 years and he has barely if ever replaced an injector. They are one of those parts that seems to never fail on toyotas. Good luck on the truck hope you get it fixed. And try to stay away from plugs that arent ngk or denso. Every car that comes in with a misfire code at work we always check the plugs and they seem to always be aftermarket plugs and we put OEM in and it fixes them.

 

[Carcrafter22]

I had this exact same problem a couple months ago, it turned out to be a coil causing it.

 

[T4RFool]

And with the CEL flashing then going off is overheating the convertor. If you drive it drive it easy cause you can melt your CAT and if you do that OEM CAT is 1600 bucks. So just beware and drive with ease.

wow, i didnt know that about the CAT. im not driving it right now, i wont be until i get new plugs. thankfully we have a third vehicle. i probably wont get new plugs for a week or so cause we live an hour away from anything.

 

[T4RFool]

Update:

Bought new NGK Platinum plugs today and went ahead and put them in hoping that this would fix this issue... it didn't. i took a couple of videos to show what it is that's going on. when i first started it up and go to revving it up it was fine, smooth all the way up but after letting it run for a minute or two it started to do this:

4runner Studder - YouTube
4runner Studder 2 - YouTube


so since its not the plugs im gonna guess that its probably not the wires since they are about a year old and doubt they went bad that quick. if its a coil, how can i tell which one it is without replacing them all. they are pricey. also, how likely would it be from the crank bolt not being tightened enough and causing this. i didn't do the timing belt so im not familiar with that area of the motor.

 

[PitbullRescuer]

I am a toyota mechanic and id say get ride of those crappy plugs i stick with oem plugs and wires. I had aftermarket plugs and wires in it when i bought the teuck and it misfired and studdered on acceleration. I replaced plugs and wires and bam its fixed. Then it stated misfireing again later down the rode and had to replace a coil. Id would say start with new plugs oem preferred but if not get only denso or ngk plugs due to the fact they are what comes from factory from toyota. And with the CEL flashing then going off is overheating the convertor. If you drive it drive it easy cause you can melt your CAT and if you do that OEM CAT is 1600 bucks. So just beware and drive with ease. Like i said start with new plugs first if its still there replace wires if its still there which i doubt it will be it would be coils. I really doubt it has anything to do with fuel injectors. I have never replaced any fuel injectors. My dad is also a toyota mechanic of 32 years and he has barely if ever replaced an injector. They are one of those parts that seems to never fail on toyotas. Good luck on the truck hope you get it fixed. And try to stay away from plugs that arent ngk or denso. Every car that comes in with a misfire code at work we always check the plugs and they seem to always be aftermarket plugs and we put OEM in and it fixes them.

You're certainly more qualified than I am but injector failure isn't at all uncommon with the 5VZ. There are quite a few threads about it on here actually.

 

[BrianSD_42]

You're certainly more qualified than I am but injector failure isn't at all uncommon with the 5VZ. There are quite a few threads about it on here actually.

I know what you mean but I also feel like they aren't that common. I didn't see a single thread about injectors for first 10 months watching T4R's 3rd Gen section then after Fightman's injector ordeal everyone seems to say "it must be the injector". I know my observation isn't scientific but I'm skeptical. On the other hand 4RunningDaily just took his to a mechanic and was told "injector fail" so I don't know.

I'm still running strong on original injectors.

Summary: I think some people are jumping to the conclusion "must be an injector" without true confirmation.

 

[T4RFool]

i have rarely heard of injectors going bad, its a possibility i guess but i use injector cleaner on a fairly regular basis which i hope isn't all for nothing. typically they tend to go bad if they aren't taken care of

 

[T4RFool]

Update:

so i got a friend involved who happened to have a code scanner.... there are not codes, no pending codes... a little odd. looked at the tail pipe while it was studdering, no change in smoke color or thickness... a little odd. so that means its probably fuel related, not ignition right? in park it happens around 3000-4000rpms but while driving it around it happens under heavy acceleration or when pressing on gas going up a hill at a lower rpm so its not dependent on rpms. fuel pump is less than 2 years old along with filter... could it be MAF? how can i tell if it is the MAF or pump? or is it something else? ideas?

 

[T4RFool]

Update:

I unplugged my MAF and the issue did not improve so i guess i can exclude the MAF from the list things that it could be i guess.... its starting to look like the fuel pump... misfire at higher speeds and difficulty climbing hills. i wish i had a fuel pressure guage

 

[T4RFool]

Update:

i bought a new fuel filter couple days ago, Wix, and got it in the mail today. went out and installed it hoping this may be the cause of my problems. got it all sealed up and started it back up. runs great, went to move it and it died and now it wont start again. any ideas? my thoughts are that it is most likely the fuel pump now. i put my ear directly to the tank and had the wife turn the key and heard no buzz or hum or even a click that would indicate that its working. its kind of weird though that it was running ok at idle before and even enough to cruise under light load before i replaced the filter, now it wont start.