Misfires, hesitation, underpowered 02 3.4L Prerunner

Hey,

Been experiencing a number of issues with my truck (2002 3.4 L prerunner, about 370km) for about 8-10 months now. Have done a variety of work on my own with varying success... Looking for some help please.

Issues
Early on (Months ago)
- Codes for misfires Generic P0300 plus specific cylinders P0302, P0305 etc
- Code for running lean P0420
Currently
- Hesitation when giving gas
- Seemingly underpowered (Highway speeds or uphill revs very loud though RPM's stay decent) Has a hard time getting into gear and going up hills
- Occasional codes for misfires up until the last week where on the highway they're all back

WORK I'VE DONE RECENTLY
- Fuel filter within the last 6 months
- Fuel pump within the last 6 months
- Spark plug wires
- Ignition Coils
- Spark plugs
- Took out throttle body and cleaned
- Cleaned mass air flow sensor
- New Battery (Not related but needed one anyway)
- Front 02 sensor replaced
- Aftermarket catalytic converter put in
- regular oil changes
- Took to a shop and ruled out that it wasn't transmission for more recent issues.


So
I can't seem to clear these damn misfires and now, related or not, it's driving differently (worse). I'm not that mechanically inclined so maybe I've missed something obvious but any tips on what to check next would be greatly appreciated. New fuel pumps shot possibly? Vaccum leak?

 

How many miles is on the truck?? This may be a shot in the dark, but what about a faulty or clogged injector or injectors?

 

Yeah injectors could definitely be a possibility. When I get home later, I’ll upload a couple pages on what you can test for misfires from factory service manual. The cam and crank sensor for example could also cause misfires, however i don’t think thats very common.

 

Hopefully you can open this pdf and it can be useful to you.

 

I’ve got the same issue, P0300. Did all the same maintenance as you minus all the exhaust stuff. Even went as far as changing the knock sensors and injectors. And I’m still having the same problem.

 

Compression test ?

Leak down test ?

 

Same issue i am having with my 04 https://www.tacomaworld.com/threads/lets-find-that-lost-cylinder-5-out-of-6-aint-bad-right.475084/

this might be a good read for you

i am to the point of having the injectors out and i cleaned them, my fuel rail also had water in it

 

use denso or ngk plugs?

 

maf going bad?

 

I agree this sure sounds MAF related to me. Cleaning a bad one doesn't cure it. Always worth a try though.

 

maybe a cracked intake hose also...

 

Air filter?

 

About 230 000 Miles

Denso plugs 2 prong. Had problems with these and previous single prong ones (were only in a few weeks before I swapped them with the proper toyota ones)

Air filter is very clean

 

Thanks guys, gonna read up on things and take another look after work tomorrow. Had troubles getting it started on my way home today Thanks
1stgenyota2014

Definitely want to do a compression and leak test now as well

Cheers

 

Could it be a faulty ecu?? Never have i ever pointed to that as a possible culprit, but it sounds like he's exercised every option already.

 

check to make sure she is mechanically sound first by doing a compression test. too many time i though I could "fix" it by taking a stab at it knowing what is wrong without testing first.

doesnt cylinder 2 and 5 share the same coil ? It is not uncomon for a split to develop in the air tube from the MAF to the throttle body. It isnt hard at all to take it off completly and then you can bend it and twist it to see if there is a leak. The hesitation on acceleration is an indication of false air entering the engine after the MAF.

 

^this was the case for my buddy’s ‘92 pickup. We went through and tested EVERYTHING because it kept stalling while driving. Turned out to be a bad ECU so we swapped it with a spare I had laying around from my previous build.

 

Listen to @Glamisman - he's a master tech!

 

PROBLEM SOLVED

Thanks again for all the input. I've got a pretty surprising/frustrating explanation for everything.

About a year ago I had the timing belt replaced at a shop I'd been going to for years... What ended up happening was the crank dampner wasn't secured properly. So over the next months it was rattling around causing misfire codes and more recently with it getting worse the lack of power and hesitation.... So a job that should have been $900 ended up costing me about double trying to replace all these parts and bringing it to shops over the next few months...



That's what it looked like before I had the worn parts replaced. (Should say as well that this aspect of my truck I'm not too well versed on yet incase my description of things seems a bit off)

I'll post some more pictures of the worn parts when I get them back from the shop that initially caused this chaos. Will be getting money back... Could have costed me my whole engine!!!


Thanks again guys,
Cheers

 

glad you got to the bottom it.