3.4L with a weird misfire issue

Hey TW,

Ive been trolling and lurking on the forums for a bit seeing all the stuff you guys do to these. For a several months I've been searching for a good deal on an 01-04 Tacoma and well... I came across a deal that is really hard to pass up. Here is the dilemma that I am in and here is the details.

2002 Tacoma 3.4L 5spd Access Cab TRD. It has 128K on it. Truck drives perfect. No skip, hesitation, rough idle...nothing at all. Originally the truck had an issue for misfires.(P0300, P0302 & P0303) Owner did spark plugs on it. Drove it for readiness cycle, CEL came back on for cylinder 1(P0301). Brought the the truck to a Toyota dealer(not the best). They told him it was a coil pack. Had it replaced, went through the readiness cycle again. The CEL came back on for Cylinder #1. Brought it back to the dealer, then they said it was an injector. Had the injector replaced...well you can figure out what happened for the 3rd time. CEL is back on for cylinder 1. He wants to off the truck and be done with it. Hes dumped enough money into it to try and keep hunting the problem. Plus he already purchased a new suv.

Anyone have an incite on these engines or point me in the right direction. I don't know a great deal about them as I am coming from the German car world(which I'm giving up on). I have always loved the 1st Gen Tacoma and now is my chance to get one for a good price. My co-worker told me that Toyota is the way to go and that I wouldn't be disappointed to own one(his whole family is all Toyota owners). He told me it will probably be the last truck I buy.

Hope you guys can help
Thanks
Rob

 

I'm gonna say run a tank of fuel system cleaner or else find another injector.

 

first off u need someone that can actually diagnose something to look at it lol.... it can alot of things man..... they are clearly not diagnosing it correctly if they r throwing parts at it

 

Exactly. And since its a misfire on multiple cylinders...there's a good chance it's not a compression issue.

I like fixing misfires.

 

me too its a challenge.... it sounds like its just #1 now... id like to see fuel trim and maf readings. id start by swappin plugs, then coils, then take a compression test then swap an injector....

 

Are the spark plugs the correct ones? This setup is coil on plug? If possible, check out the coils with a dvom. Swap coils to another cylinder an see if the misfire moves. Swapping plugs right now isn't a bad idea. Start with the basics.

 

its a waste spark system. coils are on 1 3 and 5. wires go to 2 4 and 6. but yes swapping things is still the way to go....

 

Perfect. Those coils are easy to test if need be. I would find out which cylinders are misfiring for sure. That's where you must begin. Than swap some things if necessary.

 

This is why Im thinking of buying it. I cant really work on it as its not mine. Id have to buy it and deal with it. I just dont want to get stuck and have to drop in another motor. Im pretty decent with cars, mainly the german ones.

I was trying to think of things it could be. Clogged cat, leaky intake manifold gasket, front o2 sensor, maf...It puzzing to me that the misfire keeps coming back to cylinder 1 after all 6 new plugs, 1 coil and 1 injector on cylinder #1. I would assume the timing belt was changed. I have heard about harmonic crank pulleys shifting and when someone goes to do the belt its off a tooth(on other makes)

The toyota dealer where is was brought are not the greatest. Id rather have the three stooges work on it. The dealer doesn't sell much for trucks(as they never have any) and they mainly have only cars on their lot.

 

its most likely none of those things u mentioned.... those all effect more than one cylinder. but yes it could be as simple as a plug or a head gasket.... ive also seen a bent crank tone wheel form someone doin the t belt can cause (fake) misfires....

 

I don't want to get too buried in the truck with repairs when I first get it. I though, its a Toyota it cant be anything major they dont break. The trucks are almost bulletproof. Thats why I was thinking its a simple fix. It has been maintained pretty well all its life. There is almost no rust on it which is a HUGE perk to buying it.

 

i have an 01 4runner with a cyl 6 missfire at 50 mph drives me nuts. i have done coils and wires but still missfire also swapped plug and new air filter. any dieas?

 

Compression test cyl 6?

 

going to have to. sometime the bitch runs good with no back fires and then she starts backfiring at 50 mph

 

i am going to put all new plugs in and run injector cleaner. i am thinking its an injector the truck only has 136k miles on it. 2nd owner. very well maintained. oil looks new. runs great but missfire at 50mph.

 

50 mph.... What rpm? Does it misfire at that rpm in any other gear?

 

its and auto and i think around 2000

 

i am going to seafoam the hore tomorrow

 

I appreciate all the info guys. Im gonna take a shot in the dark, see if I can get it for a lower price and then start fixing it. I'm leaning toward the tone ring. The truck was never serviced at a dealer but instead a local shop somewhere near by. Its pretty well taken care of over all. I think with 128K on it, guy drove it till it either broke or came close. Local shop did a belt and bent the tone ring causing the fake "electrical" misfire but the engine timing is on point and the truck drive like normal.

 

Since many suggested plugs, i'll just add on top of that and say that the first gens are very picky with their plugs. Pull one of the RH side plugs. It should be a dual electrode Denso. If it's a single electrode NGK or any other brand - assume the mechanics that did the last t-belt service might have overlooked something else.

Typically, single electrode plugs won't cause a single cyl misfire but it's an easy place to start and verify the amount of attention to detail the shop that was working on that truck had.

Good luck, I hope you get a good deal on it and the fix is something minor!