P0302 check engine code confusion.

hi all

first time poster. what a GREAT resource this forum is!!

did search archives but didn't find anything quite like my issue.

2002 tacoma 2.7l. 125k miles. vehicle is running well. not misfiring or seemingly lagging or anything.

check engine light came on. didn't have scanner handy so replaced plugs (and did regular service (oil, all filters etc).

light went off. came back a day later.

went to mechanic checked with scanner said code P0302 (mis on cyl 2).

swapped coils plugs and injector with cyl 1. still said same cyl 2 code.

did not check compression but if it was low (or a burnt exhaust valve) I would be missing and running poorly no?

no bad smell (like a bad cat) from exhaust.

pulled plugs, cleaned and checked connects on sensors.

reset light.

came back 1 day later.

fyi I'm down in mexico right now, not near much in the way of good mechanics (even the toyota dealership in the capital city seems pretty clueless).

any and all advice welcome. I am NOT a mechanic so I will be relying on what help I can find here.

since the engine seems to be running ok I would maybe let it ride for now, but my wife is about to drive this taco back to the US and it'll be a 2000+ mile trip so I want to make sure she's not going to have any avoidable problems.

cheers!!
lucas

 

I should add that the gas cap is only a few months old (might try to replace it anyway) and while yes the gas down here can be dirty, we've been filling the other toyotas we have from the same station without problems.

 

hmmm. only thing i can think of is that crappy, sulfer filled pemex gas...... working in a machine shop in southern california, i get so many heads coming in needing valve jobs. even though I only tear them down, i still wire brush the chambers to cleam them, and I can smell that sulfuric residue from pemex gasoline as I do this.... the residue has probably built up on the valve or chamber seats and is preventing the valve from fully seating/sealing. do a compression check to verify.

In the US, sulfur in gasoline is still being cut down to this day for emissions purposes. I don't think mexico cares. use some higher octane gasolines, octane boosters, techron, or b12 chemtool to help release any built up gunk.

also, next time you fill up at one of their gas stations, look for the warning lable that states their gas may not be suitable for vehicles in america or something.

you can read about sulfer problems further here

 

looks like theyre doing something, but won't be in full effect for some time. didn't really read into it.

 

hey thanks for the reply. the gas here is ok for US cars, though sometimes dirty. we've been down here for years and only have toyotas. haven't had issues with the gas. if I did have low compression in one cyl wouldn't the engine be running rough or misfiring? the engine seems to have normal power, though I hardly ever drive this one (it's my wife's truck) and it idles smooth. so far the check engine light as come back twice after resetting it. in both cases it stayed off for a day or two before it came back. if the cyl had bad compression wouldn't the light come right back on?

I'll try to octane booster or other product to see if that helps. assuming I can find them, would you suggest one of the products you listed over the others?

thanks again!
cheers

 

I suggest doing a leak down test on #2 cylinder just because you swap coils and it still shows misfire in #2. a compression test is good but a leak down test will tell you more.

 

b12 chemtool. and no, after resetting the CEL, the computer goes through a cycle of tests before determining if the CEL is needed. if its minor, it wont come on right away. especially if the leak is miniscual. If you did something like unplugged a coil, it would turn on immediately.

 

thanks! I will see if the mechanic I have working with me even knows what that is

we ran the engine at the shop for at least 30-40 minutes with the mechanic listening and as far as he's concerned it's not in fact misfiring despite the code? he seems quite sure that if a cylinder is missing we'd hear it. true?

forgive my (very likely) stupid and obvious question (again I am not a mechanic) but given that the vehicle is seemingly running well and I only have a bit less than a week to fix whatever is wrong before the scheduled long ass drive........

how risky would it be to make the drive without knowing for sure if that cylinder has low compression or a valve issue? I really don't want to toast this truck.

the mechanic also said it could be a dirty injector but I was under the impression that it would be a different code if that were the case

thanks!

 

b12 chemtool check! fwiw the mechanic only reset the computer the first time. he unplugged the battery and I think pulled a fuse maybe?

but then after a few days the light came back.

this morning I went in to the shop with the light on. scanner gave the same code. they pulled the plugs, swapped a coil around but when they put it all back they didn't disconnect the battery or otherwise reset the light, but it did go out??

 

P0302 comes back as an electrical/ignition fault & the first item to check is what I was going to suggest anyway ,

Toyota plug wires are notorious for going bad & even if running smooth doesn't take much to throw this code

 

thanks! I dont' think this engine (2.7l) has plug wires? the coils just seem to sit right on top of the plugs. maybe I am misunderstanding?

 

My bad, assumed it was a 6cyl...silly 4 banger......

 

this is the first toyota we've had with this motor. I like that it's not as quick off the line as the 3.4l as my wife drives like a maniac. had her in an fj60 for years kept her out of trouble

 

also in case I wasn't clear before, the CEL is off now as of this morning after having done nothing more than pull the plugs and swap two coils around. the battery was not disconnected nor any fuses pulled. not sure if that's useful information but seems like it could be?

 

Haha it may or may not...But like alot of these codes , it can be a specific,targeted issue or like the P0302 code it's pretty general & can be a few things...

 

yeah seems like it could be a whole bunch of different things, though it still seems odd that it's a misfire code and the engine doesn't seem to be misfiring?

I guess if the light stays off I should be ok to have her make the drive? she's a capable lady but I'd hate for her to have to deal with anything major on the road repair wise if I can avoid it.

I will go back tomorrow to see about a leakdown test and to see about the b12 or other recommended products.

thanks again to everyone. what a great resource!!

 

hey guys
so nobody here seems to have the gear to do a leak down test but I can get the compression checked tomorrow.
called all the auto parts stores, nobody carries the b12 or the techron. many other brands but not those. any opinions on the Lucas branded fuel cleaners? there were like 5 different ones ( injectors, total fuel system, "deep clean") etc.

 

Hmm. Cel off after tinkering with some electrical? Sounds like it was something minor along the lines of bad grounding with a spark plug. either that or a spark plug was lose enough to pass air in. everything should be fine now. chemtool can probably only be bought in the US. drive the truck as much as you can for the remaining week.

 

hey yeah all we did was pull the plugs to look (they looked fine but there were only 2 days old switch coil 1 and 2 and the mechanic just sorta messed with all the spagetti hoses and sensor connects etc. I drove the truck about 100 highway miles today seemed ok. kept it between 65-75mph, 100+ degrees outside and the AC running. I did find a bottle of chevron injector cleaner with techron in it will fill the tank and put in the cleaner tomorrow.

I really appreciate all the advice. I'm planning to use the truck a bunch this week before the wife makes the drive .

cheers!

lucas

 

An after thought. The bad ground could have been from the previous plugs. Just takes a bit for the cel to clear.