Forum banner

Missfire issue (p0300) and black smoke?

4999 Views 10 Replies 5 Participants Last post by  jasonc624
hey guys, so i have been having a very hard time diagnosing what exactly is causing random misfires on my celica, i have a 2000 gts, only engine mods are a trd intake and trd exhaust with stock headers. so the car was throwing a p0171 lean code but i fixed that with two new o2 sensors and a new maf and now the only problem is the p0300 code and black smoke out of the exhaust along with black "soot" dripping/spraying out and the strong smell of gas. m afraid my cat is going to give out (or already has) due to all of the unburnt gas, also i just took the spark plugs out the other day and they were covered with gasoline and smelt of it too, im thinking it may be an issue with the fuel pressure not letting the spark pugs spark at random times, but i checked it and fuel pressure was at 45psi... any help much appreciated thanks
1 - 11 of 11 Posts
...Good luck getting useful help around here...:fawk:

300 is a good movie that has lots of action...:blah:

However po300 is a random misfire that can be caused by multiple parts failing:bang:. Your new* o2,maf sensors may be giving your car a car a better a/f ratio, but is still failing in actually delivering the fuel to where it needs to be, and causing you're misfires:bang:.

:confused:...I don't see how your spark plugs could be "covered" with gas, I'am sure you 'ment to say oil? If your spark plugs are covered in oil* and smelled of oil*, that can be solved by a simple valve cover replacement (you hope);)

Now if indeed the spark plugs were "covered with gasoline and smelled of it to" then we're dealing with a flooded engine. You'll have to check many things.. you can get started by checking your spark plugs,coils.. Thats a start.

:blah:...My 2002 GT automatic 171,xxx miles on it, is running lean, and misfiring, everything is clean under my hood.Checked my middle aged spark plugs and saw that they we're heated (white,chalky) but still looked healthy.Only problem I am being annoyed with is i can't increase my throttle by too much with out getting a slight hesitation.

Hit me up dude

BUMP seems we have a few others with the same/similar problema.
See less See more
The 300 CEL is usually caused by bad spark plugs, coil pack, injector, or bent valve. You hope that it is not a valve issue, you should start by replacing your spark plugs, if it comes back replace coil packs, if it comes back I am doubtful it is the injectors so come back and tell us if you have any new info or anything and hopefully we can figure it out.
i really appreciate the replies guys, my car is also having trouble with acceleration and doing the same thing your car is doing silver_streak, i would suggest replacing the plugs? maybe? may be even the maf.. thats what helped my lean code and the thing is, with y car, i bought a brand new coil and switched it around and when i put it in cyl 1, it still misfired and it even showed a mifire in that same cylinder as the new coil, im beginning to think this is a computer related problem as well? im not even sure anymore, btw, i just rebuilt my engine at 60k miles and it has about 61k on it now, i did a full valve head job and crank job and replaced two pistons as well, but i remember this misfire problem even before i redid the engine, it was doing the same thing.
Wow looks like you have a lot of the bases already covered. Like I said it seems like it probably isn't your injectors, but checking wouldn't hurt. You could first check to make sure they are getting proper power, then maybe send them in to get a full cleaning and check to make sure they flow properly.
thanks, i think that would be a good idea, do u know how to do about checking their power? is there a certain method?
Sorry I don't know how to do this, hopefully someone that does will chime in.
To check your coils... unplug your coils, take out your s. plugs.. plug your spark plug into your coils point your spark plug somewhere on the chassy (any where it can ground) and crank the car.

If you see sparks your coil is fine.

To check the voltage going to your injectors you have to measure the voltage from 4 wires in your ECM to ground with the IGN ON. Your ECM is located under your hood - the little box what says "do not open" lol its by your intake. The terminal numbers are #40 #30 #20 #10 - they will be in the far left harness, the last 4 wires to the right on the top row. Take the positive lead from the meter to each wire while the black lead is on a good ground, and you should have 9-14V on each terminal. You can also OHM (resistance) test each INJ. I have this same problem in my car, and i still haven't resolved it. Here is a list of problem areas you can check.

Battery, Vacuum hoses, Open or short in engine wire, Spark Plugs, Ignition system, Injector, Fuel pressure, MAP sensor, ECT sensor, MAF sensor, Compression, valve clearance, valve timing, VVTL system, and ECM.

I find it a little weird that you have gas on your plugs - was it on all of them of just one or two? That may be a problem with your IGN system and/or plugs. Check the gaps on the plugs, or just replace them as they are not that expensive. besides that i would say swap IGN coils around and see if your P300 changes, but it sounds like your have already tried that.... The only other option is a stuck open injector. I sent mine off and had new screens put in them and cleaned - maybe you might want to look linto that. A dirty and stuck injector will give proper voltage readings, and will OHM out properly.

This P300 is a B!TC*!! I wish you luck my friend
See less See more
same code, changed spark plugs, but mine had oil on them in cylinder 2 bump
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.