[drkblubeast]

I have had a persistent CEL for a while now with the following codes:

P300: random cylinder misfire
P303: cylinder 3 misfire

'02 GTS. Symptoms: hesitation in the morning or when the engine is cold; engine sputters lightly pretty much all the time (can be heard from the air intake and exhaust).

I really need to take care of this if I want to pass another state inspection (that's been expired for over a year and a half now.. whoops). The only relevant mod that I can think of is the Injen SRI. I did the BB mod since I've had the problem, but the codes have stayed the same.

[Engine Bay]

Troubleshooting I have done so far:

- cleaned the MAF sensor multiple times
- replaced the spark plugs (iridium); moved the spark plugs and the coils around, code P303 stays on cylinder 3.

[Spark Plugs]

- ran fuel injector cleaner through the gas tank
- sprayed intake cleaner around the manifold area to see if any leaks would show, but did not notice any difference
- seafoamed the car
- ran a cylinder compression test today, got 151, 154, 147, and 155 psi for cylinders 1-4 respectively. This is lower than normal, no?

My mechanic said they took out the injectors and cleaned them, but I will check them again myself. Besides that, I'm not sure what else I can besides take the manifold off and take a look (never done this before, so I wouldn't be sure what to look for). My shop said it'll be around $2K for them to take the head off the motor. Any suggestions or ideas of what I can do myself?

 

[Smaay]

im willing to bet you have bent valves in cylinder 3.

 

[CelicaBigginer]

Check your injectors, swap out injector 3 with injector 1 and see if the misfire moves. Also what gas are you using

 

[drkblubeast]

Thanks for the quick responses guys. I will try swapping the injectors.
I've been using 89 gas for a few years now, so that shouldn't be an issue...

 

[CelicaBigginer]

I had a similar issue, random cylinder misfire and misfire in cylinder 4. I went through sparkplugs, changed the coil packs and the maf sensor. at the time I had other issues, so I changed the o2 sensors. After all that, I swapped out the injectors and the car stopped hesitating. if you switch out the injectors and your still having issues with that cylinder, you internal damage

 

[SCT09]

Also check for vacuum leaks around the intake. If a coupler is loose that could be the problem.

 

[CelicaBigginer]

There would be a lean condition if that was the case, it would trigger another code

 

[drkblubeast]

I have additional info I forgot to mention. I got a code reader, and it tells me that the following monitors are incomplete, even after driving thousands of miles:

- Catalyst
- Evap
- O2

Not sure if this will support any of the theories above...

 

[drkblubeast]

Checked my injectors, one of them was missing an O-ring at the top, so it was loose in the fuel rail. Replaced O-rings on all of them, put them back in. I believe it got rid of hesitation, but the codes came back the same.