Jess17

Hi! I’m new to here so I’m not sure if this is the right spot to post. So a few months back (Feb 15th) I have a P0303 code pop up. Had it checked to find a cylinder 3 misfire. Put new spark plugs and coils in it and it was good to go. Now four months later (July 5th) the check engine light blinked twice back on and shut off under the P0303 again. I know it can’t be my spark plugs and coils again?! Replaced the spark plugs again just to be safe.

it’s having a rough idle.. I took it to get diagnosed and they told me no issue found. But you can hear it from my tailpipe.. apparently they didn’t hear it until after I picked the car up. I had them do a compression test and cylinder 1-3 were at 170. Cylinder 4 at 150. Shop said I needed a new intake 02 sensor and a induction clean. $700 later my cars running worse, the 4th cylinder dropped to 120 and the check engine light is staying on now. Now it’s hesitating to turn over. Never did that before..

The car has 244k on it, mainly highway miles. I’m at a total loss of how to fix this misfire.. I had gas getting into my oil to where when you opened my oil cap it was so strong. Burnt bad valve? Fuel injectors? Anyone have any experience with this problem already? I haven’t popped anymore codes besides the P0303. Until the induction clean, now I had a code for my fuel being to rich.
Someone help 😩

Jess17

just unplugged all the fuel injectors while leaving it running, all made it run a lot worse so I’m assuming all injectors are ok

xRiCeBoYx

iTrader: (22)

Misfire on a single cylinder (cylinder 3 in your case) will make the car's idle sound like a galloping horse. Is your check engine light flashing or is it steady on? I see you already replaced plugs and coils, so kinda ruled that out. You can swap around the coils to see if the code follows the coil (e.g. swap cyl 2 and 3 coils and you start popping a P0302 instead of P0303).

any signs of any frayed wiring in the engine bay?

Also, moved to right sub-forum. 7thgen, not 6th

edit: that lower compression on cyl 4 and drop down to 120psi is disconcerting, btw. I'd honestly be expecting that the misfire would be in cyl 4 with that kind of info. You may be in for a head gasket change
free-er things you can check, make sure plugs are gapped properly. .044" is the spec, IIRC

xRiCeBoYx

iTrader: (22)

wtf.. I think they got you there. If you needed an O2 sensor, you'd be throwing a code for it. As far as what an intake O2 sensor is.. idk. Only sensors on the intake stream of a 2001-2005 civic are intake air temp and manifold air pressure sensors. O2 sensors are on the exhaust pipe, one upstream of the catalytic converter to measure air/fuel ratio and one downstream to monitor catalytic converter health. If they replaced the upstream O2 sensor with a non-oem one, these engines/ECUs don't play nice with aftermarket/universal sensors. Induction clean? Did they just replace the filter and wipe it down with a rag?

Fuel in the oil system... could be leakage past the piston rings. Leakdown test will be able to tell you if you have any leakage there. idk if someone else has ideas of how to tell without coughing up $200 for a leakdown test to be done. At the moment, can't think of any other source of fuel to oil leakage.. Valve seals maybe?

Jess17

idk why the guy worded it the way he did on the phone but it’s my 02 sensor connected to my catalytic converter right up front in the engine. And as for the induction clean, they basically put some kind of chemical in the engine to clear built up carbon. So I’m not to sure exactly what that process is and if it’s similar to the seafoam everyone talks about on here. I didn’t ask if he did a leak down test so I’ll give them a call to see!

Jess17

thank you I wasn’t sure what gen it was! Lol
the check engine light is steadily on now. No flashing. I haven’t checked to see if any wiring is frayed I’ll look into that! Spark plugs I bought pre gapped but I double checked them and they were on the money. And I was wondering if maybe a head gasket but no smoke showing signs of it.

xRiCeBoYx

iTrader: (22)

head gasket failure might not always show smoke. last time mine blew, didn't smoke at all, but my oil was definitely chocolate milkshake

Jess17

when I changed my oil to get the gas out of it, I was given the wrong filter. It shot oil out when I turned the car over. The new gold oil came out dark but not milky so I’ll look into that! Thank you! Would that have a separate code? Or would that just pull as a cylinder misfire?

xRiCeBoYx

iTrader: (22)

tbh, last time my head gasket blew on my 2002, zero codes, car ran fine-ish with the occasional temp rising. Was losing coolant is the only thing I noticed. Until the gasket blew blew and there was active coolant leakage from the backside of the block

If you wanna see what blown headgasket oil looks like, click the "RIP Azumi" link in my signature.