Jolley

I have a 1999 Civic EX completely stock, I get code P0304 Cylinder 4 Misfire only after engine is at temp and i restart 0-30 min later.
This all started when i purchased new battery at the Auto Parts store and restarted car.

While misfire is occurring i can pull #4 plug and verify spark present.
While Misfire is occurring i can rev motor 5-10 sec and misfire symptoms go away. I do notice some times a little bit of smoke followed by raw gas smell from exhaust
This is very repeatable, If i restart before engine is at operating temp no problems.
I have swapped injector 4 with injector 3, Misfire stayed on #4 cylinder

I have replaced and or cleaned the following

New NGK Plugs
New NGK Wires
New Distributor Cap
Swapped Distributor with know good one
Compression Good on all cylinders
Head Gasket Replaced 2 years ago
Cleaned IAC
Cleaned throttle body
Oil change

Freeze Frame Data

Code P0304
ABSLT TPS 9.4%
Eng Speed 722 RPM
Calc Load 34.1%
Map 9.7%
Coolant 203 degf
IAT 117 deg f
ST FTRM1 -5.5%
LT FTRM1 0.0%
VEH Speed 0 MPH
Fuel SYS 1 Closed
Fueld SYS 2 n/a

ezone

Valve adjustment?

See if it's been losing coolant very slowly?



Make it misfire....Shut it off before the miss stops happening. Remove spark plug from that cylinder that misses, figure out if it is wet and what it is wet with (antifreeze?)

Jolley

ezone

You probably would have had to taste the plug to find antifreeze, but I'm sure it's there.
Good info.
The overflow looks like it's boiling -- and the radiator is actually low.

It's blown the head gasket.

That explains why it misses.

Jolley

Thanks for the reply,

Today i burped coolant by attaching a funnel to radiator neck and allowed rad fan to come on a few times. i added about 1 quart of coolant during the process. once full i did not notice anything odd like gasses pushing through coolant.

let care sit for 5 min

restarted car it started and immediately died, started again and it started but had a very low idle around 400 RPM but did not stall
pushed on the gas pedal and revved just fine and returned to normal idle
i did not notice a misfire but CEL did come on, checked code and Misfire on #4 cylinder
repeated the test and attached the #4 spark plug pic. no evidence of coolant on spark plug visual and or taste test.

Do you still think head gasket? would you recommend any other test to clearly identify head gasket before i tare it down.

ezone

That's extremely low.





Coolant will enter the cylinder to get the plug wet as it sits with pressure on the cooling system.

A dribble collects then when you crank it over it splashes the plug and it won't fire until it can dry off. Meanwhile the fuel that doesn't burn collects on the plug too.Fuel makes a lot more odor than coolant.



Those engines blow the head gasket. Not as frequently as the 7th gens, but they do it and almost everything about the two engine designs are similar.



See this thread link, read the info in the first post and note it contains two videos. See the second video. That is my go to test on this particular design.
https://www.civicforums.com/forums/3...reference.html





Another way
If you have a cooling system pressure tester you could get it all warmed up, open the system and install tester, apply 15 psi pressure and let it sit overnight (would have to keep pumping it back up during cooldown), then check for the evidence (coolant) to have appeared in the suspect cylinder.

diskman2018

100% head or headgasket. I have been fighting the SAME issue on my 2000 LX. Replaced everything, swapped injectors, adjusted and adjusted. Tossed a can of stop-leak in the radiator because I really didnt care at this point. Next day it hot starts fine and drivability is awesome. Soooooo.. New head on order with all gaskets. I already shaved the warped original head about 2 years ago. 200K on the clock so Ill get a new reman head.

Wankenstein

The Devil's load will impregnate the cooling system with abhorent seed you can't fully get out.