net_manager

I got P0303 occasionally at the very beginning and later more often. It only happens during idling or when I started my car or parked my car. The misfire also happened to #3, not a random, even after switching the new ignition and spark plug with #2, it is still on #3. Also, when this happened, I noticed my fuel system status (from the scanner tool) is "open loop due to system failure". As long as the status is "closed loop", idling is fine. I tested the cylinder pressures. Every cylinder seems to have almost the same pressure (slightly different <5%). I replaced all the 4 spark plugs, ignition sets, new fuel injectors, didn't see any oil consumption, no coolant leakage or oil in the coolant.

When I opened the valve cover, I noticed a valve spring cracked. I searched online but couldn't find out how to replace it without taking the engine out. Is this an easy way to replace the spring?

Any suggestion is greatly appreciated.

Here is my car:
2011 HHR LT, 2.2L engine, 4x Auto transmission. Milage: 133K

Oldblue

There are valve spring tools to compress the spring to allow you to remove the valve keepers. You need compressed air to fill the combustion chamber with pressure to hold the valve closed.

https://www.ebay.com/itm/Overhead-Va...8307774?_ul=CA

donbrew

Either that, or you can remove the head without removing the engine.

net_manager

Thanks, donbrew. Can you give me more clues of how to remove the head - like shall I remove the intake together with it or intake first? Do I have to worry about the timing after remove the head (like what have to be done for timing chain replacement)?

RJ_RS_SS_350

Hi net_manager, to the forums!!

Check the replies again, Oldblue gave a good reply, but it went into moderation. I've made it where you can see it now.

donbrew

That is one of those thing; if you have to ask how find a reasonably priced shop.

Oldblue

If you plan on pulling the head , it’s easier to remove the exhaust and intake manifolds.
You must remove the front cover to remove the timing chain.


Here is a nice how to with two methods without removing the head.

http://www.enginebasics.com/Advanced...n%20Motor.html

net_manager

Thank you very much, Oldblue. It is very helpful. I will do it this weekend and update the process here.

net_manager

Came back to report the progress. Actually, I was wrong with my intake valve spring. The spring was ok, it has some dirty on it looking like "cracked". My bad.

Back to the original topic, I reran the engine cylinder pressure test again. This time the gauge showed #3 only 90 psi while others showed close to 210 psi. I put 1 1/2 teaspoon oil to the spark plug well of #3, the pressure measure jumped up to 150 psi. This seems to me it had a worn piston ring. But I don't see observable oil consumption. Wondering if that is possible the ring worn but no oil consumed.

Why I didn't get the correct reading before but now I got it? I observed the misfire happened much more frequently yesterday than last week, so maybe it became more reproducible. What I am confused were two things: 1) why I only saw P0303 misfire during idling or a very low speed if the piston ring worn? I thought when the speed was higher, the misfire should be worse. 2) what could I do as of now other than rebuilding or swapping an engine? Would Lucas or Bar Leak's be useful as a temp solution?

donbrew

I would run the compression again to guard against "user error". 210 sounds too high, more like 140 - 170.

You might get lucky by doing a top clean with SeaFoam, dump a few ounces into the spark plug holes and let sit over night; might be carbon on the ring lands.

BTW, any DTC fault will stop the closed loop. The computer figures if it isn't getting good data it would be better to use standard assumptions.