05 Aveo - P0300 Random Misfire
 

So, I got an 05 Aveo recently with a busted timing belt. I replaced the engine with one from an 07 Aveo (slight differences). Its in and running, but I keep getting a P0300 code which is "Random/Multiple Cylinder Misfire Detected". So, last night I replaced (meaning swapped parts from the 04 engine):

spark plugs (replaced & regapped)
wires
ignition coil

Its a waste spark ignition system, so thats about it for parts AFAIK unless there is a separate ignitor. The misfires aren't noticeable, but the code keeps coming back.

Dang I was hoping it was running so I can see what you can get out of it. Good luck!

It will be eventually. :)

Check and clean the grounds on the coil pack I believe that it should use the mounting plate for the ground. Also check for a vacuum leak using TB cleaner when the engine is running.

Does it misfire under certain conditions or can't you tell?

It could also be dirty injectors or since the timing belt broke it may have damaged one of the valves slightly a compression check should help to confirm that.

The ground is clean, checked that.

I can't tell that its misfiring.

Could be dirty injectors. Its not a damaged valve since its a new engine.

Whats your fuel pressure like?

I don't have a fuel pressure gauge handy. However, it has no problem hitting the rev limiter under full load...

Can you read the OBD2 code for cylinder balance and see if there is any discernible pattern.

I know it says random, which would seem to contradict any specific pattern, but it might make diagnosis easier if you could get any more tidbits of information.

Test compression and leak down to confirm mechanical integrity.

Swap the injectors from the original engine?

Possible false diagnosis code due to differences between year of manufacture of the engines. Check connections of the replacement engine to see that they match the original.

regards
Mech

I'm not sure what you mean when you say "read the OBD2 code for cylinder balance". I get a P0300, thats it.

I am using the 05 injectors since the fuel rail stayed attached to the vehicle while swapping engines.

All connectors matched up just fine.

I haven't done any compression/leak down testing. It seems to have plenty of power.

According to obd-codes.com:

Sounds like your getting plenty of fuel.

Looked up P0300, if it said P0301 it would be cylender 1, 0300 means the computer either couldn't locate it, or its jumping arround.

You might check your intake manifold and any attached vaccume lines for leaks.