Check Engine PO300 01 ACR

[GTSACR]

I have been trying to track down why i'm having a random misfire in my 01 ACR. SO far what I have learned is that it only happens on cold start warm ups in the morning after the car has sat all night. When it hits about 170 degrees the car starts to misfire and sounds like I have a hoped up cam in it. But as soon as it hits 190 operating temperature it goes away and everything runs perfectly. I just recently put headers on the car making it full 3" exhaust that's when the engine light started coming on. DO I need a tune for full exhaust if that's even the problem? Any help would be appreciated.

[dave6666]

What brand of headers?
What type of joints? Slip or flange?
Where are the O2 sensors located? Single tube or merge collector?
How old are the sensors?

I'm going to go with for now you have a leak upstream of the sensor that closes when things get hot. Or possibly an old sensor.

[GTSACR]

What brand of headers?
What type of joints? Slip or flange?
Where are the O2 sensors located? Single tube or merge collector?
How old are the sensors?

The brand is M&M
The joints are Flange
After breaking in the headers I replaced both 02 sensors
That was bout a 2 months ago

[Phunny]

Something like this is just about impossible to diag via the net and 90% of the shops out there have no idea how to diagnose so it can be a tough fix.

P0300


Code sets when more than 2% (1.5% LEV) misfire rate is measured during two trips, or with 10% T0 30% misfire rate during one trip.
This code also may set with no noticeable misfire if distance between crank sensor & flex plate is too great.


Monitored with Engine running, after successfully performing crank sensor learn.





Possible causes:
ignition coil circuit,
spark plug, wire, or connector,
fuel pump or filter,
injector flush,
EGR system,
injectors or connectors.
Restricted exhaust,
low fuel level,
intake restriction,
PCM power grounds,
EVAP system,
faulty PCM
mechanical Engine problem.

Fuel level sending units have been known to fail indicating 1/8-1/4 tank when tank is actually empty.

This may set code before Engine quits running.


The most common Thing for an actual single cylinder misfire is carbon tracked spark plug & plug wires. Check for even cranking rhythm.

For a rough idle that ISN' t a single cylinder misfire, the EGR valve may be sticking open open, causing excessively high intake air temperature.

At idle the intake manifold vacuum will be low & the EGR tube at the back of the intake manifold will be very hot to the touch. Cams out of time will also cause the same symptoms but the EGR tube will not be hot.








Tips

Fixed It!

BULLETIN LIST (TSB's)
BULLETIN LIST (TSB's) Bulletin list contains subject (sub of bulletin, vehicle that it applies...

Component Tests

Ignition Tests -> Fuel Injection

Operation

System is distributorless ignition, waste spark. Using one ignition coil to produce high voltage for 2 companion cylinders. Primary windings create a magnetic field that when collapsed across secondary windings create the high voltage required to overcome the greatest KV requirement in the secondary (normally the spark plug gap of the cylinder on compression stroke). This high voltage is transmitted from the coil to the spark plugs through spark plug wires.

Location

Best test Location:
Connection on coil.

Component Location:
Two separate coil packs are mounted to to rear of each cylinder head.

1)CYL #1 orientation farthest CYL from flywheel on drivers side.firing order
1-10-9-4-3-6-5-8-7-2

Connector

VIEW:INTO COMPONENT (HARNESS BACKPROBING)
5904
LEFT COIL PACK
1=COIL(-) 1 COIL
2=COIL(+) IGN(+)
3=COIL(-) 4 COIL
4=COIL(-) 5 COIL

VIEW:INTO COMPONENT (HARNESS BACKPROBING)
6379
RIGHT COIL PACK
1=COIL(-) 2 COIL
2=COIL(+) IGN(+)
3=COIL(-) 3 COIL



Tests

Resistance Test

Check primary coil resistance with coil disconnected. Connect test leads: Red=coil(-) Blue=coil(+) IGN(+)



Resistance should be 0.45-0.65 Ω at 70-80°f.

[GTSACR]

Wow Thanks a lot! I just replaced all my spark plugs and wires over this last winter I will start to check my coils next and go from there.

[Charged01ACR]

I'm having the SAME issues with my car. Been getting the (P0300) random cylinder misfire. Car runs great other than the low 1600-2000 rpm range. When I lay into it car runs like a beast.

I have BillyBoat headers, high flow cats and Corsa exhaust. I recently installed new upstream sensors (Denso) and new plugs (Champion RC12ECC with .35" gap)

Sent you a message GTSACR

[MH60M]

Maybe do a smoke test to check for Vac leaks.....maybe a PCM "Hard reset" after that last set of mods.


Mine was a blown out intake gasket causing random misfire and #10 misfire (where the intake manifold gasket was broken/missing. Couldn't see it until I removed the valve cover.

[Charged01ACR]

My intake gasket is new. I had that done when I removed the ROE