P0300 Code In Idle

[sheamus]

Hello Everybody


I keep getting the P0300 Random Misfire Code in Idle. I checked the plugs and wires. They are good. Iam wondering what it could be. Heres the log file. Thank you.

[joecar]

Hi Sheamus,

Misfire probable causes:
- insufficient spark,
- insufficient fuel,
- gross overfueling (leaky injector, leaky regulator),
- manifold airleaks,
- bad O2 sensors,
- bad MAF,
- compression loss,
- coolant leaking into cylinders,
- bad connection to battery,
- bad connection to ground,
- intermittent loss of CKP signal.

You say only you see P0300 only at idle, that may narrow it down some...

What about under load, do you get any misfires or misfire codes while under load...?

What plug wires do you have...?
What plugs...?
How did you inspect the wires and plugs...?
Are the plug wires making good connection with the plugs...?
When did this start to show up...?

[sheamus]

Thanks for replying joe.

Msd 8.5 Plugs
Ngk Tr55 Plugs

The wiring on the plugs was good. No burns on the outside edges. The Boots were good. The conections were still tight.

Plugs were clean. Not burnt or coroded/discolored.

All the grounds are tight. I cleaned off the paint and cleaned the ends. I checked the ground behind the drivers side head. I didnt take it off. But it was tight.

The battery and alternator connections are all good. Battery and alternator are good

Iam still new to tuning and efi live.

How can i check if the MAF and 02's are bad?

with Efi Live or just disconnecting them?

Also should i disconnect the fuel injectors and throw an ohm meter on them? What should the ohms be for stock injectors. As for the regulator. I have a fuel pressure guage installed in my car. Most of the time she is steady at 58 psi. On some cold start ups she is at 48 psi

Iam gonna borrow a vacuum guage. What pressure should the vacuum be at?


Thanks again for your time Joe

[sheamus]

and yes i get the code underload and what is a ckp signal loss?

[joecar]

Are yo getting any DTC's besides P0300-P0308...?

If you want, ohm these:
- each spark plug wire while bending/unbending), MSD SC's are ~30 ohms, 8.5's are IDK what ohms;
- each injector ~12 ohms;

If pressure is steady at 58 psi then regulator is ok;
also check pressure by cycling key on/off several times (with engine off), pressure should hold steady close to 50+ psi for about 1 minute... if not then either the injectors are leaking, or the regulator is leaking back into the tank.

Check for voltage drop between battery negative terminal and each engine ground, there should be no more than 0.2V.

Check for voltage drop between battery positive terminal and each of alternator and each fuse.

Log MAF, DYNAIR, MAP, HO2S11, HO2S21, HO2S12, HO2S22, LONGFT1, LONGFT2, SHORTFT1, SHORTFT2, and post the log here... by looking at the log we may be able to see if MAF and O2's are working.

At idle with stock cam, ~35kPa MAP = ~5psi MAP = ~10" MAP = ~20" vacuum...
Logging MAP should show 35kPa while vac gauge shows 20" vac
(MANVAC = BARO - MAP).

Can also pressure test cooling system to see if it is leaking (into combustion chamber);
block test kit checks for chemical presence of combustion gases in coolant;

Also check that your EGR valve is not stuck open.

If you still can't find/fix the misfire, you may have to do a leakdown test to check that all cylinders are ~equal and above a minimum.

CKP is the crank position sensor signal... if you lose this the PCM can't fire the injectors/plugs... if you loses this intermitently it feels like misfires... if you lose this your log will show RPM dropping to zero (as would your tach gauge on your IPC/dash).

Either:
- not getting enough fuel;
- not getting enough spark;
- not getting enough compression;
- not getting enough air;

Each of those has a variety of reasons (mechanical, electrical, etc).

[joecar]

I forgot what car you have...

[joecar]

Diagnostic for P0300 (attached) is a starting point...

[sheamus]

2001 z28 4l60e camaro. Iam gonna get on it tomorrow. Your the man joe. thanks

[sheamus]

Here's the log files for the MAF and 02 Sensor's

[joecar]

MAF and O2's seem to be working.

You logged MAP [V], instead log the MAP [kPa]... i.e. the other MAP pid.

(You can log more pids:
RPM
EQIVRATIO or AFR
DYNCYLAIR_DMA or DYNCYLAIR
TP
ECT
IAT
SPARKAVD
KR
GEAR
TCCMODE
VSS

If you're tuning, keep the pid channel count to 24 or less.)