rbsurfer

P0300 random/multiple misfire please help Idk what to do checked all plug wires and there all connected. Any ideas

RRsV

http://www.google.com/search?q=cts-v...ient=firefox-a

whisler151

I had this code and it turned out to be a spun rod bearing. Once it got to the point that the CEL would flash, we started digging into the bottom half and found the issue.

I hope yours is something simple. How old are the spark plugs and wires? Do you have a cam or any power adders?

ITSAV

iTrader: (1)

I always heard that a P0300 is not really a horrible code to have, and is fairly common on tuned cars....I seemed to get it every once in a while it seems...

heavymetals

iTrader: (3)

On a dark place pop the hood and see if you get any flashover from any coil.

Could be a crack in a coil.

Check the plug gaps.

Stippy17

iTrader: (5)

I OCCASIONALLY get that code in my H/C Trans Am. Erase it and it doesn't come back for months.

rbsurfer

My friends uncle races vettes so he took all brand new coils wires plugs and still misfired on cylinders 4,6,8 he thinks its a bad o2 sensor but ill know today

heavymetals

iTrader: (3)

A loopy cam with cold oil can trip a miss fire.

A bad O2 sensor won't do anything except trip lean codes.

rbsurfer

It was a bad o2 bank 2 sensor 1 (passenger side, up stream sensor)

1BADCTS

iTrader: (17)

It can cause a misfire if it's throwing off the a/f enough to cause premature or no fire. And it makes sense that it would then be random, not consistently one cylinder.

heavymetals

iTrader: (3)

I guess so!

Won't be the first time I have been wrong.

I would have thought it would trip a lean code before it would cause a/f problems to the point of miss firing.

St Louis SHO

iTrader: (3)

I see them all the time, just more on the 5.3 & 6.0l truck engines. The o2 shorts internally, and causes it to be fat as ****, kills the plugs, then you can figure it out from there.

4door-6speed

I'm having an issue like this too.
I was at Gingerman a week ago Sat. Had the random misfire code followed by a bank 1 lean code. Reset the codes and saw the bank 1 lean code come back on Sunday. Then again on the ride home. Reset again and the bank 1 lean code came on again last week. Going for new plugs this weekend. What is the best way to test the o2 sensor? Or should I just change it?
TIA

DMM

Yes! Although it will also cause rich, high voltage, low voltage, circuit performance, and cross count DTC's as well.

Unlikely. I have seen Long Term fuel trims at -100 and it still did not cause a miss. A vacuum leak is usually the only thing that will cause a lean misfire unless the fuel injector data is way off in the tune.

Shorted - an abbreviated term to indicate that an electrical circuit is traveling along an unintended path.

Shorts to what? Voltage? Ground? The median 02 sensor voltage is .450v, if it stays over or under this baseline value for too long it will set a crosscount DTC (this sets if the 02 sens. voltage does not cross this .450 threshold a specified number of times within a set duration) and will be disregarded. The 02 sensor itself generates electricity based upon the difference in oxygen content between the atmosphere and the exhaust.

The PCM averages the AFR by crossing the .450v threshold which translates into rich/lean. The sensors can get poisoned, read lazy (shooting way over like .820v then to .270v rather than staying closer to the .450 baseline), or just be dead...although most times it is indicative of another problem that has manifested (ie., vacuum leak, leaking injector, worn valve seals/guides, etc).

It would take a lot of fuel to cause a miss (enough to smell and know there was a problem), and I wouldn't think there would be that much adjustability in the fuel trims alone to allow that much fueling unless the tune had been altered. I guess if there was a rich condition for long enough (caused by a leaking injector, regulator, etc) the sensor could get poisoned and read lean over time, inducing the higher fuel trims in addition to the unmetered fuel, but that's what I would be looking for.

Maybe you're speaking in vague generalized terms when you say "shorted", although it is not actually shorted. Many people say something is "shorted" to mean its fucked up when it's not really "shorted" to anything. It really bothers the **** out of me when people describe something as "shorted" when its actually open. It's a peeve of mine.

There are different types of "miss fire's", they manifest themselves under different conditions and feel different. An ignition miss will be much more pronounced under a heavy load than that of a lean miss...something you have to get a feel for over time.

I posted to a thread a while back about diagnosing a miss and what to look for...I'll try to find that and link it here.

Edit: Here it is....https://ls1tech.com/forums/generatio...ion-issue.html

St Louis SHO

iTrader: (3)

Internally shorted to voltage (sensor itself). Seen the last 2 at 1v, which is MAX as to what a scan tool will show. Sorry to not describe it as well as I should have.

rbsurfer

Pretty much swap coils and wires and plugs and if still getting the code check fuel trim mine was +50a and that gave it away it was the sensor

NHRA140X

After some serious trouble shooting I had to do a Crank Sensor relearn , That seemed to do, however that is only one in a long list of fixes

MN_V

iTrader: (5)

When I put in a new ECU it gave an intermittent P0300 with no driveability issues. Doing the CKP crank relearn solved it. Dealer tech said it would not fix it... that there's a code just for that... but it has to be way off to get that code... don't always listen to dealers no matter how cocky they sound. Had an independent place do it with the Snap On scanner