2003 Sebring P0300

[srplowman]

I have a sebring that is having issues with a random misfire. Customer states that it occured suddenly after starting vehicle and driving it. It seems very minor when in park at idle. When put into drive this thing will act up and the entire car will shake. I've check for vacuum leaks. My gauge will read 15" at idle and will drop to about 11 or 12" when put into gear. I cannot find a leak and I'm very frustrated! can anyone point me in a better direction?

[hefaus]

Frustrated

Is it possible to have a broken valve spring..Lower intake leak.Is the timing there ....Just some thoughts for low vaccum with no apparent leaks. How are the fuel trims..keep Smiling

[Modis500]

Another hint for looking for a broken spring is an erratic needle on your vacuum gauge as the spring isn't working and the pressure differential is going into the weak hole. I know this is obvious to most of us, but when a car is kicking your butt, sometimes frustration makes us overlook the obvious.

[eightdancinghammers]

rough idle/misfire with low vacuum and no leaks can indicate a stuck open egr. if fuel trims are not lean or especially if they indicate rich you might check this out. most chryslers form this era were "speed density" fuel injection so like a carburetor they go rich with a low vacuum signal.

[Crusty]

Anything that upsets the air/fuel ratio or the ignition source can cause misfires. A weak coil, a dirty injector, a vacuum leak, a worn out plug, a plug with carbon tracking either inside or outside the hole, etc. etc. A broken valve spring can be one of several causes.
The vacuum of 15" at idle and then 11 or 12" in gear seems low. This could be either a symptom or a cause. Is it a stable vacuum or is it "bouncing"??

Check to see if this vehicle is capable of setting individual misfire codes such as P0301, P0302, P0303, etc. Not all vehicles will show individual misfire codes. If this vehicle IS capable of setting individual misfire codes, the P0300 indicates something common to all cylinders.

Try a cranking load test (electrically) to indicate cylinder capability and even go back to an old fashioned static compression test (with a pressure gauge).
Verify fuel pressure, flow and fuel QUALITY. Verify spark output to all cylinders as well. As mentioned the old fashioned vacuum gauge can also be an indicator of bad engine breathing.

Try creating a rich mixture and then create an extreme vacuum leak and watch the oxygen sensors for their capability and also watch the fuel trim changes, both short term and long term fuel trims.

[srplowman]

The needle on the vacuum gauge was steady and not erratic. I know it has a bad O2 sensor on it right now (bank 1 S2) but I've never seen an O2 sensor cause such a misfire. I just installed a timing belt a component kit earlier this week. The belt that was taken off was pretty bad and the hydraulic tensioner was barley holding any tension. Before timimg belt install the engine had a knocking type of noise due to the tensioner no longer doing its job. After the timing belt install the engine sounded great and ran a ton better! An oil change was done with the timing belt job. The next day I replaced the O2 sensor with a bosch universal part. I've never had issues with using a universal O2 sensor before. I ran the car with the new O2 sensor unplugged and made no difference. I even tried another sensor with no success. As far as the oil change I purchased a drive works filter. Could something like a crappy oil filter be at some fault?

[srplowman]

And with the EGR valve I have taken that off and inspected both the part and EGR passages for any potential carbon blockage and didn't see anything. I had also ran the car without the EGR installed but with the holes blocked where the EGR would bolt onto the intake. And of course no change!

[hefaus]

troubles

Guessing the issue should be about low vacuum.Is it possible the timing belt is out...That sure would cause low vacuum issues.Just a thought.Keep smiling.

[Crusty]

First of all I personally have no faith in ANY Bosch oxygen sensors.....too many examples to count where they were defective.
Secondly after you replace any components or even change the oil, you need to clear and RESET ADAPTIVES otherwise the vehicle will run in the previously learned fuel delivery.
Third, I would doubt that an oil filter would have any affect but I also don't recognize that oil filter name (probably not the root cause)
Fourthly, yes, as Hefaus says, the timing belt could be out and even one tooth on one sprocket could cause low manifold vacuum. We still don't know if the low manifold vacuum is a symptom or a cause.
--TEST the fuel pressure and do an injector balance test. TEST the spark output and verify the proper voltage capability of the coils.
Move on from there.

[srplowman]

One thing that doesn't make much sense to me is that if it was a timing belt issue, why would it take 2 days before it would act up? I can agree with the timing belt theory just don't know why it would take that long for the problem to surface.

[Crusty]

If that's the case, I don't think it's the timing belt. Sometimes there is an accumulation of lots of problems. They just need to be peeled away like an onion, one layer at a time. Start with basics, check, test, and either repair or move on to the next test if you don't find anything.
Once you have found and repaired something, recheck and retest as if it was a new problem and don't let hindsight narrow your focus.

I'm still suspicious of a fuel delivery problem. That's why I keep mentioning fuel pressure, fuel trim, oxygen sensor response, etc.
After each step, reset the adaptives as well as clearing codes after you check for "pending" codes and/or check the mode-$06 data.
If you hold the throttle at about 1500 rpm, what vacuum do you get??
Then snap the throttle to Wide open and watch it drop, then when the vacuum recovers what is the maximum you see. It should be well over 20-inches of mercury. Does it "sound" right when you go to WOT-?? as if it's breathing properly-??? Check for a restricted exhaust. Wouldn't be the first time a pooched O2 sensor ignored too long has melted down a converter which then restricts the exhaust and the engine can't "breathe"