P0300 misfire gradually getting worse

[Cammy98]

Alright so starting at the beginning of the year I noticed (typically at operating temperature and above) at moderate acceleration the car would misfire slightly and quickly. Typically from a stop to go I would feel a small miss.

Fast forward to present day the car still shows that misfire but has been progressively getting worse. The misfire now happens at idle and at almost any type of acceleration. If I accelerate very lightly the car runs smoothly (but thats been going away as the condition gets worse). At highway speeds the car runs very smooth unless I push down to accelerate. During acceleration it feels like im running on 4 or 5 cylinders (if you've ever felt that before). There is power there but it is definitely lacking.

Im throwing a P0300 and of course its blinking when I accelerate. Only recently (past week) has the idle gotten rough (sputtering).

I've replaced all wires (no touching on headers), all plugs and fuel filter. Im getting the ICM checked out tomorrow but I cant imagine that thing going out again, im already on my 4th one. Where else should I go from here? fuel pressure maybe?

[FIREBIRDV6RAGE]

Re: P0300 misfire gradually getting worse

is the misfire on different cylinders every time or do you feel its on the same ones.

[Gutless]

Re: P0300 misfire gradually getting worse

I am having the SAME issue. It started when I ran at the track this September. Only showed up as a misfire, usually a P300 but occasionally a P301 witch is a cylinder 1 misfire. I changed plugs, checked wires, changed coil, didnt change anything. I got mad and deleted the code from the ECM.

It has gotten worse for me too. Starts great, idles fine, drives fine when cold, but at hot partial throttle accel it deffinitly misses, boost guage flutters, bucks, down on power. It also had a really bad knocking sound and was pulling 12+ degrees of timing so I just unplugged the knock sensors.

I have attributed the knocking to low oil pressure since for some reason I have slowly lost oil pressure since that time when the P300 code racing. I assumed it killed a roller lifter or something and it only pumps up the lifter when the oil is thick and cold.

Sometimes it misses, sometimes it doesnt. Usually, when it isnt rattling it isnt missing. I assumed the p300 code was false. The real miss is because the lifter goes flat and misses since the valve doesnt open. Maybe I have to rethink that?

I was told that it COULD be an injector but that doesnt answer all the questions.

Im taking my engine out and apart in a month or so. Could let you know then what I find, I dont know.

[FIREBIRDV6RAGE]

Re: P0300 misfire gradually getting worse

if your only running on 4 cylinders then it could be cylinders (1 and 4)(2 and 5)(3 and 6) any of those pair could be the mis fires. if it is like that then track down which pair it is and you have replace the wires so that out the equation. it could be a faulty coil. carbon build up . if you have anymore info i could hep you track it down . if its a random misfire then its Crankshaft Position System Variation if this is not stored right in the pcm then it could throw the following code p0300.this happens when any thing is worked on such as

PCM replacement or reprogramming
Engine replacement
Crankshaft replacement
Crankshaft balancer replacement
Crankshaft position sensor replacement
Any engine repairs which disturbs crankshaft/harmonic balancer to crankshaft position sensor relationship.
it could be System grounds. Ensure all connections are clean and properly tightened.
Mass air flow sensor. A Mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor.
Loss of EBCM/EBTCM Serial Data. If the PCM stops receiving data from the EBCM/EBTCM, DTC P0300 can set due to a loss of rough road data..
Air Induction System. Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Inspect for disconnected or damaged vacuum hoses, incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces.
Fuel Pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition.

[Cammy98]

Re: P0300 misfire gradually getting worse

FIREBIRDV6RAGE - I can't really tell it just feels like a general bogged down acceleration and I figured with the P0300 code its not specific (at least to just one) faulty coil is definitely a possibility.

Also no major work has been done within the past year or two. Just routine maintenance at most an O2 sensor was replaced but that was back in July of 2012 and no problems since then.

To add on to this i've had similar problems like this before and it usually ended up being a plug wire melted on the header (sometimes two). This is why im getting the ICM checked out tomorrow along with the coils. I dont have any tools to get the ohm readings so if the ICM checks out ok i'll replace all 3 coils. But from my experience usually when its a coil problem the misfire is present no matter how hard im accelerating or what the operating temp is.

Fuel pressure was at about 46 idle and 40-42 with rev.

I'll also stop and get something to clean the MAF sensor with...

EDIT: I know i said it FEELS like im running on 4 but thats just how it feels/sounds. But a misfire is definitely there and apparantely on 2+ cylinders..

[FIREBIRDV6RAGE]

Re: P0300 misfire gradually getting worse

well just let me know what you find out man , maybe i could help out what it is if you cant find it

[Cammy98]

Re: P0300 misfire gradually getting worse

Alright so icm and coils checked out. Cleaned the MAF even ran it without. misfire still there. Taking it in today so I'll update again.

[ssms5411]

Re: P0300 misfire gradually getting worse

Could be a fuel injector.

[GaryDoug]

Re: P0300 misfire gradually getting worse

A friend had the same issue. The problem was an intermittent coil. It registered as P0300 (multiple) because 2 plugs shared the same coil, of course.

His scanning software (which I wrote) could tell him the misfire counts on each cylinder and when he swapped coils around, the misfires moved to the new cylinders. The guys at A-zone had told him all his coils were good.