P0300 and loss of power

[daniel0]

Need help here on how to best diagnose problem before spending a bunch of money on replacing working spark-plugs, coils, pumps etc.

I only get a P300 no other code.

Symptoms, part 1:
- Car shaking at low RPM, using Neutral and revving at intersections prevented the feeling of engine stalling.
- Loss of power on low end. - very slow to start moving, flooring the gas did very little, but at one point kicks in and jerks the car. I was going down & up a hill, and with 100kmh at the bottom, I got to about 30kmh before I cleared the hill - no power

I've recently taken the EGR off and noticed it was filthy. The valve was not retracting after pressing the spring down, after a few hours of work involved with that, I took it for a rip and it seemed just fine. Next day worked fine on a relatively short trip. The third day, out on the highway for 15 minutes, and I'm noticing power issue again. The difference is, that the rough low rpm issue is gone, but I get the CEL flashing (common with p030*) when I'm trying to accelerate and am experiencing the power loss, and jerking.

After getting home, I checked the EGR valve first (which much quicker the second time) and it was fine.
I saw this youtube video http://www.youtube.com/watch?v=9b_AGBtDdGE when I started my search, according to which the coils are a frequent cause, so I did a quick check to verify that it is not an ignition problem. I had the engine running and unplugged the coils to see/hear a change in the engine, which worked - the engine sputtered when either coil was removed. I wasn't able to test under load, but the ignition problem doesn't seem to coincide with the symptoms I'm having - or am I wrong?

One thing that I also should point out that the day that this problem occoured, I had just filled up on an almost completely empty tank of gas. Car started just fine after that, I traveled about 15km, parked the car, and that's when the problem started, so I'm leaning toward a clogged fuel filter and that's what I'll try and check tomorrow. Any way of telling if it is just bad gas? If the fuel filter turns out to be OK, what possible causes can safely I eliminate based on my symptoms?


P0300 possible causes according to service manual:

CKP sensor malfunction
CMP sensor malfunction
Ignition coil malfunction
High-tension lead malfunction
MAF sensor contamination
Excess air suction in intake-air system (between MAF sensor and dynamic chamber)
Fuel pump malfunction
Fuel pressure regulator malfunction
Fuel line clogged
Fuel filter clogged
Fuel leakage in fuel line
Purge control solenoid valve malfunction
PCV valve malfunction
EGR valve malfunction
Vacuum hoses damages or improper connection
Related connector and terminal malfunction
Related wiring harness malfunction
Poor fuel quality

 

[daniel0]

I looked at the pump, and gave it a little clean by running water on the filter. It didn't look dirty but the texture did feel a bit rocky which got better after cleaning it for a bit. Despite that, I don't think that was the issue. After putting it back and cranking it for a minute or two the engine did start, but it was rough, and the roughness never went away. I got a flashing CEL in park, checked code and it was P0300 again. I popped the hood and found that one of the coils is dead.

I'm surprised because, I did the same check before I did the pump, and the engine wasn't doing the same thing (it would be rough when unplugging one, but wouldn't die, whereas now it dies or does nothing)

Is it possible that the work I did on the pump somehow affected this? I can't imagine how that would be the case other than maybe that it stood in the cold for two days and the long rough start caused a failing coil to die.

 

[915_P5]

i had the same problem on my car and silverado, turned out to be a bad batch of gas at a local gas station. so that could be it that you stated filling up, i know gas is very high right now but maybe the lowest price isn't always the best way to go.

 

[kms1990]

yeah im with 915_p5 try to siphon that gas out as much as possible and look at color while doing it if its rusty colored or not almost clear its contaminated. notice the smell too if it doesnt smell like that distinct gas smell or its not strong it maybe watered down or have another issue. i would siphon it out and get some good gas froma trusted station in your area i always use the qt in my town their gas gives me consistent gas mileage and seems clean. you need to find that trusty station and stick with it until you get a reason not to(other than a few cents in price difference) i would try new gas before buying a coil and see,if no change then coil would be next in line

 

[hornsfan10609]

Sounds like a bad coil pack, it is possible for a bad coil to fire fine at idle and misfire like crazy under load.

 

[kms1990]

yeah,true because at idle its just sendin slow spark but at speed its sending it much faster

 

[daniel0]

Thanks for the comments,

I picked up a coil for $70 replaced it and it seems to be worked fine. Took it out for a rip and had no issues (other than the winter tires showing signs of being worn)

Was good to clean the EGR valve, chased a red herring with the gas pump, but ultimately the cause was what the aforementioned video said what the most likely cause is.

In my defense, I did test the coils under (some) load, where I held the brake and pressed the gas, but once the coil completely failed a few days later it was easy to diagnose

 

[mtnbiker26]

I had the P0300 code at around 115K miles and folks on here suggested it was failing coil packs or a cracked air intake tube (after the MAF) and that both were fairly common problems for the P5. The air intake tube was all dried out and full of cracks so I replaced it but still had the problem. I then replaced the coil packs and the problem went away.