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Misfire P0306.. but not all the time.

 
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imlon2
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2001 Chevrolet Impala


PostPosted: Tue Sep 20, 2011 5:04 pm    Post subject: Note Misfire P0306.. but not all the time. Reply with quote

Ok from the start.

I was having an issues with what felt like a fishbite, going up hills, and I could not locate where the problem was accruing from. With no codes. Lot of people suggested it was the TCC. This went on for about 2 months.

Then one morning the car start shaking at a red light, and finally my check engine light started flashing.. Once the light turn green I stepped on the gas, engine light went off, and did not come back on. This was on a Friday Sept 9th.

That next Saturday I bought new plugs (AC Delco radium), and Wires. Car ran great, nice and smooth with no fish bite systems!!

150 miles later It started shacking at a red light, engine light started flashing, and again went off has soon as I hit the gas. Took it to the auto store, and had it scanned the Code P0306. So my first thought was I needed to change my coil packs. They told me before I buy anything go back and test all my wires. Messed around with the wires and the car ran great again.. So I had the code cleared.

Yesterday 300 miles later 450 since the plugs and wires were changed out. I was going to lunch and as soon as I started my car, I could tell the car was misfiring again.. Light started flashing then this time stayed on. Took it back to a auto store, and Code P0306 is back. So while I was at the shop I changed out the Coil pack 3-6, and stated the car back up.. Still misfiring. So I took everything apart and tested the ICM.. that tested out perfect. Put everything back together, drove back to work, car drove horrible. This time I did not rest the code. When I got off work scared to drive home, that the car would not make it home, and it ran great again, great acceleration, no issues at all. And the light has gone off on itís own. Still running great today.

I was going to take it to a shop and have a compression test done, but I would think if it was a compression problem it would do it all the time. This sounds more electrical to me since it does this hit and miss.

Any Ideas?
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98ss
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2002 Chevrolet Impala
2011 Chevrolet Silverado


PostPosted: Tue Sep 20, 2011 6:37 pm    Post subject:   Reply with quote

Your cat could be clogged. I can't remember which cylinder mine threw when the cat went bad, but I know it was not a random misfire.
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nightryder
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2005 Subaru Impreza


PostPosted: Tue Sep 20, 2011 7:17 pm    Post subject:   Reply with quote

Check the electrical connection of the #6 injector and/or try swapping that injector with another one and see if the misfire moves with it.

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topgun
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PostPosted: Tue Sep 20, 2011 8:46 pm    Post subject:  misfire Reply with quote

Prob not the cat. Is it defintely a misfire or possible fuel problem? Pressure regulator maybe? Cool

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Frank3
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PostPosted: Wed Sep 21, 2011 2:40 pm    Post subject:   Reply with quote

My brother had the exact same problem with his car, except it felt like a rolling miss running under load pulling up a hill. I told him to change out the fuel pressure regulator. Hit the nail on the head with that. It started running without a problem immediately after changing it.
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imlon2
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PostPosted: Wed Sep 21, 2011 3:27 pm    Post subject:   Reply with quote

Frank3 wrote:
My brother had the exact same problem with his car, except it felt like a rolling miss running under load pulling up a hill. I told him to change out the fuel pressure regulator. Hit the nail on the head with that. It started running without a problem immediately after changing it.


I like that idea.. If its having fuel issues and #6 is the last cylinder on the rail..

Is there a way to test it?
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Frank3
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PostPosted: Wed Sep 21, 2011 7:28 pm    Post subject:   Reply with quote

imlon2 wrote:
Frank3 wrote:
My brother had the exact same problem with his car, except it felt like a rolling miss running under load pulling up a hill. I told him to change out the fuel pressure regulator. Hit the nail on the head with that. It started running without a problem immediately after changing it.


I like that idea.. If its having fuel issues and #6 is the last cylinder on the rail..

Is there a way to test it?


I can look it up when I find my manual. It dealt with monitoring the fuel pressure on the rail while running and after shutdown to see if and/or how fast the pressure drops. Let me see if I can find it.

Finally found the manual, getting to the right page for Fuel System Diagnosis was another story - page 6-890. Skipping some of the points that require a Tech3 tool to turn on the fuel pump. The procedure also stated to turn the key off, turn off all accessories. Connect a fuel pressure gauge to the fuel rail. Without a tech3, turn the key to ON - Do NOT start the engine. Repeat the key on several times to fully pressurize the rail so you read the highest pressure . The pressure on the gauge should read - 52-59 PSI. The fuel pump usually stops after turning the key to on (no engine running) after a second or two. When the fuel pump finally stops after the fuel pressure maximum pressure is reached and the pressure stabilizes, watch the pressure gauge to make sure the pressure does not drop more than 5 psi in 1 minute. Next with the engine NOT running , relieve the pressure in the rail so it drops to 10 PSI. Monitor the fuel pressure now for 5 minutes, it should not drop more than 2 psi in this time. The rest of the procedure requires a vacuum pump, a scan tool and specialized valves to shut off and isolate different parts of the fuel system. Luckily I found my problem and my brothers before we had to get any deeper into this. On my impala, the fuel pressure would not reach the specified high pressure when the system was pressurized AND would drop to zero on fuel pump shut-off.
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imlon2
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PostPosted: Wed Sep 21, 2011 10:26 pm    Post subject:   Reply with quote

I just got this your message

But I did have the fuel pressure tested and it is at 50. we sat there for a about 10 mins and it did not loose pressure. that was all with the key 'ON" and Not running. should I have turned it off to see if it looses pressure.. Since I just got this message I did not do the rest of the test. Confused
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Frank3
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PostPosted: Thu Sep 22, 2011 7:49 am    Post subject:   Reply with quote

Since the rest of the test uses a vacuum pump to see how the pressure regulator reacts to changing vacuum (simulating a running engine), maybe this is where the problem could sit.
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