Oh Gregg, P0301 - Chevy HHR Network


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Old 08-04-2017, 09:01 AM   #1
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Oh Gregg, P0301

So I have this odd issue. Its been going on all year, and first happened a few months ago and then just happened this past Wednesday. To date, it has only occurred the two times.

Its a cylinder 1 misfire, but it only occurs under heavy acceleration (3/4 throttle and above) and it will sometimes happen sometimes not. The code is never set, it is only stored as pending, and goes away after a drive cycle or two. to stop the misfire I have to shut the car down and restart. There are ZERO -problems after restart, like nothing happened.... I already replaced all spark plugs and the coil on that cylinder.

Data log revealed no issues with fuel trim, cat temp, O2 sensors, or the like. I have no clue what it could be. My dad suggested a bad ground perhaps? where is the ground located for the injectors,.... if it exists.

A/F ratio is perfect as well. I attached some pics showing the live data taken the next day. First pic is just cruising and the second is a screenshot right after a short acceleration at a little over half throttle.

I am at a loss.After the misfired occurs the car seems to go into a limp mode where it wont rev past 2500 RPM, which I found when trying to move over tto the side of the highway to pull on a side street.

Any advice on where I might want to look next Gregg runs great otherwise and like I said I have even tried testing it before and it just doesn't happen. Hell, I changed the plugs and coil pack right after the first instance, took the car out, warmed him up, and floored it for the first time ever and it didn't happen.




Last edited by RJ_RS_SS_350; 08-04-2017 at 10:55 AM. Reason: Easier to read
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Old 08-04-2017, 09:48 AM   #2
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My guess is either you got some crap in the fuel rail or your fuel pump is casting hints.
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Old 08-04-2017, 12:04 PM   #3
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I was thinking the same, but wouldn't that typically give a problem with random misfire and not cylinder specific?
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Old 08-04-2017, 12:08 PM   #4
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I wonder, how does the computer detect the misfire? What sensors are involved?
There must be a knock sensor to control the VVT, I would guess.
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Old 08-04-2017, 12:26 PM   #5
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Quote:
Originally Posted by Conax View Post
I wonder, how does the computer detect the misfire? What sensors are involved?
There must be a knock sensor to control the VVT, I would guess.
I would think it would be the upstream oxygen sensor? I don't think a misfire causes a knock.
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Old 08-04-2017, 12:28 PM   #6
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Quote:
Originally Posted by aradmahogany View Post
I was thinking the same, but wouldn't that typically give a problem with random misfire and not cylinder specific?
Is #1 injector at the 'end of the line'? Where crud would accumulate?
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Old 08-04-2017, 12:30 PM   #7
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I would think it would be the upstream oxygen sensor.
The O2's sniff all the exhaust, not just #1. Maybe they are sampled so often and so quickly the ECM can calculate which one is the culprit?
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Old 08-04-2017, 12:31 PM   #8
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This sounds like a job for a can of SeaFoam in the gas..
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Old 08-04-2017, 12:33 PM   #9
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The O2's sniff all the exhaust, not just #1. Maybe they are sampled so often and so quickly the ECM can calculate which one is the culprit?
That's my thought behind the guess.
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Old 08-04-2017, 12:34 PM   #10
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The knock sensor(s?) may be listening for the normal thumping of each cylinder and a knock as well. When the thump doesn't appear at all, it calls a misfire.
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