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2008 Chevy Suburban P0430 P1175 P3400 P0307 C0561 P0106

2008 Chevy Suburban P0430 P1175 P3400 P0307 C0561 P0106 P0121 P0300 Changed MAP sensor...
2008 Chevy Suburban
P0430
P1175
P3400
P0307
C0561
P0106
P0121
P0300
Changed MAP sensor, still rough idle. Earlier I had a white smoke but it went away. Any ideas?
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Answered in 8 minutes by:
3/21/2018
Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 5,628
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
Verified

P0430 is catalyst efficiency code, doesn't affect the way the engine runs.

P1175 indicates a cylinder to cylinder lean imbalance on one bank. An oddball code, not really meaningful by itself, but in conjunction with other codes, it makes things make sense.

P3400 tells us that the computer is not happy with the engine sensor readings, so it's disabling the cylinder deactivation system.

P0307 is a misfire on cylinder 7, which makes P1175 make more sense.

C0561 is an ABS code basically telling us that the engine computer isn't happy, so we shouldn't expect the traction control system to work, either.

P0106 is a MAP sensor erratic code. The computer is looking at the MAP value, comparing it to a table of expected MAP values, and seeing that they don't line up.

P0121 is a throttle position sensor code of sorts. Again, the computer is looking at the airflow, comparing it to a table, and saying, "Nope."

P0300 is a generic misfire code.

What I take away from this is that the engine runs really badly, primarily misfiring on cylinder 7. I would address this mechanically: why is cylinder 7 misfiring? Spark? Fuel? Compression?

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Customer reply replied 1 month ago
I just ran 50 miles at 80 mph (i35) and it ran great.Only rough while at an idle.

OK, is the check engine light ever flashing?

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When does it flash, at idle, cruising down the road? In gear, in park?

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Customer reply replied 1 month ago
all the time

OK, if it's flashing all the time, then it's misfiring all the time. You just can't feel it at 80mph, the higher RPMs mask the misfire, but the computer can still see it. It's amazingly accurate.

So, back to basics. Have you done anything mechanical to figure out why cylinder 7 is misfiring? Changed the plugs, coil, anything like that?

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Customer reply replied 1 month ago
no, how do you check the coil?

Probably the easiest thing is to just see if it makes spark. With engine running, and with a pair of insulated pliers, remove the spark plug wire from the spark plug, hold it near the cylinder head and see if a spark is jumping out of that wire to ground.

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Customer reply replied 1 month ago
ok going to try it now thank you

Great, I'll be here for awhile, let me know what it's doing.

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You know which one #7 is, yes?

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Customer reply replied 1 month ago
no which one please

#7 is the rearmost cylinder on the driver's side of the engine.

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Customer reply replied 1 month ago
7 has good spark

OK, so the coil is good. Remove the spark plug, get a look at it. Are there any black marks on the end where the wire attaches to it? That would indicate a cracked plug. Swap the plug with another cylinder and see if the misfire follows it (your P0307 would stay there, but if you swapped a bad plug to cylinder 5, you'd suddenly have a P0305, too).

When you pulled the wire off the plug with the engine running, did the engine run any differently at all, or did it sound just the same?

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Customer reply replied 1 month ago
ok working on that, it sounded the same.
Customer reply replied 1 month ago
no black marks but it doe's have black junk on the spark end
Customer reply replied 1 month ago
i was unable to test codes, i dont have a scanner available

Black junk on the spark end, OK! Can you get a picture of that and upload it here?

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Customer reply replied 1 month ago
We cleaned it and put it back. Same results.

Move that plug to another cylinder and see if #7 still misfires (does the engine still run the same when you pull #7 plug wire off).

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Customer reply replied 1 month ago
I read someone had the same problem and it ended being the lifters? I sure hope not .

It's possible. We're playing a process of elimination before we get down to that.

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Customer reply replied 1 month ago
The engine changed very little when we removed the plug wire.
Customer reply replied 1 month ago
I will have a to checked the missfire codes tomorrow.

OK. Your homework is to get a compression tester for tomorrow as well, and do a compression test across all cylinders. Do you know how to do that?

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Customer reply replied 1 month ago
we have a friend bringing one and a scanner tomorrow. He knows how.
Customer reply replied 1 month ago
Thank you sooooo much! I will touch base with you tomorrow.

Look forward to it!

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Customer reply replied 1 month ago
low compression in #7

OK, that's obviously a problem.

No matter how you slice it, the engine is coming apart to fix it.

Please take a moment to rate my answers by clicking on the stars at the top of the page, that's how I get compensated. If you need more help, just let me know, I am happy to follow up.

Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 5,628
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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