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1996 impala ss cylinder 6 misfire

Customer Question
1996 impala ss cylinder 6 misfire
Submitted: 1 year ago.Category: Chevy
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Answered in 3 minutes by:
1/31/2016
Chevy Mechanic: Tool Hut, ASE Certified Technician replied 1 year ago
Tool Hut
Tool Hut, ASE Certified Technician
Category: Chevy
Satisfied Customers: 551
Experience: Owner of a mobile diagnostics company assisting auto technicians with difficult vehicles
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Do you have a vacuum gauge?

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Customer reply replied 1 year ago

we was working on this a few weeks ago and i gave up to finish my jeep. no i am back to finish.

i already did vacuum, compression, leak down, and switched injectors

Chevy Mechanic: Tool Hut, ASE Certified Technician replied 1 year ago

What is your vacuum reading and is it steady?

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Chevy Mechanic: Tool Hut, ASE Certified Technician replied 1 year ago

Do you have a noid light to confirm that the PCM is opening injector?

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Customer reply replied 1 year ago

15psi steady and yes checked noid light on injector and spark plug

Chevy Mechanic: Tool Hut, ASE Certified Technician replied 1 year ago

MY suspicion is that it is mechanical in nature.

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Customer reply replied 1 year ago

2 things

it only happens after car runs for 5-10 min

ant the last thing i did before i got this code was take timing cover off to change gasket and seals

Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 1 year ago
JOHN aka Eauto
JOHN aka Eauto, The Car Guy
Category: Chevy
Satisfied Customers: 16,560
Experience: ase tech
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has a compression or leak down test been performed?

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Customer reply replied 1 year ago

both and good

Customer reply replied 1 year ago

yes

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago
Gary
Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1,255
Experience: Senior Technician
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Hello Sal,

Does your engine have AFM or DOD, V8 runs in 4 cylinder mode?

If so, cylinder 6 is an AFM cylinder and probably has a rotated valve lifter.

Gary

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Customer reply replied 1 year ago

they do that in 1996?

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Not sure if your has it, but you have exhausted all other testing paths.

Compression will test average, valves operate while cranking.

Can you run the engine with the valve cover off please?

You are the second customer I have had today with same problem.

Gary

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Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

GM started this concept in 1981.

Gary

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Customer reply replied 1 year ago

i just took it for a ride to get code to come back on and do leak down test while hot.

when i hook air up and cran engine over by hand there is no air coming out either valve??

now code is random misfire

will take valve cover off tomorrow

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Hi Sal,

So you had a P0306 (Cylinder 6 misfire) and now you have P0300 (Engine misfire detected).

Your engine is a V8, isn't it?

This code was not present prior to taking the timing cover off, is that correct?

Did you drop some gasket residue down the intake ports by accident?

Gary

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Customer reply replied 1 year ago

yep yep.

how bout opti vent check valve being clogged

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Is the P0306 definitely gone now, and is only a P0300?

I would say you possibly had some residue under some valve seats and it is clearing out now, it may come good.

Did you have the intake manifold off as well as the timing cover?

Gary

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Customer reply replied 1 year ago

No. I believe that check valve closer to the optispark I put on backwards I just drove it around for 20 minutes no check engine light so far

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Ok, it may have been a combination of things, but ultimately was still a vacuum leak, hence the last code of P0300, versus the cylinder 6 specific of P0306.

Great you found that with the check valve.

Is it a good system, but fraught with problems as they age.

Hope you all good now.

Go out and give her a good run now.

Hopefully good from cold start as well.

Gary

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Customer reply replied 1 year ago

well i was wrong went to drive to work today after 5 min p0300.

left it home all day cleared codes let it run til code came back now p0306

idling between 620-680rpm

any chance new opti is damaged or i ruined it

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Hi Sal,

If this only happens once it warms up, does the misfire stay there while it is idling?

We need to be sure whether the injector pulse is dropping out, the spark is dropping out, or it does have a valve not operating.

What does the spark plug look like after it is has been missing like this?

Gary

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Customer reply replied 1 year ago

black.

exhaust is sucking in air on both sides. valves?

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Yes, sounds like exhaust valve not seating.

Black from fuel, but poor combustion due to lack of compression.

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Customer reply replied 1 year ago

taking a break from this for a few days to finish my jeep.

then i will resume the repair

Chevy Mechanic: Gary, ASE Certified Technician replied 1 year ago

Ok.

I hope my advice has been of assistance to you.

Wishing you all the best.

Regards

Gary

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