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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a missfire under load on cyl 1 and 4 all primary ans

Customer Question

Customer: i have a missfire under load on cyl 1 and 4 all primary ans secondary ignition has been replaced and compression checked,known good injector tried same results only 1 and 4 missfire only after 1500 rpm
JA: Thanks. Can you give me any more details about your issue?
Customer: idles with no missfire engine has 160 psi on compression on all cyl we also shimmed crank
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Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

Good morning,

What engine do you have?

I have a feeling I know what is wrong already.

With all the swapping you have done so far, does it have injector pulse tested with a noid light on those two cylinders?


Customer: replied 1 year ago.
4.3 and we also changed injector same 1 and 4 missfire
Customer: replied 1 year ago.
the only engine a 2003 blazer has is a 4.3
Customer: replied 1 year ago.
had i said trailblazer different
Customer: replied 1 year ago.
what are you thinking gary?
Expert:  Gary replied 1 year ago.

Hi there,

I was thinking you might have had a AFM LS 6.0 litre.

With your V6, what do you mean by "shimmed crank"?

Do you mean the sensor?


1 and 4 are 360 apart, could be something wrong at the sensor face or the reluctor wheel on the crank.


Customer: replied 1 year ago.
listen dude you dont even know what engines are in your chevy vehicles--what planet are you from a 6/0 litre in a blazer? im pretty sure i know more about this vehicle than you so i am not interested in your help if you knew a 2003 blazer you would know the answer to your injector pulse question--no more help as you are not a gm tech.
Expert:  Gary replied 1 year ago.

You did not state what engine you had in the first place.

I know your engine is a V6 after you said which car you have.

I have seen dropping multiple cylinders in LS engines where the fault IS mechanical.

I have been with GM Holden all my working life.

Cylinders 1 and 4 in your firing order are 360 degrees apart.

So if you can't answer my question to you about why you "shimmed the crank", I think you mean the sensor, don't know.

Did you look at the reluctor wheel while the sensor was out, maybe it has a bent tooth?