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Truck misfireing even after a complete tune-up


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Gtb1972
New User

Sep 30, 2011, 11:10 PM

Post #1 of 4 (2134 views)
post icon Truck misfireing even after a complete tune-up Sign In

2002 Chevy Trailblazer
2WD/4.2l engine
172,000 miles

My truck is started running really rough. Took it to Autozone and they did a diagnostic test and all they told me was it was misfiring. I had new spark plugs put in as well as wires. It still was like it had no power. Did another diagnostic and it gave a code 304 and i was told it was the #4 coil so i replaced it. It seems to be running a little better but my engine light is flashing and when you give it gas it the engine sounds like it not getting gas and it fighting to stay running. Also there is a really distinct smell when you turn off the truck. Not a strong smell of gas but smells like some type of gas exhaust.

Does anyone have any ideas on what my issue is before i keep fixing things that are not fixing my problem all together. Obviously it needed a tune-up but that done so were do i go from here? I may be contacted by email at personal info deleted




Thank you
Gregg Brymer

(This post was edited by Hammer Time on Oct 1, 2011, 3:12 AM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Oct 1, 2011, 3:16 AM

Post #2 of 4 (2103 views)
Re: Truck misfireing even after a complete tune-up Sign In

Autozone can read stored trouble codes. That is far from anything that can be called a diagnostic. There is no code that tells you that any part is defective. It merely tells you what area it saw a problem. It takes an actual technician to diagnose and determine what may have caused the issue and believe me, the people at Autozone are not technicians. The PO304 simply means misfire in cylinder 4. The cause still to be determined.



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Discretesignals
Ultimate Carjunky / Moderator
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Oct 1, 2011, 9:02 AM

Post #3 of 4 (2091 views)
Re: Truck misfireing even after a complete tune-up Sign In

HT has made an excellent point.

Now you need find out what is causing #4 to miss. First, you should run a compression test, seeing how the engine has high mileage. Let us know what the readings are.





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re-tired
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Oct 1, 2011, 7:34 PM

Post #4 of 4 (2077 views)
Re: Truck misfireing even after a complete tune-up Sign In

You seem to have the ign covered. If the compression test comes out ok try swapping #4 inj with another cyln. If problem follows inj .you got it.


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