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i was driving the other day and my check engine light starting flashing on my 02 deville. then when i got off the highway it started to basically misfire. it drives fine but at red lights you can really feel it. i checked and there were 3 codes. p0300, po300 again, and p1153 (o2 sensor). did i blow a head gasket? it has a coolant leak somewhere by the alternator i don't know exactly where for sure. 1-10 how hard would it be to replace the gasket? btw there is no coolant in the oil and no oil in the coolant that i can see....maybe intake gasket??

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did i blow a head gasket? 1-10 how hard would it be to replace the gasket?

12

But seriously - do a compression test, and check all ignition components before even thinking about that.

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Yes, a misfire. So, start with the basics. If all cylinders are even compression - we can rule that out (low/no compression=poor ignition cycle).

Whatever you do, don't go old school on it and start pulling wires off one by one to find which cylinder isn't firing.

You can fry all sorts of ignition components that way (when the spark energy has nowhere to go it makes a big mess of things).

There are several spark testers out there that simply lean against the wire. But really, you should take it to someone with a proper scope and have them look.

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Chances are a coil pack went bad and the head gaskets are fine.

A flashing SES lamp is a misfire bad enough to damage the catalytic converter. P0300 is random misfire code. You do not get cylinder misfire codes P0301- PO308 on a 2002.

No spark plug wires on a 2002..

With PO300, to figure out which cylinder is missing you plug in a GM Tech 2. It will quickly and clearly show which cylinder is missing.

I would do this first, it will in the end save you a bunch of time from chasing your tail and pulling the plugs and doing a compression test etc..

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how can i test a coil pack ? and with my autozone scanner it first said p0308 then when i scanned it the next day it say p0300. can i use the autozone scanner? and what is the next step after i find out which is misfiring . i am in no rush to fix the car and i don't mind attempting to fix it no matter how big of a job it is. i have done a hg job on a 96 camaro which was hard!

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how can i test a coil pack ? and with my autozone scanner it first said p0308 then when i scanned it the next day it say p0300. can i use the autozone scanner? and what is the next step after i find out which is misfiring . i am in no rush to fix the car and i don't mind attempting to fix it no matter how big of a job it is. i have done a hg job on a 96 camaro which was hard!

I hate to tell you this... but doing a headgasket on a Camaro and doing a headgasket on a NorthStar is like walking across your front yard and running a full marathon...

Not the same thing at all... :):)

But you need to put first things first...

Find and fix the misfire...

Then proceed to something else... if needed...

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and it only misfires when the car is warmed up...think that would cancel out the coil?

Maybe... since it is only misfiring when warm... and you have an o2 sensor code... look for a vacuum leak...

A vacuum leak can cause a misfire... and the misfire will then set an o2 code...

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just checked..no leaks..is there a better way to test for leaks then by just hearing and feeling around?

One way to check is to spray a little brake cleaner or starting fluid around the intake and throttle body and vacuum hoses while the engine is idling..

If there is a leak.. the idle will change.

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sprayed it no leaks....how do you test a coil and if it were a head gasket how come the oil and water aren't mixing?

Why are you even thinking it may be a head gasket ??

Unless I am missing something... so far, you have ABSOLUTELY NO SYMPTOMS of a bad head gasket.

You only have a misfire on one or more plugs.

A misfire by itself is not an indication of a bad head gasket.

And to answer your last question... oil and water very seldom mix together on a Northstar with a bad head gasket.

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See post #6. Your chasing your tail...

I don't think the Northstars are known for catastrophic head gasket failures. If one does go bad, it tends to rear it's head over a long period of time.

Likely bad coil pack. That said, on the 2002 they are set up on banks of 4 coils each.

IF...you plug in a Tech 2...it will show which cylinder is missing...then you can swap the coil banks and see if the problem moves with the swap...if the problem moves with the coil....it's a bad coil bank. 30 minutes tops..

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And a coil can misfire when the engine warms up, because as it heats up it breaks down and starts malfunctioning. once you figure out which one it is it should be easy. Out of curiosity when was the last tuneup?

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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last tune up was couple weeks ago but i just changed the plugs and oil. i am trying to find the misfire on my actron obd 2 pocketscan (orange one) and every time i hold the read button down it just goes back to the codes? should i buy another scanner? i just started her up today and she was running fine but i did notice steady white smoke coming out of the tail pipes...probably because it was just cold.

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Toy scanners are just that. It cannot read a po301-po308 if there is no such code on a 2002.

It is interesting to note that a tune up was just done a couple of weeks ago. Was the tune up done to try to address this issue? Did the misfire issue begin after the tune up?

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so first i need a new scanner...which one would you recommend that i can use on many cars. the misfire was before the tune up so i started with the basics and changed the plugs...this scanner did record a po308 at one point... my scanner shows the evp, misfire, 5 ready, o2 and all that but only allows me to detect the code and clear it...what gets me is if it only lets me do that why would it even show all that?

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Call around to a few garages and find someone with a TECH ll that knows how to use it.

It won't cost much and won't take 5 minutes to "KNOW" what plug is missing.

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regular..i did change the fuel sender not to long ago and the fuel inside looked clean but since i'm almost empty i will drain it out, and install a new fuel filter and buy a new scanner that can be used not just on gm cars. thanks for all your help

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Geeezzz....talk about the hard way to find a bad coil pack..... now your going to drain the gas tank and put in a new filter?

5 minutes at a shop with a GM Tech 2.

On my Deville, I used to carry a extra coil pack in the trunk for this exact just-in-case problem.

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Geeezzz....talk about the hard way to find a bad coil pack..... now your going to drain the gas tank and put in a new filter?

5 minutes at a shop with a GM Tech 2.

On my Deville, I used to carry a extra coil pack in the trunk for this exact just-in-case problem.

How frustrating, some people ask but don't listen.

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