Topic: Misfire Help

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Hello Everyone!

I have an 02 Z71 with 152,000 miles on it. Just a couple days ago I was driving home and lost a lot of power out of no where, had driven from work to grocery store (approx 5 miles) ran in and when driving home (less than 2 miles) the truck just started stumbling and the service engine light started flashing. I got home and had dinner... a few hours later I came back out and started her up again, and it idled fine, I opened the hood and tried to listen for any unusual noises, but didnt hear anything. I drove about five blocks and it started to run rough again and was way underpowered... If I gave it more gas I would hear a rattling noise (I never went above 35 and didn't push things)... so I limped it back home and parked it.

On a side note, over the last two months I have had the "low engine coolant" light come on, and I topped off the coolant twice.

So two days ago I took my truck to a trusted local service shop.

They had it for a day and said that the truck had a random misfire (p0300 I believe) and seemed to be missing on cylinders 4, 6, and 8. They checked the plugs and wires, and they were fine. They said they thought it was probably the intake manifold gasket but couldn't be sure without diging into it. They advised taking it to a Dealership, I am hesitant to do that because my wife and I are expecting our first child.

She is crazy hormonal and freaking out about repair costs...so needless to say...I have little to zero money to spend. I don't mind wrenching on my truck myself, but am concerned about the cost of having a dealership diagnose things.

I have been reading for about a day now and I never smelled gas or anything else that would lead me to think it was a cat... but I'm no expert.

I did buy a new intake manifold gasket from O'Reily's but didn't open it or install it, I was hoping to get some sort of confirmation as to wether or not that sounds right...

Sorry for the novel for a first post, but any help or insight would be greatly appreciated!

[MyBigToy]

Welcome to the club.

It could be the intake gasket or a head gasket. Coolant in the exhaust for any period of time can also mess your catalytic converters up.

There have also been issues with Castech head castings cracking - here's a little information on that issue:

http://www.chevyavalancheclub.com/index.php/topic,10814.msg89749.html#msg89749

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Thanks for the welcome and reply! I read the link you posted and I hope that isn't the case, but I guess we will see!

Alright, I am going to try my hand at the intake manifold gasket. Wish me luck!

[Main One]

I doubt it's the intake gasket. There's a coolant leak somewhere and it isn't that gasket - these intake manifolds don't have any coolant passageways.  I'd say you've got head or head gasket problems.

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Well, new intake manifold gasket successfully installed! And it even started after I put it all back together!

But, it didn't fix it...

I went three blocks at 30mph before the service engine light started flashing and it was missing / no power. Went back to the house and crawled under while it was still running to see if the cats were red hot ( heard they would be if they were bad) both looked fine.

Another symptom was that at 25mph I "goosed it" and it acted like it didnt want to down shift where it normally would have...

I gotta say, even though my Avy still isn't fixed.. I feel like I accomplished a lot today! Way better feeling than sitting behind a desk or on the sales floor all day!

I doubt it's the intake gasket. There's a coolant leak somewhere and it isn't that gasket - these intake manifolds don't have any coolant passageways.  I'd say you've got head or head gasket problems.

Thanks for the reply! Is there a way for me to trouble shoot a bad head or head gasket?

Also would the, not down shifting, and lack of power when missing be related to the heads in some way?

[Main One]

If you can't find an external coolant leak I'd say it's a good bet that it's getting into a cylinder either through the head or gasket.

Sounds like you may have a bad cat too.  I don't think any of my cats that went bad ever got hot enough to glow.

[bevo]

possibly a bubble in the coolant lines? i have had almost the same problem with the low coolant always coming on and know leak, i took the top off of wear you pour the coolant in and let the truck run and you can watch the bubbles come up in the coolant reservoir.

i never had the truck messing up the way you desribe however

[paper]

If you can't find an external coolant leak I'd say it's a good bet that it's getting into a cylinder either through the head or gasket.

Sounds like you may have a bad cat too.  I don't think any of my cats that went bad ever got hot enough to glow.

I'll do some more reading on the heads and coolant leak, thanks for the direction!

Has anyone just cut the cats out and gone with duals?

If so, is there any tuning needed? I guess I'd rather pay cash to have 'em cut out and straight piped if there aren't any negative impacts to the truck...

On a side note, this couldn't be related to bad 02 sensors or a dirty MAF could it?

possibly a bubble in the coolant lines? i have had almost the same problem with the low coolant always coming on and know leak, i took the top off of wear you pour the coolant in and let the truck run and you can watch the bubbles come up in the coolant reservoir.

i never had the truck messing up the way you desribe however

Thanks, I will check that out tomorrow!

Thanks everyone for the input and help, greatly appreciated!

[oHIobellboy]

It could be the cats. Cleaning the maf is cheap and easy. Won't cost much to try it.

[Main One]

Has anyone just cut the cats out and gone with duals?

If so, is there any tuning needed? I guess I'd rather pay cash to have 'em cut out and straight piped if there aren't any negative impacts to the truck...

On a side note, this couldn't be related to bad 02 sensors or a dirty MAF could it?

Yes, you can cut the cats out.  The only tuning issue regarding that is that unless the code for the rear (after the cats) O2 sensors is masked out, the Service Engine Soon light will be on all of the time.  By itself that isn't a big deal, but then you won't know when other problems arise that would turn that on.

I don't think bad O2 sensors would cause a misfire, and if they were that bad, you'd get a code indicating max lean or rich.  A dirty MAF, maybe.  As OBB said, that's easy and cheap to try.