• If you currently own, previously owned or want to own an Avalanche, we welcome you to become a member today. Membership is FREE, register now!

Another P0172 & P0175 post

e6bill

Full Member
Joined
Dec 29, 2005
Messages
92
Location
Vinemont, AL
2003 Av Z66, 250,000 miles. 

I've had a misfire for a long time with mostly a P0300 code.  This week I finally took the plunge and pulled the intake manifold to replace the gaskets. Also replaced the knock sensors and harness due to a CEL for the rear sensor (it was rusted badly).
While I had it all apart, I also replaced the injectors.

I got everything back together today and cranked it up. Seemed to run some better at idle, but not perfect. Before, it would shake at idle, but run OK at speed and ping some under load.

Went for an extended drive (30 min) and picked up a flashing CEL after awhile.  Had the codes read and came up with P0300, P0172, and P0175 (both banks rich). Never had these codes before now. Was a bit lean before.

Checked for loose connectors, vacuum leaks as best I could, and for loose bolts.  All looked OK. MAF isn't dirty, filter isn't nasty.
What might I be missing?  Maybe the new injectors aren't up to scratch? Some degreaser likely got on the MAP sensor and might be a possibility. The MAP sensor also seems loose in its port and may have a tweaked seal, but nothing changed when I wiggled it with the engine running.

Opinions? 
 
When was last time you replaced 02 sensors?

PLugs and wires relatively new?
 
Plugs, wires, both upstream sensors were replaced when I first started fighting the misfire. Been a couple of years ago now.
 
Would make sure you have no intake leaks, fuel pressure is good and that your plugs/wires are in decent shape. If all that checks out I would suspect plugged cats...

I am assuming when you installed the intake with the new gasket you used a torque wrench and torqued them down as the factory manual states? If not you could have installed your intake gasket wrong and it is leaking still.

Rodney
 
Would any of that cause the rich condition instead of lean?  Before, I was a little lean, now suddenly, I'm rich on both banks.
 
Just was finally able to check the fuel pressure. It was hovering around 50psi at idle. That seems low.

Put the original injectors back in and the 172/175 codes are gone. Just shows P0300 now and suggests the regulator is bad.
 
e6bill said:
Just was finally able to check the fuel pressure. It was hovering around 50psi at idle. That seems low.

Put the original injectors back in and the 172/175 codes are gone. Just shows P0300 now and suggests the regulator is bad.


50psi at idle is fine, should jump 60psi if you hit the throttle and that will tell you that you fuel pump and regulator are working up to par.

The injectors you put in were they the same as stock ones?

Shouldn't be rich if you have  a vacuum leak.

The P0300 could be wires, plugs or MAS.

Have you changed the 02 sensors?
 
Plugs, wires, o2, maf, have all been changed since the problem started nearly 3 yrs ago. The map, regulator, and pump have not been changed. Just did knock sensors and harness. Prob needs the fuel filter changed again.

Cats have not been checked yet.
 
Did you ever fix this

e6bill said:
Just how bad is the rotten egg smell when a cat goes bad?  I have a slight eggy smell at the tail pipe, not gross, but there. 

My 03 Z66 (170K miles) has had a P0300 code and rough idle when warmed up for about a week. Truck is completely stock save the Spectre air filter which I just cleaned.  Also just replaced the (original) plug wires and both upstream O2 sensors (not original).  Cleaned the MAF, but haven't pulled the plugs to look at them yet.  Had laser back surgery 2.5 weeks ago, taking things slow.

Looking for input.  That 0300 code is generic enough to be about useless.
 
I'd check for broken exhaust manifold bolts.  A too-common problem that can affect the O2 readings.
 
Finally an update.  I checked for broken manifold bolts and there are a few with missing heads.

I changed the intake manifold gaskets, knock sensors and harness, fuel pump and regulator, and this is along with all the other stuff I've done (O2 sensors, plugs/wires, 2 coils, cleaned then replaced MAF, cleaned TB). I changed the injectors when I did the intake gaskets, but got a "rich" code, so I put the old ones back. Code gone.

I had an exhaust shop check back pressure in front of the cats and got readings of "3" on the driver side and "1" on the passenger side. I have no frame of reference as to what those numbers mean, however. What should they be normally?

This has been going on quite awhile now, nothing has ever had any change whatsoever. 2003 Z66 258,xxx miles.  P0300 is the only consistent code I've gotten. Brief other codes for the MAF, rich, etc.
 
They probably 3and 1 psi which is good over 5 psi is bad.

Do a compression test.
 
I'll do one soon as I can. Any input on the busted off bolt heads on the exh manifolds? I've never touched them, were they prone to cracking off?
 
From what I've seen on the website it does happen but not too often. It comes from all the heating and cooling from driving it.

PS don't put any more money into it until you do the compression test
 
If you had misfire code for long time you could have ruined the cats... as raw fuel not being burned ends up in cat and clogs her up.

Also with thay many miles I could see them being changed.
 
You likely have an issue due to the broken bolts. MAY be a pain to repair. Most cars have issues with exhaust bolts eventually. Just the nature of the beast.

You can go to ARP studs which may help some. My truck had like 5 of the 12 bolts broken when I swapped the heads on them. Replaced all the bolts with new.

It WILL affect your O2 sensor readings... Oh and if you do a back pressure test with broken exhaust bolts.. Won't tell you anything since air can get in and out of the exhaust where the bolts are broken...

Since you see broken bolts I would have them replaced. If you are able to do them yourself great. otherwise let the professionals do it as it is something that can easily get to be a bigger job then intended.

Really need to pull off the manifolds, remove all of the bolts, and replace the bolts and exhaust gaskets with new. THEN check your back pressure...

Could still be toasted cats...
 
Curious did catalytic converters clog? I got a degrade performance code & had thought try removing & cleaning by detergent soaking. My code disappeared with fuel cleaner still may try cleaning if I get the extra time & motivation to try.

The O2 sensors aren't fun to replace either not cheap sensors & I've had less expensive Amazon sensors die or heating element problems not long after purchase.
Hope you find your culprit
 
Back
Top