Hey all,

I've got an 04 Tahoe 5.3 Z71
It's got a 212/218 cam, CAI, BB tune for 89 octane but they just stopped selling that around here so I run the **** 87 with ethanol added to it. It's also got longtubes.

My mpg used to be around 18mpg, but now I'm at 12.5 in the city AND highway. New plugs, though one didn't seat right at all and isn't all the way in. No codes or misses though. However, my O2 sensors are original factory sensors from 2004 and I now have 170k miles. I don't throw codes for them, but can they be a cause for bad economy even though my wideband reads about 14.2-14.5 at idle?

 

Also I am not retuned for the longtubes if that makes a difference in mileage.

 

I would start with the problem areas of the plug and tune.

The ethanol is going to drop your mileage a bit, so that accounts for some of it. I would get that plug issue solved, get a tune and go from there.

 

What would be my best option for correcting that cross threaded spark plug on Cylinder #1? Use a spark plug thread chaser with the piston at TDC and see if it'll correct those threads? Something like a back tap?

 

The best option is pulling the head and fixing it. Head gaskets are cheap enough to warrant doing it the safe way. I am honestly pretty surprised you cross threaded it. It isn't super easy to do. If you aren't I would use Anti-seize on the threads of the plug going forward as well.

 

It actually cross threaded on the way OUT by some miracle when I did my cam swap. Not sure how that happens. My friend went ahead and decided to put it back in cross threaded... And he did use anti-seize thank god.

I'm kinda broke at the moment and was hoping that using a back tap might work. Is there a chance it will work for aluminum heads or am I just SOL and have to bite the bullet?

 

The problem is in case you get chunks of aluminum into the bore. It is your engine, but if the only symptom right now is fuel mileage I would tough it out and save until you can afford to fix the plug issue and get a decent tune on it.

 

With the piston near TDC, Try a back tap but use grease on it. This will help any shavings collect on the back tap as you thread it out.

Then blow compressed air into the cylinder and see if anything comes out. Then turn it over with the plug out and any thing should take the path of least resistance and exit the Spark plug hole.

No guaranty, But it might be the best option on a low budget.

 

I'll probably give that a try.

If I pull the head, anyone by chance have a ballpark estimate of a machine shop fixing this?

 

Also, what's everyone's thoughts of my old O2 sensors? They're going on 170k miles now, but no CEL and wideband is reading 14.2 - 14.5