I started up my truck this morning and thought I heard the tinny sound of an exhaust leak, the truck was idleing terrible. I thought that maybe the rough idle was because I hadn't driven the truck in about a week. Then a few miles into my commute I get the check engine light. So I parked it and caught a ride with a buddy. But when I checked under the hood, it looks like I have a crack in the top of one of the primaries on the passenger side where the primary meets the flange.

Could a cracked primary cause a check engine code to be thrown? Could it make it run rough by making the O2 sensor go out of whack? Could I do damage driving it at all?

Can it be welded up without pulling the header off the truck? I really don't have time to tear this apart right now.

Thanks.

 

I think YES to all of the above.
You can weld it on the truck as long as you can get at it and don't burn any wiring or anything nearby. A MIG is not dangerous to the elec system...a stick IS.
It would deffinately make it run like crap and throw your O2's out of whack.
Don't know how much richer or leaner it may make the truck run on that bank but probably not worth the risk.

 

It should be safe to drive. Getting clean air into the exhaust will make the O2 read lean and add fuel, and I doubt you'd be able to add enough fuel to wash the rings. Your mileage might go to ****, but I don't think you'll hurt anything.

As for the rest of your questions, yes as howard stated above.

 

I agree with all of the above, although I'd take care of it asap Tom. What's happening is air is entering the exhaust stream and the O2 sensor is getting an incorrect reading since it's reading the fresh air that's entering the exhaust, and richening the mixture to compensate. You'll probably have a lean code and possibly an O2 sensor code for that bank. (I just basically re-capped what was said above with different words lol)

Good thing you have a Grand Prix with new brakes as your backup

 

I want to get it taken care of ASAP, but this is just the worst timing. The GP is stored at my bro-in-laws house because our garage is demolished and there is a 20 yard dumpster in the driveway. I have no room to work on anything.

I was looking at NNBS Crew Cab 4x4s on vacation. So tempting to get one and just throw some bigger tires on it.

 

You are the man Tom

Lemme know if you need any help if you decide to get new headers or whatever. The StainlessWorks are nice, and I've already installed one set in the driveway

 

It may be a well duh, at a minimum, I would unbolt the header from the block and place the ground on the header to manifold flange before welding. Although electricity takes the path of least resistance, I would try to avoid any going through the block.