On my 04 I've been chasing P1173 forever. Replaced cats and all 4 o2's. Done multiple smoke test and found nothing. I've finally decided it must be a leaking o-ring on an injector.

So there's multiple questions here. Who sells the best/most affordable rebuilt injectors? Who sells the best rebuild kit? Is one method preferred over the other? What all should I expect to encounter and replace when I decide to swap the injectors out?

 

You probably don't need to do a complete rebuild unless you just want to. If you go to the link in my signature I believe there is a link to a write up for a cheap diy injector cleaner. Then get yourself a new set of o-rings to put on and some RTV for the plenum gasket then you'll probably be good.

Another idea is that it could be an exhaust leak. If you've got a pre-o2 exhaust leak (usually between the exhaust manifold and pipe, the gaskets kinda blow out the side) then that allows oxygen into the exhaust stream and the sensor registers that as a lean running condition.

 

Haven't dealt with mine yet so won't be of much help. Have looked around some for rebuild/service kits. Link for one below and several available on eBay from $20 and up. Looks to be a fairly simple process.

Bosch Type 3 Fuel Injector Service Kits 002 - Mr Injector Parts
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there should be a great right up on how to clean, rebuild and test injectors.
i don't remember who posted it (sorry), but it was very complete comprehensive right up.