Today went to change out the plugs and wires, had to destroy the No.5 plug boot. After I got everything changed out and got it started up the check engine light came on. This is the 3400 SFI engine, when I took out the plugs I found the previous owner mixed match NGK, Champion, and stock delco plugs. When I started it up it was idling at around 500-600 RPM and after a few minutes had a burnt popcorn smell coming out of the tail pipe. I checked the vacuum line and that all of the wires were on correctly, the plugs that I replaced the others with were four ground iridium bosch plugs. This is day two and I have read on other forums that the SFI engine develops ghost codes at the 30000 mile tune up. Any help is appreciated.

 

I'd start by getting rid of those and going back to OE-style single electrode plugs (I think GM OE plugs were iridium by '04, I'd probably stick with Delcos, though Denso or NGK are probably ok too). I'm not sure about the 3.4L Chevy V6 but I know multi-electrode plugs are known to cause all kinds of issues on some engines (including the Jeep 4.0L I6).

 

One of the plugs was a multi ground. What kind of problems do they cause in I6's?

 

Rough idle, poor acceleration, poor fuel mileage, misc. check engine codes, etc.


Generally multi-ground plugs are a gimmick and at best perform no better than stock plugs (at least in the "real world") and at worst end up causing problems.

 

Go back to original delco iridium plugs and replace the wire set so you can eliminate those two possibilities right away. I have a good amount of experience with GM, those cars in particular.

 

x2 just went through this on an 01 blazer. he paied someone to put those high dollar bosches in.. and paied me double and a case of beer to put some delcos back in.