P0430 and misfire #5

[nolimit]

I replaced my engine at 52,000 miles because of chewed up rod bearings (#6 was completely gone). The replacement motor was used. Since the motor was installed, I've put 10,000 miles on it but have had a misfire in cyl #5 (only at idle) and a P0430 code the entire time. All of the electronic components, sensors, and fuel delivery components were swapped from the original motor and there were no codes or misfire present with the old motor. I've changed the plugs, wires, fuel filter, IMRC, and tested the DPFE (it tested good).

Other than the occasional rotten egg smell (which existed before the motor swap), it runs strong and gets 24mpg around town and 31mpg on the highway.

I'm guessing the misfire is causing the P0430 since it's for bank #2, the same bank as cyl #5. If I clear the codes, the CEL will flash indicating misfire almost immediately, but it takes about 50 miles of driving for the P0430 to show up.

Any thoughts?

[DanG]

@ 52k miles, the plug wires were seated pretty well. The guys on the Grand Prix board actually found that if you mess with your wires after they've been installed for a year or so, you actually break down the conductor and can cause misfires. Maybe pick up a set of new wires from BAT and try your luck- Wouldn't hurt- I had to replace mine at roughly the same mileage 'cause I was actually bleeding spark from one to the other in the wire track (you can tell if you have white oxidation on the cladding of the wire where it rests against another- It's spark bleed). Actually failed emissions because of the random misfire. Replace the plugs too- It can only help.

[nolimit]

Thanks Dan -

The plugs were new Autolite Double Platinums when the new motor was installed. I actually put another set of new plugs in during the last 4000mi. The wires are new also, with less than 2000mi on them.

Last weekend I tore the upper end apart to check the valves and springs for cyl #5.. gave them a few persuasive taps.. put it all back together.. and didn't have the misfire or CEL for nearly three days. Then, the CEL started flashing at idle again, shortly followed by the CEL on constantly with a P0430 again.

Am I missing something? Injector maybe?

Also, there is a small silver round valve attached to the fuel rail, directly under the left side (dr side) of the intake near the throttle body. It looks like it should have a vacuum hose attached to it, but the intake sits directly over it.. should there be a hose attached there? The garage mentioned having trouble with the vacuum hoses.. and only the defroster worked when I got it back until they rerouted the lines.

Thanks again.