I owe some of y'all some beers.

I've been working out the kinks after my HG job and driving to the parts store this morning (for low PS fluid) the Service Engine Soon light came on and UltraGauge was reporting a P0308 (Cylinder #8 misfire?).

I replaced both coil packs during my HG job and new plugs, but the wires were existing (STI, unknown mileage). While I look into things, what should I do or not do with a misfire code? Is it safe to drive without doing too much damage? I was going to pull the plug and check it, and possibly seafoam the oil and change it?

 

I had the same thing after my HG, turns out the wire was not quite tight on one plug, I took it off, wiped some of the electric grease off the top of the plug, code never came back

 

Inspect and test the ignition wire(s). I would lean towards the plug wires, especially being older it's easy for the terminal to pull away from the wire when you remove them. The Karlyn/STi 721 is a very good wire set to use > https://www.fcpeuro.com/products/lan...e-rover-hls103

What brand of plugs are you using? Did you check the gap before install(even if Platinum plugs)? IMHO not a fan of Bosch plugs in Rovers. If I use platinum it's either a NGK 3546 (PFR6N-11) or 7092. If standard copper it's either NGK 2756 or 5553. Don't know why, but I always get the best performance in all my cars/bikes with NGK plugs.

P0308 code: Also start looking for a vacuum leak. Re: the seafoam in the oil, that will not do much to correct this. And please Save yourself a headache and DON'T run the seafoam in the intake.

 

I've had STI wires on my truck for 65,000 miles and nearly ten years. I had a misfire on number 6 not long after I did the headgaskets on my truck about seven years ago. I determined there was damage to the wire at the plug end and called STI. They sent a new number 6 plug wire at no charge.

 

Ill dig into the wires tomorrow and check the plug gap. Will short drives with a misfire cause damage?

Also just curious what would a vacuum leak have to do with a cylinder misfire?

 

A vacuum leak from a hose, intake manifold gasket, whatever can cause a lean condition (too much air). That interferes with the air-fuel mixture and you get a misfire. Most small vacuum leaks will be felt at lower RPMs (engine runs rough/idle might fluctuate). There is a ton of INFO/VIDS on finding vacuum leaks on the net.

"Will short drives with a misfire cause damage?" The short answer is Yes. How much....probably little just depends on how bad the misfire (lean/rich condition) is in the cylinder. The real "short answer" is you've done too much work on this rig not to get this issue sorted ASAP. Have a good look at the plugs and wires first. Something tells me it's going to be a F'd up wire. Good Luck!

 

How should I look at testing the wire and plug? Ive heard about using a spare plug to test the wire, but Im not sure how to ground it.

I pulled the #8 wire and the inside looked to be the same as the cylinder next to it.

I could also pull the fuel mix info from the UltraGauge or the odbii scanner?

 

It's a PITA but you could swap the number 8 wire with the number 7 and see if the misfire switches sides. Those two should the same length, or close.

 

Little update, I pulled the 8 and 6 (?, the one next to it) plugs to compare them. The #8 plug washer had oil on it, the other did not. They both appear burnt or black. They gave me a new plug, so I put that in #8 and started it back up. [Edit: I think I have my cylinder numbers mixed up].

This time the UG was reporting P0300, which I thought was strange. I scrolled through the UG pages and noticed on the O2 sensor page that one was reporting a very low voltage. With that I pulled out my iCarsoft and saw that I actually had 7 codes:
P0300(random/multiple misfire), P0308 (#8 misfire), P0303 (#3 misfire), P0305 (#5 misfire), P1300 (misfire sufficient to cause catalyst damage), and a pending P0134 (O2 sensor no activity detected bank1 sensor 1).

I think that would be the culprit with the bank1 sensor1 O2 sensor, however the UG was showing the B2S1. Honestly I don't know which is which, is there something to test the O2 sensors or do you just replace them?

Another concern which I'm really questioning myself is the plug order and the coil pack diagram. Is it possible I installed the pack upsidedown/backwards? Since I replaced the coil packs I've been doubting myself about that mostly the whole time.

 

Here's the wiring diagram I followed:



My iCarsoft seemed to be correct when it told me which O2 bank was giving problems, but I replaced both sides anyway just to be safe. Malfunctioning upstream O2s could certainly be giving you misfires.