Been chasing some random misfires for a couple months. I pulled, cleaned and regapped the plugs and tested them but that did not fix it. Wires are relatively new magnecors and they look fine.

this weekend I decided to replace the coils. Finally got that done but still seeing these misfires. Most prominent during idle. My next step was to replace the MAF. Anyone have other suggestions?

 

Make sure the coils are bonded/grounded to the intake and all the engine grounds are solid. You could also get one of those old school spark checker things and use them online with another wire to check them. Also small porcelain cracks are hard to see, you could squirt water around each one while idling and see a drop in rpm if there’s a bad one

 

Is there a specific method for grounding the coils? I didn't see any grounding straps when I tool them off - just the bracket they bolt to. I checked the spark with an inline tool - seems strong - misfire is only occasional and seems only apparent during idle. I did not clear the codes after I replaced the coils as I had the battery disconnected. Not sure if that makes a difference.

 

I just got my first p0307 code on the way home. Almost left me, but came back to life after a few seconds. How was it changing the coils? They've been on my list, now I guess it's time to knock it out while doing the plugs and wires. Did you do the relocation kit? Debating if it's worth the $$ or not. Sorry I can't offer help on the misfires.

 

The coils was your typical pain in the *** but I’m a noob so it took me a lot longer. I split it up over two days so I wouldn’t get as frustrated.

if you take your time you can do it by yourself pretty easily in a full afternoon. Hardest part was removing studs on the egr bracket and not braking the brittle plastic hoses and connectors. I broke the nipple off a vacuum solenoid so there’s another $50.

I looked at the relocation but decided against it as i don’t think this should be a frequent task as long as you use quality coils.

Unfortunately, replacing the coils did not fix my problem. I think I have a bad O2 sensor that’s causing my issues so I will be replacing that when it gets here on Tuesday.

 

Disco's don't do random misfires, the ECU is very good at detecting misfires. All of yours are on one bank, did you recently remove the intake? If you swap the coils left to right all your codes should move to the odds if the coils are the cause, if it stays on the evens then swap all the wires left to right (maybe start with the wires). You can also move all the plugs left to right, and finally the injectors. Loose intake manifold bolts will cause lean codes, I suppose that could also misfires.

 

Thanks for the feedback Extinct. I did remove the intake to get to the coils. I replaced the coils with new bosch ones. Not sure I am ready to dive back in there and mess with those again just yet.

Good idea on swapping the wires though. I’m going to take a break for a day or so and then take that step. Will report back in a couple of days.

 

I am chasing a similar issue though I don’t have any codes. Randomly rough at idle but only after driving for a bit and the engine is warmed up. I checked all the obvious areas (I believe) and I did find that one of my new plugs had cracked porcelain but swapping that out didn’t help.

It is odd that you have a misfire on one bank so I don’t think it would be a vacuum leak. I don’t have a smoke machine but I did remove all vacuum lines one at a time to see if I could eliminate the source (sai tubing, break booster, evap line) and I checked that all upper intake bolts where torqued.

When do you misfires occur? Only at idle
or when you load the engine?

 

Just to close this one out - it was happening only during idle. I replaced the coils and cleared the codes. No issues so far.