Hello, I have a bad misfire on #8 on my 99 Disco 2. When I checked spark, I'll get random sparks at first and then nothing. All other cylinders are sparking ok. My compression Is 150psi and my head gaskets are ok. What are my chances that it's just plugs, wires and coils?

Thanks for any help

 

Did you pull the plug and examine it? What plugs are in your truck and how old are the plugs and wires? In my opinion, odds are it's either just the plug or just the wire.

To diagnose it, try swapping the plug with another one and see if the misfire follows the plug or stays on number 8. I suggest swapping with the plug from cylinder 6 because 6 is on a different coil than eight.

 

I agree its probably plug or wire. You could try running it at night to see if you are arcing anywhere.

Supposedly a coil problem (unless its the connector on the coil) would affect more than 1 cylinder.

 

I was testing from the wires. The plugs weren't actually being tested since I wasn't getting spark from the wire itself.

 

I'm not worried about changing the coil, plugs and wires if that is the problem. I just want to make sure Its not something else and I'm missing something. Thank you both for the replies so far!

 

I had a very bad P0307 misfire on my 02. I checked the spark plug it was fouled up, replaced plug with no change, removed the wire & metered it, and swapped it just for grins with no change. Removed the intake to replace the coil pack (did both while I was back there), new kingsborne wires, and NGK Double Platinum Plugs. After replacing everything I have a much smoother running/idling D2 and no more P0300/P0307 faults.

In my case with 229k on the clock I'm 99% sure the original coil for that bank was no longer producing a hot enough spark. Cylinder #7 held in there for a good bit until it just couldn't produce a spark & then boom instant misfire faults. I say do it right replace both coil packs, plugs, and wires and call it a day for a good long while.

 

Yeah, I guess it's hard to argue with your actual experience and result. The advice I got several years ago from none other than P.T. Schram that coil packs rarely fail on a DII is, well, several years old now.

I don't think anyone was looking at DIIs with 229,000 miles on them back in November '09.

And also you tried the more high probability causes of the misfire (plugs and wires) before just throwing money at the coil packs.

I always thought a failed coil pack would cause misfires on both of any pair of paired cylinders but RAVE does say a bad coil pack can cause misfires of individual cylinders.

That said, I still think a coil pack failure is less common than plugs and wires, but I guess we need to factor it in.

 

Yep with the age of a D2 getting up there coil pack failures are going to rise. Normally the #1 misfire fault on a D2 will always be wire related as they get old, hard, and actually fall apart at the metal connectors. The OEM Light Grey Bosch wires were famous for that. Spark Plug wise D2's rolled off the line with Platinum Plugs so they should typically last up to 100K on a normal running D2.

I've also seen a few D2's with bad coil pack wiring harnesses. Just gotta do basic diagnostics and eliminate the possibilities. I've only changed out one spark plug in all my days and it was due to a cracked insulator.

 

Coil packs are CHEAP!

$16 at Rockauto.com (no affiliation): 2003 LAND ROVER DISCOVERY 4.6L V8 Ignition Coil | RockAuto

 

Fair point. I don't think they used to be that inexpensive but it's been years since I was faced with the possible need to replace them.