hi gang,
2003 D2 4.6 throwing codes for 3-5-7 misfire with the occasional cyl 4 misfire; wires and NGK Iridium plugs are only 20k old and plugs look fine (only pulled 3 & 7 so far). Previous owner did head gasket at 108k, truck now has 159k. Since the misfires are mostly on one side I'm suspecting HG or coil pack, but the 1-3-5-7 wiring is spread across both coils so I'm wondering (since I get the occasional cyl 4 code) if the whole coil pack is failing. Can coil pack be tested in situ? Should the head gasket have been retorqued at some point after replacement? I've only had it for about 3k miles so far.
Many thanks for any tips.

 

Just a shot in the dark, but are you using top tier premium gas in it? Using low quality fuel without detergents over a period of time can cause FI failures and cruddy valves which lead to multiple misfires. Maybe not in only 3k miles but if the PO also did the same...

There are some other multiple misfire causes as well if you try the search tool

 

I always run premium, and prefer Techron; can't speak to what the last guy did but he had tons of work done on it and I doubt he'd neglect the need for quality fuel.

 

Misfires on the four interior cylinders are usually not HG related. Coolant channels are on the front and back of the block affecting 1, 2, 7, & 8.

 

In my experience (both personal and reading this forum) misfires all on one side have been caused by a bad upstream (pre-cat) oxygen sensor.

The O2 sensor is the only thing common to all the cylinders on one side that is not shared by the cylinders on the opposite side.

Happened to me three years ago. My truck had misfires on 2, 6 & 8. A new O2 solved the problem.

The only rationale I can think of for why a bad O2 sensor would be the cause is that sensor voltage either too high or too low causes the ECM to supply too little or too much fuel.

This doesn't explain the misfire on #4 but perhaps that is unrelated.

 

I had misfires on the same bank and as min01 said the O2 sensor is really what seemed to eliminate the problem. I didn't have a code for a bad O2 either but I pretty much did a tune up Coils, Plugs, Wires and it wasn't until I did the 2 upstream that I stopped getting the misfires. Give that a try first and check your engine ground strap that was another thing I did because it was missing.

 

Huh, Great thing I read this thing about O2 sensor leading to misfires without O2 codes. I'm having some right now. LOL! thanks for sharing your experience guys. I was about to pull the trigger on the O2 thingy but those were the most expensive parts than tune up..

 

Oops, I forgot I had gotten an O2 code as well. Thanks a ton for the insight, I'll steer my attention (and debit card) in that direction.

 

PO maintenance records show all 4 O2 sensors replaced 19k miles ago, do these things ever fail prematurely? Is there a way to clean/check them? Like all of us I want to fix my Rover but don't want to shred my bank account unnecessarily
If I do need to replace, im not sure which one(s); if it's 3-5-7 I'm assuming driver's side upstream?
Thanks guys, great resource here.
i just wish this wasn't happening just as camping season comes to a close (and we haven't gone yet!)

 

Yes it the driver side up stream. Please let us know the results.