I recently bought a 2000 F150 with 4.2 V6, 73,000 miles. No maintenance records, so I've been doing things appropriate for it's age.

I just bought Motorcraft plugs (SP-504) and a set of Motorcraft plug wires, based on the recommendations here. Gapped the plugs to .054 and installed them. Double-checked that I have the wires going the right place.

I now have a serious misfire, mostly on acceleration. It's bad enough that I don't want to drive it. The only problem I had prior to my 'repair' was a bit of roughness on idle.

Any tips on troubleshooting this? What are the chances I got a bad plug or wire?

Thanks!

 

Not sure if this would cause a misfire but I'd recheck the wires on the coilpack. Its pretty easy to swap the #5 & #6 wires.


3 4
2 6
1 5

The electrical connector is on the 1 2 3 side of the coil pack.

http://info.rockauto.com/Motorcraft/...tml?DGE456.jpg

 

any codes?

pull off the neg terminal post and reinstall after 10 mins. resetting the ECU wouldnt hurt anything

all else fails, put the old plugs back in and report back

 

The service manual says old plugs must go back in the same cylinders they came out of. I didn't mark them. Is this really an issue?

 

You're right, it is easy to mess up. I've checked it a dozen times, and I've got them back on correctly. It runs even worse if you reverse them. :o

 

Did you use dielectric grease in the wire boots at both ends?

You MIGHT have a cracked coil pack. I had to replace mine at 84k to fix an intermittent miss.

 

It appears the problem was a bad plug out of the box. I went and bought 6 more Motorcraft plugs and installed them. Problem went away.

I checked the gap and appearance of the plugs I removed, and all look just fine.

When I bought the original six plugs (at Advance), the counter guy dropped one plug to the concrete floor. Without asking, he went back into the shelves, muttered something like "crap", and came back with (what I thought) was a different one. I wonder if there weren't any more on the shelf, and he just brought back the one he dropped. No obvious damage, but perhaps something was amiss.

Oh, well. It's taken care of now.

Anybody need 5 nearly new SP-504s? I'll send you 6, and you can choose which 5 you like.

 

he probably cracked the porcelain base and cooked the insides.

why dont you return them and get your money back?

 

yea, take em back..glad to see you got it fixed

 

A fractured insulator would certainly give you kittens. The spark was finding the easiest path to ground, and it wasn't at the pre-set gap!