4.6 plug wires (again?)?

I don't think it is plug wires.

My 86 Crown Vic with 270k miles ran like a top until this winter when it developed a miss-under-load sounding exactly like your problem.

First thing I did was put in a new set of plugs. No change. Problem still there.

Having been on the original plug wires all that time, next thing I did was put on new plug wires. No change at all. Problem still there.

Now I suspect the ignition module or throttle position sensor (TPS). I'm leaning toward the TPS being the culprit, since it occurs only when throttle is opened up. My theory is that timing advance would work off the signal from the TPS. If TPS is sending an erratic signal to the computer, the computer would do erratic timing advance, occasionally causing cylinders to fire way before TDC, resulting in random kick-backs under load, the exact problem I'm experiencing.

Here's another oddity: It almost goes away on a warm 60+ degree day. I suspect it would clear up completely on a 70+ degree day, but I don't want to wait that long hoping the problem will fix itself.

FWIW, a similar problem was completely fixed on my 87 F150 300 6-cyl pickup by putting new heat-sink grease between the ignition module and distributor housing. That might be a totally different issue though. The deteriorating heat-sink grease problem on 80-ish 300 cid engines was a well-known pervasive problem, even triggering a recall in California due to accidents it caused when engines would start misfiring severely enough to die at highway speeds (as mine did). This problem on my 86 Crown Vic is not nearly that severe.

Maybe somone out there has had this problem and knows the soluton.

thanks! george

Fuel filter? Often overlooked, but essential. Will pass gas, but dirty gas. Probably no need for additive(injector cleaner,) just motor on.

wws

It very well could be plug wires again. Make sure the air filter is clean, change the fuel filter and clean the MAF sensor first, though. Time and atmospheric conditions are the enemy of plug wires, not mileage. Wires on any car are usually only good for 5-8 years, not just Ford wires. The 4.6L in your car tends to need wires more often than many, though. Pull the wires out of the intake and look at the boots. Look for oil/coolant contamination or signs of arcing. If there is liquid contamination new wires will fail quickly, you need to fix the cause of the leak. Arcing (burn through on the boots) is often caused by not using dielectric grease on the boots. Look for a hazy grey spot on the side of the boot with a tiny pinhole in the center. Look for tracking around the bottom lip of the boot.

Here's a couple of tips specific to your 4.6:

-Only use Motorcraft wires. They will burn up cheap wires very quickly

-Use standard copper or single platinum plugs, Motorcraft or NGK are preferred. You WILL have issues if you use any Bosch spark plug in that motor.

-Always use lots of dielectric grease on and in the spark plug boots.

-Periodically inspect and clean out the spark plug wells. Valve cover seals often seep into the wells, ruining the boots.

Thanks, Tom.

I'll run all the checks when the weather improves: the wind chill is now about 8 F. We keep getting these thrice-weekly blizzards ...

For now, I unplugged the MAF sensor for a short test drive. It choked a tad when I first gave it gas, but I didn't have the miss I had previously. Maybe it's just the MAF (hope, hope).

Cheers, Puddin'

On Fri, 7 Mar 2008 08:38:30 -0800 (PST), Tom Adkins wrote: ...

"Blues starts to rolling ... stops at my front do'. I'm gonna change my way of livin' ... won't have to worry no mo'." - from "Blues Before Sunrise", Leroy Carr, maybe 1934