Plugs, plug wires, and coils: when to replace?

[JTH1972]

Plugs and plug wires have always been on my top for replacement as part of a tune-up, but I've heard with newer motors that some adopt a "if it aint broke don't fix it" approach although that doesn't make much sense to me.

The 96 V6 I recently picked up has 173,000 km (108K miles) on it and even though the previous owners kept meticulous service records on it, I can't see a reference anywhere to when or even if the plugs and wires were ever changed. I did get plugs and plug wires and I'm ready to put them in, but what's the opinion of others on that? I would assume that both these components must be close to their service life.

Does the quality of the plug wires really make a big difference too? If I got NAPA Premium (OEM equivalent) over their "Economy" wires, is it going to be that big of a performance difference?

What about the coils? Is it after a certain mileage you consider changing it due to age?

 

[Flash]

My brother has a BMW that eats plugs. He's fitted NGK Iridiums to slow its appetite down and it has worked somewhat.

I had a 1993 (Australian) Falcon that I replaced the standard NGK plugs on after 100,000kms because I thought surely it had to need plugs by then. The old plugs had very little wear and the new plugs made very little difference.

I suppose the only real way to know is to look and see.

Wires and coils can be tested.

Make sure you clean up the coil grounds, others here have reported that that makes a difference.

 

[drdoom]

100,000 miles maximum on platinum plugs, coil and wires are easily tested with a meter so I only replace those if damaged.

 

[JTH1972]

Make sure you clean up the coil grounds, others here have reported that that makes a difference.

Do you mean where it mounts or another cable?

 

[JTH1972]

100,000 miles maximum on platinum plugs, coil and wires are easily tested with a meter so I only replace those if damaged.

I picked up double platinum, as recommended by other members. If the plugs are due to be replaced, why wouldn't the wires be too? I figure if I'm that deep into it, wouldn't it be preventative maintenance?

 

[drdoom]

Prophylactic replacement of plug wire is just really outdated in my opinion. Particularly now when replacements are likely Chinese knockoffs.

 

[Flash]

If it were me i would replace the wires with something of good quality and fit a set of NGK Iridiums.
Now you know where you are and what to expect.

 

[SoNic67]

Prophylactic replacement of plug wire is just really outdated in my opinion. Particularly now when replacements are likely Chinese knockoffs.

Totally agree. The OE plugs, after 15 years look better than newer cheap ones.

Plus, I switched to fine-tip spark plugs (Iridium), and those have a much lower arc voltage, so the stress on my aged wires and coils is lessened.

 

[JTH1972]

Prophylactic replacement of plug wire is just really outdated in my opinion. Particularly now when replacements are likely Chinese knockoffs.

Well what isn't made in China nowadays anyway? Plus my options are limited on this side of the border. Only a few automotive places in my area, only one or two that don't completely gouge the customer.

 

[AppleWood]

Your mileage is well past what service manual recommends for replacing plugs, wires. As for the coil; worn plugs, possibly arcing wires will stress it beyond normal so I wouldn't hesitate to replace it as well. My 144,000 mile vehicle showed plug wires leaving an arc trace on the side of the valve cover.

Having said all that, my truck actually ran fine. One plug actually gapped at over 0.100"! I'm glad i did it though, as I now know that any problems that may occur cannot be the fault of not having a tune-up...

 

[lobo411]

Plugs are a wear item. Literally--the reason you replace them is that the various precious metal coatings/electrodes wear over time.

That's if you go by the book. If you're smart, you replace them for the above reason, but also because parts that are rarely serviced tend to get welded/frozen in place, and usually you find out at the worst possible times. I replace my plugs every 30k (I use autolite plats usually) and I can do the job in about 45 mins. Nothing's ever stuck on or frozen because it never has that opportunity.

 

[1998Exp]

Not sure how you recommend to test wires. If you meant measuring resistance, per service manual, that's a very limited test, for hard failure only. All the failures that I have seen on my vehicles were due to deteriorated insulation causing arcing, especially on those that run in the proximity of the exhaust manifold. There are tricks, like spraying water or observing in darkness, but unless you own an oscilloscope, there is no reliable test -- and even then you won't know for sure if it's the wire or the plug causing trouble. One of the original wires on my '98 developed this problem very early in its life, and the Motorcraft replacement did the same after a while. In many cases the deterioration is gradual, and there is no obvious misfire; just slowly degrading engine power due to weak spark.

There is a reason why automakers switched to the coil-on-plug system, eliminating the failure-prone wires.
I would say, if your wires have not been replaced in 100,000 or more, you are looking for trouble.

...
Wires and coils can be tested.
...

 

[JTH1972]

So I had picked up DP's as was recommended earlier. Am I better off with the iridium for the lower voltage?

 

[crunchie_frog]

So I had picked up DP's as was recommended earlier. Am I better off with the iridium for the lower voltage?

Autozone has a rebate on the autolite iridium plugs that makes them cheaper or comparable in costs to the DPs. I am giving them a try as they are probably the "best" plugs you can install. Yes, they are not needed but why not if they are the same price or less than the standard recommended DPs. I do not work for autozone, autolite nor am I invested in iridium mining.

 

[JTH1972]

No Autozone up here.

 

[JTH1972]

I was thinking of taking the DP's back to Napa and getting the NGK iridium from Can Tire firvaround the same price.

 

[Flash]

Not sure how you recommend to test wires. If you meant measuring resistance, per service manual, that's a very limited test, for hard failure only. All the failures that I have seen on my vehicles were due to deteriorated insulation causing arcing, especially on those that run in the proximity of the exhaust manifold. There are tricks, like spraying water or observing in darkness, but unless you own an oscilloscope, there is no reliable test -- and even then you won't know for sure if it's the wire or the plug causing trouble. One of the original wires on my '98 developed this problem very early in its life, and the Motorcraft replacement did the same after a while. In many cases the deterioration is gradual, and there is no obvious misfire; just slowly degrading engine power due to weak spark.

There is a reason why automakers switched to the coil-on-plug system, eliminating the failure-prone wires.
I would say, if your wires have not been replaced in 100,000 or more, you are looking for trouble.

That's why I said in a later post that if it were me I would install known good quality wires and a set of NGK Iridiums then you would know where you are and what to expect from then on.

In fact that's eaxctly what I did with my X.

IMO it's too much trouble and possibly expense to test wires when they're a wear item anyway.

 

[J_C]

In the old days when plugs didn't last as long the wires were more often reused, but at over 100K mi. it just makes sense to go ahead and replace the wires at the same time. Some may even get damaged trying to remove them from the plugs after so many miles.

Granted, wire cost could be a factor. I don't advocate getting the cheapest set available but you can spend too much with no benefit too. Many recommend Autolite wires but then I noticed that ACDelco Pro series look identical except the name printed on the wire and cost around $10-15 less. You won't notice a performance difference except possibly over the old wires if they're in bad shape, or if the new ones are so bad that they have some defect or design flaw making them unsuited in general.

Double platinum vs iridium makes little difference for the first several tens of thousands of miles. If you expect ("hope") to still regularly drive the vehicle past 50K miles from now then I'd take the double plat. back and get the iridium, but it's hard to call many things investments as a vehicle approaches 20 years old and beyond. Some people get over 250K mi. out of these and others get theirs totalled sitting in a parking lot at any time. It takes practically nothing in terms of collision damage to total it out at this age, or engine, tranny failure.

Wait on the coils until you have reason to think they're not functioning correctly. They can't be too bad if it's still running without missing even with plugs having over 100K on them.

 

[JTH1972]

I did take DPs back and got NGK iridium, as they were on sale for less than what I paid for the DPs.

With the iridium, bug warnings on package saying to not adjust gap, but does anyone trust factory gaping? I sure don't.

 

[J_C]

^ I didn't "trust" NGK Plat. gap but after checking, found they were all right.