Replace all coils or just the bad one?

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Wife called me today almost in tears. She was limping home in her beloved Rav4. It wouldn't go above 60 mph and it was shaking and missing something awful. And the CEL was going on and off. Torque lite to the rescue. Code P0303 (cylinder 3 misfire). Switched coils on cylinder 3 and 4 and it threw code P0304 (cyclinder 4 misfire). Have a Denso coil on its way from Amazon. Should I buy a spare or replace all 4 of them? Wife is spooked and doesn't want to have to limp home again. Not that having a spare will prevent that...
 
For me, it would depend on the cost of the coils. If they're inexpensive enough, I'd replace them all (or do 3 later, but don't wait too long). Some will say "if one failed, the others can't be far behind" but that's absolute speculation.
 
I would replace all four. Especially for my significant other. Peace of mind. The others may last 100,000 miles or go out next week. I'm OCD and believe in preventative maintenance. Others argue, don't fix what isn't broken. Certainly a financial decision.
 
I would do all of them, especially since it involves a significant other. FWIW Ford strongly recommends replacing the spark plugs in offending cylinders when doing a coil or injector.
 
I change them one at a time. They fail very rarely and on no set scale.

What I do is buy two to four from a salvage vehicle (genuine Toytota), then toss the spares in the trunk/wheel well.

I had to replace two on a Landcruiser V8 ~150k miles; none since (that was 10 years ago).
I had to replace on on an ES300 at ~250k about 3 years ago, now at 320k and no more.

In each case I used a junk-yard take off and it continued to work w/no problem.
 
Originally Posted by hatt
370,000 miles? I think I'd change all of them buy her a new(er) Rav4.

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In the absence of inferior, nascent plastics causing arcing through to ground by drying out or melting the only thing left to fail is the electronics.

If the "wire" and control card are made well and simply hold up....why not let 'em work?

And Lovloguy, why do you not like turbos? thanks
 
Get a spare. I've blown several toyota coils with little to no warning.

I'd go so far as getting one of those $3 ELM327 OBD dongles for the glove box and a 10mm socket/ wrench.
 
Originally Posted by Lolvoguy
Originally Posted by hatt
370,000 miles? I think I'd change all of them buy her a new(er) Rav4.

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She wants a new 2020 Rav4 in next March to May.

Amazon sells the coils for $53 each.

It has 390,000 miles in it now. If the new coil fixes the problem, I'll change out the other 3 and the plugs. Plugs aren't due until 420,000 miles so not a huge deal to do them a little early. Although, this is probably uncharted territory after the third plug change.
 
I think I'd just replace the bad one, at that mileage this thing is one major repair away from the scrapyard. Plus if it was driven that long with a misfire, there's a good chance the cat was cooked and I'm not sure this vehicle is worth replacing it.
 
Originally Posted by dishdude
I think I'd just replace the bad one, at that mileage this thing is one major repair away from the scrapyard. Plus if it was driven that long with a misfire, there's a good chance the cat was cooked and I'm not sure this vehicle is worth replacing it.


I was wondering about that. Wife drove it about 45 miles with the misfire.
 
For wife's peace of mind, get that Amazon order now, replace the bad one pronto; and get 2 or 3 junkyard units for cheap at your convenience. Keep them in the trunk so you can change them anytime. I'm not in the change-them-all-now camp because you don't know if the junkyard replacements are in as good condition as what you now have on the engine. And you're selling the car in 9 months. Good idea to change all 4 spark plugs now. If in good condition, I'd keep them and show 'em to the next owner as "proof" the engine was kept in good condition.

And cross your fingers re the cat conv.
 
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Recently on a Mini Cooper S we had a coil go bad. Its a common failure on Mini and BMW so I located a newer-design coil made by Delphi and swapped it out. Within 1-2k miles another coil on a different cylinder went bad. That seemed to be a firm trend so I went ahead and 3 more so all of the old coils have been replaced. The 2 old coils that are still good are sitting on the shelf for emergency use only.
 
I had a run in with my Camry and a failing coil recently

Made me late to work driving 12 miles with a flashing check engine light

A little bit of me died that morning
cry.gif


Turns out, it was an SMP coil that was less then a year old from AAP that failed

I'm at 127k and 5 out of the 6 factory coils still going, SMP Intermotor one couldn't last a year
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But now I don't trust any of them, I don't have the time or money to be stranded again

I have since ordered 6 fresh DENSO! coils and 6 of them new fangled fancy NGK plugs that I'll try because why not?

I'm not going to through that [censored] show again
mad.gif


You didn't tell us year/engine/milage?

If it's old enough, count on coil connectors breaking on removal

There like $11 for the set, have them on hand
 
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