Coil pack diagnosis

The old Ford has some problems and think it might be a bad coil pack (rough idle, sluggish and loss of power, CEL on). Symptoms go away sometimes, but it's there most of the time. It's the 5.4l Triton, 350K miles or so.

Is there a way to diagnose a bad coil pack without an OBD scanner? How about isolating which one is bad? This truck is OLD and I'd rather swap out one coil pack than all 8 because these trucks tend to tear the boots off when you remove them and it's a PITA to get that shit out of there. The spark plug threads tend to strip out out the hole as well.

I thought of idling the engine and disconnecting 1 coil at a time to see if there's a difference in the idle. The one (or more) that does not make the idle worse must be the bad one. Any other ideas?

Autozone will scan for free. If this car has a code for each cyl it will let you know.

OBDII scanners are pretty cheap as well. If you ever blow a spark plug out, you know who to call for the right tool.

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Originally Posted by Erni

Autozone will scan for free. If this car has a code for each cyl it will let you know.

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I'm about an hour from an Autozone, that's why I'm asking.

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Originally Posted by Irving

OBDII scanners are pretty cheap as well. If you ever blow a spark plug out, you know who to call for the right tool.

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Indeed. I don't want to go through that again.

Unplugging individual coil packs should be just fine. Disconnect the low voltage leads to each pack, one at a time. Watch out for brittle plastic catches on those things. This test will only tell you which hole isn't firing, though the most common problem is the coil. Fordtechmakuloco has a good youtube channel on this stuff.

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Originally Posted by daknee_k

Unplugging individual coil packs should be just fine. Disconnect the low voltage leads to each pack, one at a time. Watch out for brittle plastic catches on those things. This test will only tell you which hole isn't firing, though the most common problem is the coil. Fordtechmakuloco has a good youtube channel on this stuff.

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Cool, thanks. And I've been to Makuloco's site many times researching this old gal. Should have started there I guess.

Well, I was poking around a little under the hood and checked the normal stuff. Air filter looked like it could be changed out. I jus did the PCV a few months ago. Everything else looked fine. So I did the air filter. Problem solved! Weird. It didn't look THAT bad and I'm pretty damn sure I put a new one in there in Aug/Sept during the winter prep maintenance.

The CEL came back on after a few starts so I'll still do an OBD scan when I get a chance. With this many Mike's, there's always something......except a car payment.

Probably knocked some crud off the mass air flow sensor when you changed the filter. The mass air flow sensor is super sensitive and very fragile. I killed one by spraying MAF cleaner on it. Basically a wire thick as a hair that changes capacitance with air velocity flowing around it.

Also a better than average chance that moving stuff around has gotten a better connection on the sensor wiring.

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Originally Posted by GilpinGuy

With this many Mike's, there's always something......

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Yeah. There are a lot of Mikes where I work so I feel your pain.

Code reader that works with your Smart Phone. Google them. I use Blue Driver. This will pay for itself in time and money.

you can also get a 10 pack of coils off of eBay for less than $50, got a set they worked fine in my 2000 F250 5.8 and had a couple extra