How to test coil pack

Saturday I was catching the highway and when I hit 65, the engine started to lose power and bog down to 45. After 10 seconds or so, the engine was back to normal and up to speed. Wonder if one of the coils are bad. I can get the

$57 DENSO 6731201 DIRECT IGNITION COIL

DENSO 6731201 coils for about $55 each. Might just get all 3 OEM's for $175 shipped

Note, 2 of the coils are OEM and 1 is aftermarket. I have no idea how old the coils are, but I would say they have been on for a long while.

New OEM plugs and wires were installed last year along with OEM fuel filter

95.5 4x4 V6

 

i have yet to come across what the 'approximate' lifespan is of the coils (years or mileage)
does anybody know?

 

If it was just that one time, I'd wait and see. If its happening more than once - then yeah, start figuring out possibles.

If you're going to replace coil packs, I'd replace the aftermarket first. Denso is fine - its OEM. When was the last time you cleaned the throttle body?

See below for testing - snapshot from the 96 FSM

 

I would go to O'Reilly Auto or Autozone and get a free OBD readout first. It could be an injector beginning to go out. In any event, it's good to know a bit more about what's going on.

 

Where do you even plug in the OBD on my 95.5?

 

Is your check engine light on?

 

Nope

 

How smoothly does it idle? Has it done this more than once? Intermittent bogging like that feels like another problem, possibly fuel or something.

 

I don't know where the 1995.5 OBD plug is, but the tech who checks it does. Maybe somebody else here can help?

I also don't know what the parameters are to get the CEL to come on. It comes on as soon as the key engine starts in some cases, but in others it takes awhile (like, um, 100- 200 miles or so, or a certain number of start-ups). When mine came on, it would go off after driving about 10 miles, but would come back on after I turned the engine off and let it set for 10 minutes. After I found and fixed my problem, the CEL stayed off for another 150 or so miles, then it came back on, and stayed on, whenever the engine was running. Go figger...

 

I'll be getting the coils in Wed, and I'll report back. Wanted to change them when I bought the truck back in 17 becasue I changed almost everything else

 

Then not much is going to be had with the scanner. If your CEL is on then I'd say grab a scanner and check it out but not going to tell you anything at this point. CEL light is going to come on and stay on when the computer detects an issue.

 

The CEL should come on as soon as the ignition is in the ON position. A few seconds after the engine is started and running, it will go out. This is normal behavior.

What you describe is not. Whatever issue you found and fixed is either back or wasn't the entire issue and something else is going on since it "came back on and stayed on after 150 miles or so". Go have autozone or wherever check it again and see what fault code shows up. Something is wonky.

 

The first time my CEL went on it was due to a faulty injector.

The second time it turned on (and then stayed on whenever the engine was running) was caused by a vacuum leak. Thank gawd for whomever told me to use starter fluid and check for leaks!

​

Putting a clamp on the loose hose solved the problem. I never would have found it just by wiggling the hoses because that particular hose seemed tight to me.

 

Just replaced all 3 coils via Denso along with new bolts. Of the 3 old coils: one was the original oem - another was oem, but probably 10+ years old - and the last was aftermarket, probably a few years old. Feel better all are new OEM