Occasional miss--What would you check?

[ET16]

I have an occasional miss (once every 3-4 minutes) in a '02 Mercury Cougar with a 2.5L V6. Throttle body is clean, plugs are recent and I ran some injector cleaner on the last tank. I checked with my scanner a little while ago and have no codes. I was thinking I might change the wires, but I don't necessarily want to start throwing parts at the issue, willy-nilly.

Thanks for your suggestions!

 

[94supraonchrome]

try cleaning the MAF sensor with some CRC MAF cleaner, check the PCV valve as well.....

 

[javacontour]

Did you have the miss before you changed the plugs? Maybe you got a bad plug? Maybe a wire isn't well seated on the plug or the coil pack?

If you are on the factory wires, it's probably time.

If you really don't want to spend any money and you still have the old plugs, put three of the old plugs back in one bank and see if the problem recurrs. If it does, return the new plugs to that bank, and swap out the other bank.

If it's still there, then your likely suspects are the wires or the coil pack.

It could be other things, but I'd start with ignition.

What kind of plugs did you put in your Duratec?

 

[ATS-V]

I would start in this order.

1) Clean MAF
2) Change wires
3) Check plug gap (use OEM plugs) and decrease gap slightly if set at factory gap (decrease by 0.005)

My bet is on the wires, once removed to check/replace plugs they sometimes get FUBARed internally.

 

[cjhepburn]

Does the speedo or tach jump around at all?
If so my money would be on a bad wire.

 

[ET16]

Thanks for all your suggestions. I'll go through them step by step. My best guess is wires, too. I'm running Autolite XP104 plugs.

 

[javacontour]

I ran Autolite doubleplat's in my SVT Contour before adding boost. It ran well with those.

Maybe the Iridium plugs are not the right choice for the Duratec?

 

[Nick R]

Check the Coil-over-plug ignition coils and boot for damage. Alot 90s and early 2000 fords had problems with those.

 

[javacontour]

I don't think the 2.5L Duratec ever had COP. Maybe the 3.0L, but I don't think COP made it to the 2.5L

 

[Nick R]

Originally Posted By: javacontour
I don't think the 2.5L Duratec ever had COP. Maybe the 3.0L, but I don't think COP made it to the 2.5L


It's possible, I don't know for sure. But still check the plug boots and wires for damage/wear. If you want to see anything you could probably wait until its night, turn off all lights, start the car and open the hood and watch to see if you can see any sparks. If your wires are really worn, you might see a laser show under the hood.

 

[ET16]

My '02 doesn't have COP.

 

[tig1]

Wires.

 

[ET16]

Well, I cleaned the MAF and added a bottle of Techron to my tank and the miss has cleared up. I ordered wires, too--a little too prematurely, it seems.

 

[mechtech2]

Don't regret getting new wires.
A part doesn't have to be broken all the way before preventative maintenance is smart!

 

[ET16]

Originally Posted By: mechtech2
Don't regret getting new wires.
A part doesn't have to be broken all the way before preventative maintenance is smart!


That's a good point. I was beginning to think the same.

 

[swalve]

I had a 2.5 Duratec in my 99 Contour. Good engine. Ran smooth as glass, but [censored] did it vibrate at high RPM.

Anyway, as if got up in miles, it started doing the same thing. I eventually determined it was a lazy o2 sensor. It just quit reacting quick enough.

 

[Papa Bear]

Check for a wedding ring to be sure it's not an occasional Mrs. ...

 

[Papa Bear]

Seriously, my '07 Uplander sometimes gets a rough idle (in neutral, not park) but works flawlessly when left in gear at a light. No CEL...... I just ignore it.
(probably a windows based engine management program ??!!)

 

[ET16]

Well...it was the wires. I changed them today, and the miss is gone!

 

[bigmike]

Originally Posted By: ET16
Well...it was the wires. I changed them today, and the miss is gone!


I had a miss once and my dad told me to check it at night (or in the dark). Sure enough, I could see the arcing from the bad wire. Or you can hold onto them while it's running - another suggestion he gave that I didn't take him up on.