3vFanboy

A week ago I inherited my older brothers 2008 Mustang GT. He upgraded to a 2013 and was gonna sell the "black stallion" so I jumped on that as I've had my eyes on this car since he got it in high school.

The car was well taken care of and ran perfectly but I decided to tune it up just to start a detailed maintenance history on the car to up it's re-sale should I decide to in the future. I went ahead and did spark plugs, new ignition coils, fuel filter, and air filter. All OEM motorcraft parts. Toruqued everything down to spec like a good little mechanic.

The issue is after all this was installed I was listening and watching very carefully to make sure everything was running right. Sometimes when It's idling it makes a "plop" sound and the car shakes just a little bit. I mean you would really have to be paranoid to notice it. Normal?

I went through and pulled the ignition coil connectors one-by-one and each time I did that it made a BIG difference. You could really hear and see that something wasn't right there. My issue, if there even is one, isn't that at all. If there is a misfire it is a "small" one. My brother thinks I'm crazy and says it's fine. It's always done that. I'd like your guy's opinions. Thank you guys.

Oh, and the car drives perfect and smooth. I get 24-26 mpg which isn't too bad at all I don't think.

jpplaw

Most likely nothing to worry about. Sometimes the variable cam timing can make it do the thing you described, which is normal. You should also clean the throttle body and MAF just for the heck of it. Get yourself an oil separator catch can that goes in the PCV line too. Enjoy!

jesse1125

When you changed the spark plugs did you make sure the gap was right before you put them in?

AMWill

Hey 3v,

Congrats on the purchase, let's see some pictures!

As others have stated, I would make sure to check the gap on the plugs to make sure they are gapped properly.

Other then that, if it is a once in a while thing, it is most likely completely normal and nothing to worry about.

Keep an eye on it to make sure it doesn't get worse and keep your eyes peeled for CEL's.

Hope this helps and let us know if you get any more info!

-Will

3vFanboy

Thanks everyone for the replies. I feel a lot better about it now

In definataly be cleaning the TB and MAF as this probably should of been done with my tune-up anyway.. Opps

The spark plugs said "gap Is not adjustable" so I took that to heart. Is it safe to use a gapper to check as long as I'm not aggressive with it?

if I put my ear up to the exhaust pipes and listen I can't hear it "plop". It just sounds like it's rolling just fine so I might just be a little paranoid about my new car

bl817

what replacement parts did you use?

Simon1

There is a special gapping tool for the plugs. But before you buy the tool, buy one of the gap measurement tools and check the gap. I don't recall what exactly the gap should be, but it really only needs to be made smaller for higher FI applications.

The popping noise or misfire you describe is normal. I know it seems crazy, but it's normal. The tune can have a bearing on the idle "misfire", but it seems when the idle is higher it makes it go away.

3vFanboy

So I checked the plugs very gently and sure enough one was gapped at .33 the rest were fine at ~.40. I replaced the bad plug with a brand new one, I didn't even try to re-gap it. It didn't change anything for me though, the computer must be able to compensate a great deal for poorly gapped plugs.

I used all motorcraft parts as instructed by my older brother, especially for the plugs he said.

Simon- the small misfire I'm having is normal? What makes it do that? I'm not concerned, just interested at this point.

I work next to a Ford dealership in town. and "test drove" a 09. It did the high idle/cold idle thing without a miss, but once it settled down to idle it would do the "small" misfire thing. Guess it really is normal.. Strange.

So, is it fair to say my car is in good shape and I can just drive it and enjoy it now?

I'll get some pictures up once this snow melts, the Midwest just got hit with a snow storm this weekend and my mustang is just a giant snowball at the moment haha

3vFanboy

Oh, and in addition to the 09 Mustang I test drove I also checkout out my jobs Honda oddessy, dodge sprinter, and my girlfriends FJ cruiser.

The oddessy and FJ do the "small" idle misfire thing but the sprinter doesn't (diesel, non- VCT). It must be a VCT thing, huh?

jpplaw

VCT advances and retards the cam timing based on RPM. At idle you'll notice a very slight lope, sort of like it has a aftermarket cam (a very mild one though). Thats what you're hearing - the cam timing events are advanced at idle and low RPM to get more torque.