Bucking engine

[BrightExplorer]

Good morning all,

So a bit of background, 03' XLS 4.0 v6 182-3k miles...

The other day, the engine started bucking a bit while it was idling every 10-15 seconds or so. I didn't notice whether or not it was doing it while driving. I have noticed now, that it does shudder a bit at times while driving.

And still every few seconds while at a stop light, it will cycle then buck, cycle then buck...

The engine isn't throwing any codes, no dash indicators are illuminated..
And the bucks have very little to no impact on the tachometer, although sitting in the vehicle, they are quite noticeable.



My initial thought is a misfire, due to bad spark plug. As far as I know, the plugs/wires haven't been changed...

And I was going to attempt to change those this weekend.

I guess I just want input from more experienced mechanics/Ford owners, so I could know I'm not way off base and looking in the wrong direction.

Thank you in advance.

 

[mExp]

Well I'm not an experienced Ford mechanic, but at 182k miles, if those are really the original plugs they definitely need to be changed out for some new ones. Wires I might be less concerned about, but change them anyway, its cheap insurance.

If I were you I would pull the plugs to see what they look like and what the gaps measure (I think they're supposed to be something like 0.052-56).

While your at it throw in a can of Techron or Seafoam in the gas tank for good measure.

Its smart maintenance and won't cost you too much for the parts.

 

[Number4]

If those are the original plugs, their gap will be in the .070"+ range by now. Just a little outside of spec.

Could be enough to miss but not enough to throw a code.

 

[BrightExplorer]

Much appreciated... I will buy 6 plugs tomorrow and hopefully get to it sometime this weekend.

I will post result. And measurement of gap if there is a noticeable difference.

 

[TechGuru]

Much appreciated... I will buy 6 plugs tomorrow and hopefully get to it sometime this weekend.

I will post result. And measurement of gap if there is a noticeable difference.

You do know what plugs to get right?

http://www.rockauto.com/en/moreinfo.php?pk=949946

Motorcraft SP500 ONLY.

You will probably want to get them online. $18.84 vs $29.94 @ OReilly.

 

[dla]

There is a difference between bucking and misfire. Bucking is usually caused by a too lean condition, or some really bad fuel.

Old sparkplugs cause misfires.

 

[extra-medium]

You do know what plugs to get right?

http://www.rockauto.com/en/moreinfo.php?pk=949946

Motorcraft SP500 ONLY.

You will probably want to get them online. $18.84 vs $29.94 @ OReilly.

Why is that the only spark plug to use on the 4.0? I have 142K on mine and I don't know when the last time mine have been done if ever. I'm just curious if I could be able to use the NGK Iridium plugs instead of platinum plugs.

 

[Number4]

Any brand Iridium will be fine. Any car that took Platinums, should have Iridiums in them at this point. Platinums will/should fade away.

No +2 or 4's. No Rapid Fires.

 

[BrightExplorer]

There is a difference between bucking and misfire. Bucking is usually caused by a too lean condition, or some really bad fuel.

Old sparkplugs cause misfires.

The sparkplugs are probably original. I haven't changed them.

The engine seems to cycle normally then dip suddenly when idle, and at times while driving both accelerating and holding constant.

When the engine "dips" or "bucks" as im calling it, you can feel it but the tachometer doesn't move.
At idle it will do it again a few seconds later... run smooth then a few seconds lator dip again...

I'm no mechanic, so I just want to make sure I'm not way out in left field treating spark plugs when its a Vac Leak or fuel filter, etc.

 

[IPcamper]

You might also want to change the fuel filter.

 

[BrightExplorer]

And of course, when I take a video, its hard to tell anything...
Unless you guys know what you're looking for and I don't... whiiiich is probably a good guess.

But there is the slight jerking/shudder to the motor that can be felt in the steering column.

I was hoping to actually get it when it "bucks" a bit



I may upload another video when the symptoms appear to be a bit more prevalent.

 

[decipha]

bucking is when the vehicle shakes violently while driving this usually results in head trauma to the vehicle operator

misfiring is no where near a buck

an engine cannot buck in idle or when stationary it would just be misfiring

 

[Joe in NY]

Why do you guys say replace fuel filter when people have an idle problem?

Fuel filter only comes into play as bad when doing WOT and running our of fuel or cruising and the engine running lean and low fuel pressure. If you have good fuel pressure the filter is fine.

Heck, newer cars don't even come with them anymore also.

 

[TechGuru]

Actual "bucking" could actually be a transmission issue.