Slight misfire when cold?

[SoulSoak]

Hey guys,

Not a big issue but just noticed today that when I start my car it feels like it has a very slight misfire. I'll give the throttle a few slow revs and I can feel a subtle shaking. But not like a severe misfire issue, if it actually IS misfiring... it could only be one cylinder if at all. I drove home, a couple miles, and when I parked in the driveway I gave it a few more slow revs and the slight misfire and/or subtle shaking is completely absent. I have no CEL.

Now I just replaced the cops and plugs last fall with Motorcraft OEM equipment, running me $350 in total from a member on this forum, saved me decent amount. Gapped them correctly and had no issues. The car then sat on jackstands all winter long. I've recently brought it out a couple of weeks ago and have been driving it. Drives great, runs great, feels great. No complaints other than this slight misfire upon startup, it only seems to last maybe a couple of minutes.

Now I've read many times that people are advised to change the cops and plugs at the same time. Bad plugs kill good cops, and bad cops kill good plugs (If I have read correctly). Now, my question is, given the fact that my cops and plugs were changed not too long ago and only have a couple thousand miles on them... if one or two may have become defective or faulty due to the car sleeping for 6 months... can I just go ahead and install a whole new set of spark plugs without it hurting my cops?

Cuz I'd highly assume my cops are good. So can you install new spark plugs and re-use the current cops (assuming they're good) without issues?

Probably a dumb question, but I take zero chances with this car. Also, if this whole slight misfire feel upon startup is common then please feel free to inform me. Also if you have any other suggestions.

Again, the car runs great, there is no misfiring or hesitation while driving. No misfiring or pinging even at WOT. No misfiring or shaking at idle either after the first couple minutes of run time.

If anyone is unaware, it's a 2003 Lincoln LS8. Thanks for your suggestions and advice as always.

 

[joegr]

...Now, my question is, given the fact that my cops and plugs were changed not too long ago and only have a couple thousand miles on them... if one or two may have become defective or faulty due to the car sleeping for 6 months... can I just go ahead and install a whole new set of spark plugs without it hurting my cops?...

Yes, you can change the plugs without changing the cops. New, good, plugs will never hurt the COPs. If you currently have a bad COP, then it will likely damage the new plug.
I have never heard of plugs failing just because a car sat for six months. I wonder how long plugs sit in the box in the store before they are sold and installed?

A slight miss at cold idle that goes away when warm could be a slight air leak somewhere, or even an injector issue. Also, the next time the engine is cold started, look at the damper and see if you can see any wobble or if you can see the belt tensioner oscillating.

 

[SoulSoak]

Yes, you can change the plugs without changing the cops. New, good, plugs will never hurt the COPs. If you currently have a bad COP, then it will likely damage the new plug.
I have never heard of plugs failing just because a car sat for six months. I wonder how long plugs sit in the box in the store before they are sold and installed?

A slight miss at cold idle that goes away when warm could be a slight air leak somewhere, or even an injector issue. Also, the next time the engine is cold started, look at the damper and see if you can see any wobble or if you can see the belt tensioner oscillating.

Thanks for the info Joe. Now just so I can be an idiot publically and be one less PM you have to tend to, what and where is the damper?

 

[joegr]

The damper is the big pulley at the front of the engine, in the center, down very low.

 

[SoulSoak]

The damper is the big pulley at the front of the engine, in the center, down very low.

Thanks, will definitely do. If it were the damper, is it expensive and/or something I can do myself? And let's assume it weren't the damper, and lets assume I installed new plugs and the issue were still there. How do I go about diagnosing it being an injector issue? This is ofcourse after I verify that I don't have an air leak.

 

[joegr]

New damper over $700, used are more reasonable. It's probably not the damper.
I'm not sure how you'd chase down a slightly marginal injector. One thing that I have heard of is to pull the whole fuel rail out and observe the spray pattern from the injectors. There is some pain and danger in doing this...

 

[stugots]

Had the same thing happen after I had my coils replaced. Doing the new battery procedure in the owners manual fixed it. (Something like let the car idle for 15 min with and without ac on).

It has started giving me symptoms again probably has something to do with getting a new battery recently, or the tank of 87 someone put in.. After I run this tank out I will do the idle procedure (or whatever it's called) again.

 

[Gus_Mahn]

My '03 LS8 does a similar thing. It's hardly noticeable when it warmer out. Slow reving and surging idle until it warms up. It also occasionally sets a P0171 and P0174 code. Both are lean codes. I'm my case I believe it's the square keyed o-ring between the upper plastic and lower aluminum intake. They are not serviced by Ford but are available on eBay. The block to intake gasket is available. My leak was verified with a smoke machine.

 

[SoulSoak]

Had the same thing happen after I had my coils replaced. Doing the new battery procedure in the owners manual fixed it. (Something like let the car idle for 15 min with and without ac on).

It has started giving me symptoms again probably has something to do with getting a new battery recently, or the tank of 87 someone put in.. After I run this tank out I will do the idle procedure (or whatever it's called) again.

I see. I may try that battery procedure just for the heck of it. However when you brought up 87 octane, something dawned on me.

When I let the car sleep for the winter season, there was a little over a quarter tank of gas left in it. I did fill the tank up but it's still running that mixture of old and new gas. That may be the cuplrit of the entire issue.

I'll run the car down to low fuel warning, then fill it up and throw a bottle of injector cleaner and octane booster in. Then we'll see what happens. Thanks for the input

 

[LS4me]

Had the same thing happen after I had my coils replaced. Doing the new battery procedure in the owners manual fixed it. (Something like let the car idle for 15 min with and without ac on).

It has started giving me symptoms again probably has something to do with getting a new battery recently, or the tank of 87 someone put in.. After I run this tank out I will do the idle procedure (or whatever it's called) again.

Where's jrand's driving procedure when you need it???

I see. I may try that battery procedure just for the heck of it. However when you brought up 87 octane, something dawned on me.

When I let the car sleep for the winter season, there was a little over a quarter tank of gas left in it. I did fill the tank up but it's still running that mixture of old and new gas. That may be the cuplrit of the entire issue.

I'll run the car down to low fuel warning, then fill it up and throw a bottle of injector cleaner and octane booster in. Then we'll see what happens. Thanks for the input

You might want to throw some Sta-bil in there now. Old gas will definitely cause issues. When storing the tank should always be full to prevent moisture from building up in the tank; which could also be your issue.

 

[stugots]

Where's jrand's driving procedure when you need it???

Yeah not to be confused with that..

I'm sure it will figure out the idle parameters over time, but it definitely worked right after I got it back from the dealer. Thought I was just wasting gas and about 7 or 8 min in it smoothed out perfectly IIRC.

 

[stugots]

Found it. Maybe I'm just thinking it was so long because I was waiting for it to get to temp.

1. With the vehicle at a complete stop, set the parking brake (Refer to
Parking Brake in the Driving chapter for information on how to
properly reset parking brake.).
2. Put the gearshift lever in P (Park), turn off all accessories and start
the engine.
3. Run the engine until it reaches normal operating temperature.
4. Allow the engine to idle for at least one minute.
5. Turn the A/C on and allow the engine to idle for at least one minute.
6. Drive the vehicle to complete the relearning process.
• The vehicle may need to be driven to relearn the idle and fuel trim
strategy.
• If you do not allow the engine to relearn its idle trim, the idle
quality of your vehicle may be adversely affected until the idle
trim is eventually relearned.