slight stumble 1,000 rpm driving

[MasterofDisaster]

A couple days ago I noticed a slight stumble in the motor around 1,000 - 1,400 rpm on city streets. Idle is fine and smooth. 80mph on the interstate is fine and smooth. No check engine light.

I changed the plugs to Motorcraft SP-509s about six years ago at about 90k. I'm now at 134k. Car is NA. Only mods are a Rousch CAI, underdrive pulleys, and ceramic coated shorties.

Think I should change plugs & fuel filter? [The air filter is fine.]

If I should change plugs, do we prefer

• NGK 1698 G-Power;
• CHAMPION 7406 Double Platinum;
• NGK 5507 Laser Platinum
• Something else?

[I assume I have brown coil boots. I just don't remember, but since I bought 509s, I assume they're brown.]

 

[Dino Dino Bambino]

A stumble suggests there's a fuel delivery problem. It's possible you might have inadvertently filled up with some contaminated gas so I suggest you replace the fuel filter first, and check if the filter sock on the fuel pump assembly is dirty.
You could also scan the ECU for DTCs. You could have one or two even without a CEL.

 

[MasterofDisaster]

Thanks. One thing I forgot to post is that mileage is worse that I would expect for this time of year and type of driving.

 

[Laga]

Have you cleaned the MAF?

 

[MasterofDisaster]

I cleaned the MAF around Christmas. The air filter is new.

On the way home from Saginaw the check engine light came on. Came back to P0303, bad coil cylinder 3. I'm having a hard time sorting out the coil packs between black & brown boots, so I'm just going to call American Muscle on Friday to order the right ones.

Autozone was nice enough to scan my codes, but they wanted $240 for Duralast coils.

 

[Dino Dino Bambino]

I'm having a hard time sorting out the coil packs between black & brown boots, so I'm just going to call American Muscle on Friday to order the right ones.

The correct coil part no. for your application is Motorcraft DG521:

https://www.rockauto.com/info/48/DG521-FRO.jpg

https://www.rockauto.com/en/moreinfo.php?pk=1293989&cc=1441221&pt=7060&jsn=474

 

[MasterofDisaster]

Thanks, Dino. Rock Auto wanted $40 a pop for Motorcraft; they wanted that for "Premium Delphi," which is just AD/Delco, so I bailed and went to American Muscle.

UPS had my coils in Du Bois, Pennsylvania by Sat night. I could drive there in much less than a day. By Mon they were in Maumee, Ohio, and I could drive there in a couple hours. Early Tues morning they were in Flint, Michigan. At my age I could run there, and assuming I wasn't shot, be back in about an hour. UPS then delivered the coils to USPS, so who knows when the Pony Express will bring them.