2005 XLT misfiring intermittently

[zoldos]

My 2005 XLT will misfire if I accelerate too hard. When I first purchased it, the misfire seemed to happen if I was in overdrive and going up even a small hill. The check engine light would flash and I'd lose power. Then, after maybe 10-15 seconds, it would stop flashing and it would regain power. I had it fixed (some part on "top" of the spark plug above the misfiring piston) for less than $100, but I can't remember what the part was.

It was fine for several years after that, and I kept overdrive OFF at all times. But then the other day I was going up a hill to a merge lane and had to speed up to meet traffic. It misfired just as before (flashing engine light, loss of power) for about 20 seconds, then the light stopped flashing, and it ran fine all the way home. It's done this twice now in the past month.

Also, sometimes when I try to accelerate, even just a little bit, the truck "knocks" and won't speed up. If I let off the pedal, and instead gradually accelerate, it will then work. No flashing engine light when it does that.

Is this serious? I only have one vehicle and not a lot of money right now. Should I take it easy as far as driving is concerned, i.e., don't drive it unless I have to? And what can I do to fix it? I don't know anything about cars/trucks.

Any advice would be most appreciated. Thanks!!

 

[SafariGoneWrong]

My experience is this is a classic case of misfiring due to ignition. My 2006 when I first got it with 70K miles didn't like high load at high RPM...I'd occasionally see the flashing check engine light. Replacing the spark plugs fixed everything. They were shot at 70K miles. Last time it misfired two years ago it was due to me cleaning the engine--I expected problems and sure got them. It hated going into overdrive--would buck and complain. Got it home and blew out the spark plug wells and coil boots. No issues since. I'm not sure if the '05s are smart enough to turn off the injectors when sensing a cylinder misfire. I read in what I think is a valid Ford tech pub; in '06 a strategy was implemented to turn off the injectors when a cylinder crossed a misfire threshold. Anyway...there's a chance you're sending unburned fuel into your catalytic converters so you'll want to fix it soonest.

 

[whtbronco]

Yeah sounds like spark plugs and/or COPs(Coil on Plug) to me. The coils are very easy to replace. The spark plugs, well 6 of them, are not hard to replace. The other 2 spark plugs are tough to get to, but a special $25 ratchet makes it rather easy I found. I see your engine has the newer design plugs that can break off and that can be a challenge to deal with. SafariGoneWrong may have more info on the plug issue, I have never dealt with it.

You can stop by any major chain auto parts store to get it scanned for engine related codes free of charge. That will likely tell you which cylinder is misfiring so you'll know what to replace. That said if you find any bad spark plugs replace them all. I prefer Motorcraft spark plugs, but others may work okay. For the COPs don't even bother with any other than Motorcraft.

Plugs: MOTORCRAFT SP546X
COPs: MOTORCRAFT DG511

I stick with my Motorcraft recommendation for the COPs, but I have had good luck in the past with parts that RockAuto reports as the "Original equipment part" and in this case they show this for DENSO 6736003 and they are a bit cheaper. So if money is tight, you can try the Denso COPs. The COPs can also be replaced 1 at a time.

 

[zoldos]

Yeah sounds like spark plugs and/or COPs(Coil on Plug) to me. The coils are very easy to replace. The spark plugs, well 6 of them, are not hard to replace. The other 2 spark plugs are tough to get to, but a special $25 ratchet makes it rather easy I found. I see your engine has the newer design plugs that can break off and that can be a challenge to deal with. SafariGoneWrong may have more info on the plug issue, I have never dealt with it.

You can stop by any major chain auto parts store to get it scanned for engine related codes free of charge. That will likely tell you which cylinder is misfiring so you'll know what to replace. That said if you find any bad spark plugs replace them all. I prefer Motorcraft spark plugs, but others may work okay. For the COPs don't even bother with any other than Motorcraft.

Plugs: MOTORCRAFT SP546X
COPs: MOTORCRAFT DG511

I stick with my Motorcraft recommendation for the COPs, but I have had good luck in the past with parts that RockAuto reports as the "Original equipment part" and in this case they show this for DENSO 6736003 and they are a bit cheaper. So if money is tight, you can try the Denso COPs. The COPs can also be replaced 1 at a time.

Yes, that's it. It was a coil that was replaced, and it fixed it. Those are easy to change, you said? I have a decent code reader. Will it be able to tell me which cylinder is misfiring? I don't have to check while it's actually happening?

 

[SafariGoneWrong]

You'd think there would be a stored code. Be on the lookout for a P030X code where X is the misfiring cylinder. Cylinder #1 is forward on the passenger side, #4 is aft passenger side, #5 is forward driver side and #8 is aft driver side. You'll want to determine how many miles are on the spark plugs before chasing COPs. When I first got my '06, the only code was cylinder #5 misfire (P0305), so I replaced the COP but that didn't help. Hoping your spark plugs aren't original. 6 of the 8 originals on mine broke coming out, even following the Ford TSB instructions. If they've been replaced, chances are much better they come out intact. I'm at 125K miles with the original COPs.

 

[whtbronco]

SafariGoneWrong provided a good answer for the codes and coils.

Yep, they are super easy to swap. Once you replace one you'll be able to do another in just a few minutes. The rear 2 on the driver side a tiny bit tough reach, the 2 in the rear on the passenger side are a bit more challenging to reach. You need a ratchet, 3-4" extension and a 7mm or 9/32" socket. Since these bolts are little and they are not tight I use a 1/4" ratchet and socket, but the typical 3/8" size ratchet will work fine just need to be more careful not to over tighten. In fact the torque spec for the COP retaining bolts is 62in lb, best way I can describe that is just past snug while holding the ratchet by the head not the end of the handle.

You might have to remove what I call the ugly cover, which if I recall correctly is two 7mm bolts on the driver side and it pulls up and off the passenger side. Don't quote me on that. I removed mine twice in 2004 and it's been in the attic since. After the plastic intake cover is removed carefully unplug the connector for the COP you want to replace. Remove the bolt and wiggle it and pull it off. You'll have to bend it a bit to get it past the fuel rail, but this is not a concern. The coil itself on top is plastic, but the boot is very flexible rubber and that's what you'll be bending. When you go to reinstall put a little dielectric grease on the end of the boot. I use my pinky finger for the inside since it fits about perfect and yo don't want grease on the spring that connects to the plug so it's easier to just use a finger. I also put a bit on the outer side of the coil boot at the top where it seats into the intake manifold as it helps to keep dirt out of the hole in the future.

An extendable magnet is really nice to have if you have happen to drop a bolt. They are a couple bucks and can be found at any auto parts store near the register or Harbor Freight. I loosen the bolts and then pick them up with the magnet. I usually put them back into the hole with the magnet as well. Push the bolt down in the hole with the magnet and slide the magnet sideways to leave the bolt behind. Then you use the socket and extension to start the bolt and just snug it down with the ratchet.

 

[GaryH]

Yes,more than likely its one of the 8 coils. Yes, your OBD II reader will tell you which one or ones are misfiring. No, its not that easy to DIY except for coil #5.

 

[Esat]

My 2005 XLT will misfire if I accelerate too hard. When I first purchased it, the misfire seemed to happen if I was in overdrive and going up even a small hill. The check engine light would flash and I'd lose power. Then, after maybe 10-15 seconds, it would stop flashing and it would regain power. I had it fixed (some part on "top" of the spark plug above the misfiring piston) for less than $100, but I can't remember what the part was.

It was fine for several years after that, and I kept overdrive OFF at all times. But then the other day I was going up a hill to a merge lane and had to speed up to meet traffic. It misfired just as before (flashing engine light, loss of power) for about 20 seconds, then the light stopped flashing, and it ran fine all the way home. It's done this twice now in the past month.

Also, sometimes when I try to accelerate, even just a little bit, the truck "knocks" and won't speed up. If I let off the pedal, and instead gradually accelerate, it will then work. No flashing engine light when it does that.

Is this serious? I only have one vehicle and not a lot of money right now. Should I take it easy as far as driving is concerned, i.e., don't drive it unless I have to? And what can I do to fix it? I don't know anything about cars/trucks.

Any advice would be most appreciated. Thanks!!

You might be lucky for a spark plug and/or coil pack issues. Or unlucky (like me ) with a input manifold gasket leak. Leaking coolant was going to the spark plug holes and causing intermittent misfires on my case.

 

[zoldos]

So, an update: I checked the codes again, and there was nothing about a misfire, but there were 3 codes, and all said something about a high pressure sensor evaporative issue in the fuel tank. It's actually had this issue the whole time I've had it, but the mechanic said it wasn't "urgent".

I deep dived the issue, and discovered it definitely can cause misfires, knocking, rough idle, and performance issues. All of which it has to some degree.

I think getting this fixed would solve all the issues!

Comments?

 

[whtbronco]

The Fuel Tank Pressure Sensor can cause performance issues and if the codes indicate it's faulty it should be inspected and/or replaced. It could be the sensor, I had one fail in a Monte Carlo, but it could also be a wiring/connector issue or simply the o-ring seal.

 

[zoldos]

The Fuel Tank Pressure Sensor can cause performance issues and if the codes indicate it's faulty it should be inspected and/or replaced. It could be the sensor, I had one fail in a Monte Carlo, but it could also be a wiring/connector issue or simply the o-ring seal.

I was quoted around $350 several years ago to get it fixed. I think it's about time. But like I said, it *only* misfires if I like floor it. Normal driving it seems to run fine.....

 

[whtbronco]

Book time shows just 0.3hrs to replace it, but I would think you'd have to drop the tank which takes some time to do. $350 sounds about right and I'd bet closer to $500 now days. If by chance it's leaking it may be letting dirt into the tank.

 

[zoldos]

Book time shows just 0.3hrs to replace it, but I would think you'd have to drop the tank which takes some time to do. $350 sounds about right and I'd bet closer to $500 now days. If by chance it's leaking it may be letting dirt into the tank.

Thanks for the feedback! I've never seen any leaks and never smell gas or anything. Hoping to take it in next month and lay low until then.