Any problems inherent to a 2005 DOHC 4.6 Ford

[The_Eric]

Hey guys, I'm looking at a 2005 Lincoln Aviator for the Mrs. Power plant is a 300hp DOHC 4.6. It seems to run well enough- definitely has some spunk, but was wondering if there were any problems associated with it? Did Ford actually put enough threads in the cylinder heads for the spark plugs? Cam phasers?

The SUV only has 65k miles on it and is in very good shape. It does have a few issues- a drive line vibration, torque converter shudder going into lockup, sometimes a delay/bang into gear and maybe a bit of a misfire.

If we can settle on it, I'll service the transmission oil which will take care of the shudder, and look into the delay/bang into gear- possibly a range selector switch and tend to the other things. I think (hope) it'll make a nice vehicle for her.

 

[CarbonSteel]

Fairly certain it contains the two piece spark plugs which are prone to breakage on removal. Ford redesigned the heads in 2008 to accommodate a one-piece sparkplug. I could be wrong about the two-piece plugs for the DOHC, but I think they used the same as the SOHC engines.

If it does, I would not leave them in until the scheduled maintenance time, but would change them early. Since you think it has a misfiring cylinder, it sounds like a plug change should be on your to-do list should you purchase the vehicle.

 

[Gasbuggy]

Originally Posted By: 2015_PSD
Fairly certain it contains the two piece spark plugs which are prone to breakage on removal. Ford redesigned the heads in 2008 to accommodate a one-piece sparkplug. I could be wrong about the two-piece plugs for the DOHC, but I think they used the same as the SOHC engines.

If it does, I would not leave them in until the scheduled maintenance time, but would change them early. Since you think it has a misfiring cylinder, it sounds like a plug change should be on your to-do list should you purchase the vehicle.


Different engine, this has the quad cam cobra/mach 1 4.6L

 

[OVERKILL]

You'll be golden, this engine is generally excellent.

 

[redhat]

Good engine.

Sounds good, good power, smooth. What can I say... besides that I want an 03-04 Termi Cobra along side my G-Body.

 

[Schmoe]

The shudder could be rear end if you have LS differential. You could dump it and put new friction modifier in it and see if that helps. If it's not throwing codes....see if you can get a read from the computer and look for past history of codes.

 

[ksp7498]

That engine should be pretty durable. Early DOHC 4.6's had various head problems including tiny spark plug threads that could strip (just like the 2-valve) and a flaw in the coolant channels that cause the valves on some cylinders to overheat. But the head was re-designed for 2005 and this one should be fine. So to answer your questions directly, yes this year of the DOHC head has enough spark plug threads and the DOHC does not have VVT so no cam phasers.

However given the list of problems you cite at only 65k miles I'm not sure I would say that truck is in great condition.

 

[racin4ds]

Minor issues on a great engine, if you get it cheap enough and you're mechanically inclined I'd say go for it. The misfire is likely a COP, infamous for going bad.

The shudder and shift issue can be fixed with a fluid change and a bottle or two of Lubeguard red. With that low of mileage I doubt it seriously hurt in any way.

 

[bdcardinal]

The most common problem on the 4.6L DOHc engines in the Aviators/Mach 1s/Marauders besides random misfires is the "head tick" issue. There were updated castings from January 2005 that helped. What happens is there is no exit for the coolant on the back of the driver's side head. Coolant pools there and overheats the exhaust valve guides on the rear 2 cylinders causing the ticking noise. The official fix from Ford is to replace the cylinder heads.

There are kits from a few different performance shops, mostly marketed at Mustangs, that knock out the rear core plug on the head and tee into the heater core lines. It allows the coolant to exit the rear of the head to keep temperatures stable. FWIW even the Coyote engines have this issue.

When we do the heads here in the shop, we also quote out the whole timing set. Usually the mileage on the vehicles the techs don't want to go through the trouble of pulling the motor to do the heads, only for there to be timing noise when it is fired back up again. BTW it is easier, even when I was turning wrenches, to pull the motor to do heads as you can get the torque wrench in there to properly torque the headbolts.

 

[nwjones18]

As far as I know those engines are generally pretty trouble free. Do these have the 4r70w transmission? If so shudder is very common change the fluid/filter with mercon V and dump in a bottle of lubeguard red.

 

[bdcardinal]

Aviators had the 5R55S transmission.

 

[Gasbuggy]

Originally Posted By: bdcardinal
The most common problem on the 4.6L DOHc engines in the Aviators/Mach 1s/Marauders besides random misfires is the "head tick" issue. There were updated castings from January 2005 that helped. What happens is there is no exit for the coolant on the back of the driver's side head. Coolant pools there and overheats the exhaust valve guides on the rear 2 cylinders causing the ticking noise. The official fix from Ford is to replace the cylinder heads.

There are kits from a few different performance shops, mostly marketed at Mustangs, that knock out the rear core plug on the head and tee into the heater core lines. It allows the coolant to exit the rear of the head to keep temperatures stable. FWIW even the Coyote engines have this issue.

When we do the heads here in the shop, we also quote out the whole timing set. Usually the mileage on the vehicles the techs don't want to go through the trouble of pulling the motor to do the heads, only for there to be timing noise when it is fired back up again. BTW it is easier, even when I was turning wrenches, to pull the motor to do heads as you can get the torque wrench in there to properly torque the headbolts.



Good info. Here is more for anyone curious http://www.terminator-cobra.com/castings.htm There was a head revision for 2004 also that Ford started using on the later 2003 engines which I thought also attempted to remedy this problem. I owned a 2003 Mustang Cobra 10th Anniversary edition which had the 04 updated heads.

On a SVT forum I've been on for a years there is a member with something like 370,000 miles on the original engine in his 2003 Cobra. It's had the head replaced twice, even the 05+ head develops the tick eventually.

 

[JustinH]

For drive line vibration in my fords, I would install a one piece driveshaft that was high speed balanced.

Some of the ford OEM units are two pieces forged together, and they vibrate.

I forget the name of the company who makes the one piece driveshafts, but they are right outside Buffalo, NY.

My opinions on the rest of the car, change the fluid in the transmission.

The 4v aviator motor is not built like the cobra motor, even they are both 4.6L 4v. If I recall correctly it uses rods from the 2v GT parts bin. But for SUV service it will be just fine!

 

[The_Eric]

After doing some readin on the 5R55S transmission, I think I'll likely need to replace the solenoid pack and probably replace the servo pistons. Evidently there is a place making replacement servo pistons that address the worn bores without sleeving the bores. It has an occasional funky shift flare, leading me to think that the bores are starting to wear and leak. I'll get the scan tool out to verify the harsh engagement isn't due to a range switch first though.

While I'm there I'll see if I can figure out the rough idle. Likely an ignition coil as others have said...

I've already been in contact with Pablo for some Severe Gear and SS ATF... So if the deal goes down, I may post up some pics of the repairs and maintenance.


Thank you to all who chimed in- makes me glad I don't have to deal with weird spark plug issues and cam phasers.