2008 Mercury Mountaineer with 4.0L engine AWD

40 - 50 mph it stumbles/misfires(?) owner was told it was sticking valve and would need to rebuild head. Said they "scoped" it and there is scaring on the piston.

I think thats BS because it only does this during that speed range when it settles in to overdrive. If it were a valve, it would be sporadic not only in a given range.

I want to buy the SUV today but want morale support on my thinking. A buddy had a ranger with a similar problem and it was a bad cam. synchronizer. Not the position sensor but the part that looks like a distributor with no cap!

Thanks!

 

Reason for asking if this has one: I have looked at rock auto, parts geek and several box parts stores and can't find the part for this vehicle. Maybe dealer only? maybe it doesn't have one? maybe wrong part name?

 

I don't find evidence of one from the factory service manual either. Did your friend's Ranger have the 3.0L V6? That engine did have a synchronizer which usually would have a chirping noise prior to it causing driveability issues.

Does the seller of the Mountaineer have the scope images which show piston damage? I guess I haven't even checked to see if the 4.0L is an interference engine, but I'm not sure it is. If not, then the valve should not be able to contact the piston. And if it were a "sticking valve" I would expect, like you mention, that this would cause issues more often than only at higher vehicle speed. I'm not sure what to suggest though, other than if you purchase it, doing a cylinder decarb and full tune up.

-Rod

 

Thanks Rod

The ranger was an 05 I believe with 4.0L

I'm getting it at a price that I could afford to replace the engine with a remanufactured engine and still be all right if needed but I believe it is a lot less drastic than that!

 

That would be the SOHC 4.0 which has a cam on top of each cylinder head so no it doesn't have a cam synchronizer like the older pushrod motor.

 

Well, I bought it! Yes, it is the SOHC so Conanski I guess your right!

Within the next several weeks I will be attempting to eliminate each electrical item to determine the problem. I did run the scanner on it and got "P0302" #2 cylinder, which doesn't tell me a whole lot.

I had a 2004 Ranger 4.0 SOHC that had a bad rocker arm bearing and gave same code. I'll keep you all informed!

Thanks

 

By the way, on this SOHC engine, what tells the coil to fire and which cylinder? the cam sensor?

 

There is a cam sensor same as all the ford motors with overhead cams.

 

The crankshaft position sensor tells the coil when to fire. Actually, to be more precise, the crank sensor sends the signal to the ECM, and the ECM tells the coil to fire.

 

OK! thanks

 

Today is the first day I was able to do some troubleshooting on the misfire. I have determined that there is no current at my number 2 injector. I hooked noid to 1 and flash, hook to 2 and no flash. pulled wires out of plastic protector and someone has cut the original wires and added a new connector. I removed the new connector and hooked straight to the original wires and still nothing, tried noid on 1 again and it works. So I have a dead injector circuit for number 2 cylinder.

I want to let it cool down and check it at cold start up because the misfire is not noticeable then. I want to determine if it is heat related or just dead.

What might cause this and how do I trace that down?

 

More info: The purple wire that feeds the 2 injector is hot. My test light will light up when I connect to the purple wire then touch it to a ground. The grey/yellow wire does nothing.

 

OK. I think the injector was not pulsing because the computer was not letting it. I reset the computer and tried it again and it started pulsing. Obviously, this had been a problem. Not only did it have the new plug for that injector but i traced the grey/yellow wire to the PCM(?) (the main computer with the 3 harness plugs) and previous mechanics had isolated it and I could see the little hole in the wires insulation where they had tested that wire.

I then started researching "how to test a Cam Sensor". A lot of info/instruction on how to test Crank Sensors but not so much on the Cam Sensor. I decided to remove it and do a visual check. There was some sludge on the end from the magnet inside (think thats right) so I wiped it off and started it up. Surprise! It ran a lot better. I took it on a 30 mile drive and didn't misfire one time. New Cam Sensor is on it's way!

 

Today I will reattach the injector connector and just drive it to let the computer reset the system. I may also replace the O2 sensors because of all the lean and rich running but that will be after I put some miles on it.

 

I haven't looked the wiring diagram for you particular truck yet, but typically Ford controls injectors via the ground (transistor switch in the PCM) and the positive feed is constant. It sounds like your feed is fine, but if you're lucky there's an open in the ground between the injector plug and the PCM. Hopefully it's not a problem in the PCM, but you can check that pretty quickly by testing for continuity at the PCM connector.

Good job troubleshooting, and good luck! If you need pinout information let me know and I should be able to dig that up this weekend.

-Rod