2012 F-150, 150ishK miles, V-6.

I've been having problems with this thing for over a year. It started with the engine not wanting to turn over if the temperature was near or below freezing. It could be 30 degrees, engine would turn but not turn over. Jumped it, replaced battery, still did it. I could have it not start at 6:30 in the morning when it was 32 degrees, and then start at 10am when it was up to 40 degrees...which means when I would have it towed to a shop, they would say it started just fine, nothings wrong with it. At the same time it was doing all of that, it was misfiring.

The first shop I took it to checked for vacuum leaks, no leaks found. They also cleaned the throttle body and replaced the plugs, wires, and fuel injectors, still misfired, still wouldn't start when the temperature was 32 or lower. Took it to another shop. Told them it was misfiring, told them what had already been tried. They replaced the plugs, wires, and fuel injectors....again. They thought the not starting was the fuel pump and mentioned something else...fuel pressure regulator IIRC. They replaced the fuel pump, and that seems to have solved that problem. As far as I know they didn't not touch the fuel pressure regulator because it wasn't listed on the bill they gave me. But, it is still misfiring. I tried cleaning the MAF just to see, that didn't do it. My codes checker shows it misfiring in 3 cylinders...4, 5, and 6. I have no idea what it could be, or what to else to try. Any ideas? I'm totally at a loss of what to do with it. To be honest, I would hate to have to take it to the local Ford dealership simply because I don't trust them not to screw something up. I've had very bad experiences with them...like the time they checked the oil and didn't put the dipstick back in, or the time they drained the radiator to replace a bad brake booster, and didn't refill the thing with coolant, I could go on.

 

I would assume that they replaced the COPs (coil-on-plug). Did they replace the COPs?
What oil are you running in this engine?
Please post the DTCs

 

IIRC, the first shop I had look at it replaced the COPs and coil pack...I've been fighting with this for a year, so it's hard to remember everything. It has Motorcraft 5W20 in it. The codes I got were PO300, 304, 305, 306. I even cleared the codes before I checked to reply to you...the codes came back.

 

Hefeweizen,

Thanks for the info. I am not overly familiar with this engine so lets wait for the experts to chime in.

jimboy

 

This sounds to me like a coolant temp sensor issue. I did one for a guy on his 05 explorer just before I bought it off of him. Usually they will throw a code up but not all the time since it can cause multiple random misfire issues as well since the computer doesn't know how to adjust timing/fuel as it has no temperature data to go off of. When the coolant wasn't refilled did you have them refill it properly insuring there are no giant air bubbles in the system? This can cause a lot of issues as well with misfiring. Also could be timing chain/belt problems being that it seems like only one bank of the motor is misfiring.

 

I filled the coolant myself. It wasn't totally drained, they just didn't fill it all the way back up. I think it took close to a gallon or so to get it back to where it's supposed to be. That was long before the misfire problem showed up.

One other thing it's doing, that might be related. When I start it with the engine totally cold, the RPMs go above 2000 as they should, with no misfires...doesn't seem to be anyway...then drop within just a few seconds to about 700 or so. It used to not do that. That started about the same time as the misfires. When it idles, it idles below 500. If I put it into neutral, the rpms will go up to about 500, but put it in gear, and it drops below 500. That's what made me think it was a vacuum leak...or the brake booster. Brake booster was fine, no vacuum leaks as mentioned. But the check engine light doesn't start blinking at me until the RPMs drop.

 

The RPM's of the motor will change when shifting into gear as the motor is now under a load so that's pretty normal although your idle RPM sounds really low. For a cold start, especially in the colder months you should be holding a high idle for a few minutes so if it is dropping in a matter of seconds that would also lead me to believe that the ECU has no idea what the temperature of the coolant is and isn't adjusting fuel/timing properly. I am fairly convinced at this point that your coolant temp sensor has failed as it will cause all of the issues you seem to be having. This is just my opinion though as I am just going off your posts but that's what I believe it to be. This sensor has nothing to do with your temp gauge though. That gauge is ran off of the cylinder head temp sensor which is different.

 

I can give it a try. Where is it located? I Googled it and came up with different locations.

 

I don't know for your specific motor but i'm sure someone here has probably mentioned it before. Best bet is to just pop the hood and check the locations mentioned on google. Just make sure it is the coolant temp sensor and not the cylinder head temp sensor.