Hello all
Im finishing up a head gasket job on my 03 4.6 2v. I got everything back together and it runs except at idle it only hits on cylinders 2 3 5 8 (that's exactly every other). This happens until it hits about 2,000 rpm then she snaps out of it like a light switch and runs like normal. Everyone I have talked to says its the ignition timing but this truck is COP ignition. If anyone has had this problem or knows of a possibility please lmk. Thanks in advance

 

That would be a "bank" problem. The injectors are bank-fired at times. At idle they should be sequential, but still each bank is using a separate O2 sensor. One guess might be an O2 sensor problem. Causing that bank to run lean or rich.

Does it happen all the time or only when the engine is warm or cold? A cold engine should be open loop for a while and not use the O2 sensors.

Anyway, it sounds like an injector problem. You might try Noid lights to see what the injectors are doing.

 

I cracked the water neck during installation. Currently I’m waiting on a new one and have the old one RTVed together. With all the RTV in the water neck there’s no room for a thermostat. So the ECT is lucky to get over 110. Also I thought that the banks where a entire side of the engine bank one being cylinders 1-4 and bank 2 being cylinders 5-8 therefor making my problem be on both banks.

 

I got distracted by "exactly every other" and Ford's odd way of cylinder designation Actually, it's the two end cylinders on bank 2 and the two middle cylinders on bank 1. So, even weirder than you thought.

How do you know which cylinders? If it's running on four it must be hard to tell.

https://www.f150hub.com/maintenance/cylinder-map.html

 

While the engine is acting up I can unplug the coils on the problem cylinders and there’s no difference but when I unplug one of the cylinders that I know its firing on it then almost dies trying to run on 3.

 

The fact the cylinders are firing at higher rpm and not lower rpm is weird. I think you need better diagnostic data to determine which cylinders are firing and when. You need some real time monitoring to actually see what is going on..

 

Might be that something is causing the PCM to go in to fail-safe mode. Usually it's overheating, according to the Owner Manual. Shuts off half of the cylinders. Not clear which cylinders you're looking at. Your description has conflicting data. 2 3 5 8 are not "every other".

Why did you have to replace the head gaskets? How well did it run before?

"How fail-safe cooling works
If the engine begins to overheat:
• The engine coolant temperature gauge will move to the red (hot) area.
• The and the symbol will illuminate.
• The “Service Engine Soon” indicator light will illuminate.
If the engine reaches a preset over-temperature condition, the engine will automatically switch to alternating cylinder operation. Each disabled cylinder acts as an air pump and cools the engine."

 

I don't know you can do head gasket r&r and not know it must timed correctly. I'm surprised it runs, would be very surprised if all the valves are still straight.

 

It ran great before the I did the head gaskets but it was spitting oil out in between the head and the block. For a wile I was just living with it but it got to the point where I couldn’t keep oil in it.
As per your overheating theory I currently don’t have the thermostat in bc of a cracked water neck that’s RTVed together. The engine stays cool but it never worms up. Would the PCM go into fail safe mode bc it’s not seeing the right ECT #s and if so why would it go into fail safe when I first start it.

 

I had that thought to but before I started the engine I pulled the spark plugs out and rolled it over 3-4 full rotations with a 9” ratchet on the crank. I couldn’t see myself being able to bend a valve with a 9” Rachel on the crank. Also if it had a bent valve then how would it run at higher RPM.