I've built and installed a stroked 4.6l with a 9.5:1 compression ratio. The build went well until the engine was reinstalled. The engine will not turn over with the plugs installed. It turns over like mad with the plugs out. I've had the battery and starter tested, they checkout fine. I'm running out of ideas and things to check. I'm hoping that someone out there might have some other things I should check. Thanks!

 

i know you said you had the battery and starter tested but thats really the only two things that make sense. it could be a connection however. ensure the battery and all associated cables have a good connection (nothing corroded).

if the engine turns over without plugs that means that the resistance from compression with the plugs in is to much for the starter.

either the starter is bad or its not getting enough power.


edit: what about the solenoid? have you looked into that?

 

Could mean your pistons are hitting the plugs. Is the gap still OK on the plugs?
Have you run a compression test?

 

Are the COPs good? Is i that factory Ford alternator? I hear it is weak.

 

I've even purchased a new Optima battery, no change. Tried jumping it with my F350 PowerStroke running, again no change. Thinking I might have the wrong plugs for these type of heads I pulled them and checked for any signs of damage from being hit my the pistons, they too checked out.

 

Is the starter even engaging when you hit the key with the plugs in?

Take the plugs out, disconnect the battery. Take off the accessory belt on the crank. Can you turn the motor by hand say with a breaker bar?

After each test, put one plug in then test again. If you find at one time you can no longer turn the crank by hand after installing a plug, you found the problem cylinder.

 

Checked the plugs for damage when I removed them. I didn't however recheck the gap. I'll check that out tonight...thanks!

 

Turns over fairly easy buy hand with the plugs out. I like your idea about putting plugs back in one at a time. That could narrow it down in a hurry to one or more cylinder(s). Not sure I can get through all of them tonight but it's worth a shot.

 

What plugs are you using and which heads? They changed the design in 2007. The plug placement/thread also changed.

 

They changed the design mid-year 2008. I'm using this newer design with 12mm plugs vs older model 16mm plugs.