dealer changed 1 of my heads ( 2000 4.0 ohv) as was cracked with i believe a scrapyard head and milled the other ( as is my impression of what they did) as warranty repair purchased this ranger through them and had coolant loss since day 1...what would lower my power since they did this? i was happy with the power prior to them touching my truck... only thing i can think is i changed the plugs prior to bringing in it and when they changed the scrap yard they left the plugs that were in it....any suggestions would be appreciated thanks

 

check compression, thats the first thing that comes to mind, something might not have gone togther right. you'll see the plugs when you remove them. that would be my starting point.

 

the plugs look new ( replaced them before bringing it in) going to check if they put platinums....everything i ever had platinums in ran worse.. thinking maybe the valve components of the replacement head are worn...did a used oil analysis when i got it home ( was brought in for coolant loss) when it arrives thinking of bringing it to a different dealership for inspection

 

You're going to need to keep platinum plugs in it in my opinion. If it was a warranty job they would use a new head. If the heads were milled it would change the compression ratio a tiny bit but not enough to really notice. My best bet would be that the timing is a little bit off.

 

they used a scrap yard head ( ford dealership did the work, as bought through them and has coolant loss since day 1) my mustang 5.0 ran way better with regular plugs, this year ranger didn't come with them factory ...being distrubutorless timing can be outta wack? they milled the other head... had way better power prior to them touching it...the jacobs dis ignition is not supposed to be run with platinums which is my first guess...picked up some seafoam today to see if that helps i doubt they disassembled the scrap yard head to throughly clean it.... never would buy anything from this dealer again...bbb complaint and complaint to ford thus far has gotten me no where..first time i bought it in for coolant loss told me nothing wrong took a used oil analysis to get somewhere with them

 

Guys I really doubt a set of fresh plugs would cause a clear drop in power.

I'd suggest a compression test first and foremost.
If that check out.. maybe the exhaust is plugged.
Maybe the cams are not timed properly.
Maybe it has low fuel pressure.


Help us out a bit.. is it down on power all the time? Or just under certian conditions? How is idle and tip in power/rpms?

Rich

 

all the time in comparison to before more so in lower rpms lacks the hit it had before... sounds like my best bet to get a dealer to look at it...lack the equipment to diagnose it properly

 

If it's down all the time.. I'd want to check cam timing. If the cams jumped off a tooth when assembling it could do that. (this is a common mistake when rebuilding the Ford V8 mod motors)

Rich

 

no overcam on the 4.0 ohv...so that elimitates that possibility?

 

also if fine before head change... rules out the exhaust being plugged? or still possible?

 

Have you pulled the plugs out and see if they cracked one. When I had my 2.0 rebuilt in my 88 ranger by the dealer way back when I had a similar problem. I took it back to the dealer and they found one of the plugs was cracked.