4.0 spark knock issue

[RonSerling]

Good afternoon all,
A good friend of mine has a Ranger with a 4.0 in it that has an issue. He took the motor out of it at about 225K miles and went thru it. He tore it down and took it to one of the more reputable machine shops where they did a total rebuild on all of the parts. Boiled block, bored .010 over, new cam bearings and so on. Same with the heads a complete overhaul. All the internals were replaced with new parts. He built the engine and put it in. He said to me that when he starts it it runs flawlessly but after it warms up a bit and he is on the freeway it starts to develop a spark knock. So he called me and asked my opinion. I thought about it but really could not come up with anything. I did have one idea but it sounds like something out of left field. I thought what if when he was assembling it he forgot to pull the pin out of the cam tensioner ?? Is it possible that this could cause the problem as the truck warms up ??? I just thought that if he didn't pull the pin as the truck warms up the chain stretches therefore causing it to go out of time and producing a spark knock !! So at this point I am not sure what to tell him but if anyone can help with any ideas or info it would be appreciated. Thanks

 

[Shran]

Is this a OHV 4.0 or SOHC engine?

My '94 will spark knock under heavy load in hot weather but it has a lot of miles on it and I think it's got an excess of carbon built up in the combustion chambers - it rarely gets driven and it smokes a bit. There is a TSB out there for it to clean them out, I guess it is pretty common. I would be kinda skeptical of that in a new engine.

How sure is he that it's spark knock and not something else? The CEL will illuminate on mine when it's doing it...pretty obvious "pinging" versus other engine noises I'm familiar with.

Has he tried higher octane fuel? Was the compression ratio altered when the engine was built? Just spitballing here...

 

[RonSerling]

The engine is an OHV. I drove the truck a couple of time and I am 99.9% sure it is spark knock. He, like I, only run mid grade or premium fuel in our vehicles. No compression ratio changes that I am aware of as I was told all parts were standard replacement with the exception of .010 over pistons. But the pistons were the same configuration as the ones he replaced.

 

[RonD]

What year Ranger, 1990-2000 used the 4.0l OHV?

There are 2 basic kinds of engine pinging/knocking
Bad spark timing, spark plug gap should be, 0.054 on 4.0l, wide gap
Lean fuel mix, test fuel pressure, 35psi 1990-1997, 60psi 1998-2000
This type of pinging/knocking could happen warm or cold, but Lean mix more likely after warm up when choke is off

3rd kind would be removing EGR system from a vehicle programmed to have an EGR system
4.0l had one after 1994, but Calif. Ranger 4.0ls had them earlier
EGR allows a more aggressive spark timing, so removing it can cause pinging/knocking
No EGR pinging/knocking would only happen after warm up, EGR is not used when engine is cold
Clogged EGR counts as no EGR, lol

 

[4x4prepper]

> All the internals were replaced with new parts

Including the wrist pins?

Was the engine blue printed, where he made a list of everything that was replaced and how big and how much it weighed? People have assembled engines before and been stuck before by having all pistons being .10 over, except for one, as an example.

I would start with the easy thing first, was the knock sensor installed correctly and is it functioning ?