Hi forum,

I'm a hobbyist ,and to be clear not a mechanic. Learning as I go.

I have a NF Fairlane V8 (5.0 302 EFI) which has developed what I think is a bottom end knock. Symptoms as follows:
- Doesn't appear on startup, only when warm. Does not go away.
- Knock sounds faster when applying throttle (obviously)

I've changed the oil to 20W60 Penrite HPR30 Mineral Oil.

Engine also seems to have a blown head gasket (small white vapor coming out of exhaust once warmed up).

At this stage, I just want to diagnose the knock, before I send the motor away for a tear down and rebuild (or look for alternative options).

For curiosity sake, I bought a copy of Todd Monroe's book "How to rebuild Small Block Ford Engines" and found a section that says to disconnect each spark plug lead one at a time, to see if the knock noise changes / goes away.

It also mentions that if the car is equipped with solid-state ignition, always ground the lead that is disconnected, Otherwise, the ignition system can be damaged. Something similar is also mentioned in my other book that says "DO NOT OPEN CIRCUIT any high tension cable with ignition switched on or with engine running, as the control unit can be damaged".

From what I'm reading above, I'm guessing that by disconnecting a spark plug lead, I run the risk of damaging the EFI computer? So this is my question basically. As to what to do with the motor, I'll assess that a bit later.

Would greatly appreciate any advice on the above.

Cheers

Disconnecting the spark plug wire while the engine is running is a common method of identifying the cylinder contributing to the knocking. If the knocking reduces or disappears when a particular cylinder stops working, it may be related to problems in that cylinder. {DESCRIPTION}

Thanks for your reply mate.
Haven't had much of a chance to use the car, but I will go ahead and disconnect the ignition as I'm also looking at doing a compression test.

Agreed with you. This is a good and easy way to know the issue.

Have you verified the base timing?
If you think you have rod knock it's quite possible your blown head gasket has causing bearing damage if the water builds up in the cylinder when the engine is off.