This is not my truck. It isn't even a Ford. This is happening on a 1990 Chevy gas V8 (Big mamma). But the way I figure it, and engine is an engine.

This thing is worrying me. It is making a banging sound. I know what valve clacking sounds like because my old 2.8L used to do it 24/7. Valve clacking is usual small rapid tapping. This is more like a whack whack whack whack whack. Like something bigger and hitting harder. It is mostly when the engine is under a load accelerating and not at idle.

The mileage is not high (less than 100k) but it has a lot of hours on it. This is a fire truck so it sits there idling for a long long time.

What could this be and should I expect a piston rod to come through the hood sometime soon?

 

Anyone? Anyone?

 

could be a piston, rod bearing, wrist pin, it may have a broke valve spring, if its an automatic, it could be the torque converter, flywheel...

 

Gee, that narrows it down.

It is an automatic. This truck has a lot of use on it, it is all either idling or hard driving with no warming up. I'm afraid I might have to have a mechanic evaluate it. I'm just hoping to get an idea of the possible problems here so I know what we are getting into. If this thing is going to blow up in a month, I need to start planning an new EMS Rescue truck.

 

Could be a rod knocking, if u wanna do a little of ur own diagnosis...grab a long extension and while it is running, try to pin point where it is coming from. u could also check the oil pressure with a manual guage...

Does it increase with engine RPM? does it get better or worse when warm/cold?

 

The banging gets faster with RPM and cold or warm has no effect.

 

No, I would probably be looking for it to make an appearance near the oil pan.. not hood

Sounds like Rod Knock to me too.

 

definatly sounds like a bearing knock...just pin it to the floor and blow it up...be sure to take a video :-D

 

main bearing or rod bearing
I have seen a broken rod come through the side of the engine but never the top
increased noise under load usually means one of the main bearings is shot
454 / 7.4L ??? - probably just drop in another engine

 

Sounds like a rod knock. Happens alot in engines that sit at idle for long periods of time. Low oil pressure/insufficient oil flow across the bearings wears them out.
Check Advance Auto and see if they can order a reman engine for it. Buddy of mine got a Ford 460 long block for an old f-350 super duty for ~800 bucks from there.
You'll spend about as much money and time trying to fix that one as you would by just replacing it. And then you still may have more trouble with it in another month.

 

Believe me, there is nothing I want to see more than this truck to explode. However, in all seriousness I really do need to determine if it is on it's last leg or not since it is a front line emergency vehicle. If the engine is beyond repair, we will probably be replacing the entire truck. I'm going to be scheduling it for a visit to the Chevy dealer this morning.

I do believe it is the 7.4L. I know it is the biggest one you could get for it and you can fry an egg on the hood when it is warmed up.

 

The easiest way to diagnose a rod knock... Crank engine, allow it to idle down, manually pull spark plug wires off spark plugs one at a time(re-installing them if no audible difference). Determine if the knock decreases. If you get to one cylinder that makes the knock basically go away, then it is a rod bearing(or another faulty part on that cylinder).