Knocking while running and after engine turned off

[JackSmack22]

So essentially while the truck is running I hear knocking after the engine heats up. After I’m done driving and shut the truck off, it will continue to knock for about 10 seconds slowly dying out. It’s roughly about a knock or two every 2 seconds. I feel it coming from the engine. How do I diagnose this and what might the problem be?

 

[alwaysFlOoReD]

I would suspect something to do with the cooling system. I've had similar symptoms when overheating. I hope that's not the case for you.

 

[JackSmack22]

Thanks for the insight. It’s runnin old coolant right now so I’m going to do a flush and fill and see for any change. Any other suggestions in terms of a fix? I’d also like to add that the engine does not seem to be overheating, unless my gauge is broken. However my ranger has a very unpredictable idle. Some days it starts great some not so much. However it never likes to idle for more than 5 minutes withought wann

 

[alwaysFlOoReD]

You could get a new rad cap. If the system isn't pressurizing then it could boil at a temp below normal.

 

[Brain75]

Since this is in the 4.0 sub, I assume this is on a 4.0.... let me ask for a little clarification on first post, you are getting 10 full seconds of dieselling (running on after ignition is cut) on an EFI 4.0?
I had heard that dieselling was basically a carb only problem and came from an incorrectly setup carb (generally too rich, too high idle).... but I guess the other causes would still apply, wrong octane gas (too low), too much timing added, etc...

Now the wrong octane gas would explain both knocking and dieselling w/ more knock especially if the idle is set too high. just clarify, are we talking EFI here and you are getting 10 real seconds of run after ignition cut not just a second or maybe 1.5....?

 

[JackSmack22]

I looked into dieseling, I don’t think that’s the problem because the engine does go off as soon as I turn it off. It almost seems just like a knock after. Nothing else. But it does go for about 10 seconds slowly dying. I definitely put the right octane gas in but your point is correct if that were the case. I appreciate all the help from this forum.

 

[Bgunner]

Maybe a video with audio of the issue would help? I'm a little confused to exactly what is happening and I think a vid would help to explain and clear up some confusion.

 

[alwaysFlOoReD]

The knocking starts after the engine is running and warmed up. It continues after shut off for 10 seconds of so, getting quieter as time goes on.
That doesn't fit dieseling. Dieseling only happens after the engine is shut off.
It does fit an overheating engine, or an engine with hot spots, or low rad fluid.
It may be something else as well, but I can't think of what.

 

[Brain75]

agreed, I just read the first sentence as being dieseling or unclear - once cleared I am at a loss honestly... ac equalizing pressure internally, radiator dropping pressure or metal on metal thermal contraction (my radiator pops/clicks while cooling but that is a long way from "knock" - my GM and almost every other vehicle I have had does that)... kinda out of my element on this one without a sample of the sound.

 

[SenorNoob]

It does fit an overheating engine, or an engine with hot spots, or low rad fluid

This^ Hopefully just low coolant. Maybe a small leak.

 

[4x4junkie]

Yeah an audio recording of some sort of the noise would really help here.

 

[Shran]

I also have started hearing a weird noise like that at times. Once while idling at a stop light last week and once while parked right after I shut the engine off. It sounds like a dull thumping inside the dash on the passenger side. Does your sound like that? It happens so rarely that I haven't been able to listen carefully yet.

Could be cooling system related... steam, etc. '94 and up usually have a vacuum operated coolant shutoff valve right where the heater hoses go into the cab. Could have something to do with that too. Check the vacuum lines under the hood, common for them to get brittle & broken off.

I am thinking it has to do with the HVAC blend door though. My '94's HVAC plenum is different than your '97, I think yours operates entirely off vacuum so if it is leaking under the dash somewhere or the vacuum actuator is bad, the blend door might be flapping back & forth.