Loud thumping noise

[jwsfarrier]

Hi all! Need to call on this great pool of knowledge again. Drove my truck down to the store this morning, all was normal. Started it back up after setting for no more than 5 minutes it fired and ran with a loud thumping sound I thought coming from drivers side. It is a deep thump not metallic. I was able to limp it back home a few minutes away hoping I didn’t do any damage. Up until that point it was running like a top. I pulled the valve cover to see if anything was amiss there and all looked good. This is a motor with roughly two thousand miles on it and have not been hot roddding it by any means. It is the 89 f250 in my signature. Be for I go nuts and start tearing stuff apart , hoping for some direction. Thanks a bunch

 

[jwsfarrier]

Also, fluids looks good. Nothing seems to be leaking from anywhere. The frequency of the noise increases with rpms. It’s darn sure loud when you are up close to it

 

[79jasper]

Run it with the valve cover off.
Same for the intake and filter.
Also listen at the exhaust pipe.
Feel around the exhaust manifolds for leaks.

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[Thewespaul]

Thumping isn’t good. Sometimes sticking lifter causes it

 

[jwsfarrier]

Thanks you guys! No,it does not sound good at all. Definitely not a sound you want to hear coming from your engine compartment. I was wondering if it could be a lifter or some thing. Would it make a sound like that if your exhaust valve was sticking closed. I have limited experience diagnosing anything like this. I have done much of the work myself on the rebuild with the help of this great forum. I have gained a lot of knowledge and experience but still pretty green. Fingers crossed it’s nothing catastrophic . I’m working out of town for a few days but will do some more diagnostics when I get home Sunday

 

[hoodshauler]

Did you have the heads redone when you rebuild it if so did you use the upgraded valves? @Dsl_Dog_Treat on here had a similar problem maybe he will chime in


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[jwsfarrier]

I did have the heads redone. Not sure exactly what was done with the valves, but I don't recall hearing about any upgrades other than the valves springs, which was done

 

[hoodshauler]

I did have the heads redone. Not sure exactly what was done with the valves, but I don't recall hearing about any upgrades other than the valves springs, which was done

My bad I meant push rods if your head had to be resurfaced they needed to use a slightly shorter push rod.


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[Macrobb]

Not sure what to tell you other than I've had a loose intake rocker do this - the piston going down literally sucks the valve open causing the thumping.

Also, sticky lifters will do it sometimes - my 93 will occasionally fire up and thump for a bit before smoothing out. Usually, it has to do with being parked in gear up a hill and having the engine slowly rotate and the truck very slowly crawl back down as the weight of the truck overcomes the force needed to turn the engine over.
My guess is that as it rotates, it compresses the lifters(which now don't have oil pressure) and over time(seconds to minutes) they compress, resulting in a loose pushrod. Once the engine fires up, it takes a number of revolutions for the oil pressure to re-fill the lifters.

 

[jwsfarrier]

Thanks hoodshauler. I put the original push rods back in as they were all good. I had also read that the lifters would be able to adjust to the difference should they take some off the heads. I'm not sure how much if any they took off the heads. I know they decked the block, but everything seemed to be within tolerances. I measured piston protrusion and all. I guess I'll start by looking at a couple of push rods and see what I have. It's still baffeling how it ran so good then didn't. Could just plain be a case of tolerances stacking up and the part finally giving out . Thanks Macrobb, all info helps. What you are describing could be the case. I'm hoping not to have to dig that deep but, whatever it takes. Thanks again

 

[franklin2]

Why don't you get it warmed up, and with it idling loosen the hard injection line nut on the top of the injectors one at a time till it starts leaking. This will cause that cylinder to start missing, and you can listen to see if it affects the thumping. That would at least narrow down if it's one cylinder and which one is doing it(possibly). Do them one at a time, re-tightening each one after the test.

 

[jwsfarrier]

Thanks franklin2. Not a bad idea. I think in will try that. I really hate to run the engine at this point for fear of doing anymore damage. Maybe I'm just paranoid, but it's really a bad sound. If I plug in the block heater I can have it already warmed up so less time running. I like the idea of trying to isolate what cylinder is making the noise. I'm going to pull the push rods on the drivers side since I have the valve cover anyway and if that shows me something. If not I'll play with the hard line then the injectors. I'll keep ya posted

 

[Macrobb]

Thanks franklin2. Not a bad idea. I think in will try that. I really hate to run the engine at this point for fear of doing anymore damage. Maybe I'm just paranoid, but it's really a bad sound. If I plug in the block heater I can have it already warmed up so less time running. I like the idea of trying to isolate what cylinder is making the noise. I'm going to pull the push rods on the drivers side since I have the valve cover anyway and if that shows me something. If not I'll play with the hard line then the injectors. I'll keep ya posted

Oh, you haven't pulled and looked at the push rods yet? Yeah, that's first thing to check.
A bent pushrod will do this, definitely. If you do have one bent, you'll need to replace it... but also figure out why it bent.

 

[jwsfarrier]

Good to know,thanks. Yeah as soon as I get home Sunday I'm on it !

 

[BeastMaster]

Do you get a thump once per revolution, or once every few seconds?

I had the latter in a gasser.. the problem was a stuck closed thermostat, and the thump was what was left of my coolant pressuring itself back into the overheated engine, then explosively flashing to steam, and blowing out the radiator.

The engine somehow survived, but I do not think it will ever pass smog again.

I believe that was that car's last hurrah... and the final incentive for me to get the diesel van.