Thumping Cat??clogged maybe?

[DBD]

I dunno maybe his is a better fit in exhaust, but I put it here because of how it may be effecting the engine.

I have a 93 supercab 4x4, 3.0L 5-speed. It makes the weirdest sound. After getting warm, there is a "THUNK.... THUNK. THUNK" from under the floorboards. I gotta think it's coming from the catalytic converter. You can feel it, as if there's a guy under the truck lightly kicking at the underside of the floor. I assume it is happening while driving as well, but typically I notice it when stopped at a light. It also does it (briefly) after stopping and cutting the ignition.

I have been sorting through several things so far to get this thing running right. Ran some sea foam through, and some injector cleaner, put my K&N in from the other truck, and also cleaned the MAF. Each of those things perked it up a little bit, but there is still a lot of hesitation to the engine.

What are the symptoms of a plugged up cat? Is That what I've got? I wanna say it's fouling the plugs, but I have not pulled them to see. I have stalled it a couple times when it hesitates, and then it is tons of cranking before it will start.

Ideas??

 

[Ditchbanger]

Same

Same thing happens to my 93 3.0. It usually does it after i shut it off after being warm. Its only done it once while i was stopped and it was running. I havent figured out what it is yet either...

 

[Rolled Ranger]

My 91 4.0 is doing the same thing. It is a loud rhythmic thump after it warmed up. It would be really bad if it was from the engine but you can feel it in the floor. And it doesn't change with engine rpm. And i heard it do it after I turned off the engine once. It has been doing this for almost two weeks. I am hoping I will be able to get it figured out today or tomorrow. I finally have a little bit of free time. I will report back if I find anything out.

 

[triumphrider-1]

Check these things as well maybe:
http://www.therangerstation.com/forums/showthread.php?t=78421&highlight=thump+floor

 

[hondaxr650]

Kinda sounds like a cooling system thump. An air pocket in the system can cause the coolant to boil in the block and thump against the back of the thermostat. The heater system transfers the thump into the floor boards. Make sure it's full and the air is bled out.

 

[Rolled Ranger]

Kinda sounds like a cooling system thump. An air pocket in the system can cause the coolant to boil in the block and thump against the back of the thermostat. The heater system transfers the thump into the floor boards. Make sure it's full and the air is bled out.

Good call. This is what I determined it to be. From under the Hood it sounds like it is commingle from the engine but continues for a few secondes even after the engine has stopped. Found a coolant leak from the bell housing.

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[DBD]

Kinda sounds like a cooling system thump. An air pocket in the system can cause the coolant to boil in the block and thump against the back of the thermostat. The heater system transfers the thump into the floor boards. Make sure it's full and the air is bled out.

How do I get the air pocket out if ther is one there?

I went and got a vacuum gauge and did some tests. My dad told me that if it was a clogged exhaust the vacuum would be low at rpm. Although it was slightly lower than at idle, there was hardly any change in vacuum numbers when I unhooked the exhaust after the y-pipe and tried it. So I'm not convinced there is anything wrong with the cat(s). The engine running lousy might be unrelated, I don't know.

Other guys who had the noise: was the engine running badly as well, or was it just the noise?

 

[Rolled Ranger]

Mine has been running great. A failed cat can cause a rattling noise and not a thump. It will cause it to bog down in higher rpms or to not rev up at all if it is really bad.

 

[DBD]

Hmm yeah I heard/felt it doing the thump routine when I pulled up at work this morning. Put my hand on the heater box, and could feel it there. So looks like my engine performance woes are unrelated. Unless of course this air pocket problem is throwing off a temp sensor.

 

[DBD]

Engine trouble turned out to be a bad MAF. took it to an "actual" mechanic to get that figured out/taken care of.

Upon getting the truck back, the thumping is mostly gone, but it is still there in a slight way. Don't know if the mechanic really messed with the cooling system.

When I parked at home and heard the thumping again, I left it run, and popped the hood. Revved the engine a bit, and I can see the upper rad hose flatten under suction. Not all the way flat, but it compresses a noticeable amount. What's up with that??

 

[Rolled Ranger]

I believe a flat hose can be caused by a bad rad cap. When it cools down the cap is not allowing coolant to be sucked back in from the overflow causing a vacuum. Make sure the hose is also not weak and squishy.

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[DBD]

I believe a flat hose can be caused by a bad rad cap. When it cools down the cap is not allowing coolant to be sucked back in from the overflow causing a vacuum....

What I was describing was engine running, and at operating temp. The hose would flatten itself when I grabbed the throttle in hand and revved it a bit.

Speaking of bad caps though, I had taken the cap off earlier and it puked out a bit of coolant. I thought nothing of it though, it made sense to me, given the layout of that ridiculous hose up and over the alternator. I take it a system like this needs to drink up from the overflow, and ends up with level higher than the cap. Is that correct?

 

[DBD]

I took the rad cap off my BII which I still have around (but I'm trying to sell.... Pssst! Wanna buy a BII?) it was a newer looking motocraft unit. The one on the ranger looked like it probably was the same one that rolled off the ford line. Anyways, it seemed like that made the thump go away. However after further driving and listening, it was still there, just very slight. If the radio was on I couldn't tell it from bass notes in songs.

So I went and picked up a brand new prestone cap at partsource. Preliminary finding is that this has stopped the thump entirely. Will report if otherwise.

 

[kimcrwbr1]

Keep an eye on the coolant level in the reservor. Check it in the morning before you start it. You dont want the engine sucking air when it cools down.