Pro Tip (Humorous)

[AZJeff]

PRO TIP: Don’t let foreign material fall into the intake manifold and then fail to retrieve it before starting the engine.

 

While installing the new intake manifold gasket on the MJ the other day, I decided it would be a good idea to keep stuff from falling into the hole where the throttle body mounts, and so crammed a hunk of old tee-shirt as a “plug” in this hole, and it worked just fine.

 

When I installed the throttle body, I pulled the tee-shirt plug out and bolted up the remaining intake parts.

 

Now came time to start it up.  It starts right away, and runs smoothly immediately.  I let it warm up, and check for fuel rail leaks, and all seems good to go.   Now for a short test drive.  I pull out of the garage, and about 400 yards down the street, the engine starts running rough.  REAL rough.

 

I nurse the machine home, and shut it off.  I look under the hood, and see nothing amiss.  No loose hoses, no disconnected wires.  I start it back up, and I hear a VERY noticeable whistle coming (like a MAJOR intake manifold vacuum leak), and it seems to be coming from around the area of the throttle body.

 

I pull the throttle body and begin inspection.  The gasket on the bottom looks fine, but then I peer into the intake manifold, and see a small amount of cotton rag material off to one side of the opening.   That’s odd….

 

I grab the rag piece, and start pulling.  Out comes a HUGE hunk of tee-shirt, about 15 inches long, and about 4 inches wide.   Judging by the burns on the one end, it apparently ran all the way down one of the runners of the manifold, and was probably getting beat up and burned by the intake valve.

 

After I removed the piece, I spent a while fishing in the manifold for any other pieces, but nothing came out.  

 

I reassembled it all, and started it up.  It ran pretty crappy for a few minutes, and then the engine smoothed out.

 

My theory is that the hunk of tee-shirt rag I stuffed into the throttle body hole was actually TWO rags, and when I pulled out the first one, the second one fell down into the manifold and I failed to see it.   When the engine was idling, the rag stayed put.  Once I started moving down the street, the airflow in the manifold sucked the rag into the intake port for cylinder #2, and it began to choke on that cylinder, creating the rough running.

 

Now before any of you declare me unfit to work on anything more complicated than a door knob, please know that I have been working on cars for almost 55 years.   I had done LOTS of intake manifolds, so this wasn’t a venture into uncharted territory. It WAS, however, the first time I ever left a rag in an intake runner!!  

 

In the end, it’s pretty funny.  Had my error been made on a more modern engine with limited (or no) valve clearance, I would have been tearing the engine apart after that mistake.   Thank God the AMC six is too primitive to have problems dealing with a few bits of cotton rag.

[Eagle]

That sounds like something I would do -- or might have done. Be thankful it was a tee shirt, not a nut or a washer.

[Pete M]

you got lucky, no doubt about that.