I have been working on this truck I picked up about a month ago. Just as I got the motor all dialed in and running great I ran into a bit of a road block.

Wednesday night I took the truck down the road with my best friend behind me. When I get on it over 2000 rpms it blows blue smoke out the exhaust. It never did that before and started out of now where. I went back to my shop and sure enough, if I hold the throttle up over 2000rpms it smokes pretty heavily. At idle and on start up there is no smoke at all.

What confuses me is why is it only smoking when under the motor is above 2000 rpms? My initial thoughts is it is probably rings, not valves. The intake and plenum gaskets have been done. I looked down the throttle body and I see no oil which would tells me the plenum gasket is good.

Any ideas? I priced a lower end rebuild kit and the cheapest I found was $974! Ouch!

Thanks in advance for your input!

 

O2 sensors maybe?

Im not even close to 100% sure but isn't blue smoke when the engine is running too rich or too lean? If so it maybe an O2 sensor?

I would wait for some more input though

 

Blue smoke is mostly oil (burning oil somewhere)

Black is fuel (to rich)

 

You could have a blown plenum gasket causing you to burn oil.

The plenum gasket is one of the biggest problems on these trucks

 

I hope its not the plenum gasket... cause its brand new!

 

What'd you replace the plenum with? Gakset brand? Did you get a new pan or keep the same one?

Blue smoke is oil burning and if its smoking that bad I doubt its coming through the plenum, but maybe. I'd check head gaskets and piston rings.

 

I used the FelPro replacement gasket and cleaned/reused the stock pan.

This weekend I am going to have to do a compression and/or leak down test on the motor and see what it tells me.

 

at 2000 RPM the vaccume on the motor increases.. as all motors do.. could be a bad PCV valve stuck open allowing the intake to suck in oil from the vavle covers.. most likley not to blow that much smoke but its a possiblity.. ALSO that stock pan isnt the greatest and even though you have no sighsn of oil it can still be sucking through some where ... the hughes pan and gasket fix is the best... besides welding it togehter..

also ironically your rings could have gone bad.. or some dirt or something worse could have scorne a cylinder wall and burn oil.. could also be valve seals in the heads...

a leak down test/ compression test would be the best place to start

 

Agreed

 

360, you said you recently replaced the plenum gasket. How long were you having problems with it and did you ever discover in horror that you ran the truck with the oil sucked out? Before I knew about the plenum, I went to Jiffy Lube for an oil change before a long trip. In less than five hours, I sucked all the oil out of the engine and never saw a low oil pressure indication while running a 75. Couldn't have been good for the girl, they sure don't like being worked hard while dry. My dipstick couldn't find a drop of lube. Pulled into a truck stop and put in over three quarts. I swore to bring hell down on JL when I got home as I figured they forgot to put the oil in. Homeward bound, the same thing happened. Learned about the plenum and fixed it. Almost got a rebuild instead figuring the rings had to be shot. I was lucky, she purrs like a kitten and still likes being pushed hard without a single puff of blue smoke. Sounds like you might not be so lucky. I gotta go along with the rest, your rings could be the problem. Should be fairly obvious when you do the test.