hi i have 81 eldorado and its been sitting in my yard for 2 months i replaced the cap, coil and the ingnition module and i started up right away but the motor started to knock whats wrong with it

depending on the knock .. one of two things .. 1/bad gas - spoiled from sitting for an extended time .. 2/internal piston/rod problem .. good luck .. depending on the car condition, it would be worth fixing .. i've always wanted this body style, black, biaritz !!! good luck

thank you for replying and helping me with my problem. if its bad gas would it be best it i let the car run a let it burn all the bad gas because it never knocked before. and that caddy u always wanted is the same caddy that i have it a kick ass car

I would drain out as much of the bad gas as possible. Then fill it up with some premium and install a new set of plugs. Just be sure to set the right gap.

thank you buddy i didnt think bad gas would make a motor knock

Yeah, the longer gas sits the weaker it gets. It makes it hard for the engine to light it off. Especially with old worn plugs.

thanks larry

No problem. It's good to see someone keeping the classics on the road.

it could be a rod if it is in the bottom end of the motor

He said it didn't do it before when it was running. So unless a bearing seized from sitting I don't think it would be a rod knocking.

Cadillacs of that era will get a knock that sounds a lot like a rod knock, but it may not be. Sometimes a chunk of carbon with fall off the valve and create the noise. Run the car at a high RPM, at the same time pour some water out of a cup into the carb. The small amounts of water will break up the carbon deposit. I've done this many time on cadillacs.