just finished painting and tuning up my 250/engine bay. we recieved a new sending unit and changed it. it had been driven the day before and we started it after changing the sending unit. the engine was running smooth. the next morning i start it up and the exuast sounds like a v8 and is popping (usually my glasspacks don't sound this loud). im unable to back it down the driveway. we take it to the shop the next morning, they only ran compression tests and listened to it. cylinder #3 has low compression, the rest were 25. they said 10 and lower was bad. we didn't want them to tear the engine down just yet but told us we may have a burnt valve. we have tuned the carb (which was a remanufactured 1barrel we bought a year ago) a mechanic checked it a few months back and said it needs to be replaced, there was something wrong but I don't recall I wasn't there. After he tuned it, she ran fine up until now. we ran some transmission fluid through the carb and blew the engine out (incase of a stuck vlave.) all our plug wires fire but with #3 off it doesn't change a sound. she has no power going down the road but starts up easy, runs rough on idle and under driving. we removed the valve cover, lifters are all moving fine as well as timing. we have replaced almost everything besides the engine itself under the hood. it happened overnight which is the problem, we don't know what could have caused this. -sorry for you guys having to read this but I wanted to know if you guys can figure a problem out from all this. we don't really want to completely rebuild or swap but if we have to we have to, any idea's of the problem? thanks
is #3 geting spark. check by pulling the plug off with the motor off then put a screw driver in it and set it so there is a gap between the screw driver and some metal, like the valve cover. start the motor. if spark is jumping from the screw driver the wires cap and rotor are good. if they are good then try swaping the plugs from one cylinder to another to see if the miss moves.
weve replaced all plugs and all spark plugs. #3 was also as clean as can be the 2nd time we changed it. everything seems to have a spark.
check the spark again...if nothing changes when you pull the wire...pull the plug and stick the wire back on and ground the plug. spin the engine and see what you have...
"we take it to the shop the next morning, they only ran compression tests and listened to it. cylinder #3 has low compression, the rest were 25. they said 10 and lower was bad. " does anyone know what's the stock compression on this engine? these seem like some pretty low #s...
Ya they seem really low. I wonder if the shop is bsing.... I don't think it would even run if it only had 25psi. OP: #3 needs spark and compression to fire. You need to go get a compression tester and recheck 3.
i wasn't at the shop but these are the #'s my dad told me they said. they mentioned all the 25's were good compression for my engine except #3, so idk. would one bad cylinder cause the car to have next to no power, it seems like a carb problem from driving it.
My I6 was 80ish Psi. Those numbers are not good. Missing a cylinder will cause it to run rough and weak. Low comp will also cause it to be weak.
a leak down test needs to be done on that motor. its where air is pumped into each cylinder when its on top dead center. the is a gage on the attachment that shows what percentage is leaking. you can also find where the air is leaking from by finding where its coming out of. it will be coming out of 3 possible places. the carb, indicating a leaking intake valve. the exhast pipe, indicateing the exhast valve, and the valve cover breather/oil fill. there will be a little bit coming out the valve cover because of the gaps in the end of the rings but it should not be much at all. this is the only test that will tell you what is wrong with out taking the motor apart.
Leak down is what I was thinking with the 25 and 10 numbers. Perhaps they were talking about percentage of leak down. 10 being good 25 or more being bad. Just a thought. I think someone got there signals crossed with your compression numbers.
