Rough idle, misfiring at high rpm

[fly_25]

Hello everyone, my Buick 3.8 is having a hard time. The engine hasn't ran in a long time and I recently replaced the head gaskets but I just can't seem to get it to run right. The idle is really choppy at 15° timing and smooths out when I drastically increase the timing. It won't idle below 1000 rpm or it will just die and misfires like crazy at anything above 2000 rpm. Any suggestions? Vacuum lines are all new and I'm getting about 17" of vacuum at 1000 rpm. Compression tests shows 130-110 psi

 

[SoFloG]

What's the carb situation?

 

[fly_25]

Sorry guys for posting and not following up. I measured the valve lift of each cam lobe with a dial indicator at the top of the pushrod with the rockers removed and found #5 exhaust lobe lift to be .100" lower than spec so I'd imagine this is where my problem is

 

[CopperNick]

Wiped a cam lobe or killed a lifter? The built in suicide button when the oil pump is at one end of the motor and the oil pan pickup all the way at the other and the oil has to travel from the pan to the pump and then up and into the galleries. Just too much distance.



Nick

 

[SoFloG]

Sorry guys for posting and not following up. I measured the valve lift of each cam lobe with a dial indicator at the top of the pushrod with the rockers removed and found #5 exhaust lobe lift to be .100" lower than spec so I'd imagine this is where my problem is

I doubt that's significant enough to cause the problems you're having. What is the carb situation?

 

[Clone TIE Pilot]

If the motor hasn't run in a long time then the valves or piston rings may have become sticky. Internal parts can become sticky from extended periods of non use.

 

[fly_25]

Lifters are all solid so I think it's a cam lobe. The cam lift is normally .240" and I measured .143". I recently did the head gaskets and cleaned up and lapped all the valves at the same time so I'm betting on the cam lobe. And my carb is the stock dualjet 210

 

[fly_25]

You can see how round the lobe is in this picture (second from the last) and the lifter has uneven wear. Looks like I will be replacing the camshaft and lifters

 

[spongbob]

View attachment 230793 View attachment 230794
You can see how round the lobe is in this picture (second from the last) and the lifter has uneven wear. Looks like I will be replacing the camshaft and lifters

Any time you change a cam. It's generally time to do the valves at least the exhaust valves valves have everything to do about idle quality ( strength)