Is it possible for a hydraulic lifter to suddenly over-pump? Car ran fantastic last week, until friday. Now it has what sounds like a dead#3. Checked spark, and injector. I don't have a compression tester yet, and there is no additional noise coming from the engine. Plan to pull valve covers tomorrow, replaced plugs last weekend with NGK's with no change.

I dont know about over pump but they have a tendancy to drain out and sometimes take quite a while to pump back up which will result in loud clatter and running like crap until they finally do. Sometimes this can take a while especally if your oil is dirty.

#3 has an increased chance of dropping a valve seat from what i am told, which when it happened to me sounded really similar to when a lifter wont pump up.

A broken rocker arm had similar effects as well, dead cylinder, loud clatter.

How long have you ran your engine like this? On occasion my hydos have taken 15+ minutes to come back to life. One time i had to change to a lightweight oil (5w30) to get them to pump back up before switching back to my regular oil.

I've had them not pump up if the car sat for months. This is different, no noise at all. No clatter or knocking. Just dead feeling.

Jeff,
Hydraulic lifters can't over-pump. There is a keeper that keeps the "floating" part in there. Only way they could do what you are describing is having done an adjustment while they were not pumped up, then later when they pump up the adjustment would be too tight.
Might be an electrical problem instead. Injector connection or ground for the injectors.
Tom

....I agree with most that was said....Try an ajustment again
start at 0 lash...... (sometimes they can be finicky)check injector connector's

Check all the basics first.......spark plug wires, and connections. Wire shorts., distributor cap, rotor.Points.....You droped a cylinder , but I would not attribuate it to the hydrolic lifters until all else is checked first. Clogged injector, etc.

Electrically everything is ok. It could be clogged injector, thats on my to try list today. I believe it's a valve or piston because the megasquirt is showing a big change in my idle vacuum, it's at about 60KPA, It used to run around 30KPA. Gonna loosen up all the valves today and see if it changes, but knowing my luck it's gonna be something more serious.

Update- adjusted valves to zero lash +1 turn. Runs great now ! Replace rubber hose on intake, idles better now. BTW 1 3/8 ID coolant hose works perfect for the NLA 1.7 ones.

No it doesnt and the NLA hose is not NLA...call George..

Rich

Oh yes it does. Fits like a glove. George said to buy the 2.0 ones and put hose clamps on.