Can valve adjusting cause hard startup or stumbling? I have a brand new motor and the preload hasn't been reset since the initial install when the motor was being built.

Can this have ANYTHING to do with a hard stumble going from open to closed loop?

 

Valves too tight will not let the engine create much vacuum. It will run especially rough at low RPMs and have no power.

 

Well if they are now loose then yeah the SOB might not run at all!

Bret

 

Yeah - What shoebox said, but going from open to closed loop operation & valve lash would not be related issues....that's a programming problem. Tell us the build of the motor... stock? modified?

You shouldn't have to re-run the lash if it was done correctly the first time.

 

I heard no matter what once the car is started and the breaking in has begun, you have to reset the lifter preloads?

 

That's not always true. If the valves are too tight, the intake and/or exhaust valves may not be closing all the way. This can cause the a/f mixture to leave the combustion chamber before they are ignited....causing false O2 readings. These readings will be ignored until the car goes into closed loop. This condition can cause the car to run like crap, and run even worse once the car goes into closed loop and the car starts adjusting for the off mixture.

 

That would not be the cause of the problem he described though. At idle and cruise, yes, the computer is looking for 14.7 AFR through the O2 sensors, and at WOT it will resort to programming. A hard stumble would be programming issues. Unless I am reading you wrong, your description of closed vs open loop are reversed.

 

O2's can't sense raw fuel in the exhaust. They sense gases and not liquid.

 

Right, but they can sense a false lean or rich condition. If the fuel is leaving the combustion chamber before it's ignited, it will ignite in the exhaust manifold/header primaries. This ignition will leave behind gases, not proportional to the actual a/f ratio being injected into the combustion chamber.

 

Ya can tune it so rich it shows lean and so lean it shows rich.