1986-z51

1986 cp. Chasing a low speed buck-jerkey feeling. 4th gear 3rd gear low rpm. I am thinking a timing issue. set timing a 8 deg. an its worse. back it down to 6 deg still there just not as bad.Got my scanner on it an timing advancing to 42 deg at full trottle. I know the est moldule controls the timing,with knock sensor imput. could this be due to no egr valve.it is block off, an i think the timing is pulled back when the egr valve is comanded. mods are comp cam 260 dur 444 lift. headers. is all ready got new plus-wires-cap an rotor. I am a due it you self guy. this 1s got me.

Cliff Harris

I think you meant ESC (Electronic Spark Control) rather than EST module. It sends a signal to the ECM when it sees knocks. The ECM then backs off the timing to stop the knocks.

Is this something new? Maybe you're just bogging the engine?

I suggest looking at your harmonic balancer. The outer ring might have slipped, giving you inaccurate timing (happened to me on two different Corvettes).

Rodney_Gold

I had an issue on my 95 where when datalogging , timing was retarded up to 10 degrees when the EGR was in its duty cycle at WOT acceleration also jerky at steady state low rpm.
It was actually a vac leak thru a slight crack in one of the metal pipes from EGR valve that goes into the manifold , at steady state , the car was "jerky" at WOT the crack widened so much as the car accelerated which resulted the fact that the intake charge was way too lean (I run open loop , at WOT the motor always runs open loop as far as I know) and it was pulling back timing.
I deleted EGR in software and made block off pieces for the EGR valve and the pipe that went into the intake - problem solved. Took me a while to get to the solution of this problem.... Very difficult to "diagnose".
If it's not that , I would look for vacuum leaks before doing anything else , check and triple check for this...