BlazinOR

OK, this problem has come and gone at random - symptom -

Truck is warm (K5 w/TPI406) - taking off from a light, it's all of a sudden sluggish.............used to think it was a myriad of other stuff but I finally used my Auto Xray to check some parameters - only thing that looks goofy is the timing retard - during these symptoms, and only during these symptoms, the retard is on the order of 15* or therabouts............then as the symptom goes away the timing retard goes back to near 0*. No audible knocking, and it is NOT under a load that it does this - only taking off or coming back into the throttle after a slowdown. Full throttle once it is cleared up shows basically NO timing retard. Motor has all new ignition parts, new MAP, new knock sensor, new 24 lb Accel injectors, etc. Other than this sporadic problem, it runs AWESOME. Has VSS hooked up, EGR, everything that should be used is working. Nothing in particular seems to bring it on.

What would cause the ECM to retard the timing that much with no apparent cause?

Any help/opinions appreciated.

BlazinOR

Any ideas?

8Mike9

Might be a fauly knock sensor, or ESC may be randomly retarding the timing..in that case the ESC would be at fault.

Try bypassing the knocksensor first, then look into the ESC.

Ed Maher

I've heard grumpy mention a topic known as tip-in knock. I believe it's casued by the slight lean conditionthat occurs in the lag between the throttle moving and your ECM reacting. If thats your problem the only way to 'fix' it is in the chip or disable / desensitize the knock sensor.

Grim Reaper

Ed is on the right track. Especially if you have a "tight" convertor or quickly upshifting. The best thing to do is "bring the spark advance" in slower. Guys with tall gears like 2.73s have to often do this.

To bring the "spark advance quickly" you need to have a looser convertor or lower gears. Also, look at your Knock Sensor's "Attack" and "Recovery" rates.

tpi_roc

Are you logging knock counts??

BlazinOR

OK, how to bypass the knock sensor? SImply unplug it, or is there some kind of resistor I need?

ESC retarding timing - my ignorance is showing, but is this on the chip or ..............?

Desensitizing the knock sensor............how?

Thanks to all you guys for the input!

SATURN5

I have heard you can "tune" a knock sensor by how much torque you apply when installing it. Also some have used a 45* pipe adapter screwed into the block, then the KS into it, but I would think that would be a last resort..cheers, Bob

Grim Reaper

Blazin, if you got that eprom burnin equipment like I suggested months ago, you could "tune" the KS for how much retard you'd let it take out.

BlazinOR

Yeah, I know Glenn, me bad.............

Just that after the discovery was made that I had 19 lb injectors instead of the expected 24 lbers, and then put in the new Accels the BLM's and Integrator numbers are right on. Believe me, I still plan on doing the chip burning project but it got out-prioritized. Had other 'wheeling-related projects to get done for the spring trail runs.............then a steering box leak that ended up 'forcing' me to go to crossover steering (about a $500 investment but well worth it). Ah, you know the drill..............

I'd still like to know if I can just unplug the KS to make sure the drivability problem related to the timing getting retarded is gone, without throwing a code.