Timing question.

[Rickerbucks]

Under exceleration the spark map works fine but under very light load / idle I get some weird behaviour with regard to timing and I would like a second opinion.

When lightly cruising, the spark is at 37 degrees. With light excelearation it stays there. When I take my foot off the gas, the retard drops to 27 degrees but there is no where on my spark map that has 27 degrees.

In addition when doing a log of a 1500 rpm, third gear rolling along cruise, the spark will be at 37, and then can get really spiky jumping up and down very rapidly between 37 and 27 even though nothing else appears to change. Under these conditions that car is 'lumpy' for want of another word.

So is this normal. What is happening for 10 degrees to be taken out apparantly randomly? Is there something in my parameters that I need to change? I was familiar with this when stock with a knock sensor etc but surely that is moot now.?

Thank you

 

[bobc455]

One possibility is timing trim- if the ECU sees that the TPS is at "idle" position, the timing trim will try to take out timing to get the idle speed down. Maybe try to zero out your timing trim.

-Bob Cunningham

 

[Rickerbucks]

Yup that was it Bob. I set the line to zero. The next question is, what does that table do? Wjhat is it for.

the reason that it may of got pychotic on me is becasue my TB is not 100%. the bushings are worn and sometimes the blades to not close properly. There is a sort of 'leak' as a result.

But what should I be using that table to do?

 

[bobc455]

As an example, if your idle setpoint is 650 and the engine is actually at 680 (maybe the throttle blades are holding the idle speed up), the "timing trim" will retard the timing a bit to bring the idle speed back to setpoint.

It might also help the car coast down (i.e. engine brake) at the end of the quarter mile, since the TPS is in the idle position but the RPM is too high.

A lot of people zero that table out and leave it that way, it can get confusing to tune when you set one value and it goes for a different value. After the car is 99% tuned and you think you might need it, keep it in mind.

-Bob Cunningham