ignition timing drift - spark latency hardware

[chris_brathwaite]

how much ignition latency correction is required to make the ignition drift or retard under acceleration stop and read exactly as the timing table demands. i am at 100us right now.

rb25det engine


what method is recommended to test after blipping the throttle and adjusting latency till it continues to read spot on the commanded timing?

right now i have a fixed ignition advance and the timing is retarding about 2 or 3 degrees before catching back up to the fixed timing after blipping the throttle.

let me know your thoughts.

how much latency to use?
is the method i'm using correct?
and how much latency have you used to keep ignition timing exactly at the timing table commanded?

data log or msq will not show this issue.

[kaeman]

When I looked at the manual for setting up the ignition and timing, it tells you to set the timing to like 15 degrees or 10....where ever your engine will idle smooth. then check that the timing indicated is equal to the timing the Megasquirt is demanding. If not then adjust the tooth position until those numbers match, then slowly rev the engine watching the timing mark, if you engine retards when the engine revs, then you need to use the latency setting, but it recommends a small number like 1 or 2, then check again, then add more if you need it until your timing stays fixed. 100 micro sec seems like a large number... my engine timing used 3 micro sec to hold steady. it was losing about 2 degrees at 5500 rpm. and three fixed it ...
I would retest and start with a small number and slowly add to it, if you end up in the high numbers above 30 I would check for problems with the ignition components, ie.. coil, ignitor, trigger pickup wiring.....
Good luck.

[chris_brathwaite]

on what engine? i started small and increased till drift was more negligible. as each ignition system is different i kept going. some use 50-80 others can use over 200us.

[racingmini_mtl]

Spark latency is not a transient thing. It should be done at fixed RPM. What you're doing is not accurate because the spark delay you are measuring when blipping the throttle is not only due to the ECU and ignition system side but also your timing light. To eliminate the timing light component (as much as possible), you need to make the measurement at a steady RPM. Then you adjust the latency to have the correct reading. And even at fixed RPM, some timing lights are not very good at high RPM because they do introduce a false latency so you need to simplest and most direct unit possible.

Jean

[kaeman]

I am using ls coils on an early small block, using the ms3x board to drive the coils. I didn't know that the numbers up into the 100s would be normal, the help just said a small number....I assumed that meant 10 or less.
Are you using spark trim tables, they are turned on but set to all 0.0..
Do you have any other ignition corrections applying themselves? MAT temp adjustments, or cold advance curve.
I don't remember if the mat temp corrections will be applied when the timing is set to fixed. look at a datalog and check the timing, the mat timing adjustment, and see if its triggering while you are trying to do this procedure.
Good Luck.

[chris_brathwaite]

Spark latency is not a transient thing. It should be done at fixed RPM. What you're doing is not accurate because the spark delay you are measuring when blipping the throttle is not only due to the ECU and ignition system side but also your timing light. To eliminate the timing light component (as much as possible), you need to make the measurement at a steady RPM. Then you adjust the latency to have the correct reading. And even at fixed RPM, some timing lights are not very good at high RPM because they do introduce a false latency so you need to simplest and most direct unit possible.

Jean

ok then it is set correctly,i just wanted to ensure that is correct. and blipping the throttle didnt matter. held it at 5k and set the latency to prevent the drift. then checked it at 6k it was still spot on.

thanks

[chris_brathwaite]

I am using ls coils on an early small block, using the ms3x board to drive the coils. I didn't know that the numbers up into the 100s would be normal, the help just said a small number....I assumed that meant 10 or less.
Are you using spark trim tables, they are turned on but set to all 0.0..
Do you have any other ignition corrections applying themselves? MAT temp adjustments, or cold advance curve.
I don't remember if the mat temp corrections will be applied when the timing is set to fixed. look at a datalog and check the timing, the mat timing adjustment, and see if its triggering while you are trying to do this procedure.
Good Luck.

yes it can be, last note said latency can go up to 270 on ms ecu before hitting the limit. tested at full warm with no corrections on.