Ref Sync Issue

[insomnia]

Hi guys,
i have a strange issue with a 4 cyl engine:
ref trigger wheel 18-1, sync 1 event every 720°
i use mode 7 for other 4 cyl engine, with ref trigger wheel 24-2, working fine.
Because the OD is very small, not possible to cut 36 tooth, the owner
decide to choice 18....When we try to start the engine, no sync, sync error appear.
with mode 2 the engine want to start. Crip is ok, checked 2 time...sync sensor wiring etc
all looks ok. my last idea is: is that important to have 4,8,12,16,20,24,28,32,36 tooth?? 18/4=4,5
is that my mistake????
Thanks for any advice.

[IDP]

18-1 is Mode 5, 1 missing twice/cycle

[insomnia]

Hi IDP,
you're right! i use mode 5 and not 7, i write wrong in my post...

[MarkMc]

Have you got your edges correct? Does the ECU become synced with the spark plugs removed?

[insomnia]

Hello Mark,
now it"s time to work on this old project. After your advice i remove the spark plugs
and the ECU work fine. Spark and injection are working, no sync or ref error.
Is the engine speed too low by cranking? and/or one missing tooth gap too small
on a trigger wheel with 50mm? Can i fix it if i use 18-2?
Thank you.
Francois

[Dragon]

If you are making the trigger disc yourself, why do you have to use missing tooth?
I think 12 teeth should be fine for your application.

[MarkMc]

Send a ref sync capture for me to look at, one with the plugs in and one with them out. Also the current ECU configuration would be good.

When it comes to missing tooth modes (my preference) you need to understand that the cranking consistency and also cranking speed become very important. Generally I would not recommend 18-1 as it is a little low in the tooth count for a missing tooth mode but this really depends on the cranking speed. I would predict you need about 250rpm cranking speed (consistently) to make this work well.

Always look at what car manufacturers do for guidance generally 36-1 is the minimum although bike manufacturers use down to 24-2.