Megasquirt-3 Sync loss and remedies

Megasquirt 3 - Sync loss and remedies

Intro - Symptoms - Reason codes - Sync error logger - Solutions

Introduction

Many Megasquirt installs use some kind of trigger wheel with a tooth pattern on it. The code in the Megasquirt decodes these patterns and determines engine position for fuel and spark. Under certain conditions (typically noise) the incoming signal is disturbed and the Megasquirt loses syncronisation with the wheel. This is called a sync loss event or a sync error.

Symptoms

Feels like a misfire or a false rev limiter
RPM in datalog suddenly drops to zero
RPM in datalog suddenly spikes up
"Lost sync count" increments while "SecL" counts up normally.
(NB. If SecL suddenly drops to zero this is a "reset" which would likely be caused by a major voltage spike on the power feed.)

Taking and reviewing a datalog is a required step.
This datalog extract (viewed in Megalogviewer) shows the rpm (yellow trace) dropping to zero and at the same time the "Lost sync count" increases. The "Lost sync reason" shows reason code 2.
sync loss datalog

Reason codes

0	no problem
1	init error
2	missing tooth at wrong time
3	too many teeth before missing tooth (last)
4	too few teeth before missing tooth (last)
5	1st tooth failed test
6	nonsense input (last)
7	nonsense input (mid)
8	too many teeth before missing tooth (mid)
9	too few teeth before missing tooth (mid)
10	too many teeth before end of sequence
11	too few teeth before second trigger
12	too many sync errors
13	dizzy wrong edge
14	trigger return vane size
15	EDIS
16	EDIS
17	second trigger not found when expected
20	subaru 6/7 tooth 6 error
21	subaru 6/7 tooth 3 error
22	Rover #2 missing tooth error
23	420A long tooth not found
24	420A cam phase wrong
25	420A
26	420A
27	420A
28	36-1+1
29	36-2-2-2 semi sync failed
30	36-2-2-2 tooth 14 error
31	Miata 99-00 - 2 cams not seen
32	Miata 99-00 - 0 cams seen
33	6G72 - tooth 2 error
34	6G72 - tooth 4 error
35	Weber-Marelli
36	CAS 4/1
37	4G63
38	4G63
39	4G63
40	Twin trigger
41	Twin trigger
42	Chrysler 2.2/2.5
43	Renix
44	Suzuki Swift
45	Vitara
46	Vitara
47	Daihatsu 3
48	Daihatsu 4
49	VTR1000
50	Rover #3
51	GM 7X
52	36-2-2-2 tooth 30 error
53	rc51 semi error
54	rc51 re-sync error tooth 6
55	rc51 re-sync error tooth 16
56	rc51 re-sync error tooth 18
57	fiat 1.8 tooth 0
58	fiat 1.8 tooth 3
59	fiat 1.8 tooth 6
60	fiat 1.8 tooth 9
61	36-1+1 first
62	36-1+1 second
63	QR25DE semi failed
64	QR25DE lost running sync
65	CAS360 running
66	NGC8 semi failed
67	LS1 semi failed
68	LS1 resync failed
69	YZF1000 resync failed

Note! Most of these simply show that there's a problem and don't particularly pinpoint where it is.

Sync Error Logger

The "Sync Error Logger" can be very useful to record the defective tooth pattern and display it in the tuning software. See the Tooth logger manual

Solutions

Having identified that you have a sync loss problem, you need to attempt to eliminate it.
Check for any basic problems

Loose sensor

Loose cabling

Sensor wires running close to spark plug wires or coils

Slop in timing belt

VR sensor wired backwards

Fouled plugs causing misfire

Non-resistor plugs

Excessively rich mixture causing misfire

Excessively lean mixture causing misfire

Having ruled out all those possible causes, you should enable some noise filtering. See the noise filtering settings

If you have a question, comment, or suggestion for this FAQ please post it on the forum.

No part of this manual may be reproduced or changed without written permission from James Murray and Ken Culver.