Sync loss with spark plugs in

[rmoehle]

Hey all,
Engine won't start due to inconsistent RPM readings with sync loss.
I did some troubleshooting and discovered that with the plugs removed, RPMs are consistent, and there are no sync errors. With the plugs back in, RPMs are jumpy, and there are sync errors (mainly #97).

See attached logs - "open" for no plug, and "plug"
(ignore the RPM difference between 01 and 02 - battery was dying, and I got a charged one)

Any ideas?? Thanks!

[rmoehle]

attachments 4-6

[rmoehle]

msq

[AbatelliCristian]

are you using resistive plug?

[LAV1000]

are you using resistive plug?

+1

[rmoehle]

Not sure, I'll have to confirm. Should I be?
Didn't read that recommendation anywhere in the manual.
Thx

[rmoehle]

I confirmed that I have resistive plugs.

The strange thing is, the first start of the day, RPMs are rock solid. On all subsequent starts, it does the 0-cranking-0- thing. I can't explain it.
I have a feeling the compression is impacting the crank sensor's reading more than signal noise.

Any additional ideas??
Thanks

[LAV1000]

So it is a 4 cill 1.3 engine, prepared for turbo ?
Most turbo's have low compression, no hard work for startermotor.
Are you sure the sparks happen to the right cilinder, no swap of leads/coils ?

Are you going to run 4x barometric pressure (400 kPA) ?
Should be a very very big turbo

[rmoehle]

Yes 1.3L I4.
Ah I've removed the turbo temporarily to get it running NA, then move to turbo.
Yes, spark is wired correctly, but it still seems it's simply the presence of the spark plugs (and resulting compression on the crank signal) vs spark trigger.
Thanks

[LAV1000]

Looking at the last log, as soon as voltage drops to 9.3 Volts the lost sync counts starts counting up.
Battery old/weak ?
Try jump starting see if this helps.

[rmoehle]

I suspected that and tried jump starting last night. Voltage drops from 13.4 to ~10 on crank.
Given, the battery is a little old. I'll try to connect a newer one and report back.

Even so, what impact would that much of a drop have on crank signal? I was under the impression MS3 should work down to 8V.
Thanks

[LAV1000]

I suspected that and tried jump starting last night. Voltage drops from 13.4 to ~10 on crank.
Given, the battery is a little old. I'll try to connect a newer one and report back.

Even so, what impact would that much of a drop have on crank signal? I was under the impression MS3 should work down to 8V.
Thanks

Voltage seen in logs is an average over time, so it my have lower periods.
The whole ms unit inside runs on 5Vdc.
Regulator for 5Vdc needs a few voltage more to work correct and the microcontroller has to put everything in a save state before the voltage drops below 5 Vdc.
That is the reason why they build in some margin.

[billr]

How about the CKP/CMP sensors, are they powered by the 12V in any way? Maybe one of those can't handle low-voltage dips elegantly.

[rmoehle]

CMP is on 12V, but it accepts 12V or 5V, so it's rock solid, as seen on the composite log.
CKP is VR; CKP+/CKP- from the MS3, and since the MS3 is on 12V, it could be impacting CKP (sync loss seems to coincide with some ckp teeth). I'll provide the MS3 its own power and see if that helps.

[rmoehle]

Issue FIXED
Tried running the MS3 on its own power source - no change.
Flipped the polarity of the crank sensor, changed capture to Falling edge, and selected crank-cam to invert, and the engine started right up!
Now to tuning throughout the rpm range. Thanks all!