Repeatable loss of RPM signal only during cranking

[babbit bearings]

I am fairly new to MS3 and never tried to create a log before, did I do it right?

2015-08-23 with filter.msl

2015-08-23_18.38.21.msl

MS3 Gold on stock LM7 GM 5.3L with a Z06 cam & a 67 mm turbo.

Once started the engine runs fine, but always starts very strangely. Engage starter, engine spins normally, but doesn't fire or even seem to attempt to fire even with extended cranking, then abruptly it fires up with authority, it instantly goes from cranking to running smoothly, no stumble, no misfiring like it was loading up on fuel...

I assumed I had something wrong with cranking pulse, priming pulse, etc, but the log seems to show the RPM dropping to zero when the starter is engaged an the engine is turning over, but in a consistent way.

Without filtering and with filtering on it seems to be the same.

Am I reading the log right?

[grom_e30]

you are getting some sync loss during cranking thats not ideal and will make starting more difficult. if you read the manuals on capturing a composite log and post that up it will show the signals the ecu is getting from the crank/cam sensors and make diagnosing the problem easier.

[babbit bearings]

Thanks, I will read up on that and post the results.

[babbit bearings]

First attempts, shows the sync error, but I don't think this is really what you wanted...

[babbit bearings]

I read on a Miata forum that increasing the dwell battery correction fixed a very similar problem, so I changed it to 300% @ 10 volts... no change, the sync still drops out.

I am going to put two batteries with a charger and see if low voltage is an issue for the sensors.

I think the sensors might have 300K miles on them, so they will be next, but I didn't have this problem with an MSD 6012 box and carb, so...

[grom_e30]

there does not seem to be any adjustment for the inputs on your ecu, so some basic things you can check is supply voltage i believe its meant to be 12v on your setup where are they getting the power? make sure the crank and cam sensor wires are away from sources of electrical noise like ignition coils and starter motor or heavy gauge power wires. are you running resistor type spark plugs.

[babbit bearings]

With two batteries and a charger I made another log and found Reason 68 & then 91.

I wonder if the timing chain being really loose can cause the cam to get out of sync during cranking. It is the original with about 300K miles.

I think it is possible to run this engine on crank sensor only I will try that tomorrow.

[grom_e30]

slop in the timing gear yeah that could do it, i think the x24 pattern dose requires the cam sensor

[babbit bearings]

batch and semi both generate Lost Sync Reason 91, and the RPM signal drops in & out about every .400 seconds during cranking.

I am going to change the sensors but I doubt that it will do any good.

[jsmcortina]

Try upgrading to the current firmware release. A change was made a while back that helps some 24X LS installs. I forget whether that change made it into 1.3.3

James

[babbit bearings]

Try upgrading to the current firmware release. A change was made a while back that helps some 24X LS installs. I forget whether that change made it into 1.3.3

James

Will do thanks.
Craig

[babbit bearings]

FIXED!

Update => No more sync loss during cranking!

Thank you Sir.