Exhaust VVT DC% incorrect at start up, MS3X Gen Coupe 2.0T

[joshclifford84]

Intake cam phases nicely in all conditions, but on ignition and startup the exhaust cam pegs at 100% DC(full retard) and causes hard starts. It quickly compensates(DC reduces and exhaust cam advances to resting position), and works correctly during normal driving(retards when commanded by table etc.), but starting is intolerable. I feel as though I have tried every combo of settings and joined the forum just to ask this. Intake cam is at 0% DC during ignition and start, I would like the exhaust to do the same. MS3X is working flawlessly on this car otherwise, so I would hate to have to add my own control to fix this problem.

Additional info:

Table is of retards, so my table has 0 deg in idle range( ie a table value of 10 is 10 deg retard). More duty = retard, and otherwise works perfectly besides on start up.
2013 Genesis Coupe 2.0T engine, dual VVT. 100% stock, low miles, no CEL.

[Matt Cramer]

[joshclifford84]

Of course. I have attached a short data log showing VVT duty and angles during start up. It actually seems that the intake VVT duty also pegs during start up, it just doesn't cause such a large impact as the exhaust does so I neve notice until now. I would like them to be held in their idle positions during start up. Otherwise they seem to operate normally during all other conditions (besides some fine tuning). Thanks for the help.

Also, VVT solenoids powered by 12V ignition source. Activated via VVT and Nitrous outputs from MS3X.

[Matt Cramer]

The cam may not be fully synced; with the range you have entered, it should only be able to read from 0 to 46 degree cam advance. It seems to be getting a bad read on the cam position sensor and this may be causing the wrong duty cycle.

[joshclifford84]

Thank you for the reply. Can we(in software) force VVT duty until some condition is meet? For example, If I start engine with VVT wires disconnected, then connect them after startup(via temporary switch) the angles do not fluctuate. My plan is to use one of the programmable outputs to do this with a couple fets or something but It would be nice to be able to adjust a few values in the tune to do so. Again, thank you for your input.

[joshclifford84]

To solve this problem I used a programmable output to trigger a relay when RPM is above 2000, with hysteresis also at 2000 so it triggers once and stays on. The VVT outputs are on the NO terminals so that they are disconnected normally. This works well, disabling cam phasing during start up and allows for a smooth transition when VVT outputs are connected. Thank you for your replies.

Also just in case someone struggles with this down the road... while testing the programmable output, I found that the software crashes(goes "offline") if you toggle the conditions that activate the output too much. For example, I used TPS for test purposes to see what state/voltage was considered "on" and to make sure my relay was activating. I though it was fly-back at first,so I added diode but did not help. Manually toggling the output within the settings does not seem to cause the crash, so I believe it's cause in in software. During this "crash" the ECU seems to function just fine, I guess it could be my laptop also.

[jsmcortina]

I tested your MSQ on the bench. With engine at zero RPM and during cranking, both VVT outputs are off as desired.

Your datalog shows that the VVT outputs never energise (?) portp is zero the whole time. EDIT: VVT uses PWM outputs, so these are likely not reported on the raw portp log field.

So, I'm not seeing the problem you report?

James