Nethawk

I'm wrapping up a VVT swap into my 1992. I have everything working and running at this point except VVT. I'm running MSPNPPro for 90-93 chassis. When I enable VVT test mode and mess with the duty% I can only get no advance or full advance. It switches over at about 40% duty.
Intake cam angle is about 265deg at 0-38% duty, then it jumps to about 310deg at 40-100% duty. There is no in between. The intake is truly advancing above 40% duty because the engine becomes choppy and requires like 2.5k rpm to keep running.

What I've done so far to fix this:

• Pull VVT solenoid out of engine verified the spool valve movement
  • At about 25% duty the spool valve begins to move. It fully moves over at about 65% duty
  • I'm fairly confident I have everything hooked up properly form an electrical standpoint because of this
• Cleaned and inspected the passage ways in the 'valve block' on the valve cover
• Cleaned out the intermediate pipe thingy with the 4 orings on it

The problem still persists. Does anyone have any experience with this type of VVT failure mode? Some advice would be appreciated before I fire the parts cannon for a new solenoid, or pull the engine apart to inspect the VVT actuator in the cam gear.

curly

iTrader: (25)

Can you post your tune? And do you have an oil pressure sensor for the ECU?

Nethawk

Tune is attached. No oil pressure sensor to ECU. Factory 'real' oil pressure gauge on cluster shows about 60psi when testing this with engine warm and about 2-3k rpm

Ted75zcar

iTrader: (2)

VVT only has 3 states. Retard, hold, advance. DC below the Hold DC will retard to min BTDC, DC above hold will advance to max BTDC, and hold DC will maintain the current angle. Hold is a function of several factors and is dynamic.

Nethawk

I triple checked everything is electrically set up properly with a scope. Screenshot shows the control pulsing to ground as expected. Square wave changes with duty, and carrier frequency is 308Hz ish. So that is working as intended.

My understanding with the VVT was that more duty = more advance. I thought the PID control would account for dynamically changing oil pressure and viscosity to get the right angle. Doing some more research it sounds like Ted75zcar is right that there really are only three states? As far as megasquirt tuning, how does one find what to use for min/max duty%? Also should we be enabling the 'hold duty' setting. How do you determine the hold duty?

Ted75zcar

iTrader: (2)

Min and max are best determined iteratively. For VVT their main purpose is to prevent wind-up in the control system. Basically, you get the closed loop control dialed in enough to determine the maximum and minimum DC that is used over all operating conditions. Use CLT to disable VVT during cold start (DC held at 0), and the target table to ensure 0 degrees of advance below rpms where you have roughly 30psi.

Do not use the Hold duty feature on MS. It is a static, and the Hold duty will move based on multiple variables, for example oil viscosity (which itself is a function of many things like age, oil weight, oil temp...). The integrator term in the control loop will servo to the current Hold duty when tuned properly.