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I just swapped a 1.8 VVT engine into my 90' NA
I do have a weird issue with enabling vvt right now.
If I calculate my min and max angles, there is only like 10 degrees between them.
I do have the idea that even when the ecu is telling to use 0 vvt angle, the car is issuing more angle.
Because when I enabled VVT with 0 angle at idle, I had to add like 20% fuel to get my original AFR back.
You're minimum VVT Duty is at 30%, have you tried lowering that to 0?
If its to high the VVT Valve cant return to its resting position and you'll always have a bit of VVT.
Also tested this with 0% min duty(And the vvt test mode overrides this setting)
the problem is once I enable my vvt with 0% duty, it immediately jumps to an angle which is too high.
That is why I was thinking is has something to do with the oil pressure running through the system.
I uploaded a very clear log (and my tune)
You can see I rev the engine to 3k rpm, and go from 0% vvt duty to 100% with the vvt test mode.
The absolute angle goes from 295 to 304.5
The rpms drop a lot. Is this normal for 'only' a 10 degrees angle change?
I only post from mobile and rarely download logs/tunes anymore. Please post a screen shot showing RPM, MAP, CLT, VVT target, VVT duty, VVT angle, and oil pressure and oil temp if available. Use a sweep marker starting at 0% duty cycle and ending after 100% duty cycle and after VVT angle has stabilized.
OK, there are several points of interest we should clear up here ... please do your best to address each one
The Trigger angle in you ignition settings seems larger than what I am accustomed to seeing, This is the angle that you needed to have in order to get your fixed timing target?
Have you ever replaced the timing belt on this engine, or for any reason had the belt off and then re-timed the engine (mechanical)
Your crank advance of 0 degrees is super low, how did you arrive at this setting?
Procedural guidance: your CLT in this log is lower than what I would recommend for any VVT work. It is advisable to do VVT characterization at full operating temperature.
Now some specifics ...
Your min angle is indicative of a falling edge trigger capture, I believe most Miata installs use rising edge. This is supported by the trigger offset from above. I would suggest that you switch to rising edge, re-set base timing. You should see the min angle above get more into the area of what you see on this forum
Your RPM is dropping significantly when you run you test. As you have pointed out, your AFRs are whack, but with a map of close to atmo I suspect your VE table is just dumping fuel into the motor. The motor will run very poorly during this test, so just expect that. Use the throttle to maintain the engine speed when determining the max angle. You can even temporarily pull some fuel out of the high load-low RPM VE cells to keep the engine from going pig rich.
I think the above will get you in good shape, but work with it and reply back your findings.
EDIT: (not corrected above) - I did just look at the DIY basemap, and it is configured for falling edge, so my statement above WRT edge capture may be incorrect. This does call into question the mechanical timing.
We first went over all the mechanical timing components, but they were all ok
Then I tried to swithing the ignition capture to rising edge and... It was fixed
I just could not believe how my engine was running so well with ignition capture set to falling edge?
But i'm a happy man now, thank you for the usefull input!
WRT rising vs falling ... it really doesn't matter too much which one you use for non-VVT or VVT-turned-off situations. Where it can get tricky is with VVT turned on, or if you have a different crank trigger setup (like a 36-2). For VVT, the reference trigger (CAM) is monitored at all times. This trigger slides around the base (crank) trigger with changing cam advance angles. This is when the ECU needs to have better information relating the two separate triggers and where to expect them relative to each other.
For non-VVT installs you tune out the edge capture with the angle offset when setting fixed timing. Stock trigger (crank) pulses are super short and you can move the fixed timing reference from the back (falling edge) side to the front (rising) side of the pulse (and visa versa) and get good timing. A 36-2 OTOH has a huge gap between the falling edge and the next rising edge. The trigger offset is limited in code (for some unknown reason to me) to something like 20 degrees, which may not be enough to dial out the "-2" gap on the 36-2.
Anyway, have a nice weekend.
EDIT! : just to confirm, you reset fixed timing after changing the edge capture I hope. If not, you need to or your spark advance table will be way off the actual ignition timing.
02-11-2023, 07:23 AM
VVT angle question
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