Changing incorrect Injector deadtime after tune

[DerekAE86]

So I've been ironing out all the little drivability quirks and one issue I'm chasing has lead me down the path to believe my deadtimes are too high.

What's happening is under constant light load (like cruising at around 7% TPS) if I gently back off throttle down to around 3% TPS the mixture gets very rich. Looking at the log I found the Effective PW has dropped to its minimum (0.2ms) so the ECU isn't letting any less fuel be injected for this "backed off throttle, but not overrun" condition.

CLL then kicks in and tries to reduce fuel, but obviously can't. Which leads it to go to full minimum clamp position and then when I gently apply throttle again I get a momentary lean condition as CLL has to reset back to 0% correction.

I'm currently using Mazda MX5/RX7/RX8 Denso "Yellow" 450cc injectors. I've struggled to find the factory specs on them,
but digging through various Mazda forums and looking at the Mazda base tunes provided in the PCLink software it appears my deadtimes are significantly higher across the entire voltage range.

Because I'm using Modelled fueling if I just go and change the deadtimes now it will really throw out the VE fuel table.
Is there a way to apply a correction to the VE table to account for the change in deadtime?
If not - is there any particular tuning strategy I can use to help fast track getting the VE values close again?

I was thinking of setting up a rather aggressive LT CLL on a single axis for RPM only and free revving the engine to see what kind of offset each RPM range wants then blanket applying that % across the main fuel table RPM columns.

Then remaking the LT CLL table for TPS vs RPM and just doing some gentle driving to let it figure out the more nuanced areas.

[Adamw]

Set the minimum PW to 0 will allow it to go at least a little leaner without adjusting anything else - assuming the deadtimes are set longer than they should be.  Or lower fuel pressure and just apply an overall multiplier to the fuel table.  If you adjust the deadtimes you will generally have to retouch the whole fuel table, especially all the low-load areas. 

[DerekAE86]

36 minutes ago, Adamw said:

Set the minimum PW to 0 will allow it to go at least a little leaner without adjusting anything else - assuming the deadtimes are set longer than they should be.  Or lower fuel pressure and just apply an overall multiplier to the fuel table.  If you adjust the deadtimes you will generally have to retouch the whole fuel table, especially all the low-load areas. 

Thanks I'll def try this first before doing anything extreme. I have a fuel pressure sensor connected so if I lower the fuel pressure does that still need a manual multiplier on the fuel table? I thought if it pressure referenced it would automatically compensate for any change to fuel pressure?

On that topic - currently my fuel pressure regulator isn't connected to a vacuum source so its a stable pressure at all times. Connecting to vacuum would lower the pressure even more during low load situations correct? If I don't need to update the fuel table because it's already fuel pressure referenced I might do that too.

[RyanG]

6 hours ago, DerekAE86 said:

if I gently back off throttle down to around 3% TPS the mixture gets very rich. Looking at the log I found the Effective PW has dropped to its minimum (0.2ms) so the ECU isn't letting any less fuel be injected for this "backed off throttle, but not overrun" condition.

CLL then kicks in and tries to reduce fuel, but obviously can't. Which leads it to go to full minimum clamp position and then when I gently apply throttle again I get a momentary lean condition as CLL has to reset back to 0% correction.

I had exactly the same problem so I know your pain! I used 3D CLL trim limit tables referencing TPS delta to try and minimise it until I got a chance to correct injector data and retune.

[Adamw]

2 hours ago, DerekAE86 said:

I have a fuel pressure sensor connected so if I lower the fuel pressure does that still need a manual multiplier on the fuel table? I thought if it pressure referenced it would automatically compensate for any change to fuel pressure?

Yep, if you have a FP sensor and you are using the "FP Sensor" fuel system type then it will be taken care of automatically.  And yes, connecting the FPR vac reference would be a good option too.  

[DerekAE86]

6 minutes ago, Adamw said:

Yep, if you have a FP sensor and you are using the "FP Sensor" fuel system type then it will be taken care of automatically.  And yes, connecting the FPR vac reference would be a good option too.  

Sweet I'll dig out the manual and drop my fuel pressure to the lower end of the factory specs, hook up the vac reference and make that change to the Minimum Effective PW. Hopefully it masks the problem until I descide if I want to change injectors to something that comes with an accurate data/test sheet.