Playing With Injector Opening Time

skinny · Nov 15, 2012

i've finally got my car to start and idle reasonably well on the EV14's (525cc) but still not perfect esp when cold (seems to need a lot more PW than i would have expected).

was thinking maybe the opening (dead / latency etc) time might be worth a fiddle, at the moment it's still as per the stock injectors (1.00ms)

i'm a bit confused by what i've read on the internets plus what it says on my data sheet from the Fuel Injector Clinic.

First up, the data sheet shows 'injector voltage offset' - is that the same as opening time? so at 45psi (ok for mk1?) i have 1.25ms at 12v and 0.95 for 14v.
So for 13.2v i'm looking at around 1.16ms?

However, info out there disagrees...

Injector Dynamics (EV14's) have this chart for 725cc's

so around 0.92ms at 13.2v but with my injectors being smaller size, this would imply even smaller opening times.
From the group buy thread, i found these settings

650cc EV14's

Barry Spiers said:
Dead time @ 13.2V (ms) - 0.560

So i'm guessing my injector voltage offset is not the same as opening time and i should be looking at setting my opening time to around 0.55ms. What does this actually do - what will happen in cranking, and what changes can i expect to my VE table etc?

Mr Slow · Nov 15, 2012

Dead time, it's the time it takes for the injector to fully open and close without injecting any fuel.

Unfortunately with your ECU you can only set the deadtime for a static voltage, but as voltage increases deadtime decreases, so you can only really get a ballpark figure.

The numbers provided by ID are a good start, plumb those in, and then go from there. If they're significantly different to what you currently have (and they look it), then expect to have to add fuel into your VE table. Currently you're telling the ECU it's injecting no fuel with a deatime of 1ms, but based on the ID flow table you're actually injecting 0.5ms of fuel

Unfortunately the injector driver circuit on your MS is different to the the injector driver circuit that ID will have used to provide those deadtimes. Fortunately you can work out the deadtime of your injectors.

Switch between 2 squirts alternating and 4 squirts simultaneous the AFR if the deadtime is incorrect will differ wildly. Adjust the deadtime until the AFR is the same (idle quality may not be however!), once the AFR is the same then the deadtime is correct.

Cranking you may have to adjust on a MS1 as you're going to either be reducing or increasing the amount of fuel injected and MS1 uses injector ms as it's scale. For MS2 and MS3 it's a %age of the VE table IIRC so no change will be required. (Or is it req_fuel I can't rmember, if the latter that'll need to be adjusted slightly too).

FWIW EV14's have large VE numbers in the VE table compared to stock injectors, it's nothing to worry about, just ensure you hit the AFR you desire and don't worry about the actual VE number.

skinny · Nov 15, 2012

cheers mate - you have the opening time setting but you also have the injector offset (ms/v) on the MS1 so it can compensate (linearly at least) for changing voltage.

so with a dead time setting of 1ms on the ECU compared of 0.5ms, the voltage is opening the injector before the ECU expects it to?

For cranking yeah MS1 is just injector PW. I guess req_fuel being based on the injector size doesn't need to change with the dead time, the changes in the VE table are all i'll need...

just to confirm, the injector voltage offset that i've got on my data sheet - that's not the same as the dead time...? it's only for working out the voltage compensation

Playing With Injector Opening Time

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