Hi,

what are your experience with priming to help engine start, especially cold.

Is this helpful? If yes what are roungh settings for this?

 

Prime is extremely useful as part of a sequence intended to purge the fuel feed (including injectors) of residual/accumulated voids. You get a much more stable set of conditions for crank and afterstart.

Prime is not particularly useful as a "cold start" variable, as it is not mandatorily correlated to crank in most vehicles. Transition from on to start (cranking) is determined by the operator and uncontrolled.

I recommend you review the cranking pulse width and cranking pulse taper functions as more appropriate for detailed cold start tuning.

 

Ted, won't the priming pulse help with cold starts because it gets some fuel into the intake before cranking, thus getting some vaporization happening before those first couple engine cycles during start? I believe the Fuel pump primes when the key hits on, there is a user controlled delay (Startup/Idle->Injector Priming Delay, I'm using 0.2 S) and then the injectors prime, then you start cranking. Maybe I'm confusing those settings though.

After typing that I went back and found an HPA video where they talk about it and they said the priming pulse would happen when the ECU detects RPM, so unless Speeduino is different from the industry standards I'd assume HPA/Ted are correct.

Timestamp should be 25:26, but youtube isn't cooperating

Alex,
I'm using 35 mS @ 5 C and taper pretty linearly to 5 mS at 75 C.
These values (especially at cold) are way higher than I think they should be based on the research I've done, but that's what has resulted in the best cold starts for me. It hasn't gotten that cold here yet, but in the ~15-20C (~60-70 F) temps the car has been starting really well. If anything, my hot starts usually take more cranking than my cold starts surprisingly.

 

You aren't wrong, and scaling prime with temp is certainly something I do as normative. They key here is to not tie crank enrichment to prime as the primary correction.

I didn't notice this was speeduino until after my initial comment, but assuming it functions like MS, prime occurs with key transition from off to run (at the end of the delay). On return style systems with most aftermarket fuel pressure regulators, I implement a delay of 1-2 seconds. Rationale for this is beyond scope, but trust that the engineering analysis supported by empirical data across conventional regulator architectures has been done.

There is nothing that forces transition from run to crank in a known time. Furthermore, there is nothing that would prevent the operator from cycling back to off and to run again, which has now added double the prime pulse (as an experiment, try this a few times and see how your start/backfire is impacted). There is also nothing to force waiting for the delay to complete and prime to occur prior to transition from run to crank (effectively eliminating prime all together). Once you consider all of the workflows and use conditions, the faults in using prime as the first order correction are obvious.

The only direct correlation we have functionally is cranking pulse. Fortunately we have the crank pulse taper, which if used properly, effectively enables a prime pulse event at the run to crank transition event.

this is "OEM quality" tuning guidance, not "did this with no issues" stuff. Probably more advanced than most need to be concerned with.

 

thank you all for answers, I will try values SimBa provided

Im trying to improve basemaps I give to customers. Its a little problematic when I dont have any NB or NA miata at this moment

 

Hello again!

took some time for me to perform experiments on one of customers Miata (mk1 NA 1.6). Have to say I see not much improvement, if any. speaking of cold start.

But maybe there is another reason it needs to crank long to start? Idle control, spark, ve map, warmup enrichment, afterstart are already well adjusted I think