Priming pulse timing
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Author:  Peter [ Mon Oct 07, 2013 8:12 pm ]
Post subject:  Priming pulse timing

So I tuned my priming pulse yesterday night, because the reset button on my TA card has exceeded its life cycles. So this morning I went out, and tried to start it, and it was like the old days before the priming pulse where it just cranks over, and never fires. I'm thinking what's going on here is that it's priming so quickly that the fuel pump doesn't have a reasonable amount of pressure in the system. So we're thinking the priming pulse should happen on the first crank event. Unless somebody has a better idea. Maybe batch injection below 200RPMs or maybe dynamic tolerance since that engine doesn't seem to stay synced while cranking.

Author:  Fred [ Mon Oct 07, 2013 9:57 pm ]
Post subject:  Re: Priming pulse timing

Without any priming you should eventually get enough fuel to light off. If it cranks forever, then you've simply not got enough fuel, and you were likely starting up into a more correct zone using the priming pulse alone. So, up the fueling on your cranking row in your main table, you should have something down around 150 200 rpm, increase fueling there until it will eventually start. The priming pulse just wets things and purges the injectors such that the normal pulses are not used up doing that, and can immediately take effect.

I'd like to add that a good fuel system will have a check valve on the pump and hold pressure indefinitely such that the insta-prime actually works. Maybe something is lodged in yours (or your regulator) allowing leaking, or maybe I'm unrealistic about the effectiveness of such valves. I've pulled fuel lines off of cars in junk yards before, though, and had them spray everywhere with high pressure still inside.

I wasn't aware you were manually intervening in the running of your car, AGAIN, either! :-p LOL, this is like that time you had your mum pushing a prime button on the dash. Please report these issues BEFORE you wear out your reset button so we can work together to solve them and make you (and everyone who follows in your brave footsteps) happier! :-)

I like the prime once triggered idea. It could also time out after say half of the pump time out, and inject the priming pulse then. Something to consider, for sure.


Author:  Fred [ Wed May 28, 2014 6:14 am ]
Post subject:  Re: Priming pulse timing

On my TBI setup I'm quickly learning that I need two things:

1) A monster prime to fill the entire carby-style manifold, preferably WITH the throttle open
2) Much more enrichment during cranking to ensure SOME of it makes it to the cylinders.

Today was the coldest day on record for the month of May where I am :-) I'd say around or right on 0C.


Author:  Fred [ Thu May 29, 2014 7:20 am ]
Post subject:  Re: Priming pulse timing

Turns out I was just losing sync all the time. Noticed the rhythmic nature of it this morning, and happened to be logging, so checked the log and found what I suspected. Much better now, so my thoughts on fueling will be unclouded by the misinterpretation of "it won't start" :-)

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