Made the switch to efi last year. (Methanol, 8 - 160 bl holley injectors. Belt drive pump. Primer with methanol nozzles in the manifold...which worked fine with mfi.)
Ever since, I have struggled to start this darned thing without a pop in the manifold. Often I get away without it first cold start of the day. Sometimes a little better if I crack open the throttle. It will start, but I'm pressing my luck with this pop in the intake.

The tune cycles the injectors at the hit of the ignition switch. I have tried more or less or no primer.

Anyone ever struggle with this and figure out how to avoid it?

Bucky,
If the efi nozzles are fed by the mechanical pump expect no help from them until the rpm is up high enough to meet the psi requirements.

I take it the mfi nozzles and an electric pump are being used to get it started?

Opening the butterflies never works with standard MFI as you know. If it helps to open the BFs with the electric primer would that indicate you are on the button too long and its too rich to start?

I figured that. Even if I don't use the primer it pops. Usually within the first one or two rotations. Then it starts. Even pushed out the gasket on the tunnel ram in the shop once.

I thought about eliminating the primper pulse on the efi injectors...maybe residual pressure gives a little squirt? Or turn off the electronic fuel at start and see if it still does it.
It is a boosted combo if that makes a difference.

A couple of ways I have seen it done.
1: an electric pump with enough power to get the pressure up tied to the main line after the mechanical pump. An on/off solenoid is between the pump and the main fuel line. Once it is obviously working off of the manual pump the electric is shut off. This way also has the benefit of priming the mechanical pump.

2: I sell 20 gpm pumps to some folks. The much larger cc per turn of the pump has enough power to bring the pressure up at cranking rpms. Naturally the faster you can spin it the easier it gets.
Sometimes this requires a rethink on the bypass to dump enough fuel back to the tank.

Come to think of it there is no real reason you can't run that at 1 rpm (idle) with your old mfi nozzles. 2 things have to be addressed though. You either have to reduce the nozzle size a lot to feed it what it needs for idle
OR
throttle back the electric fuel pump to say..2 lbs.
Still too much?. reduce lbs some more.

It's weird. I used this same little facet style pump and a no2 solenoid and two mfi nozzles to prime when I was on mfi and never ever did it pop. Same system but now efi, and here we are. Weird. Maybe if I just shut off the efi fueling during cranking and fire it up on the primer only and see if it goes away?
I wonder if a leaky efi injector would do this?

efi should start without the aid of an extra pump.too much air not enough start enrichment.or another setting like number of revs before fire possibly

quote:

Originally posted by rusty:
efi should start without the aid of an extra pump.too much air not enough start enrichment.or another setting like number of revs before fire possibly

Remember this is a belt drive pump.

thats what we ran with efi ,it started easy no priming

I'm just not entirely convinced that it is a fuel problem. I can give it as much fuel as I want with the primer. Seems ignition related at least a little. 25 degrees cranking.

what kind of efi
is it possible to suck air through the primer system

on the fast system were were lots of settings to tell it to fire after x number of revs,start fuel enrichment,fuel and timing in that area of the map

It's an MS3Pro-Ultimate from Megasquirt/DiyAutotune.
I do have a solenoid on the primer to keep air from sucking....not that those don't start leaking eventually. But usually the idle will show that right away.
I have it skipping the first three pulses. But I just thought about it, and that is a 64 tooth wheel. So maybe I need to skip more to let it clear.

I am also using a primer pulse as soon as the ignition is hit. It just fires all of the injectors once. I'm thinking maybe that is a bad idea. I doubt there is much in the way of residual pressure left in the system anyhow. And anything that is may squirt out and be a problem when that first spark happens.

i am not familiar with that system ,but the things you describe are similar to what i was thinking about. the system we ran had (like)10 revs to fire or so .always seemed like a lot but would fire like a street car even with the belt pump.another thought those systems use lots of battery power ,monitor volts at the pop to be sure you are above 10 volts

I hate to admit to watching them...but the efi guys on tv seem to crank over for a bit before starting too. This may be the key for me. Of course it will build pressure too. All good.