Author Topic: Slow start, fuel drainback?  (Read 1044 times)

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CV355

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Slow start, fuel drainback?
« on: January 07, 2025, 02:22:15 PM »
While my engine fires up consistently, it usually takes a few seconds from turning the key to successful ignition.  This is with a Holley Super Sniper EFI, electric fuel pump, -10AN supply, and regulator on the -8AN return.  I do not have a check valve anywhere in the fuel lines, and I notice that the fuel pump doesn't load up for a few seconds so it's probably priming free-flow before it builds pressure, hence the delay in ignition.

If I allow the fuel pump to prime for 3 seconds and load up (audibly) by leaving the key on "run/on" prior to attempting to start, it fires up quicker but still takes a second or two.  Holley says starting should be nearly instant and no dwell is necessary.

Is that a typical issue?  Should I have put a check valve up by the Holley unit to prevent drainback?

66FAIRLANE

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Re: Slow start, fuel drainback?
« Reply #1 on: January 07, 2025, 03:39:54 PM »
Are you referring to starting after sitting for a few weeks, a few days or a few hours? Do you have a fuel pressure gauge near the Sniper? If so you can see how long it takes to build pressure when you prime under these various conditions.
"If I allow the fuel pump to prime for 3 seconds and load up (audibly) by leaving the key on "run/on" prior to attempting to start" This what you should be doing, especially when cold, so as to allow it time to provide the Prime shot. There is the odd occasion (very cold) when I will deliver two Prime shots.
Yours sounds very similar to mine and I have zero drain back issues (separate surge tank). After sitting for a few days I think its just the combination of fuel vapours depleted from the inlet tract, the fact that the prime shot has to drip around the edges of the butterfly and longish runners compared to a smallblock.

CV355

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Re: Slow start, fuel drainback?
« Reply #2 on: January 08, 2025, 07:28:28 AM »
Are you referring to starting after sitting for a few weeks, a few days or a few hours? Do you have a fuel pressure gauge near the Sniper? If so you can see how long it takes to build pressure when you prime under these various conditions.
"If I allow the fuel pump to prime for 3 seconds and load up (audibly) by leaving the key on "run/on" prior to attempting to start" This what you should be doing, especially when cold, so as to allow it time to provide the Prime shot. There is the odd occasion (very cold) when I will deliver two Prime shots.
Yours sounds very similar to mine and I have zero drain back issues (separate surge tank). After sitting for a few days I think its just the combination of fuel vapours depleted from the inlet tract, the fact that the prime shot has to drip around the edges of the butterfly and longish runners compared to a smallblock.


That makes sense, I figured that might be the case.

Typically, weeks.  According to Holley, the prime shot happens at the first crank trigger through the Dual-sync, so if I have no fuel pressure then there's no prime shot. 

I try not to let the engine go a month without firing and warming up.  Maybe I'll add in a bypass switch to the fuel pump relay so I can manually prime without involving the Holley unit. 

Hot starts are faster, but still not "nearly instant" like Holley is saying it should be. 

Rory428

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Re: Slow start, fuel drainback?
« Reply #3 on: January 08, 2025, 09:02:22 AM »
No idea about that aftermarket EFI stuff, but the OE systems have a check valve built into the fuel pump, to prevent losing system pressure. My 99 F350s V10 can sit from late October until April or May, and it always will fire up within a second of turning the key. I would like to think that the aftermarket stuff would be similar.
1978 Fairmont,FE 427 with 428 crank, 4 speed Jerico best of 9.972@132.54MPH 1.29 60 foot
1985 Mustang HB 331 SB Ford, 4 speed Jerico, best of 10.29@128 MPH 1.40 60 foot.
1974 F350 race car hauler 390 NP435 4 speed
1959 Ford Meteor 2 dr sedan. 428 Cobra Jet, 4 speed Toploader. 12.54@ 108 MPH

My427stang

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Re: Slow start, fuel drainback?
« Reply #4 on: January 08, 2025, 04:07:58 PM »
It depends on the pump, but many systems, OEM and aftermarket use a check valve.  If you can find one that flows enough for your use, won't hurt.

I do not have one on the Mustang with an in tank pump, starts easy, with the truck I have an in cab tank and need to let the pump prime
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Ross
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66FAIRLANE

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Re: Slow start, fuel drainback?
« Reply #5 on: January 08, 2025, 05:56:11 PM »
"According to Holley, the prime shot happens at the first crank trigger through the Dual-sync, so if I have no fuel pressure then there's no prime shot."
Mine is just the plain Sniper not the Super Sniper and it primes about 3 seconds after key on when pressure has built. You can hear it click the injectors. I wait for this then go for start. I would be surprised if they are different. Are you sure Holley were not referring to Cranking Fuel?