Sniper EFI

[Holey76 - Square Nut]

Hi all.
I installed a sniper EFI on my 76 k5.
So here's the problem: when cranking engine, the power is shut off to the efi cpu, causing it to reboot while im srying to fire it up.
How do i supply a switched + that does not get shut off during cranking ?

 

[Bent77]

Head back to the install manual and get out your meter. My guess is you landed the ignition on wiring into something that drops out while cranking. There are also 2 dedicated wires to the battery

 

[Holey76 - Square Nut]

I'll search for a clt that doesn't shut off on crank. Thank you.

 

[mrk5]

You have to be careful because some power sources that are live with the ignition on get cut off when cranking. Makes it a little hard to check by yourself.

 

[Bent77]

I'll search for a clt that doesn't shut off on crank. Thank you.

On my 77, I think I used the original power feed to the HEI as a trigger wire to a relay direct off the battery. Key on, injection on for the control side power

 

[Fastereddie]

I was gonna say, use the big pink that feeds the h.e.i.

 

[shady]

I used the wire that feeds the HEI for my fuel pump once, and it caused all kinds of drivability issues. Be careful on what you hook to that as far as potential amp draw.

 

[Bent77]

I used the wire that feeds the HEI for my fuel pump once, and it caused all kinds of drivability issues. Be careful on what you hook to that as far as potential amp draw.

That’s why I use it as the signal for the relay, then clean power from the battery

Mine has been that way since I injected it in 2015

 

[Holey76 - Square Nut]

On my 77, I think I used the original power feed to the HEI as a trigger wire to a relay direct off the battery. Key on, injection on for the control side power

I considered that, and, still may. That's prob the best route to go.
Thank you.

 

[Holey76 - Square Nut]

You have to be careful because some power sources that are live with the ignition on get cut off when cranking. Makes it a little hard to check by yourself.

Ya, i had the switched + sourced from a ckt that shuts off during cranking. That makes it a bit tough for the engine to run
It'd start, then die, as the efi cpu was rebooting.

 

[bigjimmy82]

Helped a friend put the Jeep 2 barrel system on his 4.2, finding a hot while cranking feed was one of the trickiest parts haha, glad you got it figured out!

 

[Holey76 - Square Nut]

Soldered a wire to the HEI +, Used that to fire a relay, and relay was sourced direct to batt. I had considered that, then a member suggested it... It worked perfectly

 

[pblaze725]

Did you get the hyperspark dizzy with the kit or are you still using the HEI?

 

[cheavyk10]

On my throttle body efi (Summit Max-efi) the main power comes from the battery but for the keyed 12 volt I just used the choke wire since it was already there on top of the engine. Both wires were the same gauge anyway. I was able to keep the HEI with this setup.

 

[Holey76 - Square Nut]

On my throttle body efi (Summit Max-efi) the main power comes from the battery but for the keyed 12 volt I just used the choke wire since it was already there on top of the engine. Both wires were the same gauge anyway. I was able to keep the HEI with this setup.

I didn't consider that. Rats. Well, its done now, and changing that to a non start circuit was all it needed.

 

[Holey76 - Square Nut]

Did you get the hyperspark dizzy with the kit or are you still using the HEI?

Still using hei.
I really wasn't sure i wanted a cpu controlling my timing, as I'm running 11.75:1 and without a knock sensor etc, how would the cpu know if it's pinging, or running where it needs to be ? So i kept it basic.

 

[Fastereddie]

Still using hei.
I really wasn't sure i wanted a cpu controlling my timing, as I'm running 11.75:1 and without a knock sensor etc, how would the cpu know if it's pinging, or running where it needs to be ? So i kept it basic.

The distributor doesn’t know if it’s pinging either…

 

[Holey76 - Square Nut]

The distributor doesn’t know if it’s pinging either…

Right. But i delay timing to stop pinging, will the cpu's readjust what I've done?
Maybe I'm not clear on how a cpu determines appropriate timing.

 

[Fastereddie]

Right. But i delay timing to stop pinging, will the cpu's readjust what I've done?
Maybe I'm not clear on how a cpu determines appropriate timing.

You can input whatever timing curve you want in the cpu.

 

[Blue85]

The difference is that the distributor only allows very broad changes to timing and an ECU lets you do anything. If you get a ping in a small area, like high load from 3000-3100RPM, you have to basically turn the entire mechanical advance down, effecting everything at higher RPMs. The ECU would let you pull timing in only the problem area. Additionally, a distributor is not 100% repeatable with how all the parts move, so you have to leave some margin.