Sniper EFI conversion

[Davin Reckow]

Looking for some insite on converting an 89 GMC from TBI to a Sniper. Specifically the wiring harness. It appears from the wiring diagram the factory ecm is independent of the lights, gauges, wipers, PW, PL, etc. Trans is a 700R so maybe the converter lockup is ecm. so my thought is eliminating all the wires from the engine harness, leaving starter, alternator, temp and oil gauge inputs. Is this correct? Curious how the fuel pump maybe wired as well. thank for the assistance. Davin

 

[ccreddell]

You can eliminate your ecm. The only thing it would effect is the converter lockup. And theres a solution for that. Cant remember what it is at the moment, but I'm sure someone will chime in here.

 

[Davin Reckow]

on a 70 wagon 700R conversation I used a TCI vacuum switch. I assume the same thing?

 

[Erik the Awful]

That and a pressure switch in the 3-4 circuit.

 

[Davin Reckow]

does the ecu feed the transfer case or Hvac? started pulling wires. is there a good wire coming from the key through the fuse box connector to supply power to the sniper, same for coil and fuel pump. Any trick to getting the wires out of the sealed connector on the heater box side.

 

[Davin Reckow]

do I need to keep all the Hvac and transfer case connections to the ecu. is the ecu spilt so to speak as a engine control and a body control module?

 

[alignman88]

I’m doing the same on my ‘88 RCSB that’s getting a large displacement small block. The Chiltons manual PN 28624 88-98 truck contains all the wiring diagrams, as well as diagnostic amperage/ohm information for testing. It will supply your answers. I am cleaning up and sorting out the factory wires and identified what will be re-used. It does appear the ECM will be mostly bypassed when done. The torque converter lockup control is my last real question, we will try to let the factory ECM do it, of not there are TONS of torque converter lockup control boxes on the market. I’m following thread and My Sniper should be in end of week.

 

[ccreddell]

If you want your Sniper to control your timing also (and you should) you might want to read this article. Its the way Im going to go...

https://www.onallcylinders.com/2017/01/20/ask-away-jeff-smith-rotor-phasing-relates-efi/

 

[alignman88]

I spoke with Holley tech support. Timing must be controlled with a CD box. They have a Hyper spark locked out distributor, CD box, and coil all plug and play and very affordable. Speedway sells a kit (Holley doesn’t) that contains the distributor and throttle body parts and supporting pieces. After hearing horror stories about FiTech and support, I had excellent response from Holley. Friends with 2000HP outlaw drag cars and their engine builder swear by the Holley systems both track and street. I am documenting this build and will make a build thread soon to follow.

 

[Davin Reckow]

alignman88 so I am behind you a little ways on the conversion. my harness is spread out on the table. so on the factory harness I just need to eliminate the engine control items to start with. obviously the ecu will need power and ground. so the wires I already clipped (oops) going to the HVAC I need to splice back together. On the fuel side are you tagging into the stock relay and using the sniper to trigger the relay and then supply power to the fuel pump.