Need wiring help converting TBI to Holley Sniper

[Lerner383]

Im putting a mildly built 383 in my 99 yukon 4x4 OBS. I have a holley sniper unit sitting here as well as a hyperspark distributor and ignition box. Also I have an MSD trans controller for the 4L60e.
I have some questions on the best way to wire up the Sniper and engine sensors in order that the gauge cluster, A/C, 4x4 switches, etc. will work.
1. Do you throw out the factory harness and just wire into the firewall connectors, or do you just use a few of the factory sensor connectors such as coolant temp, oil press and tach? I’m looking at this big bundle of factory wires here and it looks like a mess. I have a feeling it’s fairly simple from what you guys are saying but I just need to know where to start.
2. I want to keep the factory A/C too. Any help is much appreciated my wiring allergies are flaring! I’d be lying if I said I wasn’t tempted to throw on an edelbrock carb, rip the a/c out and run with the 270 air conditioning I grew up with two windows and 70mph…

 

[Erik the Awful]

I have a 700R4, so there will be some differences, but I simply disconnected sensors as I needed to hook them up to the Sniper. Then I rolled the parts of the harness I'm not using into a bundle and zip-tied them out of the way. My Sniper distributor is still sitting in the shop, awaiting installation, but once I have it in I'm eliminating the ECU from TCC lockup and replacing it with a vacuum switch. Then I'll be able to remove almost all of the factory wiring.

The factory wiring supplies power to the TBI injectors and uses the ECU to switch ground, so I used the red injector wire to power the Sniper, and I'll likely use the blue to power the distributor.

I don't remember anything that would keep you from keeping the A/C. You can also tap the A/C clutch power to send a signal to the Sniper to bump up the idle, but I'd have to look at the documentation again to sort out which wire.

 

[Lerner383]

Hey thanks for the reply! I really appreciate it.
So just to clarify, are you still using your factory dash gauges? I figured I would keep the factory sensors hooked up to send signals to the dash, and then use an additional coolant sensor for the sniper. I know some guys on here are using the factory ecm to control the 4L60e, but I think since I already have the MSD controller I’ll use that as a stand-alone to control the trans. But I suppose I need to keep the factory 4x4 harness back there to control the transfer case.
The guy at Holley told me that a 1995 chevy truck throttle cable might work better than trying to use this long factory cable to operate the Sniper. Any thoughts or experience on that?
There two vss sensors on the tail shaft of the t-case, does it matter which one I use for the sniper? Thanks again!

 

[GoToGuy]

Does holley have any tech installation, or tech support? No assembly or tech info for install?

 

[Erik the Awful]

So just to clarify, are you still using your factory dash gauges? I figured I would keep the factory sensors hooked up to send signals to the dash, and then use an additional coolant sensor for the sniper.

On mine, the dash sending unit and coolant temp sensor are two separate sensors. I just popped the old coolant temp sensor out, put the Holley in, and connected it. My dash still reads the temp.

The guy at Holley told me that a 1995 chevy truck throttle cable might work better than trying to use this long factory cable to operate the Sniper. Any thoughts or experience on that?

If you use the TBI throttle cable, you absolutely need the throttle extension - probably also for the Vortec. Holley charges $15 for an extension that would have cost them less than a buck to include in the kit. It's a way to squeeze more money out of you, but they don't advertise it, and so all the Chevy owners are wondering why the Sniper has such horrible pedal response. https://www.summitracing.com/parts/sne-20-16

Does holley have any tech installation, or tech support? No assembly or tech info for install?

In my experience, no. I dorked the connector for the handheld and emailed Holley's tech support asking how to get replacement pins for it. They never responded. For reference, the display on a Holley Sniper uses a 4-terminal CAN connector, specifically a Mizu-P25, P/N 52117-0411 with terminals P/N 50039-8100. $4.24 from Mouser, plus $7.99 shipping. The terminals are 22AWG. I figured this out without Holley's help.

The Holley TPS is from a late TBI, and the IAC is from a '99-02 GMT800. The Holley versions are cheap junk. Both of mine have failed.

I probably need to write a thread on all the things I've learned pro and con on the Sniper.

 

[Lerner383]

Thanks a milliion for the help! I bet my coolant sensors are the same. The one in the head is a 1 wire connector, and the sensor that was right by the thermostat in the vortec intake is a 2 wire. That cable extension looks like something I could fabricate myself. I kind of gathered from the folks at Holley that they don't get into the tech support for these swaps on the "newer" vehicles that have electronics.

 

[Erik the Awful]

That cable extension looks like something I could fabricate myself.

I thought the same, but to get it right you're investing a couple hours. It was worth it to me to use the wallet wrench. That's where they getcha!

 

[Lerner383]

I hear ya.. but they say that est. shipping date is feb 24 or so… I was at the grocery store today and they were out of campbells soup..