Experience Installing Holley Sniper

[boughtnotbuilt]

We replaced the 71 4 barrel carb on my sons' new (to him) '71 GMC 2500 camper special with a Holley Sniper and I thought I post some notes on our install after the fact.

He went with the Sniper master kit (that includes fuel pump) and the electronic distributor and the Hyperspark box so the full monty with timing control.

We ripped the fuel lines and mechanical pump, carburetor, AC unit and heater unit in the engine bay and cab (it was missing half it's parts and we are going to go with something like vintage air eventually) along with a lot of wiring and 'improvements' the PO had made. We disconnected and removed the cruise control and the brake controller and all the vacuum lines related to those. The engine bay looked so much better after all that.

I fabbed up a simple plate to cover the holes in the firewall where the heater and AC lived and we mounted all the sniper electronics to that.

We spun the motor to TDC and dropped the new distributor in. It looked like it was off by a tooth, but we'd done it all right and didn't change it. (it turned out to be right)

We pulled the sending unit out of the in cab gas tank to find the float and gasket shot. This truck has two saddle tanks, both of which had been abandoned at some point by the PO and we are going to live with figuring out why until later. We temped up a return line by drilling a hole in the sending unit and mounting the supplied bulk head fitting. It worked, but the gasket leaked the first time we filled and the float was bad, so we ordered a new sending unit with a vent line that we used for the return.

We install the supplied filters and fuel pump on the inside of the frame rail and ran new supply and return lines to the back of the throttle body.

We installed the throttle body unit and hooked it up to fuel, throttle and kick down cable, and to the rest of the harness. We dropped the exhaust and installed the O2 sensor just behind the connection,which was just after the hooker header collectors.

We did some moving around of things on the Edlebrock intake put the coolant temp sensor in the intake and installed an new swivel thermostat housing to give it some space. We removed the plumbing pipe someone had installed on the water pump and plugged the heater in and out for now.

We reused the same +12 ignition for keyed +12 and ran the BAT +12 and GND straight to the side posts of the battery as recommended.

The instructions were pretty good, our only problem is the Sniper instructions didn't assume you were using a Hyperspark, so the wiriing diagram was wrong. In the end, it's pretty easy to wire, but it takes a while to grock the entire thing.

We primed the pump and it fired on the first try and checked the timing mark against the computer just to make sure we got the timing right. But, the upper radiator hose leaked, then the fuel inlet leaked, then the oil pressure sending unit leaked. Once we dealt with all those, we took it out for our first real drive, only to figure out we were out of gas. We filled at a gas station and that's when we realized the fuel tank gasket had failed and we filled the cab with a nice coating of gas. Once we siphoned the fuel level down to a safe level, we finally were able to take it out on a decent drive.

It did take us quite a while to get the idle right. We were fighting one small vacuum leak (abandoned vacuum line not fully plugged). We went through Holley's process for setting the IAT and could not get it to work. We finally assume the IAT was bad and removed it. Called Holley, they didn't believe it, put the IAT back in to prove it to them and it worked. I can only assume the IAT wasn't in all the way in and it was moving on us. Once that was solved, we bumped the idle up to about 780 from 750, got the IAT set correctly and now it idles nicely.

The new fuel sending unit arrived and we got it installed cleaning up that problem. But, we can't really road test much it as the power steering pump is failing and we need to address that and a damaged (but functional) steering box before we go crazy. I took a quick look at the tune using the Holly software and it seems decent. It's doing a fair degree of adjusting in a few areas of the fuel table, but we're going to have to wait to get enough time on the engine before I can make any changes to the tune. But, timing and everything else seem good. The smell out the tailpipe certainly improved.

I can put up pictures of anything people might find interesting.

We don't really know how it compares to the carbed version, as the carburetor was in such bad shape that it ran like crap when we got it.

I'm glad to hear it went well. I also purchased a sniper master kit but havent installed it yet. My plan is to install the return the same way you did. My only question is, how noisy is the fuel pump? I've heard mixed things about how loud it is right under the cab floor.

Thanks and good luck

[boughtnotbuilt]

It's loud and it never stops. But, once the engine is running and the car is moving, you don't really hear it in that steel soup can of a cab.

[yysenhimer]

Great write up, thank you.

[notsolo]

Thanks for sharing. I would like to see how you did the o2 sensors. also What is the recommended psi for the pump? If you ran an in line pump maybe cut out the noise. Excess noise in the cab would drive me nuts.

[firedemon]

what year did you get the sending unit with the return line for my 67 only has one line coming out . got a pic ?

[boughtnotbuilt]

The sending unit is this - it's from a '72.

https://www.jegs.com/webapp/wcs/stor...rsistYmm=false

It's jegs part 78508.

The only challenge was the outlets face up rather than to the passenger door as the '71 did, so we had to trim the end off the fuel line coming up through the floor and used 6" of hose for the end. We also used 18" of submersible hose to get from the sending unit to the bottom of the tank to prevent airation.

The sniper wants 58 to 60 psi, which I think is pretty common for TBI units. I assume when you said in line you meant 'in tank'. And I can't think of anyway to put a pump in the gas tank in the cab.

When we convert the truck to a flatbed, we're going with a large frame mounted tank in the back and that will have an in tank pump.

I'll see if I can get a picture of the O2 sensor. It's hard to get to. We got a bung from our local muffler shop - I don't think they even charged us. Drilled a hole just big enough for it to sit in and welded it up. the kit comes with a clamp on mount for people with no access to a welder. You drill a hole and then mount this plate over the hole and hose clamp it down with a heat resistant gasket. We opted not to use that as it looked like an invitation to problems down the road. Air leaks around the O2 sensor can cause real problems when trying to tune later. Ours ended up about 6" to 8" from the collector. These hooker headers are old school monsters and end up way back.

[Bearhawg]

Great write-up. Thanks for sharing the information. I've been thinking about going EFI for a while but didn't want to install a rear mounted tank. I did't think a return line was possible with an in cab tank. I'll have to check mine out and see how the lines run and if I can use the sending unit you listed.

Thanks again.

[boughtnotbuilt]

We were also able to use the original sending unit by drilling a hole in the unused detent and installing the supplied -6 AN bulk head fitting. You attach some submersible gas line on it so it sits on the bottom of the tank and it's all good. There were already two holes in the floor, so we used that for the return.

The only reason we had to go to the new sending unit was that the float in ours was bad and you can't buy just the float (that I could find).