Wanted to convey some lessons learned regarding a Holley Sniper 4150 EFI installation that I performed on my 1970 Olds 98 455 in 2019. It took roughly a year to iron out all of the issues. It does run very good at the time of this writing.

My configuration consists of the Holley SNIPER TBI Master Kit (BLACK Part # 550-511K), Holley Dual Synch Distributor (565-296), Holley Sniper Coil Driver Module (556-150), an Edelbrock Performer 2151 Olds 455 Intake Manifold, custom 2.5” dual exhaust with Magnaflow mufflers, MSD Blaster Coil 8222, MSD 8.5 MM Spark Plug WireSet (31199), and NGK-7189 XR4IX IX Iridium Spark Plugs. The Sniper EFI throttle body controls the timing and a radiator electric fan.

The Holley Sniper Master Kit included the following:

1) Sniper EFI Throttle Body Assembly (ECU)

2) Coolant Temperature sensor

3) Bosch Wide band oxygen sensor

4) Clamp on oxygen sensor bung

5) 3.5” Touch Screen Controller

6) Output Harness (controls fan)

7) Main harness and ignition adapter

8) Universal electric fuel pump

9) 20 FT - 3/8 I.D. EFI Vapor Guard Hose

10) 3/8” Vapor Guard Hose Clamps

11) Post Fuel Filter 10 micron

12) Pre Fuel Filter

13) -6AN to 3/8” Vapor Guard Hose End

14) Fuel Cuff (240MM long)

15) 9/16” Stat-O-Seal

16) -6AN Bulkhead Nut

17) -6AN Bulkhead Fitting



Overall, the installation went relatively smoothly although I had to purchase more items to complete my installation:

1) Holley Sniper EFI to Holley Dual Synch Harness ( 558-493) (connects throttle body to Dual Synch distributor)

2) O2 sensor bung (welded on bung to exhaust tube)

3) Innovate Motorsports 3729 O2 Sensor Heat Sink/Extender (helps extend the lifetime of O2 sensor)

4) Lokar Throttle Cable and Bracket Combo (CMB-03-0038) (existing throttle cable was binding up)

5) Fuel Pump Cover (removed mechanical fuel pump so needed a cover)

6) Canton Racing 85-154 Phenolic 1/4" Carburetor Spacer 4 bbl (eliminates whistle from dual plane intake at certain RPMs)

7) Blue Sea Systems 4 circuit and jumpers (rewired to provide clean switched power to Holley system)

8) Earls Oil Filled 100 PSI Pressure Gauge (ERL 100187ERL) (check electric fuel pump pressure)

Can not emphasize the need to provide clean switched power to the various components. In my particular configuration, I had to provide switched power to the ECU, distributor, coil, and coil driver module. The easiest solution for me was to rewire reliable switched power to a jumper block then route the power to where it was needed. Note, the main throttle body (ECU) is also wired directly to the battery and this connection is separate from the switched power connections. Routing the power wires and signal cables away from coil wires and spark plug wires minimized any EMI issues. Knock on wood, never encountered EMI issues.

Exhaust leaks affect the self learning program and overall performance. Highly suggest welding on the O2 sensor bung and buying the O2 sensor heat sink/extender. I originally installed the clamp on O2 sensor bung and destroyed an O2 sensor within 3 months. The engine ran very rough and was overfueling because the O2 sensor was erroneously detecting a “lean” condition, hence the ECU was overcompensating with overfueling. I then welded the O2 bung and installed the O2 heat sink/extender. This helped solve the self learning issues and smooth idling. Also, I have not replaced an O2 sensor since then.

Exhaust gaskets should also be checked for leaks. I had to replace the “donut” gasket connecting the exhaust manifold to the exhaust pipe. Also, I replaced the crossover pipe block off plate on my custom dual exhaust system for good measure.

Vacuum leaks also affect the idling and low RPM performance. Had to replace all of the vacuum hoses to ensure no leaks occurred, including the vacuum hose on the TH400 transmission. The Comfortron was a nightmare because of all the vacuum hoses it uses. Believe it or not, a year old PCV valve and its associated valve cover grommet affected the vacuum by 5-6 KPA. This condition caused an issue trying to perform the throttle blade adjustment procedure. After PCV valve and grommet replacement, the throttle blade adjustment was a piece of cake.

The Holley fuel system suggestions should be followed, especially the 3/8” return fuel line to the fuel tank (if your system has it). I used the 5/16” return line already plumped in my car but ran into engine roughness issues. Once I plumped in the 3/8” inch return line, the engine ran much smoother.

After correcting all these issues/opportunities to excel, I ran into intermittent overfueling/rough running engine issues. Over three months, it finally degraded to hardly running at all – barely idled. Took off the air cleaner and looked down at the injectors. Lo and behold, the passenger side injectors, both primary and secondary, were squirting way too much fuel. Huge droplets were squirting onto the inside of the air cleaner. After videoing it and sending the video to Holley Tech Support, they replaced the Throttle body/ECU under warranty. It has run fantastic since. Moral of the story, if you encounter rough running/overfueling, take off the air cleaner and look at the fuel injectors.

Will save the tuning, timing curves, and AFR experiences for another post. Was truly an adventure because Oldsmobile 455 baseline tunes/templates for the Holley Sniper system are very few.

Overall, am glad I installed the system. Once the reliability issues were fixed, it has performed flawlessly. Also, the Holley forums contain a wealth of information to troubleshoot a malfunctioning Sniper system. Now, the answer to the big question – has it improved in MPG?

Elevation is at 3000’ and I travel over mountain passes to get anywhere. With my old 455 engine, a Pertronix Ignitor III system, Blaster coil, new spark plug wires, and NGK-7189 XR4IX IX Iridium Spark Plugs, I was getting a persistent 14-15 MPG on the road. The new engine with the Holley Sniper EFI is currently getting about 14-15 MPG and still self learning. Time will tell.

Hope this helps anyone interested in a Holley Sniper installation understand some of its idiosyncrasies.

 

Forgot to mention other important info regarding the MPG comparison. The old 455 engine had an Edelbrock 1407 Performer 750 CFM 4 barrel Carburetor and Edelbrock Performer 2151 Olds 455 Intake Manifold. The carburetor had been tuned with various metering rods and jet configurations to maximize mileage.

 

Thanks for the insight. Your experience will be helpful to others considering a FI swap!

 

Did you use a wideband/afr meter to tune it? In addition did you use an adjustable vacuum advance in the original combination?
I’m an EFI guy but if the afr’s were similar in both combinations, then the mileage difference should be negligible. Otherwise it’s an apples to oranges comparison. The only advantage would be with timing, which can still be optimized to some degree with an adjustable vacuum advance.
Just asking.

 

Did not use wideband/AFR meter. Used old fashioned trial and error method. Changed configuration(s) and documented MPG and road conditions (weather, wind, temperature) over long time periods. Had to drive a lot and stimulate the economy (i.e., bought lots of fuel).

 

Did not use adjustable vacuum advance in original configuration.

 

I figured, as most don’t do what they really should. As mentioned, apples and oranges comparison. Just sayin.

 

How is an AFR meter used to tune the EFI? Should the operator shoot for 14.7:1 AFR when cruising by slowly changing the parameters? It's my understanding that the Holley Sniper also has a function which enables/disables the self learning. I would think that should be disabled when using an AFR meter to tune the EFI.

 

I had tuned my Q-Jet by leaning out the part throttle AFR until I got a lean miss on the highway. I then slightly richened the mixture just beyond where the miss disappeared. At the track, I played with the timing until I found the best performance. I then started adding vacuum advance until I got a little pinging, once again backed off the advance until the ping went away.

Having said all that, I do occasionally get some part throttle light (and I emphasize light) ping while accelerating. Crowd the throttle, the ping stops.


When I installed the Holley Sniper, I duplicated the same timing and AFR parameters. It was no big deal to get 17-18mpg with the Q-Jet, the Sniper is about the same.

The only way your going to find the “happy place” is by experimenting. You need to find what YOUR engine wants, don’t give it what you think it needs.

EFI or carbureted, the AFR are similar. It’s just how the fuel is being controlled that’s different.

 

Very nicely detailed post. Thank you for sharing.

I think the biggest advantage you have now is that the performance and mileage should be repeatable and slightly improved over the long haul, and should require little to no maintenance or "fiddling" like a carb and conventional distributor would take.

Also, it will be much better for your elevation changes and run better at higher elevations than the carb that would be mis-calibrated for higher elevation without specific tuning.

Do you have any pics of the setup underhood?

 

Battenrunner,

You are correct the Holley Sniper will be better for elevation changes and also temperature changes. Currently we are experiencing +50 degree temperature swings (32F to 85F) while a simple road trip to the Oregon coast (370 miles) will encounter elevations between 5200 ft to sea level. The Holley Sniper performed flawlessly in this situation (recent Oregon Coast road trip over 800 miles). Was interesting to observe the Closed Loop Correction AFR on the hand held monitor. The Sniper adapted over the various conditions and ran smoothly.

Do not have any pics of the setup underhood - yet. Will post when I take some.