5.7 Mercruiser EFI Conversion

[Nfowler]

Hey, thought I would share some info on my latest project. I ditched the finicky Quadrajet on my 5.7 for a Holley Sniper EFI kit. Had to source a manifold riser spacer from performance fuel injection ($80) to accommodate the O2 sensor, found a nice stainless return to tank fuel fill adapter from CP Performance ($50) to avoid removing or drilling into the fuel tank, and used an existing threaded plug for the Coolant Temp sensor. Manufactured my own throttle cable bracket adapter due to clearance issues with the sniper unit. But once I got those issues out of the way the rest of the install was a piece of cake. Be sure to wire your fuel pump in accordance with SAE J1171 which requires the fuel pump to be wired through the oil pressure sensor so it won't prime unless the engine is cranking. Record actual static fuel pressure to later enter in the EFI parameters this allows the ECU to accurately calculate the injector pulse width. (see link). Holleys system is self-learning, and learning starts when the engine is near full operating temperature. Obviously the software is geared towards automotive applications so that doesn't even start until the coolant temp sensor hits 160 degrees which is about 10 degrees higher than my average operating temperature. To address this you need to open the base configuration in the Sniper software (free download from Holley), navigate to the coolant temperature enrichment table and adjust the enrichment down to 100% from 120 degrees and up. Then adjust the Fuel Ratio Offset to 0 at the same temperature in the adjacent table (see link). Now that you have that dialed in you can set your RPM axis scale and MAP axis scale to suit your engine (mine doesn't rev to 7000) for better resolution and to allow for fine tuning later. Next step is to set your Target Air Fuel Ratio, that's what the ECU will use as a reference when learning and during all closed loop operation. I used a healthy 13.4 at idle, 13.7 at cruise, and 13.0 under wot. Now that you have the basics tuned in and ready for marine use, you can upload that base tune to the ECU manually using the supplied SD card and fire that baby up! Any questions please don't hesitate to ask, I can't be happier with the results my boat has never run this smooth. Rough total including a couple pipe fitting adapters I had to source for the temp sensor and the fuel system, $1700. Money well spent.

See some pictures here --> https://imgur.com/a/RtXh0JM

 

[alldodge]

Turning in the 13's you need to make sure your knock sensor is working. Under heavy load need to be in the 12's

 

[Nfowler]

If you look at the pictures in the link, any operation above 94kpa on my map is 12.5
but it’s 13.0 from 88-94. Which is only 45-60% throttle position on the datalogs I’ve taken. I just posted the numbers the software entered in those boxes automatically. There’s also, acceleration enrichment tables that add fuel depending on the rate of change of throttle position and manifold pressure, that kick in under acceleration. I have been watching the monitor like a hawk and barely ever hit 13 when going wide open. I’m optimistic about it but I’m still a little paranoid so I keep out of trouble

 

[alldodge]

Look at your plugs every once in a while

 

[dollar7499]

Hi Nfowler, I am about to pull the trigger on the Sniper EFI Qjet conversion rather than troubleshoot another flooding carb.. Do you have an update on how the rest of your season went with the Sniper? Did you mount the screen? You never mentioned upgrading your fuel pump. Were there any other parts you realized you needed? Thanks! John

 

[Scott06]

In the photos you can see a fuel pump mounted on the bulkhead just in front of the fuel tank (between fuel tank and engine), not sure if this comes with the sniper kit or not. Would assume they supply it with kit to ?

would note that photos show proper injection rated hose clamps used here vs std worm drive clamps , make sure you use that and proper pressure and marine rated hose

 

[QBhoy]

Nice work. Is this a tbi system presumably?

 

[GA_Boater]

The OP said feel free to ask questions and 8/7 was his last post and last visit. If he doesn't show this will be closed as it's been idle for 6 months.

 

[Wellcraft1996]

Hey, thought I would share some info on my latest project. I ditched the finicky Quadrajet on my 5.7 for a Holley Sniper EFI kit. Had to source a manifold riser spacer from performance fuel injection ($80) to accommodate the O2 sensor, found a nice stainless return to tank fuel fill adapter from CP Performance ($50) to avoid removing or drilling into the fuel tank, and used an existing threaded plug for the Coolant Temp sensor. Manufactured my own throttle cable bracket adapter due to clearance issues with the sniper unit. But once I got those issues out of the way the rest of the install was a piece of cake. Be sure to wire your fuel pump in accordance with SAE J1171 which requires the fuel pump to be wired through the oil pressure sensor so it won't prime unless the engine is cranking. Record actual static fuel pressure to later enter in the EFI parameters this allows the ECU to accurately calculate the injector pulse width. (see link). Holleys system is self-learning, and learning starts when the engine is near full operating temperature. Obviously the software is geared towards automotive applications so that doesn't even start until the coolant temp sensor hits 160 degrees which is about 10 degrees higher than my average operating temperature. To address this you need to open the base configuration in the Sniper software (free download from Holley), navigate to the coolant temperature enrichment table and adjust the enrichment down to 100% from 120 degrees and up. Then adjust the Fuel Ratio Offset to 0 at the same temperature in the adjacent table (see link). Now that you have that dialed in you can set your RPM axis scale and MAP axis scale to suit your engine (mine doesn't rev to 7000) for better resolution and to allow for fine tuning later. Next step is to set your Target Air Fuel Ratio, that's what the ECU will use as a reference when learning and during all closed loop operation. I used a healthy 13.4 at idle, 13.7 at cruise, and 13.0 under wot. Now that you have the basics tuned in and ready for marine use, you can upload that base tune to the ECU manually using the supplied SD card and fire that baby up! Any questions please don't hesitate to ask, I can't be happier with the results my boat has never run this smooth. Rough total including a couple pipe fitting adapters I had to source for the temp sensor and the fuel system, $1700. Money well spent.

See some pictures here -->

https://imgur.com/a/RtXh0JM

Hello I have a thunderbolt 5 ignition system on my boat. It's a 350 5.7 V8.
I was told from tech. from Holley that my sniper EFI wouldn't work right if I didn't remove the Thunderbolt-5 module and distributor and I needed to purchase a Holley MSD Ignition and purchase a Holley marine distributor. Did you change out these two parts to get your Holley EFI to work correctly?