Sniper 300 I-6 Update after cross country trip

It took me a while to get to the point of updating the group.  I have moved to WA from GA, retired from the Navy and am getting settled at my new place.

The truck ran pretty well and I got nearly 15 MPG, having a truck weight with myself and my boy was right around 5400 pounds.  My only issue was that a major heat wave combined with high altitude driving resulted in some hairy unplanned stops in the mountains.  I'm pretty sure that's called vapor lock...  I was hoping to avoid those type of issues with the in-tank Holley fuel pump install but it didn't work out that way.  As long as I kept the tank above 1/2 full, I didn't have vapor lock problems but on a 5,000 mi road trip and a 16.5 gal tank, it was a little inconvenient and not always easy to get fuel when you need it.

Also, getting uphill at high altitudes with my 3.08 gear and 4 speed while loaded down was quite the patience testing experience.  A turbo would have been a very nice addition to my build last year. And maybe an extra gear in the transmission.

The LMC leather seats and cup holder buddy seat were excellent!  My wooden steering wheel kit wore through the copper of the horn contacts and my horn no longer works.  I used dielectric grease to lubricate but it's a very thin coating of copper on those rings in the kit.  Kind of disappointed.  At least it LOOKS sexy though, right?

Cheers!

Are you running a return on your fuel delivery? The secret to fully nuking vapor lock is to run a return line and return-type pressure regulator... this ensures the carb/injectors are always seeing fresh fuel; stagnant fuel is what causes the in-line portion of the issue.

Tyler wrote

It took me a while to get to the point of updating the group.  I have moved to WA from GA, retired from the Navy and am getting settled at my new place.

The truck ran pretty well and I got nearly 15 MPG, having a truck weight with myself and my boy was right around 5400 pounds.  My only issue was that a major heat wave combined with high altitude driving resulted in some hairy unplanned stops in the mountains.  I'm pretty sure that's called vapor lock...  I was hoping to avoid those type of issues with the in-tank Holley fuel pump install but it didn't work out that way.  As long as I kept the tank above 1/2 full, I didn't have vapor lock problems but on a 5,000 mi road trip and a 16.5 gal tank, it was a little inconvenient and not always easy to get fuel when you need it.

Also, getting uphill at high altitudes with my 3.08 gear and 4 speed while loaded down was quite the patience testing experience.  A turbo would have been a very nice addition to my build last year. And maybe an extra gear in the transmission.

The LMC leather seats and cup holder buddy seat were excellent!  My wooden steering wheel kit wore through the copper of the horn contacts and my horn no longer works.  I used dielectric grease to lubricate but it's a very thin coating of copper on those rings in the kit.  Kind of disappointed.  At least it LOOKS sexy though, right?

Cheers!

What tank are you running?  If you dont have baffling it will lay down when you get low on fuel due to fuel slosh resulting in fuel pressure drop.

You shouldnt be expericing vapor lock as from what I could find the fuel would have to reach 100* to actually boil into a vapor.  But when you increase pressure like with a cooling system it raises the boiling point. Seems to be that for every 1 psi the temperature is increased by 3* to the boiling point.  At 60 psi that would be 180* increase in boiling point with in the fuel line itself.  Add that on top of the 100* for fuel to boil into a vapor and you have to have fuel temperature pushing 280* to even vapor lock.

I also wonder if it could be a tune issue as well.  While Holley sells these as self learning systems they really benefit most from having a tuner actually create a tune for it.

Ty - That's pretty good mileage, but the problems with the fuel system sound like a real pain.  But I'm with the others in thinking it really isn't vapor lock.  From what I understand the Sniper should be running right at 60 psi and I really doubt it could vapor lock for the reasons Rusty pointed out.

Are you sure the pump's pickup is at the bottom of the tank?  If not it could be sucking air as the fuel moves around in the tank, as Rusty pointed out about baffling.

Thanks for the info and comments, guys.  I'll call Holley and look into this some more.  As far as your inquiries go:

1. The Sniper kit I bought came with a drop in holley fuel pump which I ensured was at the bottom of the tank.  I was concerned with fuel starvation so I purchased a strip of their hydramat and installed it at the suction.  Based on my front yard experimentation, it would have been extreme down angles that uncovered the suction of the fuel pump since the pump is installed in the rear flat portion of the fuel tank on the rear-axle side of the sending unit.  My truck has the 16.5 gal driver's side frame rail mounted single tank and no baffles.  There are some pictures of my install somewhere on this site...

2. The kit includes and requires a fuel return line and pressure regulator.  I run near 60psig when the key is primed and just about 50psig while operating.  When I set up the return line, I ensured it dumped right at the suction of the fuel pump and keeps the hydramat soaked with fuel.

3. Perhaps I don't understand vapor lock.  What I think was happening:  the return line from the engine bay was heating up the fuel tank.  This combined with low atmospheric pressure and beyond 100F ambient temperature caused the fuel to flash to vapor in the suction of the fuel pump when there was not enough fuel volume to dissipate the heat.  The fuel pump is a centrifugal type, so once vapor became the medium inside the pump cavity, the pump lost suction and starved the engine.  After I pulled over and waited a few minutes, I had to toggle the key a few times to get fuel pressure to register on the gauge near the Sniper throttle body.  Once I had regained pressure indication, the truck fired right up and I made it a little farther down the road.  This would repeat until I made it to a gas station and filled up.

Standing by for feedback!

Maybe move the return line away from the mat?

Ty - I see what you mean about "vapor lock", and I suppose it could happen the way you described as at the inlet to the pump it us under atmospheric pressures.  But do you have any reason to think the fuel is getting that hot in the return?  Is it running close to the exhaust?  Could you insulate it?

On the other hand, you said "I run near 60psig when the key is primed and just about 50psig while operating."  The 50 # seems low.  But in reading through the Holley Sniper Quickstart Manual I don't see a number for the pressure when running.  I see that the regulator is set to 58.5 at the factory, and that for initial startup "Fuel pressure has been verified at the Sniper EFI throttle body and is between 55 & 65 psi".  So maybe 50 psi when operating is ok.  

Anyway, I think I'd call Holley and find out what they say.  Something is obviously wrong.

Tyler wrote

Thanks for the info and comments, guys.  I'll call Holley and look into this some more.  As far as your inquiries go:

1. The Sniper kit I bought came with a drop in holley fuel pump which I ensured was at the bottom of the tank.  I was concerned with fuel starvation so I purchased a strip of their hydramat and installed it at the suction.  Based on my front yard experimentation, it would have been extreme down angles that uncovered the suction of the fuel pump since the pump is installed in the rear flat portion of the fuel tank on the rear-axle side of the sending unit.  My truck has the 16.5 gal driver's side frame rail mounted single tank and no baffles.  There are some pictures of my install somewhere on this site...

2. The kit includes and requires a fuel return line and pressure regulator.  I run near 60psig when the key is primed and just about 50psig while operating.  When I set up the return line, I ensured it dumped right at the suction of the fuel pump and keeps the hydramat soaked with fuel.

3. Perhaps I don't understand vapor lock.  What I think was happening:  the return line from the engine bay was heating up the fuel tank.  This combined with low atmospheric pressure and beyond 100F ambient temperature caused the fuel to flash to vapor in the suction of the fuel pump when there was not enough fuel volume to dissipate the heat.  The fuel pump is a centrifugal type, so once vapor became the medium inside the pump cavity, the pump lost suction and starved the engine.  After I pulled over and waited a few minutes, I had to toggle the key a few times to get fuel pressure to register on the gauge near the Sniper throttle body.  Once I had regained pressure indication, the truck fired right up and I made it a little farther down the road.  This would repeat until I made it to a gas station and filled up.

Standing by for feedback!

Sounds like the pump lost its prime hence why it died if you had to cycle the key a few times to get it to finally start.

The hydramat is something i was looking at myself to possibly do instead of baffling but I think I will be slipping some metal pieces into my new tank and tack welding it into place around the low sump portion of the saddle tank on mine.  The thing that has me concerned with the hydramat is I read that they are good for 5 years or 50,000 miles.  I dont want to have to be pulling my tank every 5 years/50,000 miles to change a $100+ hydramat.  Hence I am looking at the OE sock and just try and build some baffling in my tank through the large sending unit opening.

Do you have the return directed to the hydramat?  The return is recommended to spray on the mat itself.

Also try pulling your fuel pressure regulator out and checking it 50 psi while running is quite low it should be around 58 psi while running thats what the built in regulator is set for.  Many people had issues with the built in regulators having low or high fuel pressure and it caused problems.

Gary Lewis wrote

Ty - I see what you mean about "vapor lock", and I suppose it could happen the way you described as at the inlet to the pump it us under atmospheric pressures.  But do you have any reason to think the fuel is getting that hot in the return?  Is it running close to the exhaust?  Could you insulate it?

On the other hand, you said "I run near 60psig when the key is primed and just about 50psig while operating."  The 50 # seems low.  But in reading through the Holley Sniper Quickstart Manual I don't see a number for the pressure when running.  I see that the regulator is set to 58.5 at the factory, and that for initial startup "Fuel pressure has been verified at the Sniper EFI throttle body and is between 55 & 65 psi".  So maybe 50 psi when operating is ok.  

Anyway, I think I'd call Holley and find out what they say.  Something is obviously wrong.

55 to 65 psi is what Holley recommends but their built in regulator is 58.5 psi preset.  They really want as close to 60 psi as possible.  The 55 to 65 psi range is for people that are setting up an external pressure regulator vs using the built in one.  Many people toss the built in one cause of low or high fuel pressure due to the regulator acting up.

Mine thankfully doesnt have a built in regulator but I will be using a Corvette filter/regulator assembly as that is all we use on LS conversions at work and never had a problem with them not maintaining preset 60 psi fuel pressure.

Gsmblue wrote

Maybe move the return line away from the mat?

Yep you dint want the return any where near the suction as it aerate the fuel.
Dave ----

Thanks everybody.  Looks like I've got some work to do once I get settled into my new house.
I'll get on the phone with Holley today and go from there.  It'll be a while before I can drop the tank if that's required but after I speak with them, I'll share their direction with you.
Happy Friday!