Fuel delivery loss in an engine swapped 80

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so I know this isn’t quite the place to be asking this but I’ve run out of options. I’ve got a 350 sbc with a Holley sniper system in my 80 series and at high altitude especially I’m constantly losing fuel pressure. I’m running a return style system that almost perfectly mimics the factory fueling system in a stock 80. I’ve got an in tank pump and a return line running to the very bottom of the tank. Holley says that my return line is probably too close to my fuel pickup but that doesn’t make sense as to why this only happens above 10,000 ft. I know it’s strange but it sounds and feels like vaporlock but Holley says that’s completely impossible. It’s happened with 3 different pumps, one of which was an external pump, has happened 4wheeling and running up over highway passes. The failure mode is always the same. Motor stalls, fuel pump sounds like it’s pulling air and occasionally building pressure. When it does build pressure (and I’ve verified this with a gauge) it’ll either run for a split second and drop pressure immediately or will run with the specified pressure until all of a sudden the system drops off to 0 and the motor stalls. I’m not yet 100% sure if the pump is shutting off or if it’s just pushing air or something resembling it but every time this happens the fuel prime before start up sounds like it’s not building any pressure and that’s reflected by the gauge readings. Any ideas would be greatly appreciated.
 
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Holley says that my return line is probably too close to my fuel pickup

Do they think that the return line is dumping fuel into the tank, causing splashing and aerating the fuel that's being picked up?

What kind of fuel pump are you running? Is it in the tank like the original, or outside?
 

cruisermatt

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you can't have vapor lock with an intank fump.

Is your wiring good or is all hackjob garbage? That's usually what it is
 
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Do they think that the return line is dumping fuel into the tank, causing splashing and aerating the fuel that's being picked up?

What kind of fuel pump are you running? Is it in the tank like the original, or outside?
So I told them that I have the return line at the very bottom of the tank and it’s pointing away from the fuel pickup, I’m running some generic in tank fuel pump that matches my flow requirements for my motor. It’s also set up almost identical to the factory pump for a 3fe. I had a second fuel pump that I installed on the trail yesterday but had zero Change. But this has also happened with the supplies Holley external pump with their master kit and it was exactly the same failure. That one I finally replaced at the top of I 70 at the Eisenhower tunnel. At this point I’m thinking heat soak is causing fuel boiling. I can get deep into how the lines are routed on that if you want.
 
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you can't have vapor lock with an intank fump.

Is your wiring good or is all hackjob garbage? That's usually what it is
What I’m discovering is it may be fuel boil but I’m trying to figure out how to solve that

Wiring is fairly good, better than the absolute garbage you find on school busses from the factory (Im a diesel tech so I have a decent idea of what im doing)
 

cruisermatt

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Is your fuel tank consistently over 200F degrees?
 
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I’m running some generic in tank fuel pump

This makes me suspicious, but only because so many people have had problems with aftermarket fuel pumps.

If your problem is fuel boiling, why do you think that you hear the pump sounding like it's pumping air? Wouldn't you expect the pump to still be picking up cool fuel?

Does this happen with a reasonably full tank?
 
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This makes me suspicious, but only because so many people have had problems with aftermarket fuel pumps.

If your problem is fuel boiling, why do you think that you hear the pump sounding like it's pumping air? Wouldn't you expect the pump to still be picking up cool fuel?

Does this happen with a reasonably full tank?
So the thing that makes me think suspicious that it’s not really the pump is that it’s done it with a factory Holley supplied external pump too, exact same failure mode too. And the pump sounds like it’s having zero fuel flowing through it, sounds totally unloaded and then at some point will bring to create pressure and then sounds like it’s actually under load. It’s a very different sound. The fuel pressure is regulated internally in the sniper it’s self and it’s just a basic spring style and I doubt it’s faulty for that reason. Always holds the right pressure when it’s not having this problem. And it’s done this from full to empty, doesn’t seem to care.
 
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So your just tooling around Leadville and all of a sudden it dies? Or is it going up a pass?
So it’s done it over I 70 climbing, cottonwood, independence and many more passes over 10k but never really around just town, I could run up to Leadville at some point but I think it has to do with high load on a steep pass or low speed crawling since it’s not getting much air flow.
 
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Where is your fuel line located in relation to your exhaust? I know you said you're running a stock fuel line setup, but are you running your exhaust inboard of the frame? If so, I'd imagine you'd be really close to the passenger side exhaust and if your issues are when you're pushing it hard, that exhaust is getting super hot, which could boil your fuel. You could test the theory out by running a temporary fuel line on the other side of the frame keeping it as far away from the exhaust as possible.
 
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Where is your fuel line located in relation to your exhaust? I know you said you're running a stock fuel line setup, but are you running your exhaust inboard of the frame? If so, I'd imagine you'd be really close to the passenger side exhaust and if your issues are when you're pushing it hard, that exhaust is getting super hot, which could boil your fuel. You could test the theory out by running a temporary fuel line on the other side of the frame keeping it as far away from the exhaust as possible.
So the exhaust is a little funky but they run on the outside of the frame rail and dump in front of the rear tires, the hoses run on the inside of the right frame rail so just on the other side. The hoses run up the firewall and the exhaust is about 2 feet away at that point because they are block huggers and drop straight down near the axle.
 

SoTexCruiserDoc

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All at altitude only (>10K+)? What kind of fuel are you running (ethanol free?)? I had a bad fuel boil problem this summer (first time ever btw) up there with a stock 1FZJ set up. Several in our group touted the tactic of using ethanol free fuel when spending a good bit of time up high. That is theoretical and unproven as far as I know, but I’ve decided to do it when up high for the day…
 
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All at altitude only (>10K+)? What kind of fuel are you running (ethanol free?)? I had a bad fuel boil problem this summer (first time ever btw) up there with a stock 1FZJ set up. Several in our group touted the tactic of using ethanol free fuel when spending a good bit of time up high. That is theoretical and unproven as far as I know, but I’ve decided to do it when up high for the day…
Seems like it’s only at high altitude until I conked out on me and wouldn’t fire up again at all on my way home in Colorado Springs. Whole thing said no more, couldn’t tell if it was fuel related because I was stuck on major road
 

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