Had a fuel pump problem yesterday.....

[streetk14]

Hey guys,
I had a bit of an issue yesterday and maybe someone here could shine some light on it. I took my Camaro out for a nice, long cruise since the weather has become very nice in the last few days. It was probably mid-70's, not hot by any means.

The car drove great the whole drive, then when I was heading back home I made a full-throttle blast getting onto the freeway and the motor fell on it's face at 4000 rpm. It was like hitting a rev limiter and did this in every gear I tried. I took the car home and starting doing some checking.

What I found was my fuel pump sounding very high-pitched and almost making a "honking" sound when I turn on my key. The pump usually has a deep sound when it primes the system. I realized right there that it was fuel related and let the car cool off for 20 minutes or so. The pump returned to it's regular tone, and I went to the gas station to fill up since I had about 1/2 tank left.

I filled up and took a little drive to see how it would run. The power had completely retuned and pulled very strong up and above 6000 rpm. I'm not really sure what caused the problem. The fuel tank was pretty warm to the touch, but not hot. I do have a dual fuel line system that retuns all unused fuel from the rail to the tank, and a fairly large Walbro 255L fuel pump. I'm wondering if all the low rpm cruising caused excessive heat in the fuel and eventually overheated the pump.

The other thing I can think of is that my Magnavolt (fuel pump booster/relay) could have gotten too hot and was reducing voltage to the pump. Unfortunatley, I did not have my volt meter handy to check the output when it was going on. The Magnavolt was pretty warm, but so was my ECM that is located right next to it.

So, what do you guys think? Do I need a single line system to help reduce heat? FWIW, this is on a Magnacharged LSx powered '67 Camaro that dyno'd at 505 rwhp.

Andy

[camcojb]

this happened to many guys on Power Tour, and is the reason I bypass my fuel before it gets to the rails or engine compartment. The bypassed fuel is hot and on a longer run the fuel in the tank gets much hotter than normal as there is less and less in the tank. The hot fuel gets the pump to cavitate, making it louder and dropping pressure. Once you filled the tank you put a bunch of cold fuel back in, dropping the gas temp and temporarily fixed the problem.

You can run a fuel cooler in the return line, but I just bypass it at the back, or at least before the engine to eliminate the issue.

Jody

[streetk14]

this happened to many guys on Power Tour, and is the reason I bypass my fuel before it gets to the rails or engine compartment. The bypassed fuel is hot and on a longer run the fuel in the tank gets much hotter than normal as there is less and less in the tank. The hot fuel gets the pump to cavitate, making it louder and dropping pressure. Once you filled the tank you put a bunch of cold fuel back in, dropping the gas temp and temporarily fixed the problem.

You can run a fuel cooler in the return line, but I just bypass it at the back, or at least before the engine to eliminate the issue.

Jody

Thanks Jody,
I remember hearing about a bunch of guys having fuel system troubles on Power Tour, but couldn't remember exactly what the symptoms were.

I'd consider using the Vette pressure regulator/filter at the rear of the car, but I don't think it is boost referenced (no vaccum port) if I recall correctly. I am using a stock GM pressure regulator on the rail of my Magnacharger that is boost referenced right now. What do you think my best option is? I'd prefer to not have to re-do my complete fuel system, but could be done if needed.

Andy

[camcojb]

Thanks Jody,
I remember hearing about a bunch of guys having fuel system troubles on Power Tour, but couldn't remember exactly what the symptoms were.

I'd consider using the Vette pressure regulator/filter at the rear of the car, but I don't think it is boost referenced (no vaccum port) if I recall correctly. I am using a stock GM pressure regulator on the rail of my Magnacharger that is boost referenced right now. What do you think my best option is? I'd prefer to not have to re-do my complete fuel system, but could be done if needed.

Andy

simplest thing is to simply move the regulator off the engine so it regulates before the rails. Many universal regulators like Aeromotive, etc could be mounted on the frame rail before the engine or someplace similar and they're boost referenced if your regulator can't be moved.

I use an Aeromotive regulator right off the pump at the back of the car. Further forward is fine, but this is simple and clean, and I don't need to boost reference it. In your case up front more, like near the firewall on the frame rail would be simple and could still be boost referenced without a 20' reference line.
Jody

[streetk14]

simplest thing is to simply move the regulator off the engine so it regulates before the rails. Many universal regulators like Aeromotive, etc could be mounted on the frame rail before the engine or someplace similar and they're boost referenced if your regulator can't be moved.

I use an Aeromotive regulator right off the pump at the back of the car. Further forward is fine, but this is simple and clean, and I don't need to boost reference it. In your case up front more, like near the firewall on the frame rail would be simple and could still be boost referenced without a 20' reference line.
Jody

Well, it looks like I have some options. I don't really have a problem with running a reference line to the rear of the car, I could just run it along side the fuel line. I'd rather put it near the tank for a cleaner look under the hood, plus the benifit of less heat from friction, etc.

Does it matter where the regulator is mounted in relation to the tank/fuel level? I wouldn't think so since it's being fed from an in-tank pump, but I had to ask. Thanks,

Andy

[camcojb]

Well, it looks like I have some options. I don't really have a problem with running a reference line to the rear of the car, I could just run it along side the fuel line. I'd rather put it near the tank for a cleaner look under the hood, plus the benifit of less heat from friction, etc.

Does it matter where the regulator is mounted in relation to the tank/fuel level? I wouldn't think so since it's being fed from an in-tank pump, but I had to ask. Thanks,

Andy

I run the regulator right off the pump, which is near the level of the bottom of the tank, but not necessarily below the tank level.

The issue with the reference line is not running it to the rear of the car, but the distance may cause a slow reaction of the fuel pressure, especially coming off boost (may keep the pressure high for a little longer, causing a rich condition). Not sure this will be an issue, just letting you know.

Jody

[DRJDVM's '69]

I'm interested in the issue too since I'm about to re-do my fuel system. I'm running an Aeromotive A1000 in tank pump and one of their regulators. The regulator I have is a 10AN feed, 8AN return and 2x 6AN carb feeds.
I was planning on mounting the reg in the engine compartment so I could use both 6 AN carb feeds. I guess I could mount it near the tank and run a single 6 AN line up to the engine.
If I do the heat sink/cooler option, the best place is to mount it in the return line rather than the feed line, correct ? Since the problem is the heat effecting the pump, not a vapor lock issue right ??

[Blown353]

I'm interested in the issue too since I'm about to re-do my fuel system. I'm running an Aeromotive A1000 in tank pump and one of their regulators. The regulator I have is a 10AN feed, 8AN return and 2x 6AN carb feeds.
I was planning on mounting the reg in the engine compartment so I could use both 6 AN carb feeds. I guess I could mount it near the tank and run a single 6 AN line up to the engine.
If I do the heat sink/cooler option, the best place is to mount it in the return line rather than the feed line, correct ? Since the problem is the heat effecting the pump, not a vapor lock issue right ??

Well... 2 answers.

If you wanted to really go all out you could run a cooler in the line feeding the carb (assuring the fuel going into the carb is as cool as possible) and also run a cooler on the return line to keep the fuel in the tank and the pump cool to prevent vapor lock.

However, since the main issue you are trying to prevent is vapor lock because of fuel in the tank being overheated, it's best to put the cooler in the return line so it cools the fuel going back to the tank. If you run the regulator back at the tank and not in the engine compartment the rate of fuel heating is GREATLY slowed as it is no longer passing through hot fuel rails. However, you still have the radiant heat input from tailpipes plus the heat generated by the fuel pump itself to heat the fuel load, but the main heatsoak source (the engine compartment & rails) has been eliminated and typically the fuel will stay cool enough just by shedding the heat to the tank itself when is then cooled by air passing over it as you drive. However, sit long enough on a stretch of hot asphalt with no real air movement (i.e. stuck in traffic) and it could still be a problem.

It is in the end a vapor pressure problem. There is vacuum on the inlet side of the pump. As the fuel heats up and the vapor pressure changes, the fuel no longer remains a liquid and begins to vaporize in the vacuum conditions encountered in the pump intake. This causes cavitation which is really hard on the pump and also disrupts flow & pressure on the outlet side of the pump.