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External Fuel pump issue

Old 11-11-09, 07:41 PM
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External Fuel pump issue

I am not sure where to put this question. Since I suspect some of you that race may be running an external setup, that runs for long periods of time in adverse conditions, I thought this section may be the best.

I am running a Aeromotive Marine A1000 fuel pump in my RX7, all my fuel lines are oversize from the back of the car to the front including the return line. I use a vacuum sensitive fuel pressure reg increasing with boost.

http://www.aeromotiveinc.com/products.php?prod=44

On my trip home my fuel pump started to get loud and I was having trouble idling. I was having no issues at highway speed, I had my laptop hooked up and was monitoring lambda and I was not running lean at all.

This still concerned me, so I was poking around the Aeromotive website and found this in the Faq section. Very interesting and sounds exactly like my problem except I am getting it after 5+ hours not 30 minutes.

2.) After 30 minutes or so of driving, fuel pressure starts falling, then the fuel pump gets louder and/or seems to quit running altogether. The pump also seems hot to touch. Whatís wrong?
You may be experiencing EFI vapor lock. Fuel system hot spots, the cause of vapor lock in carbureted engines of the past, and modern EFI engines where no return line is employed, are eliminated with the use of a bypass regulator placed after the fuel rail, in the engine compartment. Still, thanks to underhood engine heat, fuel in the EFI bypass system does slowly warm up as it is recycled through the fuel rail(s) and back to the tank. The longer an EFI engine runs, the higher fuel tank temperatures can become. Unlike the more common carburetor vapor lock, where fuel is heated to boiling in the float bowl(s) or fuel line(s) under the hood, EFI vapor lock is often caused by hot fuel in the tank and/or cavitation. Excess pump noise along with fluctuating or dropping fuel pressure often indicate cavitation is occurring. The exact point where gasoline changes from liquid to vapor depends on its temperature and pressure. A combination of high fuel temperature and low pressure are the primary cause of cavitation. In a return style EFI fuel system, the most likely place for these conditions to exist in the same place, at the same time, is at the fuel pump inlet. The most common cause of cavitation is installation error. Once cavitation starts, it will feed upon itself. As vapor enters the pump, it displaces liquid fuel required to lubricate the mechanism, allowing metal to touch metal, creating even more friction and heat. Once the pump begins to super heat, a complete vapor lock may develop. In order to prevent cavitation and vapor lock, correct fuel system design and installation are vital. Ensure inlet filters meet hi-flow, low restriction requirements and they are kept clean. Keep the tank full on hot days. Reduce fuel pump speed during low load, idle and cruise conditions. Carefully route fuel lines and plan component placement to avoid exhaust heat. Do not overlook proper tank ventilation, if the vent line or vent valve do not allow ample air to move freely in both directions, fuel delivery problems will never fully resolve. Any conditions that restrict the pumpís access to fuel in the tank must be addressed. Read Tech Bulletin #101, Fuel Filtration and call the Aeromotive Tech Line if you need further assistance.
I have some ideas. One being rerouting the return line into a coil setup where I can pack the coil in dry ice (or regular ice if there is no dry ice) and use the return line as a sort of cooling system for the fuel tank.

I drove up to North Carolina for the weekend to play in the mountains. 750 miles one way from Florida, the drive up was incident free, but I was also dealing with near freezing temps by the time I got up there. I only started having problems once I got back in Florida where the temps were approaching 90į again. Also considering I had been on the road over 6 hours as well.

It seems I am heating up my fuel tank gas, once I stop, even at 1/2 a tank, and top it off the problem will go away for another 1/2 tank (140 miles or so) before it comes back. Read on...

I noticed some noise on Saturday, after driving all day, very spirited driving may I add, as well. (after the ambient temps were up in the 70's) But no idle problems and once I topped off the tank it was gone. Plus I parked the car shortly after that so the gas got cold in the tank.

Other solutions include a 2 step voltage system where during cruising the pump voltage drops and works less.

A final solution includes ditching this setup and going back to an in tank setup.
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Old 11-13-09, 05:07 PM
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Check the pickup.
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Old 11-13-09, 05:45 PM
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What do you have as a prefilter to the pump? You could be heating the pump more as you do more gas recirculation on a low pump, but your symptoms seem to extreme for that.

-Andy
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Old 11-20-09, 02:43 PM
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Pickup is fine, and prefilter is to Aeromotive specs which I cannot remember right now.

Since this trip, not a problem, driving around town all day nothing.

Its only on road trips when everything gets heat soaked. Not at track days because I get 5mpg and go through the gas too fast, plus less is recirculating back to the tank.

On the road trips I am pumping more fuel back to the tank, and its sitting in there longer.

My only solutions are either to do a 2 step setup on the pump so it slows down during cruising.

Or the cheap solution is to not fill the tank up over 1/2 on road trips and stop more frequently, this way the gas is always cool and fresh cooler gas gets put in more often. <-- this sucks but I think it will work.

I am considering putting in a temp gauge into the fuel tank to monitor it on the next road tip and see exactly what is going on before I do anything drastic.
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Old 03-08-10, 12:05 PM
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Originally Posted by Jims5543 View Post
Pickup is fine, and prefilter is to Aeromotive specs which I cannot remember right now.

Since this trip, not a problem, driving around town all day nothing.

Its only on road trips when everything gets heat soaked. Not at track days because I get 5mpg and go through the gas too fast, plus less is recirculating back to the tank.

On the road trips I am pumping more fuel back to the tank, and its sitting in there longer.

My only solutions are either to do a 2 step setup on the pump so it slows down during cruising.

Or the cheap solution is to not fill the tank up over 1/2 on road trips and stop more frequently, this way the gas is always cool and fresh cooler gas gets put in more often. <-- this sucks but I think it will work.

I am considering putting in a temp gauge into the fuel tank to monitor it on the next road tip and see exactly what is going on before I do anything drastic.
I know this is an old post but to anyone else having this problem you can run a fuel cooler. Same as your transmission cooler. Just run your fuel lines to it. This will cool the fuel before returning it to the tank.
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