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Old 10-24-2009, 07:22 AM   #1
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Fuel pump assembly questions

Im having an issue where the focus falls flat on its face at about 4k-5k rpms. It feels as if its out of fuel at that point. I have questions about the factory returnless sytem. I purchased a new pump from a parts store and installed it in the factory assembly. It leaked terribly around the top of the pump and the other "tube" that feeds back into the fuel pump assembly. The o rings didnt seem to seal properly. I purchased a used assembly from a salvage yard and put the new pump in it and it also allowed fuel to leak from around the 2 o rings. I bypassed the stock lines on the original fuel pump assembly with a piece of fuel line that would connect the pump directly to the filter. When doing this the stream of fuel is very solid and powerful! When hooking everything up in the factory configuration, the flow of fuel from the pump thru the stock lines to the filter is very weak and pulsating with lots of air bubbles. So, my questions are...... is that flow pattern normal and what is the purpose of the tube that attaches to the fuel pump cap that returns fuel to the assembly. It seems to me the fuel would take the path of least resistance and just continually circulate thru the pump and back into the assembly? Would it hurt to bypass the fsctory lines completely and drive with fuel line connected from the pump directly to the fuel filter.I'm just not familiar with a returnless system and its function. Normally Im a pretty good gear head but I come from the DSM/EVo turbo world and this focus really is foreign to me. thx for any help

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Old 10-24-2009, 03:28 PM   #2
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If it's leaking from the O-rings on the line there has to be something wrong there, not seated properly, O-ring torn/wrong size, etc. I've seen that line hold 70psi W/O issue.

The fuel stream should be pulsed, not a steady stream. With a dead head system the pump is driven by PWM to hold the commanded rail pressure (there is a sensor on the feed end of the fuel rail).

The other line on the top of the pump housing is for the EVAP system. There should be no fuel in it at any time. If there is you've got a big problem on your hands.

The problem with the older Foci was the fuel pump assembly. On lower amounts of fuel and hard corners the pump would starve and the car would stall. Ford had a 'extended customer satisfaction program' for this and it might still be good. If you call Ford and ask them and give them your VIN you might be able to get a new one free. I believe the time limit has passed, but worth a shot nonetheless.
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Old 10-25-2009, 06:39 AM   #3
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Well after a long day of testing and replacing yesterday I'm no closer to solving the problem. I have approx 30psi of fuel presuure at idle. If you are driving at full throttle the pressure will reduce to less than 5psi and the car will miss above 4000rpm. I tried 2 pumps, 2 assemblies, bypassed the assembly and hooked the pump directly to the fuel filter and it would still starve at high rpms. I have approx 5 volts at the pump at idle but I never got a chance to check it a full throttle. Hopefully today I will. The voltage seemed to go up as I applied throttle driving up and down my driveway. I was thinking maybe its not getting full voltage at full throttle and causing the pressure to drop off at high rpm. The regulator seems to be functioning properly. If i remove the vacuum line the pressure will change. Not sure what else it could be????
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