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Fuel Delivery Problem


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12 replies to this topic

#1 jxavierf

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Posted 04 December 2005 - 08:07 AM

Ok here goes......I driving down the road rpms at 3k. all of a sudden they drop to zero.....if I don't do anything, the car dies......if I quickly pump the gas, the car "catches" and returns to the 3k rpms. This happens at random.....maybe every half hour or so of driving. And this didn't happen six months ago. I've deduced that it is a fuel delivery problem, but more precisely crap in the gas tank. So I drained the gas tank, flushed it, replaced both fuel filters, put one gallon of gas in the tank with a whole can of SeaFoam. Ran it hard to brake up any crap in the fuel lines......still has the same problem. I 'm at a loss? :banghead: Can't figure it out. I've adjusted the air/fuel mix to specs. Am I it right to assume its a fuel problem? Suggestions? Thanks......

#2 jxavierf

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Posted 04 December 2005 - 08:21 PM

Bump........

#3 Subarian

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Posted 05 December 2005 - 01:07 PM

Since you have a carb, my first suspicion would be a sticking float needle valve.

#4 jxavierf

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Posted 05 December 2005 - 02:55 PM

What's the best way to fix a sticking float needle valve? I Seafoam the carb requently. Or should I purchase one? Where is it located?

Thanks....

#5 Subarian

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Posted 05 December 2005 - 03:30 PM

The needle valve is located in the inlet. The float pushes the valve closed when enough fuel is in the bowl. It's not difficult to change. If you buy a rebuild kit, it will come as part of the kit, or you can usually buy them separately as a valve and seat.

#6 jxavierf

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Posted 05 December 2005 - 03:58 PM

Is there a good way to test this before I dismantle my carb and buy a kit?

Thanks........

#7 Subarian

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Posted 05 December 2005 - 05:45 PM

The old mechanic's way of testing it was to let an engine idle until it starts to die. When it stumbles, you hit the carb with a screwdriver handle to knock the needle valve loose.

Where your problem occurs off idle, I don't know for sure this is your problem. If you have the stock Hitachi carb, you've got some solenoids that adjust fuel mixture. In any case, I'd say your carb is due for a rebuild. Running any kind of cleaner through the fuel system isn't the same as taking apart a carb and cleaning it. If you've got 36k on your car, the carb probably hasn't ever been rebuilt. Gasoline separates into varnish-like residues with time, and it's actually more harmful to a carb to sit for a long time than to run.

I can't say this is definitely the problem your car is having, but if I were working on it, the carb rebuild is where I would look first.

#8 jxavierf

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Posted 05 December 2005 - 08:14 PM

Thanks for the input. The carb is less than a year old. The car sat for a long time, so I had to replace some critical parts. I did a search and found similiar symptoms due to a faulty Fuel Pump Control Unit. I'm not looking at the fuel pump as a problem because they seem to outlast the engines. Anyone know anything about FPCU's or any suggestions on where to look?

#9 jxavierf

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Posted 08 January 2006 - 07:55 AM

Delayed Bump...........thanks for any suggestions.

#10 Cougar

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Posted 08 January 2006 - 06:41 PM

I wouldn't count the fuel pump out. In fact that would be my first choice as the source of the problem. I would set up a test light to monitor the voltage to the pump. If the light goes out when the problem occurs then you can check the control circuit to the pump.

#11 jxavierf

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Posted 09 January 2006 - 05:55 PM

Thanks......I do have a voltmeter, but am not too familier with how to properly use it. How should I go about hooking it up to test the fuel pump.

If the fuel pump is the source of my problems, where should I purchase one?

Thanks...........

#12 Subaru Jim Maple Ridge

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Posted 09 January 2006 - 06:38 PM

You could check to make sure that your gas cap is breathing properly. I remember that sometimes the old styles could build up a vacuum at highway speeds, preventing the pump from pumping enough volume. Just a guess. You can check it by running without the cap long enough to see if it happens again.

#13 Cougar

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Posted 10 January 2006 - 09:39 AM

Using a voltmeter is pretty easy. Do you have a digital meter? If so, all you need to do is set it to read DC volts and put the red test probe wire in the volts, ohms, and current connection and the black test wire in the common connector. If the range setting on the meter is automatic then the meter will select the correct voltage range. If the ranging is manual, then select a range that will handle more than 12 volts. Then use the probes to measure across what ever you want to test. A digital meter doesn't care what the polarity is and if the voltage is negative with respect to the common lead then a minus sign will show on the display along with the voltage reading.

If you have an analog meter, the type with a meter movement, then you will need to select the proper voltage range and keep track of the polarity. The black common lead needs to be on the grounded side (usually this is the minus side but not always) of the circuit. It is good practice to place the black lead of either meter to the grounded side of the circuit unless you are doing something different than a normal measurment.

I think the fuel pump connection is under the rear seat on the passenger side. You may be able to wrap a small wire around the connect to monitor the power to the pump.




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