Question about 1990 Isuzu Pickup

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The fuel pump has four ports; one for fuel from tank, one for fuel to carb, one for fuel return. What attaches to fourth port?

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A pulse fuel pump has four tubes connected to it. One tube connects the fuel tank. Two tubes connect each carburetor and one tube connects the crankcase of the engine. When the engine revolves, the tube connecting the engine delivers fuel with a pulse of pressure at each revolution. The diaphragm pulsates with the pressure. At the top of the pump are two chambers. They are separated by a pair of one way valves. These valves ensure that the fuel that passes through does not come back. Fuel flows from one chamber to the other at one pulse and at the next pulse, fuel moves to the engine.
The bottom end of the engine crankcase is continuously subjected to a high or low pressure with every pulse. This pulse is transferred to the fuel pump by a pulse tube. The pulse line connects the pulse chamber. The pressure of the crankcase is pushed by the pulse through a pair on one way valves and fuel passes continuously, and in a correct measure, to power the engine.

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Posted on Nov 09, 2010

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SOURCE: 1990 Isuzu pickup with 4ZD1 engine has a fuel pump

This is a dual action fuel pump, and the fourth port is for manifold vaccuum

Posted on Nov 10, 2010

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Just put a new delphi fuel pump in my1996 grand caraban did this twice. Still im geting no pressure at the shrader vaulve. Van runs on either. The pump and regulator are the same assembly is the pump the...


Not likely. It is also not likely that the regulator is in the fuel pump assembly. Some people mistake the check valve in the pump as a regulator. Also, some vehicles have a pump module which includes the fuel gauge sensor and that can be mistaken as the regulator by some DIYers. The caravan uses a return-loop fuel system. This means that the pump is cycling fuel from the tank to the fuel rail on one line and the fuel that is not needed at the injectors flows back through another line to the fuel tank. This is done to prevent the pump from building up too much pressure and allows the fuel flowing through the pump to keep it cool. Because of the looping system, there needs to be a flow restrictor (aka regulator) at the fuel rail to provide a constant pressure source for the injectors. The regulator is normally at the end of the rail and will have a vacuum line attached. Pull the vacuum line, place a rag at the vacuum port, and crank the engine. There should be no fuel coming out the port. If any fuel comes out of the vacuum port, the regulator is faulty. The regulator could still be faulty even if there is no fuel from the port, but fuel leakage is an easy way to be sure. If the regulator is not providing proper restriction to maintain pressure, then the fuel simply flows in a circular loop from and back to the fuel tank without enough pressure to allow the injector to do their thing,

Nov 07, 2014 | 1996 Dodge Grand Caravan

1 Answer

98 buick regal the lines attached to the gas tank what are the used for?


Those are vapor return lines. The engine uses some of the fuel, but not all so vapor not used will be sent back the fuel tank and reused by the engine. It's all a part of the emissions operation of the vehicles. Rather than porting the excess fuel into the air like the old vehicles did they created a return line to the tank to save fuel, protect the environment and get you better MPG or Miles Per Gallon.

Sep 17, 2014 | 1998 Buick Regal

2 Answers

Fuel pressure 1998 jeep grand cherokee 4.0 L V6


You should have a test port on the Fuel Supply rail, use a tool from a local auto parts "Tool Loaner program" where you can borrow tools for free,w/a deposit of course,then follow the steps provided;

MPI Fuel System Pressure Test

The MPI fuel system used in vehicles equipped with a 4.OL engine employs a vacuum balanced pressure regulator. Fuel pressure should be approximately 55-69 kPa (8-10 psi) lower with the vacuum line attached to the regulator than with the vacuum line disconnected. System fuel should be 214 kPa (31 psi) with the vacuum line connected to the regulator and 269 kPa (39 psi) with the vacuum line disconnected. CAUTION: Some fuel may be discharged when connecting fuel gauge to fuel rail.
  1. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail (Fig. 7).
  2. Remove vacuum line from pressure regulator.
  3. Start the vehicle.
  4. Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi).
  5. Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi).
  6. If fuel pressure is not approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage. CAUTION: Fuel pressure will rise to as much as 655 kPa (95 psi) when the fuel return tine is pinched shut, shut engine down immediately after pinching oft fuel return line.
  7. If fuel pressure is low, momentarily pinch shut the hose section of the fuel return line. If fuel pressure remains low, inspect the fuel supply line, fuel filter, and fuel rail inlet for blockage. If fuel pressure rises replace fuel pressure regulator.
  8. If fuel pressure is above specifications, inspect the fuel return line for kinks and blockage.

Capacity Test

  1. Remove the cap from the pressure test port in the fuel rail.
  2. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to the pressure fitting on the fuel rail (Fig. 7).
  3. Start the vehicle. Pressure should be approxi- mately 214 kPa (31 psi) with the vacuum hose connected to the pressure regulator and 269 kPa (39 psi) with the vacuum hose removed from the pressure regulator.
  4. If the pressure is not to specification, check the following before replacing the fuel pressure regulator:
  • 4a - Inspect the fuel supply and return lines/hoses for kinks or restricting bends
  • 4b - Check the fuel pump flow rate. A good fuel pump will deliver at least 1 liter of fuel per minute with the fuel return line pinched off. If the fuel pump does not pump adequately, then inspect the fuel system for a plugged fuel filter or fuel pump inlet filter (sock). Fuel pump flow rate can be done by connecting one end of an old A/C gauge hose to the fuel test port on the fuel rail and inserting the other end of the hose into a container of at least 1 liter capacity. Run the fuel pump by installing a jumper wire into diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the fuel return line or most of the fuel will be returned to the fuel tank.

May 19, 2014 | 1996 Jeep Grand Cherokee

1 Answer

What would only let one side of carb get fuel and open up


its a carb, and as such only needs to have a constant float bowl level.
Te sami pump runs a regulator built in, you test that with a pressure gauge.
one side?
did you read the FSM on topic>
here
http://www.acksfaq.com/sitemap.htm
see chapter 4 on carb and pump
the carb has only one input, and that is fuel line to the float valve.
the pump , however does have a loop,
that is because it has a regulator and returns unused fuel to the tank,
kinda like EFI does.

The pump has 3 nipples, 1 suction port. and 2 pressure ports.
1 pressure port is the return line an the other is carb.
the return tube is the top tube of the pair.
the pressure reg holds pressure at 3 to 7 PSI
if the float bowl stays at spec level at all times, even full engine load.
then the pump ,float and valve all work as designed.
that leaves, carb internal problems/
never blame a carb , if the distributor adavance, parts are stuck.
check advance first. then tune carb.

Mar 02, 2013 | 1986 Suzuki Samurai

1 Answer

Fuel runs from back tank to front sometimes


If your driving a ford truck the fuel pump assy that is in the tank that is recieving the gas is leaking and allowing fuel to enter. Ford uses a valve in the fuel pump assy that is activated when fuel pressure is applied to it and it opens a port and allows the excess fuel to return back to the tank. They do not use a switching valve between tanks just whichever pump is activated allows fuel to return to that tank. When this valve fails fuel is returned to this tank all the time, pumping it from one tank to the other.
If you dont have a Ford the switching valve assy. is probably faulty.

Jul 14, 2012 | Cars & Trucks

1 Answer

Van die on road ,its able to start with a shot of hot shot but dies ,fuel leaks out rack bleeder valve when pushed .fuel pump is 175 dollars and cant be returned .plz do you have any ideas


Get yourself a fuel pressure gauge and don't guess and start thrrowing parts at the think only to cost you more money,

Get a fuel pressure gauge, 2.4 L, 3.0 L and 3.8 L engine = 49 PSI (Pounds per Square Inch)Remove the ground cable from the negative battery postand also remove the fuel tank filler cap. Attach fuelrelease tool onto the fuel rail test port, then placethe open end into a suitable gasoline container andproceed to bleed down the pressurized fuel system.

3.3 L engine = 55 PSI (Pounds per Square Inch)Remove the ground cable from the negative battery postand also remove the fuel tank filler cap. Attach fuelrelease tool onto the fuel rail test port, then placethe open end into a suitable gasoline container andproceed to bleed down the pressurized fuel system

Jul 27, 2011 | 1999 Plymouth Grand Voyager

1 Answer

Chevy 4.3 v6 edelbrock performer carb and hei distributor with vacuum advance. Which port on the carb do I connect the vacuum advance to? And where do the fuel lines hook up? Got the crank breather/pcv and...


Not sure which design carb you have but here's a rule that works for all carbs. Attach the vacuum advance hose to any port coming from the carb baseplate (bottom). If you don't have a free one, you can use a "T" in another line or if there's a fitting on the manifold you could use that as well. Just make sure that the line has full vacuum at idle. (check with a vacuum gauge or just put your finger over it and feel for vacuum) Since it's pretty old, it would be good to put your finger under the advance mechanism when you attach the line (running) and make sure the small rod that goes into the distributor moves when you do that. if it does not, then the advance diaphragm is bad and you will need to replace it. Use small rubber plugs to block off any unused ports.
As for the fuel line. You should have a threaded inlet on the fuel bowl. The line attaches there. If you need to make a line, you can get one from any parts house, cut it to length and use rubber fuel hose to join it together with the one already on the fuel pump. When running new line, keep it away from exhaust manifolds, belts and pulleys. Best to put an in-line filter in the hose....that will keep the carb clean. If it's a four barrel (doubtful for that engine) you would need a fuel rail that joins both carb inlets to the single line from the pump.
If you have a problem understanding this, just ask and I'll clarify it for you.

Jul 09, 2011 | 1985 Chevrolet K1500

1 Answer

I have a 1986 454 C30 silverado dual fuel tanks . my fuel pump is split so got a new but the new 1 only has one 3/8 in port , and the old has two a 3/8 and 1/4 , is the 1/4 one a return line


Short answer, yes. It is to reduce the chances of a vapor lock forming by returning vapor and hot fuel back to the tank and keeping cool fuel circulating through the pump.

Nov 23, 2010 | 1986 Chevrolet Chevy

3 Answers

Where is the fuel pump on 84 camaro


if this car has a carburator it located on the front of the engine pass side! if its a tune port its in the tank

Apr 09, 2010 | 1984 Chevrolet Camaro

1 Answer

1983 toyota pickup 4x4 22re engine


Clogged fuel line... maybe fuel filter clogged. Air compressor can clear line. Blow out the line coming in to the carb from the tank.

Aug 03, 2008 | 1983 Toyota Pickup

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