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94 Fuel Pump Problems


wormfriskie
03-16-2014, 07:55 PM
My fuel pump quit, would it be worthwhile to check the oil pressure sender first before I drop the fuel tank? Does it tie in at all? Any one else have any fuel pump problems?

Tech II
03-16-2014, 10:22 PM
Most oil pressure senders/switches, are backups to the fuel pump relay.....

Way to check the circuit, is disconnect the harness to the fuel tank.....4 wire harness......2 wires for the fuel pump, two wires for the fuel sender to the fuel gauge....you attach a test light to the harness half, going away from the tank....attach it to the 2 wire fuel pump circuit.......

Turn key to "on", don't crank....should light for 2 seconds and then go out.......now crank the vehicle.....light should be on steady.....if this is the case, and you have no fuel pressure, you need a pump....

j cAT
03-17-2014, 05:16 PM
My fuel pump quit, would it be worthwhile to check the oil pressure sender first before I drop the fuel tank? Does it tie in at all? Any one else have any fuel pump problems?

since you have a 1994 caprice the fuel pump not running will require a fuel gauge hooked up to the fuel rail . you will need 40 psi key on engine off. you can also jump the fuel pump feed at the under hood fuse box. then go to the rear of the vehicle behind the license plate and see if you have power at that connector that goes into the fuel tank to the pump. if the 12 volts is at that connector you hear no pump run and have no pressure then the pump may be bad or the in tank fuel pump connector is burned open this happens when the fuel level is always below 1/3 of a tank.

if you have no voltage at this rear connector then this can be the in trunk driver side connector,fuel pump relay , vats key / security system. etc...

these do not use the oil pressure that I know of. uses the distributor pulses to shut down fuel pump.or the key error .......

Blue Bowtie
03-23-2014, 08:46 AM
JC - The '94 does use the auxiliary oil pressure switch as a redundant backup to the pump relay (orange to gray wires), or at least mine does (Impala).

j cAT
03-23-2014, 08:57 AM
JC - The '94 does use the auxiliary oil pressure switch as a redundant backup to the pump relay (orange to gray wires), or at least mine does (Impala).

that must be another electrical change GM did thru the 1994-1996 model years.

my 96 has no oil pressure switch .

lately many are having these type issues with these vehicles. the internal electrical connections at the fuel pump are over heating. people running with less than 1/4 tank of fuel and with the senders screwed up you have about 3 gallons in the tank at 1/4.

with my tank when at 1/3 level most i can fill to is 18 gallons. so with 23 gallon tank I only have 5 gallons in there..this has changed over the years . when new I could only get about 14 gallons at 1/3..

j cAT
03-26-2014, 07:37 PM
JC - The '94 does use the auxiliary oil pressure switch as a redundant backup to the pump relay (orange to gray wires), or at least mine does (Impala).

the 1996 does have an oil pressure switch . this is for the dash oil pressure indicator light . when the oil pressure drops to 3 psi or less the oil pressure dash light comes on.

the 1996 fuel pump relay is turned on when the ignition is turned to on , engine off for 2 seconds. if no distributor pulses are created......
when cranking the engine the fuel pump will continue to run because the pulses are being received from the distributor. the fuel pump relay will be energized.

if you loose all your oil the engine will still get fuel pressure. until it locks up..

j cAT
04-04-2014, 01:25 PM
JC - The '94 does use the auxiliary oil pressure switch as a redundant backup to the pump relay (orange to gray wires), or at least mine does (Impala).

I found a diagram for the earlier 4.3L L99 caprice vin W. in that schematic the oil pressure switch is connected across the fuel relay power contacts that feed the fuel pump. the fuel relay drops out after the start , then the oil pressure switch takes over.

on the 1996 the oil pressure switch just controls the dash light. also the fuel relay is always energized with normal engine operation . the PCM controls the fuel pump relay with OPTI distributor signals.

why this was done at the end of production is weird.

wormfriskie
06-30-2014, 05:16 PM
Well, finally got around to it, just replaced the fuel pump. It runs fine now.

j cAT
07-01-2014, 08:51 PM
Well, finally got around to it, just replaced the fuel pump. It runs fine now.

many are now having problems with the in tank wire harness so if it acts up again this may need replacing..

irish12671
06-05-2015, 12:09 AM
I have no power to the new fuel pump.I installed a New oil pressure switch also.

j cAT
06-05-2015, 04:01 PM
I have no power to the new fuel pump.I installed a New oil pressure switch also.

the in trunk wiring need be checked. see that the grounds are connected. also connector [s] in trunk get corroded ..driver side of trunk wiring harness and the grounds at the lid hinge. purple is the feed wire I believe to the fuel pump.. at the under hood fuse box is the fuel pump prime wire. with a fused feed connect this un connected connector to 12 volts with eng/ key off see if the pump runs. this is in with the 2 wires that goes to the low pressure ac switch right next to the fuse box... wire with connector not connected is red. this is the prime wire for fuel pump.. if its not working then got to trunk area and using meter find out where its lost....

rachet16
05-26-2016, 02:01 PM
I have a 94 caprice 4.3 L V-8 won't start , no fuel pressure a t schrader valve. I pulled the fuel filter it was clean turned key no fuel at the fuel line with the filter off. I can feel the relay click and I hear the pump cycle but only after I turn the key briefly to the crank position ( just a bump) the pump cycles about 2 seconds.

rachet16
05-26-2016, 02:11 PM
The car has been sitting a while about a year. I was having start issues when it was humid or raining the car would start after prolonged cranking I assumed it was the opti distributor. It got progressively worse and strande me once so I parked it while I saved my pennies for distributor parts wires plugs etc.. Finally ready tk get it going and started diagnostics to find I have spark at the coil and plug wires but no fuel? It was getting fuel when I parked it.
I cannot retrieve any trouble codes by jumping the aldl cooling fans run but no check engine light no 12 code. Check engine light does come on when I turn the key with no jumper. I have never been able to retrieve codes since I've owned it .

rachet16
05-26-2016, 02:16 PM
Are there check valves in the tank? Can I blow compressed air back into ,the tank from the fuel filtel connection to clear the pick up line in the tank?

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