Fuel issue - Chevy Impala SS Forum
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post #1 of 16 (permalink) Old 03-12-2017, 09:59 PM Thread Starter
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Fuel issue

Put a new fuel pump and sending unit in my 95 SS. Bought it from Rock auto it's the spectra brand. Well my issue is since I put it in the fuel hand does what it wants. Someone's its on full others it's empty. When I installed it the tank was empty. Put 15 gallons in it and it never got past a quarter tank. Then days later went up to full. And stays there until almost empty. I've dropped the tank since to make sure the float arm was in the small clip and it was. Well the other night the car quit on me. Fuel pump wasn't coming on. Started the next day and had been running fine for 3 days. Now it quit but it finally started back up to get home. So my question is does it sound like a pump going bad. And has anyone dealt with returns to rock auto
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post #2 of 16 (permalink) Old 03-13-2017, 06:21 AM
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Put a new fuel pump and sending unit in my 95 SS. Bought it from Rock auto it's the spectra brand. Well my issue is since I put it in the fuel hand does what it wants. Someone's its on full others it's empty. When I installed it the tank was empty. Put 15 gallons in it and it never got past a quarter tank. Then days later went up to full. And stays there until almost empty. I've dropped the tank since to make sure the float arm was in the small clip and it was. Well the other night the car quit on me. Fuel pump wasn't coming on. Started the next day and had been running fine for 3 days. Now it quit but it finally started back up to get home. So my question is does it sound like a pump going bad. And has anyone dealt with returns to rock auto
Sure sounds like you got some sort of "in tank" issue still going on. When you replaced the Pump and SU, did you also replace the intank harness? How were the connections on the Bulk Head connector pins? These pins and the harness at the bulkhead, typically the ground wire will get burnt. Maybe there was some corrosion there and it's not making a good connection?

the next time the pump is dead, use the 12V Prime override wire to put power directly back to the pump which will bypass the Fuel Pump relay and keep power to the pump instead of just the 1-2 second prime with key on. Pump still not run? Then I would unplug the 3 connector plug at the bumper and test for 12V using BOTH the ground and 12V pin of the Connector to assure there is 12V AND Ground at the connector end. If there is, then it's time to drop the tank again .....cause your problem is in the tank.

Keep in mind that the Pump and the Float level are pretty much 2 separate circuits which can work independently of each other but do share a Ground wire. What I like to do before installing the assembly in the tank is to connect the 3 wire plug and disconnect the FP fuse, then key on the car and manually move the float arm while having someone watch the Fuel gauge needle move. At least you can assure the sending unit float arm is most likely ok. You can also put a meter on it and look at the ohms reading as you move the arm.

If all looks good, do you maybe have a defective fuel pump? It's hard to say but is ALL looks good with wiring and the circuit, there is not much else it could be but an intermittent fuel pump.

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post #3 of 16 (permalink) Old 03-13-2017, 07:24 AM Thread Starter
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I forgot to mention that Everytime the fuel pump isn't working my gas hand pegs or way past full like the bulkhead plug at the bumper is unplugged
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post #4 of 16 (permalink) Old 03-13-2017, 08:29 AM
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QUOTE:
"Put a new fuel pump and sending unit in my 95 SS. Bought it from Rock auto it's the spectra brand."

Me too, me too and me too.

You mentioned you've since dropped the tank once already AFTER installing the new pump. But, it sounds like enough issues to drop it again. Outside of the 'relay bypass test' 4Doors- mentions, I would carry a bat to smack the tank to see if it wakes up the pump next time it does dead. I would side with the 3 or more things known to be bad or go bad with the wiring-connections-harness, as opposed to presuming the new pump is defective.

The bright side is (like some of us) you should be pretty good at dropping that tank in about 30 minutes by now.

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post #5 of 16 (permalink) Old 03-13-2017, 08:53 AM Thread Starter
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How do I do the 12v bypass
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post #6 of 16 (permalink) Old 03-13-2017, 09:23 AM
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You may have bent a pin when installing the wiring. I would pull the tank and check the connectors. A friend of mine had a bad connection through the sending unit to the exterior wiring. You may have even disconnected the float arm from the potentiometer that sends the signal to your gauge.

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post #7 of 16 (permalink) Old 03-13-2017, 11:05 AM
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Quote:
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I forgot to mention that Everytime the fuel pump isn't working my gas hand pegs or way past full like the bulkhead plug at the bumper is unplugged
The fact that the gauge goes wonky the same time the pump quits , says to me , you have a ground issue.
When the ground fails, the pump circuit is pushing power back up the gauge wire.

This could be internal, bulkhead, outside connector or ground in trunk.

With key on, I would put power to the red under hood test connector ( at fuse box) and then start tugging-manipulating the harness while someone watches the fuel gauge and you listen to pump.
If nothing obvious , try a temp new ground to the connector where it comes out at the rear of the tank.


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post #8 of 16 (permalink) Old 03-13-2017, 03:32 PM
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the ground and all the wires to pump also a connector are in the trunk driver side . those wires/connector do screw up .
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post #9 of 16 (permalink) Old 03-13-2017, 05:26 PM
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Quote:
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How do I do the 12v bypass
I guess your asking about the pump prime circuit override wire under the hood? Connect this wire to a 12v source and it will cause the pump to run continuously.

Connector ID

As far as troubleshooting, this thread has some good info....

Methods for testing fuel pump

I'd start with the basics first before dropping the tank again just to insure the problem is not outside the tank. You only have 3 wires to check, technically just 2 for the pump but as wagon said you got a shared ground.

When checking for 12v at the connector, don't use the Chasis for your ground connection. Instead, try to use the ground wire in the connector. At least then you will know you got a good ground connection to the terminal. If you were to use your meter across the 12v pin and a bare ground somewhere else on the car, you won't find the bad ground at the connector. As mentioned, this ground originates from inside the trunk and could be loose, missing or corroded.

The ideal would be to have the car at a point where you have no fuel pump running. At least then you could use the 12 v override wire to see if the pump works. If not, go back to the 3 pin connector and assure volts and ground there. If that checks out, then the problem is most likely in the tank.

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post #10 of 16 (permalink) Old 03-20-2017, 10:17 PM Thread Starter
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Ok fellas. Sorry its taken a few days to reply and keep yall posted on whats going on I went on vacation. Well I finally get back home to work on the impala, and she fires right up. Fuel gauge still did what it wanted but didn't peg out. So I check all my grounds in the truck and make sure I have 12 volts going to the fuel pump with the bypass wire under the hood continues to run fine then about 20min into it running it dies and fuel gauge pegs out way past full like if you were to unplug sending unit harness from bulkhead by rear bumper. So I drop the tank pull out the sending unit to inspect in tank wiring harness and everything looks good. Float arm is in the clip and wires look good strainer looks clean. Put sending unit back in tank and put 12 volts to the sending unit wiring from tank side and pumps fuel fine. Watched it pump out the tank into a gas can for about 15min. Leave tank on jack hook fuel lines back in and plug to bulkhead under the bumper and car fires right off and fuel gauge is reading half a tank and that's what it looked was in the tank from opening where sending unit goes. I really don't believe that its fixed. Usually the fuel hand stays on full then it would move to a quarter of a tank. I keep up with gas by my mileage. I'm lost now. Because when its died on me the fuel pump wont prime and the gauge is pegged way past full. Really not trying to drive the car don't want to get left stranded.

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