Intermittent Fuel Pump issues - Chevy Impala SS Forum
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post #1 of 27 (permalink) Old 06-15-2019, 03:14 PM Thread Starter
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Intermittent Fuel Pump issues

Hey guys, a little more than a month ago I posted about a problem I am having with my 96SS. I did not get it fixed before I left for tour but I am back at it now and still need some help. Heres the details....

Fuel Pump intermittently cuts off/on
Replaced Sending Unit, Fuel Pump, and Fuel Filter, still same issue.
Fuel pressure is steady at 40psi
Connected the bypass connector next to the fuse box under the hood to + power and it does make the Fuel Pump run continuously.
Metered the Relay, has 12V
Metered the Fuel Pump connector black and grey wires and got 12V.
Car will start and run for a little bit after several times of it intermittently priming itself, so I know the engine will actually run.
I am at a loss here. Anyone have any suggestions on where to check next? It really seems like its a loose connector that is barely making connection somewhere.

Thanks in advance for any help guys.

Matt MF'N Mills 96 Black SS NAISSO Member #6125
Mods: T-56, Suncoast Ram Air Hood, S-Class Mirror LEDs (thats right bitches), Smoothie Bumpers, 50% windshield tint, Train Horns, Clear Corner Lenses, Corvette Engine Dress, 2.5" Custom Exhaust, Carbon Fiber dash, Oil, Volt, and Vac gauges, 3 Gauge Pod, Body Bushing upgrade, T/B bypass, Red Bowtie, LT4 Knock Sensor, F-Body EGR valve & Servo, Moog suspension, A/C drip mod, SEM Blacked out interior, CIA Headers
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post #2 of 27 (permalink) Old 06-15-2019, 05:02 PM
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Matt, just a thought

Do you have a oil pressure gauge?..or has the "oil" light ever flickered?

IIRC when the OP sender senses 5 or less PSI it cuts fuel. The sensor could be bad if this is the case...or your have major issues with internal motor...but you would likely also be hearing a knock.

Then there is always the WTF happened because my car has been sitting and now something is not right.

is the 40 psi of FP with vacuum hooked to FPR? if without vacuum than 40 is low. Typically FP is 45-48 without vacuum and 36-40 with at idle with it increasing some as you increase rpm

I also have toured for decades and after being gone for several weeks or months a perfectly running car when I parked it is no longer happy about something. Frustrating

\'96 BBB 383/T-56
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post #3 of 27 (permalink) Old 06-15-2019, 05:28 PM Thread Starter
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Yes, this is a WTF happened because my car sat for a month. Then sat for another month after I started fixing this because i had to leave again.

The PSI is a steady 40 with the vacuum line plugged in. When I unplug the vacuum line it goes to 60PSI when its priming then settles back at 40PSI.

Never had any oil light come on at all.

Matt MF'N Mills 96 Black SS NAISSO Member #6125
Mods: T-56, Suncoast Ram Air Hood, S-Class Mirror LEDs (thats right bitches), Smoothie Bumpers, 50% windshield tint, Train Horns, Clear Corner Lenses, Corvette Engine Dress, 2.5" Custom Exhaust, Carbon Fiber dash, Oil, Volt, and Vac gauges, 3 Gauge Pod, Body Bushing upgrade, T/B bypass, Red Bowtie, LT4 Knock Sensor, F-Body EGR valve & Servo, Moog suspension, A/C drip mod, SEM Blacked out interior, CIA Headers
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post #4 of 27 (permalink) Old 06-15-2019, 06:22 PM
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Quote:
Originally Posted by Matt M View Post
...
Fuel Pump intermittently cuts off/on
Replaced Sending Unit, Fuel Pump, and Fuel Filter, still same issue.
....

Thanks in advance for any help guys.

May be out there, but could it be you're misreading the symptom? Unless you're reading that current to the pump is actually breaking, then the so-called cutting off could be electrical. As in IC, ICM or opti (or its harness). On another note, I was out of the country an extended period and my black car was not acting at all right when I returned. I had good luck after - disconnecting batt a long time, and just doing a bunch of adjustments to make sure they were on. IAC, TPS, cleaned the EGR valve, sprayed the MAF, etc. It decided to run well again but I don't know what did it. It could have even been the double shot of Techron! lol



Now for the bad news. That new pump may have a non-steller connection with the harness. My new pump and harness and sender did. I got to drop the tank and redo the whole thing a second time just a couple weeks after the new parts.

\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock module!
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post #5 of 27 (permalink) Old 06-15-2019, 08:48 PM
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Have you tried bypassing the VATS, or programming it out?

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post #6 of 27 (permalink) Old 06-15-2019, 09:31 PM Thread Starter
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I have not tried anything with the VATS. Its really acting like theres a connection thats loose and just barely making enough connection to come on and turn off again. This one sucks.

Hey, besides the ground right next to the battery and the grounds in the trunk on the angle pieces next to the trunk hinges, are there any other grounds I could/should check?

Matt MF'N Mills 96 Black SS NAISSO Member #6125
Mods: T-56, Suncoast Ram Air Hood, S-Class Mirror LEDs (thats right bitches), Smoothie Bumpers, 50% windshield tint, Train Horns, Clear Corner Lenses, Corvette Engine Dress, 2.5" Custom Exhaust, Carbon Fiber dash, Oil, Volt, and Vac gauges, 3 Gauge Pod, Body Bushing upgrade, T/B bypass, Red Bowtie, LT4 Knock Sensor, F-Body EGR valve & Servo, Moog suspension, A/C drip mod, SEM Blacked out interior, CIA Headers
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post #7 of 27 (permalink) Old 06-16-2019, 01:22 PM Thread Starter
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We can add Fuel Pressure Regulator to the list. Swapped that out this morning and no change unfortunately.

Matt MF'N Mills 96 Black SS NAISSO Member #6125
Mods: T-56, Suncoast Ram Air Hood, S-Class Mirror LEDs (thats right bitches), Smoothie Bumpers, 50% windshield tint, Train Horns, Clear Corner Lenses, Corvette Engine Dress, 2.5" Custom Exhaust, Carbon Fiber dash, Oil, Volt, and Vac gauges, 3 Gauge Pod, Body Bushing upgrade, T/B bypass, Red Bowtie, LT4 Knock Sensor, F-Body EGR valve & Servo, Moog suspension, A/C drip mod, SEM Blacked out interior, CIA Headers
www.lightingprogrammer.com
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post #8 of 27 (permalink) Old 06-16-2019, 01:30 PM
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in tank electrical connection needs to be on the likely suspect list....

just like DMX, Artnet connections in your work....fing up somewhere in the rig

\'96 BBB 383/T-56
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post #9 of 27 (permalink) Old 06-16-2019, 04:19 PM Thread Starter
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Nope, new sending unit, new fuel pump, same result.

Matt MF'N Mills 96 Black SS NAISSO Member #6125
Mods: T-56, Suncoast Ram Air Hood, S-Class Mirror LEDs (thats right bitches), Smoothie Bumpers, 50% windshield tint, Train Horns, Clear Corner Lenses, Corvette Engine Dress, 2.5" Custom Exhaust, Carbon Fiber dash, Oil, Volt, and Vac gauges, 3 Gauge Pod, Body Bushing upgrade, T/B bypass, Red Bowtie, LT4 Knock Sensor, F-Body EGR valve & Servo, Moog suspension, A/C drip mod, SEM Blacked out interior, CIA Headers
www.lightingprogrammer.com
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post #10 of 27 (permalink) Old 06-17-2019, 08:18 AM
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Try swapping the fuel pump relay with another relay? I had a buddy (not on the forums) just spend $$$$ on a new fuel pump and sending unit while on a trip only to have the same issue when he got home and discovered that the relay was going bad.

"The unexamined life is not worth living." - Socrates
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