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Wondering what parts we might need to consider throwing at it, if any... When it was stored, it was working perfectly, and fuel was siphoned out. We had forgotten that when it was attempted to fire it up again, and so got much cranking but no catch/turnover once we replaced the battery. Apparently, it did start up once the air cleaner was removed and fuel dumped into the engine directly, though, so the assumption is that fuel is not being fed correctly and that means a new fuel pump.

I don't think it likely that would fail from non-use all this time, though, and am wondering if it might be an issue with priming given that the tank had been sitting bone dry for a number of years and minimal gas was put in even once we remembered there wasn't any, I'd say maybe 3 gallons...

Is there some diagnostic procedure we might take to confirm the need for a replacement pump before we go through the whole process of dropping the tank to get to it? Is there anything else that might be at fault? What other issues might be expected after such a long period of storage?
 

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Is there some diagnostic procedure we might take to confirm the need for a replacement pump before we go through the whole process of dropping the tank to get to it?
When you turn the key to "on", you should here the fuel pump running for about 3 sec. If it doesn't, try powering the fuel pump at the connector under the back of the car with a car battery. If it works than you have probably have a wiring issue, and if it doesn't the fuel pump is likely bad.
 

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Insert the following sentences between the first and second ones above:

"If it does not then hit the underside of the tank with a 2X4, and if the pump clicks on then the internal pump harness connections are suspect. The prognosis of replacing both pump and harness remains the same though. If it does not then inspect and reseat the outside ground, which is can lose connection over time."

If redoing the ground restores the pump then the "primer timeout bypass" hanging red pigtail under the hood near the fuse box can be used for further testing of fuel system.

As for the OP's last sentence related to fuel only:
A. Replace the fuel filter.
B. Confirm the vent return hose is intact at the forward side of the tank.
C. After B. then search for a diagnostic on testing the EVAP system (solenoid function, rotted/broke hoses)
 

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1996 ImpalaSS WX3
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There’s also a direct lead to the FP power wiring in the engine compartment, it’s a loose connector with nothing going to it, on the passenger side by the AC dehumidifier at the rear towards the firewall...
It actually comes off the wire loom going to the dehumidifier.
Apply battery voltage and listen for the FP to come on, If it comes on there’s a wiring/connector issue somewhere between the ignition and FP, if it doesn’t come on, FP is dead...
you can also push in the Schrader Valve (Looks like a tire valve stem) on the injector rail after applying power to see if you have any fuel pressure... Careful, if the injector rail is pressurized, it will spray out some fuel...
Hope that helps...
 

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I just realized 96 Black previously mentioned the FP timer bypass connector, I just didn’t know what it was called...
That’s the connector I was referencing.
 

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When you turn the key to "on", you should here the fuel pump running for about 3 sec. If it doesn't, try powering the fuel pump at the connector under the back of the car with a car battery. If it works than you have probably have a wiring issue, and if it doesn't the fuel pump is likely bad.
I’m not familiar with applying voltage to the FP wiring under the back of the car, on my Impala there’s no way to get to the FP wiring connectors at the tank without dropping the tank.
I could be wrong...
But that’s why there’s the “Fuel Pump Timer Bypass” connector (Thanks Black) under the hood...
 

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Wondering what parts we might need to consider throwing at it, if any... When it was stored, it was working perfectly, and fuel was siphoned out. We had forgotten that when it was attempted to fire it up again, and so got much cranking but no catch/turnover once we replaced the battery. Apparently, it did start up once the air cleaner was removed and fuel dumped into the engine directly, though, so the assumption is that fuel is not being fed correctly and that means a new fuel pump.

I don't think it likely that would fail from non-use all this time, though, and am wondering if it might be an issue with priming given that the tank had been sitting bone dry for a number of years and minimal gas was put in even once we remembered there wasn't any, I'd say maybe 3 gallons...

Is there some diagnostic procedure we might take to confirm the need for a replacement pump before we go through the whole process of dropping the tank to get to it? Is there anything else that might be at fault? What other issues might be expected after such a long period of storage?

What do you mean it fired up when you dumped fuel directly in to the engine? It's not a carb. How would that work? The fuel has to be pressurized. You should hear the pump prime when you turn the key on. Or you can jump the test wire as others have suggested. Get a gauge and measure fuel pressure at the rail.

On my car, the injectors were stuck shut. I just replaced them.
 

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That would be my final suggestion fuel system wise.
If you get pressure to the injector fuel rail and it still won’t start, last step is to check for clogged injectors...
That old fuel sat in the injector rails (and fuel filter) even if you drained the tank.
My best guess is still the FP itself or the wiring itself inside the tank. An empty fuel tank is a great condensation machine over time and can cause rusted connectors if the fuel level was drained below them.
Which it sounds like is quite possible if drained as far as you said you did.
 

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I’ve always been told to fill the tank all the way full and then use a high quality fuel stabilizer in the tank and run the car for 5 - 10 minutes to get the stabilized fuel mixture into the fuel rails as well.
Then when you put it away there’s no room in the tank for condensation to form and keeps the FP covered and thereby protected and kept from corrosion.
My last FP replacement (had original in it) was because a ground wire inside the tank finally had become loose and corroded and melted part of the FP/Guage rheostat wiring junction along with burning the insulation bare on some of the wires.
So I replaced it all.
 

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1995 Cadillac Fleetwood Brougham
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I don't think it likely that would fail from non-use all this time
This is exactly what happened to my Fleetwood that sat for a decade. The wiring went bad, likely from corrosion.

What do you mean it fired up when you dumped fuel directly in to the engine? It's not a carb. How would that work? The fuel has to be pressurized.
This is not true. You can get an LT1 to run by spraying starting fluid or gasoline into the throttle body. Ask me how I know.
 

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This is not true. You can get an LT1 to run by spraying starting fluid or gasoline into the throttle body. Ask me how I know.
I know you can do that. I've done it too. That's not what he said he did though.
 

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You emptied the tank, but you may not have drained the fuel line from the tank to the injectors. So ... in 10 years ... well, let's just say it won't burn. You may just need to bleed the line, if it's not glued shut from varnish. You can do this by running the pump for a couple of minutes to cycle all the gas around and back into the tank. Check your fuel pressure at the shrader valve just behind the fuel pressure regulator. No pressure, no gas, no anything.
 

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Discussion Starter #13
Thank you to everyone for such a lot of helpful information!

I'm determined to tackle this getting this boat on the water while I still have the time and money to do it, so I'm going to see about getting to this in earnest this week, or at the very least ensuring that all the necessary parts and tools are procured. I did also notice that the fuel gauge is incorrectly indicating a FULL tank of gas, despite there being at most now only about 5 gallons, tops. I would guess that means getting into the tank then, regardless of the pump status, to replace whatever sensor or float needs fixing for that? Would this part (Spectra Premium Gasoline Fuel Pump D128B1H) solve both problems or is there a more preferred brand of replacement that I would be better served by?

We have been putting this off for so long because we just weren't ready to really dig into it all that deeply if it wasn't going to be a relatively simple repair. The prospect of dropping the tank just made it all that much easier to procrastinate, and now it's been about a year, I'm ready to get this beast out of my carport one way or another, even if it ultimately comes down to selling it in it's "as is" condition. (But I would prefer to avoid that, if only because the prospect of getting a tow up and down the long narrow and just slightly z-shaped driveway is even more daunting - it's got a running tally of side mirrors claimed from different cars over the years, especially the wider ones, and I actually did the passenger side of my Cr-z TWICE. The Impala is such a nerve-wracking chore to navigate that squeeze, I won't even attempt it without help from someone with eyes outside the car.)

And apologies for my vocabulary lacking in accuracy, as I am just the research leg of the repair team. Most of the hands on is done by the fella who would seemingly rather rebuild the vehicle a part at a time before actually going through the trouble of joining enthusiast forums to ask about narrowing down the problem first. While my willingness to search out and read through pages and pages of other people's encountering similar problems has been able to save the day on numerous counts with some unorthodox solutions that otherwise wouldn't have been something he would ever think to try (a battery drain issue in a bmw caused by a worn casing on a bundle of wires in the trunk hinge, for example, rectified with a couple inches of tape), my lack of direct experience with the mechanical side can result in some things getting lost in translation when I post about a specific problem myself. I'd be better off if we had everything pertaining to just one or two cars, but almost every problem we run into is on different system on a different car, which limits the application of what I have already learned.

With that in mind, I will also thank you for the assumption of my being a complete novice in any instructional details. Even though I will mostly be passing along the information to my partner for the actual work, it helps to understand what I am relaying to him so I can effectively nag him about how he's doing it wrong :p...
 

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I know you can do that. I've done it too. That's not what he said he did though.
You mean because I said starting fluid instead of gas?

Would this part (Spectra Premium Gasoline Fuel Pump D128B1H) solve both problems or is there a more preferred brand of replacement that I would be better served by?
That is the part that you want. That will be all you need as far as the tank is concerned. Make sure your wiring, filter, and lines are good, and you are all set. However, the same part costs $61 on RockAuto: 1996 CHEVROLET IMPALA 5.7L V8 Fuel Pump & Housing Assembly | RockAuto

If you did want to upgrade the pump to a better brand, try Delphi #FE0114, or GM Genuine #EP376. Both also available on RockAuto.
 
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