the fuel pump feed comes from the under hood fuse box. the relay in there. out side the fuse box is a wire [RED]with no connection to it . that is the pump prime wire. you connect a fused power wire to it. that will keep the pump running .. or feed to pump so you can find out if its a wiring /connector issue or ground like in the trunk driver side area .

 

I am assuming you have a 94-96.


Did you try putting a pressure gauge on the Schrader port? Can you hear the pump run when you turn the ignition on? It should run for about 5 seconds, then stop.


You can also check for voltage on the wires to the pump at the rear bumper. Black is ground and gray is the pump.

 

As Fred suggested, do you hear the pump prime with key on? You should hear it for about 2 seconds. If not, as jcat mentioned, use the prime override wire to keep constant power to the fuel pump which overrides the 2 second only prime. When using this test wire, I just connect a length of 14 awg wire with a male spade crimped on the end that pushes into the test wire. Then connect the other end to the battery positive or you can just use the post by the fuse panel which is close anyway and comes right off the battery. This test wire bypasses the FP relay/oil pressure switch circuit.

If still no pump running, temporarily unplug your test wire and move back to the rear of the car. Back near the rear bumper on the driver near the tailpipe you should see a 3 wire plug. It will have a Gray, Black and Purple wire in it. Unplug this connector and using the end of the disconnected plug closest to the bumper, see if there is continuity from the black wire to any bare metal part of the car or the battery ground. If you have continuity, then you know you at least have ground to the plug.

Now see if there is 12v going to this plug. Reconnect your test wire and move back to the rear of the car again. Now check across the black and gray wire of the plug. Do you have 12v there at this connector....I suspect you probably do. Well that's good and bad....good that you found the problem, bad though cause now you need to drop the tank. The problem is most definitely in the tank. Most likely a burnt harness or corrosion on the internal harness....pretty common. Once the tank is down and the fuel pump assembly removed, you can apply voltage and ground to the pump for a second or 2 just to verify that the pump runs. Most likely the pump is good but you need to decide if it's worth just throwing a new pump in there while the tank is down.

If you do replace the pump, stick witha GM pump (ep376?) or something witha good reputation like Walbro. There are other options too if the wiring is toast and the connectors on the bulkhead look charred. Consider a kit offered by racetronix but I may avoid their fuel pumps but their wiring kits and Componets are top notch stuff.

 

Thanks for the info,

And yes I do have a 94

I am setting up a time for my brother to make the drive down with the tools to test the electronics and the pressure, I dont have many tools here at college. I just wanted to see if I could single out if its the fuel pump so he wouldn't have to bring as much stuff with him.

So to start I am gonna want some wire, and to connect that to that red prime wire near the fuse box and attached it to the positive of the battery or the post by the fuse box? (sorry I'm not sure where that post by the fuse box is, can you explain more?)

 

this is the fuel pump wiring for the 94-95 cars.

 

better to check with a fuel pressure gauge. Even if the pump "runs"...it may not be putting out enough fuel "pressure"

A FP gauge screwed on tot he schrader valve on back of fuel rail will quickly tell you

 

just have to comment on the fuel level that you operate in the vehicle . these fuel level sensors indicate more fuel than you really have in the tank . what happens is because of this old style tank the fuel pump gets hot with low fuel and the fuel gauge tricks you out on the amount you have in there.

make sure you have more than 1/3 of a tank when operating at all times.

another issue with this design . when these were built, there was no alcohol fuels ,,,, the tank design IMO is a design that exposes tooooo much air to the fuel, this then causes the fuel [alcohol ] to absorb the moisture and create crap . this crap then can/will restrict the fuel filter.

many have had these problems with these cars.

 

I have been trying to drop my tank to install this Spectra unit I got off Amazon, will let you know next weekend how it works.

 

I have been trying to drop my tank to install this Spectra unit I got off Amazon, will let you know next weekend how it works.

I think you'll be happy with that unit from Spectra for a new part. Actually the new GM piece appears to be redesigned and is very similar. So for the money, Spectra seems to be a good choice. What I was not happy with was the puny ground wire they use and chose to modify the unit when it was last out for another pump upgrade. You may be fine if you just leave it as is or if you want to modify it, here is some more info....

http://www.impalassforum.com/vBulle...tin/34-engine-problems-maintenance/1239986-fuel-sending-unit-gm-vs-spectra.html

The sending unit portion of this seems pretty accurate compared to the old resistor setup they used to have. As long as the Float arm is installed correctly, they seem to reflect accurately to what you actually have in the tank....at least on my unit it does.

What Fuel Pump you gonna run in that new unit? I would stay with AC Delco or Walbro unit only. Stay away from the pumps offered by Autozone or other parts houses. You may also want to consider soldering the wires directly to the bulk head connector and not use the plug.

 

It includes fuel pump... Price dropped by 4 bucks too, pretty good deal if you ask me.

https://www.amazon.com/Spectra-Prem...=sr_1_1?ie=UTF8&qid=1479147245&sr=8-1&keywords=spectra+fuel+pump+impala+caprice

 

That's a heck of a good price for the sending unit AND the Pump. Without knowing the brand of Fuel Pump, I would be very leery. I didn't see the brand name mentioned in the Amazon link.

It's just that I've been burned by bad parts before and dropped the tank more times than I care....so I'm always skeptical of parts in this area. Hopefully, the pump is fine and provides many years of service for you.

 

Yeah, I'll roll the dice on this one. It just needs to work long enough to get me home. And once I become expert on how to separate the damn lines, I won't mind dropping the tank if I have to. ;^)

 

FWIW, I had a Delphi pump run for about 15 minutes. That was the OEM supplier too!

I have had my ACDelco for 25K and all seems fine, minus this constant low pressure I have (36-38psi, instead of 42-45psi) Might be a bad FPR too. Take that with a grain of salt.

Looking at the Walbro and the Delco, I say you probably cant miss with either. The Walbro seems real nice and the price is pretty competitive.

If I could do it again, I probably would do a Walbro.

Get an OEM ACDelco sock while you are at it.

 

I have had my ACDelco for 25K and all seems fine, minus this constant low pressure I have (36-38psi, instead of 42-45psi) Might be a bad FPR too. Take that with a grain of salt.

.

42-45 (43.5) is what FP should be with vac line off. 36-38 with it on...so your #'s are good

 

Follow up question, while were on the topic of fuel pump issues - my pump runs when I key on, but idle is 31-32 psi and 40 WOT without pulling the vacuum line. the FPR is brand spanking new Delphi Unit (bought two, just in case actually)... so I don't think its that but im wondering is that pressure is too low.

when the vehicle is at a stop in gear, it begins to surge. the surge grows and grows for seconds until the car will either right itself and then restart the cycle OR stall out. it fires back up just fine after stalling, however. no CEL's, no codes stores. '95 impala SS. ICM is brand new, FPR brand new, Coil brand new all within 800 miles. two cans of carb cleaner have told me there are no vacuum leaks to be found and im kind of stumped. Opti is less than 5k miles old, plugs and wires are also brand new.

any help or ideas?

 

my pump runs when I key on, but idle is 31-32 psi and 40 WOT without pulling the vacuum line. ... so I don't think its that but im wondering is that pressure is too low.

your fuel pressure should be 43.5 with the vacuum line off.With it on it generally is around 37 and will raise when you hit the gas

your #'s are on the low side...

with the FP gauge hooked up so you can see it under SUSTAINED WOT...does it drop or hold

 

So I'm very sure my fuel pump should be getting power. When I got into the car and turned on the ignition switch, I could hear the little whirl sound which I assume is the mechanism attempting to prime... So the next step is borrowing a fuel gauge, correct? So from my experience last time me and my bro did this, I remember the little nozzle being on the back of the engine. Should I need help running this test? or could I just plug it in and turn the ignition switch and get results?

Thanks for the help and the replacement fuel pump recommendation as well.

 

You can easily do it yourself.

Chrisfix on YouTube has a video showing him doing it on his lt1 corvette. Just look up 'fuel pressure test Chrisfix' on youtube.

Sent from my SM-N910V using Tapatalk

 

Found it. Thank ya, bud!

 

Follow our pressure guidelines while following his procedure steps for a successful diagnosis.

If FP replacement is necessary, either ACDelco by my experience or walbro per a few other people's recommendations.
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Caprice tank straps are available aftermarket on Amazon or ebay.

 

found them! we talking about the Spectre ones? They seem to work decently?

 

That is correct. They work fine. They have wagon tank straps as well, thanks to a member of the longroof forum.

 

Pardon me for dredging up an old thread, but I'm researching information before posting a question that might already be answered. Just out of curiosity... Why the flexible P-shaped hose from the pump to the pickup? Why not a straight shot?

 

Duplicate post - I looked for my previous post, but it had not come up quickly.

 

The S bend tube is used because the pump carrier is able to move on the return line. It is spring loaded to keep the pump on the bottom of the tank at all times. It can move up and down about 1 1/2 ~2 inches.

I discovered this when modifying one for a larger pump. I made one that was stationary, and measured unit the same length as the OEM one out of the tank, and when I put it in the tank, I could not get the flange to go to the top of the tank. I ended up cutting 1 inch off of the modified sender, and it fit correctly.