It sounds like you just have a defective pump. Its pretty unlikely you need some sort of high capacity pump. Glad to hear your on the right track. You will probably have it fixed and done by this time tomorrow.

 

I'm curious. How did you determine that it was the pump? How many have you replaced? Sure, pump replacement is way more sexy than digging to find out whether the pump is really weak or whether you are getting good power. It is unlikely that you need a Racetronix 255 lph pump. What difference would a full tank vs 1/4 tank make? Tried bypassing pump power yet?

 

aklim, what else could it be??? aside from me checking pressure with no vacuum which ill do as soon as I have 5 mins.. I don't see what else I could possibly be,


I don't know maybe a dozen fuel pumps over the years.. what diff doest it make?




I dint think its losing signal... if I get on the gas then hold it steady the gas pressure goes up.. it only makes sense that the pump is not keeping up. if I key on the gas pump works.. aside from the gas pump losing signal mid accellartion I cant see that being the issue... the pressure loss is linear... and its a brand new pump.


re filling up the gas tank.. if the pump is having a hard time keeping up already and gas level is low and I goose it and the gas sloshes to the back of the tank, out of the weak "sump" .. its gonna be even lower on pressure....


I literally watched this happen... as I drove with the gauge taped to my windshield... then got gas and drove more... it was obvious.

 

I think what he trying say is that if you don't have the proper voltage to the pump or the proper ground then it is not going to work the way its intended. There is no way to explain why he didn't just say that in a clear and unambiguous way, unless that's not what he means.

 

well yeah its got 12 volts with key on...


and the ground seems good...


so unless something its intermittent... im good.. and it would be really hard to diagnose on the road..


and if it was actually loosing power , fuel pressure wouldn't be a linear drop .. it would just instantly drop...


just ordered a new one under warrenty.. so I guess well see.. atleast I know what my problem is now..


and with the gas tank full, I FINALLY got to experience what this car will be like.... I thinki im finally digging my VETTE!!!!... its got some *****... should be super fun...

 

Look at it this way. The more demand, the harder it is to keep up if the power to the tank is flaky BUT NOT OUT COMPLETELY. Racetronix makes a kit to run the pump from the alternator but maybe you can temporarily rig something up with a switch? I also don't know about your car but IIRC, my scantool has fuel pump voltage as a parameter? It is hard to imagine that all those fuel pumps were bad. 1? Sure. 2, doubtful.

You have to ask yourself why there are so many bad ones. I might have a smaller Walbro one, 190 lph, IIRC you can test it with but I think you may have a power issue.

Your other thing might be whether you have a pulsator that is giving out. Did you use a kit from Racetronix where, among other things they have a section of fuel hose that is rated for fuel submersion to replace the dampener?

https://www.amazon.com/1985-1996-Cor.../dp/B000FN0BEC

 

alkim...

sorry i mis-interperated your question...

Ive personally replaced about a dozen fuel pumps.... but only one on this car.

i ordered a new pump under warranty. but ill see if i cant get my buddy with the snapon scanner to come over tonight and see if fuel pump voltage can be checked with it..

or ill throw it on my lift and goose it with a volt meter on it..

it still seems weird to me that it only drops pressure while driving.. i can get on the gas all day long in neutral.. but while driving and i get on it... it drops...

 

Why? Driving in gear puts a load on the engine. That takes more fuel. It might be able to keep up without a load but with a load, it is too much.

 

i never really thought about or realized that , i always just kinda figured the engine RMP dictated the amount of air/fuel that was needed. didnt think load figured into the equation.

 

I can cruise in my truck at 17 mpg or haul a 8000 pound load and get 11 with the wind at my back or get 9 with the wind against me.

 

Fuel pump voltage cannot be checked w/a scanner.

Run some long jumper wires from pump+ to cabin. Hook up your volt meter to those wires....go for a drive. That is, if you believe there is an electrical issue to the pump. The way that I interpret your description of the symptoms, it doesn't sound like an electrical issue. Sounds like a pump that can't keep up -either b/c it's defective, or there is a leak; possibly at the pulsator as Aklim suggested.

.

 

Any idea what the pump voltage from the scanner is reading?

I was going to suggest running a wire from the alternator like I think the Racetronix kit does but that sounds easier.

 

Not sure what you're asking... Scanner can't read pump voltage. ECM has "no idea" what the volts to the pump is.

 

My Auto X-ray has a "pump voltage" parameter. Is that just alternator voltage or what do you speculate it might be? I have never used or tested it.

 

You need to Verify whether or not that there is an adequate [Power and Ground] source at the Fuel pump.

As Tom mentioned in an earlier post running a separate source of Power, and Ground from the Battery [fused] will provide a good data point.

This could be as simple as a faulty Fuel pump relay, or rusty Ground.

 

It's not likely a relay; the oil pressure switch parallel feeds voltage to the pump once there is oil pressure....so even if the relay were completely bad, the oil pressure switch should "step in" and provide battery voltage to the pump.


I can only figure that it's reading battery voltage and assuming that is what is going to the pump (b/c it should be). But there is no "feed back"...there is no sensor at the pump that measures voltage, so it's not possible for the ECM to "know" what voltage is actually getting to the pump. All the ECM's interaction w/the pump is; the ECM grounds the FP relay. ECM doesn't even know if the relay has batt voltage going to it, so it surely can't "know" if or how much voltage is getting to the pump.


Some later cars have modulated fuel pumps. Ford especially. The ECM varies voltage to the pump to control pump speed, and thus, fuel pressure. In this type of vehicle, that function on your scan tool would show what the ECM thinks it's sending the pump for voltage. IDK if there is feedback (a sensor) at the pump. My guess is that parameter is for another car, or if it shows a value on your car, it's an assumption based on battery voltage.


Guys, in an effort to not confuse the OP, this symptom (as it's typed out here):
when I get on it in gear the fuel pressure drops ...the pressure loss is linear
^That doesn't sound like an electrical issue. It could be...but typically if there is an electrical issue it would behave in a more on/off fashion...and engine output would reflect that w/ pretty violent "bucking" as the pump comes on and off.


.

 

all good ideas...

thanks... ill get on it tonight /tomorrow.. now that i know what the problem is this will be a breeze... I have already removed the pulsator. im very much so expecting the pump to be faulty... but ill check my wires and do a jiggle test.. maybe a jumper wire.. or just do it on my lift so i can stand at the pump while the car thinks its moving..

 

Carefully inspect the terminals and wiring at the fuel pump connections, and at the sending unit connections right at the top of the tank. In the extremely unlikely event there is an electrical connectivity issue then one of these two places is where it is most likely to be.

 

thanks tom...

i would agree with all you said...

and yeah thats why i noted that its a linear drop off.. not acting like the pump is shutting off.. its acting like it cant keep up

ill still do some double checking just to be sure.. because double checking is how i figured this out in the first place....

new pump is in the mail... god i hate waiting for mail order parts.. but in this case its warranty to i have no choice. its a bosch pump so i didnt just buy a cheapo.

and i still have to install the new brake booster and do the wire testing while i wait ... so i guess ill have something to do when i get the kid to bed tonight.

updates to follow in the next day or two im sure..

thanks again to all!!!!!

 

Ok, so wiring is good at the pump and upon further inspection.. The fuel pressure drops even quicker after driving the car a bit... But once hot itll drop sitting in neutral while revving on it... gonna ohm put the 9th injector just incase.. but its coming along...

Also I found this, behind the distributor.. Its a green wire, then the connector.. Then its black.. Where does the black wire go? It's just a frayed wire that had electric tape on it now.