I swapped out stock fuel pumps on my 91 Conv and now the pressure drops to zero within a second or two after shut off. I put the original one back in and have the same issue. I have a pressure gauge in line after the fuel filter and before it enters the motor. The hold was within specs before the swap. I am almost 100 % sure everything went back together correctly as there is not much to changing fuel pumps, but the hold pressure is not there.

Any ideas gang? Anybody ever encounter this before?

B

 

my FC does this, i really couldnt tell you why it does it, but i wouldnt worry about it. Steve tuned my car and told me there are no ill affects of it. How many times did you see it hold? Mine held the first time i turned my new pump on, after that, it has never held sense.

 

Air in the gauge line? Bleed the air out and try again. I've a car outside that hasn't been started in several hours and it's still holding 25psi.

I'm not sure it matters all that much. Ignorant about that myself.

 

It held everytime before I swapped it out. It would slowly decrease, but within the FSM specs.

I know there is nothing seriously wrong with this. I am trying to sell my Conv and want to get it to how it should be. I don't like having to crank the start for 6-8-10 seconds to get the pressure built up and the potential buyer thinks there is a problem...which there is.

B

 

No, the gauge was in place the whole time before during and after the swap. The pressure is in the proper range when it is running.

Refresh my memory Hailers, I know you are the foremost expert on this, but when the key is initially turned on but not cranking, should there be pressure inline or is that only after you start cranking the engine over?

And don't anyone suggest leaving the jumper wire in all the time. I want to fix what is wrong, not band-aid it to sell. I don't swing that way.

B

 

&&&&&Refresh my memory Hailers, I know you are the foremost expert on this, but when the key is initially turned on but not cranking, should there be pressure inline or is that only after you start cranking the engine over?&&&&&&&&&&&&&&&&&&&&&&&&&&&

On a SERIES FOUR CAR the pump only runs if the key is HELD to START.

Turning to ON does not turn the pump on for even a nano second.

I'm talking about with the jumper NOT installed in the conenctor in the engine bay.

I'm really glad you asked, especially since you have a SERIES FIVE CAR.

I do not own one nor have even touched one of those.

So I might have been giving out BAD information on the fuel pumps working with the key to just ON, when talking about SERIES FIVE cars.

So settle this for me. Turn the key to just ON and see if the pressure goes up or NOT. It's possible that the series five acts different since there is an input from the ECU for series five that does not exist for series four.

So I described how a series four pump works above, and you can settle whether or not a SERIES FIVE pump comes on when the key is turned to just ON (Not Start, but ON only).

You'll be doing me a big favor if you do this. Thank you.

By the way, you made me paranoid. After looking at the car out front, I wondered "IS THIS GAUGE BUSTED AND STUCK AT 25????" So I undid the Bnut and the pressure fell. So my gauge is good and the fuel pump check valve is holding in an outstanding way. On one of my other cars it only holds for twenty to thirty minutes at a figure above 25.

 

Hailers, I can't tell you exactly what a S5 does, because I don't think mine is working correctly.

The issue I am trying to get addressed is in the back relating to the fuel pump. Since that is what I was working on, I believe that is where I am having my "hold" problem. The fuel pump operates correctly, but when the key is shut off, I believe it is dumping all the pressure back into the fuel tank. There is nothing to taking the fuel pump off and putting another stock one on. And when the hold problem happened, I returned back to the original one.

It just seems like that is where the issue is being the problem happened after I did this.

I think the S5 operates the same as the S4 in the pressurization, but I can tell it takes twice as long on the cranking now to get it to start like it is taking long to get up to normal operating pressure.

B

 

it hardly matters that it holds, the pump builds the pressure back up when it primes.

 

I don't know why it's not holding. There is bound to be a checkvalve in the pump itself but for some reason both yours are not shutting off/closing. There's got to be a reason they made these things where you turn the pump off the rails still hold pressure.