Fuel pump prime-how much pressure?

[DMAN302]

Well I installed a 255 walbro pump today to replace a 190 walbro pc that was cutting out intermittenly and all seems good to go. However I have found from 0 pressure sitting to first prime I am only acheiving low 20's pressure...after several primes I am only seeing 24psi max. I will say when testing the pump via test connectors under the hood, the pressure spikes to 40 and imediately drops to the 20's as stated. Once running pressure is consistant 34 vac line on and 41 vac line capped and disconnected. Should I be concearned regarding the prime pressure?

 

[Mr. Rustypwnz]

looks fine to me

 

[HISSIN50]

Derek, you know I'm slow to get this stuff.

If it primes to 40 PSIG (per your underhood gauge) but then seems to fall right off as soon as the pump is done, I'd wonder if your FPR is the cause.

If you can only prime to 24 PSIG unless you jump the self test connector (duplicating the ground path of the ground strap in the computer, but remaining constant), that'd be a little more curious.

Did you swap FP relays before the pump? Do you have the same voltage in (from the starter solenoid) as you have going out (egressing the relay for the pump)?

If it doesnt crank any longer than it should and it holds pressure once running, it'd be more of a curiosity thing for me.

Is any of this what is actually happening?

Good luck Derek.

 

[DMAN302]

Well see if I can explain a little better...when I turn the key the pump primes...needle spikes to 40...as it always has, post spike the needle settles at 24-25psi and will repeat this cycle regardless of the number of times you prime the system..spike then 24-25 and holds pressure. Then at start pressure ups to 34 vac line on and if line is disconnected pressure shows 41..as it should. Any quick throttle and pressure jumps perfectly. My only concearn is the prime pressure...it is repeatable every time it's primed unless the car was recently run and pressure is still in the 30's (pressure will hold in the 30's for a good while after shut down of engine).

 

[DMAN302]

Wanted to add...new relay was given to me, new pump and filter are in place...car is running flawlessly. I have still noticed however that the relay under the seat will get somewhat warm to the touch after the car is running for a bit...this I find curious...but after a 20 minute drive all is well and the car runs like a violated bunny

 

[HISSIN50]

Glad to hear it runs well - that's what matters. The new pump arguably has more amperage draw, so the relay may stay warm. About the only thing I can think of is to make sure all the terminals fit the relay tight (loose connections = heat). I'll try to remember to check my relay and let you know if it's hot (hard to tell when it's 100*F outside).

With the drop in pressure only after the prime-out, I'm not real sure. It could backflow a little (it doesnt take much to drop the needle at the Schraeder) or the FPR just drops some pressure quickly. Because it holds pressure better after being driven, I'm inclined to think it's the former, but I really dont know.

If you didnt have a showcar, you could use fuel line crimpers to carefully crimp the return line at the exact moment Mrs Derek turns the key off (after a prime, where pressure would fall back into the 20's). If pressure holds, the FPR would seem to be the issue. If pressure still falls, fuel is retreating from the way it came, back to the tank (we know your injectors arent leaking).

That's the best I got.

 

[DMAN302]

*walks in room with head hung low*...installed the filter backwards.......after a ofuel to the face this morning the FLOW indicator is now facing the correct direction....oh boy.

 

[HISSIN50]

Well Derek, I'm glad you found that because I wouldnt have suggested it.

No biggie - it was an easy fix. If it makes you feel better, one time during an all-night thrash on a Euro car (I was installing the double-wishbone suspension with new Delrin control arm bushings), I got done (at first light) and noted some wicked positive camber on the front passenger wheel.
When I had the arms on the bench (installing new ball joints on all 4 arms) I had one upper arm upside down. Since I tossed the BJ in the arm upside down, I installed the arm upside down.

It happens. Now go enjoy!

 

[JChalfan]

I've installed a flywheel before and forgot to tighten the bolts. I figured it out as soon as I started the car.

At least you got it figured out.

Jeff

 

[DMAN302]

Ah the joy of doing all our own work...still wouldn't trust a 'professional' to come within 10 feet of my little girl , rather screw it up myself . Thanks for the support guys I know we've all done it, but it can be so damn frustrating.