I have a 406 with a stock TPI setup, 42lb injectors, jet adjust fpr and I have been trying to toon the car with tuner pro. Whats happening is when I start the car cold I have 46psi fuel pressure, then when the engine heats up and has been idling for awile the pressure drops to 34psi and my tune leans right out. Do you guys think this is a tired fuel pump, or could there be something els rong?

Oh yeah, there is also a sucking hum noise comming from the back of the car that comes and goes when the car is has been running for awile, I can hear it best when I'm in the car. I took the gas cap off while it was running and doing that tonight and it stoped, but my fuel pressure stayed the same. could this be a purging problem, or bad pump also?

Please help, you guys are the best

 

the hum your hearing is the fuel pump... its the priming/running of the pump. i notice with my car (that i have the walbro 255lph high pressure pump) after i turn the car off after just priming the pump (no starting) that it stays on and i can hear gurgiling in the tank/back of intake. this must mean that the pump stays on to bleed the excess gas/pressure outa the fuel rails and sends it back to the tank.

that hum is def ur fuel pump and thats normal.

if you dont hear a hum then ur pump has just DIED!

can i ask how much vacume u have with the engine running? cold and hot at idle? vacume is really the only thing that controls Fuel pressure, u should have LESS at idle with vacume attached. EX: mines set to 43psi, at idle with vacume i have about 38 or so and as soon as i step on the gas-vacume decreases and fuel pressure increases. THis is normal.

when u set fuel pressure say to 46psi, you do this with vacume off and engine running. this will be your MAX fuel pressure, so no matter how little vacume u have the engine will never get more than 46psi. but with vacume attached it will decrease ALOT! seeing 34psi is not bad at idle.

Heres the kicker tho... watch the pressure as the engine is idling with vacume on. if u see say 34psi and then u stab the throttle and fuel pressure DOES NOT increase then u have an issue. i would assume its the fuel pump which is not long for this earth. make sure u have fuel pressure set correctly with vacume off, then test.

side note... ur injectors are rather large for your 406, esp with a stock TPI which will limit ur RPM power to about wat...4000rpms lol. since it chokes the stock 350 TPI at about 4200-4800rpms. your 406 will be sucking way to much air for that TPI to support beyond 4000. but im sure its a stump puller with major low end tq.

not sure how u tuned it or how well its tuned but i would think a lower PSI would prob help u unless the motor likes the 42lb at 46psi. would would really make the injectors about 43lb.

 

Thanks for the reply black bird
I will do some tests and let you know what I find
But also, would you know how the fuel pump works power wise. Like how many Volts should I see at the pump when its running to be working properly?
The more Voltage you put to it, will it work better (will I see a psi increase if I hook direct battery power to it?

 

Also, whats the best pump to buy these days (quality, price, performance)

 

fuel pump should see about 13-14v i believe. they are very sensitive to power just as the injectors... getting below the required voltage would effect the pumps efficiency greatly. if the pump doesnt see at least 12v it will not work properly. same as the injectors, the injectors see less than the 13.5v they will not open and close correctly causing rough idling etc.

hooking it up directly to a battery will only give it 12v max... thats only what the batts are rated to give out. if u have a batt gauge in your car... turn the key to the on position but dont start it, u will see the batt gauge will read less than 13v. car batts are 12v systems and the batt will only put out (by itself) 12v... its the altinator that shows 13.5-14.4V on the gauge, this is what helps it charge. so basically the alt is rated to 13.4-14.4v.

your gona hear different things and most ppl dont know that WALBRO is the best. they are the company that make the pumps for edelbrock, BBK, holley etc. you want the walbro 255lph intank stock replacement pump. this doubles the fuel output compared to stock, (stock is 90-100lph). this pump will support up to 700hp NA i think. the walbro pumps are basically just repackaged and put into a holley/BBK/edelbrock box and they charge u another 60-100$ for the same pump. the walbro255lph pump can be had for less than 100$. there is another pump its the same thing, but its the walbro 255lph high pressure. the regular pump operates to 60psi max... the high pressure is essentially the same pump but it can run at higher pressures... i believe up to 70psi. this is great if your running a supercharger/turbo or some other power adder. i got the walbro 255lph high pressure for 100$

http://www.walbrofuelpumps.com/

cant remember where i got mine but it was 100$ shipped.

also u dont want to throw more volts at the pump than is required. more is not always better. and im sure your car is putting enough volts. if you want check it, there is a plug that connects to the lug coming outa the tank. its right above the rear end against the floor panel (back part of rear seat) or cargo area. its a weather pack connector. this is wat provides the power to the pump. you should see 13-14v at idle in park. and it will fluctuate as the power at the engine fluctuates (if u have underdrive pulleys etc)

 

Thanks for the link & Info Blackbird

So I checked some stuff out and this is what I found

1) Voltage at battery and pump is good
2) When I first start the car, I have 46-50psi fuel pressure and 14-15vac at 1050rpm
3) By the time the car is warm and idling at 800rpm the fuel pressure has dropped to 38psi (still have 14-15vac)
4) So I let the car keep running to where I see the fuel pressure stop dropping, thats right around 34-35psi
5) At 34-35psi I pull the vac line off the fpr and I see 42-43 psi, same when I crack the throttle.
6) Also I will add if I rev it up to 1300rpm - 4000rpm, the engine has 20vac

So what do you think, tired fuel pump and I have compensated with the adjustable fpr?

Also the hum I hear is deff not the normal hum of the fuel pump running, it kinda sounds like a vacuum lock, like a said its not all the time, its only when the car is hot and even then it comes and goes every couple minutes. If I take the gas cap off it stops.