Isn't the fuel system only pressurised from the tank, to the pressure regulator, to the end of the injectors only? This question will come up more later.

I started with cold start problems, sometimes during hot/warm times as well. I checked the fuel pressure, but the pressure readings where spot on. But, the pressure would not hold, and withen 30 seconds, would bleed completely down to zero. Took about 15 seconds to bleed down to 35#s and then another 30 seconds to bleed to 0#s.

The first suspects where:

#1 The fuel pump (replaced pump earlier, but used rubber hose instead of the plastic tubing)
#2 The Fuel Pressure Regulator
#3 Leaky Injector

I removed the fuel rail, and found out the #1 injector had a cracked secondary seal. So, I replaced all the o-rings and secondary seals on the rail, and the pressure regulator as well. While I had the fuel rail off, I looked for any of them leaking, or dripping, saw no evidence of this. I did not check the spray with jumper wires however. I then re-installed the fuel rail and injectors.

Pressure then bled down to 35#s after an hour or two, then 6-8 hours later, it would bleed down to 17#s and hold steady.

I just did a plug change, it's colder in the garage today. Those are the only two changes before I decided to check the pressure again.

It now takes a few hours to bleed down to 35#s, but it's holding steady.

Now, the plugs all where a little carbon fouled, but they all looked the same visually. I know I'm running rich, because I need a reprogram for a few mods I have installed. So I think leaky injector is out, as well as I'm not getting any codes.

I don't think the plugs keep fuel pressure holding, as that's not how I was raised.

So, why is it holding at 17 pound increments, and where is it going? How often to rubber hoses in tanks fail, or leak?

My cold starts are gone, but I don't want a leak in the system anymore. Getting closer to that goal, but need advice and opinions.

Nice site yall have here

 

so, now it is slowly bleeding down to s5# and pretty much staying there?

if so, you are good to go, that is exactly what it is supposed to do

biggest thing that is required is that the fuel in the lines stays there, so a prime at key on will instantly create the needed pressure(~43psi)


I think the last spec I found was no more then 10psi drop per 1/2 hour, or something like that

 

Might want to mention a few specifics about your car, like the year, model, engine and any major mods. Its sort of hard to get into the details of the fuel system without knowing that.

 

Well, that's good to hear. I was told that the pressure should hold steady and not drop more than 3-4 pounds after the prime was over. I'm used to carbs mostly, just "getting into" fuel injection. But yes, now the car so far is holding at 35#s or very close to it. It's hard to exactly tell with the pressure tester I have, it isnt exactly labled well.

Sorry about that. The car is a 99 v6, 3800 series 2. 41,230 miles on the odometer. It has only minor mods like an aftermarket air box, ram-air hood, and new gears. I know the PCM should be reprogrammed to tune the richness out from the extra air going in, but that would be a late winter project.

Idle pressure: 45psi
No vac on regulator pressure: 54 psi

Both of those are to spec for this engine. I hope this helps.


edited: I usually run several tests per new parts to tell if the first was a fluke. This time I have only done one. Before I go to bed, I am going to check it, and run another test.

 

I'm sorry for two posts in a row, but I finally rechecked the pressure. It's finally down to 17-18 pounds and holding again. It did take twice as long to do so this time however. I reprimed it, and no doubt I will get similar results by morning.

EDITED: And the third test, which I performed last night. The pressure held to 35#'s all night. This is very confusing.

 

Any more opinions, or should I consider the problem fixed?