04 V70 Inconsistent Start Problem Topic is solved

[swirskai]

Pressure measured -> 0 psi. Can't get the car to start at all right now, and will only get a low rough idle briefly before it stalls.

The symptoms, in culmination with the collective advice have led me to a bad fuel check valve. Thank you to everyone who commented, even if it wasn't was you though I learned an awful lot about the cars electronics, sensors, and starting conditions.

So after a bunch of digging (making sure I had the metal tank, and I didn't have a plastic one with a thin metal cover on it or something crazy) I bought a pump from FCP; Bosch 30794624.

I've watched a few videos online.. any suggestions? Figured I'd ask, as its about to happen in a college parking lot with juniors and seniors. You could say I'm taking every "prepared" measure possible without my garage at my disposal. Got a vacuum, siphon hose, and a nice set of 6 point metric sockets.

It looks doable, something like:
1)Remove Back seat
2)Remove Side cushions by door
3)ABS sensor
4)Bolts, bracket, and backseat rest
5)Access both covers -> PICTURES
6)Pull out old pump/sender unit/ sensor on hanger
7)CAREFUL will sensor, install new pump/module
Put back together

[abscate]

P2s have a lot fewer fuel pump problems than earlier models. I’m a bit concerned you’re problem is upstream in pump control electronics. Did you get a confirmation that’s you have fueldelivery problems?

[swirskai]

P2s have a lot fewer fuel pump problems than earlier models. I’m a bit concerned you’re problem is upstream in pump control electronics. Did you get a confirmation that’s you have fuel delivery problems?

Well describing the symptoms with the fuel pressure gauge hooked up, the gauge would read 0 psi and the rail is filled with fuel. Initial cranking fires for a 1/2 seconds and dies. As the key is cycled in the ignition the idle will improve slowly, especially with longer cranks and high frequency.

After 10-15 cranks the car would usually start, assuming that pressure is building upstream of the pump by way of just the pump itself. After 10 cranks you can smell fuel, I'm assuming that's just excess in the cylinder.

Either way, its horrid for everything in the car so I've tried to do so since the pressure gauge test. I was extremely reluctant thinking it was the pump, because the key characteristic to the problem is no power loss, or even performance loss once the car is on. Drives fine and can cruise 62 mph @ 2200 rpm like its meant go forever.

This led me to believe the check valve, which an inline valve would work but at 270k in the salt, and -40 to 110 Fahrenheit I've learned to leave rubber alone. And only one fuel pump was done before (somewhere in the 150-200k range) so it's on its way out either way.

[jimmy57]

I agree with fuel pump as the most likely cause. I have had a few of the P2 models in the 04-09 year range that had the intermittent start problem. Some would do it a few times and then go hundreds or thousands of miles and then have a repeat. I put fuel pressure gauge on and the pressure would drop away quickly when it was happening. WHen the fuel rail drains back to tank on the ones with dead end fuel systems it takes a lot of cranking and it will go dead a few times, depending on how much fuel drained. The only way to get the rail purged of air is through many many injector cycles or by cranking while someone holds open test port schrader valve.
The check valve balls are plastic now and all it takes is a flake to peel away and the problem starts. If the ball moves then you're good for a while. If the peeling puts striations all round then it will leak every time. The ones I found bad and replaced pump on had lots of fuel volume and would make great pressure once the vapor was purged. There can be other causes but the other causes will not give you proper current draw measured at pump or fuse EVERY time the key is cycled or engine cranked over. The fuel rail will be full of fuel and fuel pressure will hold for more than an hour when it is another cause.