Would appreciate insight on my cold start issue

[RenaissanceMan]

Originally Posted by andrewwynn

My e53 was 50psi. You're m54 engine, correct?

Yep, m54. X5 3.0i.

[andrewwynn]

So I'm concerned that you got 40psi. Afaik it's supposed to be 50 i don't know how it started with 40psi. I think the type of injector just uses math and pulse timing with 50psi assumed.

Any chance your gauge isn't reading correctly?

I'm really not aware of cases where FPR will fail to a wildly different value and still regulate but you said both steady output and holds over time so it's not the o-ring.

I'm wondering if the way the ignition switch is wired, they use a separate parallel set of contacts for determining when to send power to the fuel pump.

Relay is far less likely to intermittent fail than the pump. Did you say you replaced the pump?

The FPR will hide a failing pump for a very very long time (months if not a year or more) so it's not uncommon for an old pump to give you the exact symptoms you describe.

If you are running E10 gas the life expectancy is 5000 hours. Multiply your average speed (typically about 20-30) by 5000. Eg 27*5000=135000

Wife's car had average speed of 27 and the pump failed at 133,000 133000/27=4925.926 estimated hours!

If your pump is over 5000 hours it's overdue for replacement.

[RenaissanceMan]

Originally Posted by andrewwynn

So I'm concerned that you got 40psi. Afaik it's supposed to be 50 i don't know how it started with 40psi. I think the type of injector just uses math and pulse timing with 50psi assumed.

Any chance your gauge isn't reading correctly?

I'm really not aware of cases where FPR will fail to a wildly different value and still regulate but you said both steady output and holds over time so it's not the o-ring.

I'm wondering if the way the ignition switch is wired, they use a separate parallel set of contacts for determining when to send power to the fuel pump.

Relay is far less likely to intermittent fail than the pump. Did you say you replaced the pump?

The FPR will hide a failing pump for a very very long time (months if not a year or more) so it's not uncommon for an old pump to give you the exact symptoms you describe.

If you are running E10 gas the life expectancy is 5000 hours. Multiply your average speed (typically about 20-30) by 5000. Eg 27*5000=135000

Wife's car had average speed of 27 and the pump failed at 133,000 133000/27=4925.926 estimated hours!

If your pump is over 5000 hours it's overdue for replacement.

According to my Bentley manual, fuel pressure should be 50psi with the car not running, and between 36 and 46 psi while running and idling. So that’s why I’m assuming my readings are normal. Fuel pump has never been replaced fwiw.


Sent from my iPhone using Tapatalk

[80stech]

No that's exactly backwards, it's 50 PSI with the fuel pump running (doesn't matter if the engine is running or not) and 46 ish when the fuel pump stops. If you would have left the relay in place when you did your testing you could be more confident about your diagnosis.

[RenaissanceMan]

Originally Posted by 80stech

No that's exactly backwards, it's 50 PSI with the fuel pump running (doesn't matter if the engine is running or not) and 46 ish when the fuel pump stops. If you would have left the relay in place when you did your testing you could me confidant about your diagnosis.

Thank you for the clarification. So after testing again, here is what I’m seeing:

With car off and fuel pump power jumpered at the relay plug: 50psi

With pressure tester still connected and with relay replaced, I then start the car. Pressure tester still reads 50psi.

I then shut the car off. Pressure very very slowly will drop after about 5 min it’s about 47-48psi.


Sent from my iPhone using Tapatalk

[andrewwynn]

I totally missed the off and running running.

If it is fifty running and forty and holds off that's close to factory though i think mine was more like Forty five initially off.

It should hold ≈ half overnight i didn't notice if you said how long.

Notwithstanding, symptoms due suggest aging pump if it's old. Divide odometer by five thousand in miles and compare to your average speed

[80stech]

There should be a quick initial drop (to the 40-46) as soon as the pump stops so you probably have an issue with your gauge connection. That is often an issue.

It would be good to get the gauge reading properly and then leave it hooked on until you get a no-start so you can have a better idea of what's going on but if you are having good success with the jumper then there is a good chance that the problem is the relay so you just try that since you have it coming anyway.

[andrewwynn]

Could there be some other problem with the check valve or FPR that's giving the condition of not immediate drop? Usually the pressure will drop five psi as soon as the pump is off.

[80stech]

No, the drop is to the regulator setting without the back pressure of the syphon jet which drains almost instantly. The drop is happening, it's just that the gauge is not reacting to it because of the poor connection, likely the schrader valve is not getting pressed far enough. That happens a lot more than you would think and has been talked about more than once even on this forum.

[andrewwynn]

Schrader valve holding fluid in the hose makes sense!