Fuel Pressure

[callen]

loosing residual fuel pressure over night in 94 530 so have to crank a while before it starts. Sooo either check valve in Pump, pressure regualator or leaking injectors......best way to determine which one.
Don't currently have a fuel pressure guage...might though buy one.

Callen 94 530i 91 535i 89 735il

[632 Regal]

you have an electric fuel pump, should pump up almost instantly. You probably have another problem like vacuum leak or need to change the plugs.

[Martin in Bellevue]

There is a retrofit in line check valve to be placed between the pump(tank) & filter. The check valve in the pump assembly wears & allows the line to bleed down overnight.

I don't have the part number handy, but Pat@BMA knows the item. It is cheap enough to try first.

[Bill R.]

http://www.bimmernut.com/%7Ebillr/images/bmwfuelpumpcheckvalve.jpg
There is a retrofit in line check valve to be placed between the pump(tank) & filter. The check valve in the pump assembly wears & allows the line to bleed down overnight.

I don't have the part number handy, but Pat@BMA knows the item. It is cheap enough to try first.

[JonE]

Does anyone know how long of a "crank" starts to become a concern? Are we talking more than a couple seconds, ten seconds? or what? Both of my BMW's take a couple seconds or so to fire up, cold.

[Bill R.]

had it you'd know it... its more than a couple of seconds, more like between 7 and 10 seconds...






Does anyone know how long of a "crank" starts to become a concern? Are we talking more than a couple seconds, ten seconds? or what? Both of my BMW's take a couple seconds or so to fire up, cold.

[Bill R.]

occur because fuel would boil in the fuel line between the gas tank and the engine because of the low pressure of the fuel and the heat absorbed by the line from the exhaust and other sources. One of the reasons that the fuel pump was placed in the gas tank on most injected cars is that this way the entire fuel line from the tank to the engine is under pressure , typically 35 to 45 pounds. By raising the pressure in the lines it raised the boiling point of the gasoline quite a bit, helping to prevent vapor lock from occuring in the fuel line. The check valves job is to ensure that the fuel lines always have fuel under pressure right up to the injectors. If you have a bad check valve then the pressure will drain back to the fuel tank and the fuel in the lines will mostly likely boil at some point close to the engine causing a vapor lock condition, which requires more cranking of the engine to get fuel to the injectors to overcome this. So the fuel pump was actually moved to the tank for a good reason.






QUOTE=Bill R.]had it you'd know it... its more than a couple of seconds, more like between 7 and 10 seconds...[/QUOTE]

[JonE]

So Callen, is this a cold start problem only? Either way, it sounds as though checking that fuel pressure might be worthwhile, and, like Jeff said plugs and vacuum leaks.

[Bill R.]

more noticable on hot start, but leaking injectors or a bad fuel pressure regulator will definitely affect cold start too.. Knowing Callen, i'm fairly certain that the plugs have been changed and typically a vacum leak wouldn't affect cold start much. The temp sensors and the engine computer determine how much fuel to inject on the initial cranking when cold, if it had a vacum leak it might run poorly immediately after starting but when starting I don't think its taken into acount on a cold start.








So Callen, is this a cold start problem only? Either way, it sounds as though checking that fuel pressure might be worthwhile, and, like Jeff said plugs and vacuum leaks.

[Bill R.]

more noticable on hot start, but leaking injectors or a bad fuel pressure regulator will definitely affect cold start too.. Knowing Callen, i'm fairly certain that the plugs have been changed and typically a vacum leak wouldn't affect cold start much. The temp sensors and the engine computer determine how much fuel to inject on the initial cranking when cold, if it had a vacum leak it might run poorly immediately after starting but when starting I don't think its taken into acount on a cold start.

[callen]

Thanks Bill...had a tear well up......

it is only on cold start up....in the morning especially when it's cooler outside it will take 10 seconds of cranking before she fires up...when hot not a problem. Soooo she's loosing pressure slowly. When it does crank doesn't spit and sputter so kinda figured the injectors probably aren't leaking. Had to buy a new pump...really like the inline valve...will check into that.

Callen

[callen]

Went by Dealer today to pick up valve...less than $3.00 dollars....wow. What are the plastic caps for?

Thanks

Callen

[JonE]

Aren't they to cover the nuts/bolts? Just thought I might've heard that...

[Bill R.]

tank, I guess they don't want any sharp edges since your adding new fuel lines to that area...






Went by Dealer today to pick up valve...less than $3.00 dollars....wow. What are the plastic caps for?

Thanks

Callen

[DaCan23]

$3 stealer part? Let us know if it works, might be my fix too...

[callen]

will do....

[callen]

Cured the Problem!!!

FYI...94 530 150K miles....slowly over last couple years as the weather got cold (relative, Houston) it would take a while before she fired. Once warm no problem. Late this summer it took a while to crank regardless if she was warmed up or outside temp. It got really bad last month so ordered valve through BMW...installed this past weekend and she now cranks right up. All the time. Installation was pretty simple.....did need about 3" of additional fuel line between the valve and Fuel filter. Idle seemed to improve.

Callen