Help interpret fuel pressure test

[JMI]

Been having this ongoing problem with the 1989 535i stalling at idle. Have checked all the sensors/switches, ECT, CPS, TPS, and AFM. Replaced the ICV, distributor and rotor, and plugs.
Today I checked the O2 sensor which has less then 20,000 miles, it was OK.
I also finally got a fault code I could read (the CEL stays light now) it is #1222 which in my car means too rich/lean an idle.

So as for the fuel pressure test I did today. With the car idling, the pressure was 35.5 psi. Seems low as per Bentleys (43.5 psi, +/- .9 psi). Pulling the vacuum hose off the Fuel Pressure Regulator caused the pressure to rise (as it should per Bentleys) to about 45 psi. With engine running and slowly clamping down on the return from the FPR the pressure rise rapidly till it was off the gauge (0-60 psi gauge).

This appears to suggest a bad FPR? If it was the fuel pump the pressure shouldn’t jump as the return is clamped, right?

TIA

Jim

[BillionPa]

sounds right to me.....

when did you replace your fuel filter?

[JMI]

sounds right to me.....

when did you replace your fuel filter?

That was the very first thing I did when this problem first reared it's ugly head, about 6 weeks ago :p

[JMI]

Anyone else got an opinion?

[Jeff N.]

Anyone else got an opinion?

You can try running with the FPR vacuum line disconnected (plug with something) and see if it runs better and fixes the CEL. The FP should rise about 7 PSI with the line connected - getting you close to the typical 42PSI.

I have a hard mounted FP gauge in the car and notice that the FP isn't particularily accurate. It will range from high 30's to mid 40's on any given day. My FPR is pretty new...

Bill R. has comment as well that the FP on these cars somes to range somewhat.

Jeff

[Ross]

Does the stalling go away with the regulator disconnected?

[Bill R.]

connected its going to be in the range that yours is. Fuel pressure is checked statically with the engine off key on, thats when you get 43.5. With it idling and vacum being applied to the regulator it will read about what yours is doing. There is nothing wrong with your regulator.





Been having this ongoing problem with the 1989 535i stalling at idle. Have checked all the sensors/switches, ECT, CPS, TPS, and AFM. Replaced the ICV, distributor and rotor, and plugs.
Today I checked the O2 sensor which has less then 20,000 miles, it was OK.
I also finally got a fault code I could read (the CEL stays light now) it is #1222 which in my car means too rich/lean an idle.

So as for the fuel pressure test I did today. With the car idling, the pressure was 35.5 psi. Seems low as per Bentleys (43.5 psi, +/- .9 psi). Pulling the vacuum hose off the Fuel Pressure Regulator caused the pressure to rise (as it should per Bentleys) to about 45 psi. With engine running and slowly clamping down on the return from the FPR the pressure rise rapidly till it was off the gauge (0-60 psi gauge).

This appears to suggest a bad FPR? If it was the fuel pump the pressure shouldn’t jump as the return is clamped, right?

TIA

Jim

[BillionPa]

so the next step is the flow rate test the injectors?

[stu1]

Checked all the hoses? Air leaking in somewhere?

[JMI]

Thanks, guys

Jeff N - Ran the car for about half hour -10 miles - seems there was some improvment but not conclusive.

Bill R - I also did the pressure test statically - removed fuel pump relay and jumped from 30 to 87, key on - pressure never got over 36 psi. Be interested in what you think it could be

stu1 - will be replacing some hoses soon

Billionpa - will do a flow test when I can - still suspect a bad fuel pump

TIA

Jim

[Karl]

Fuel pressure sounds about right. The Idea of the vacuum line on the fuel pressure regulator is that the fuel pressure is referenced to the manifold pressure (vacuum). So at idle you should read lower fuel pressure.

I'd recommend you start by searching for vacuum leaks. Those will let unmetered air in, and definitely affect your idle. Remember that the whole crankcase runs at a vacuum, so something like a bad valve cover gasket will cause a vacuum leak. In my car. leaking rear main seal whistled at idle from air being sucked in, but the sound went away when I opened the throttle. Less vacuum didn't suck air through and blow the engine's whistle.

[Bill R.]

disconected but 36 statically... You must have low voltage then when your checking it statically to have that much difference, especially since when its running the injectors are using some of the fuel that the pump is providing, yet you still have 45psi.
The regulator must be working, based on your numbers, so i'd guess you got a low reading statically due to the battery voltage.




Thanks, guys

Jeff N - Ran the car for about half hour -10 miles - seems there was some improvment but not conclusive.

Bill R - I also did the pressure test statically - removed fuel pump relay and jumped from 30 to 87, key on - pressure never got over 36 psi. Be interested in what you think it could be

stu1 - will be replacing some hoses soon

Billionpa - will do a flow test when I can - still suspect a bad fuel pump

TIA

Jim

[JMI]

disconected but 36 statically... You must have low voltage then when your checking it statically to have that much difference, especially since when its running the injectors are using some of the fuel that the pump is providing, yet you still have 45psi.
The regulator must be working, based on your numbers, so i'd guess you got a low reading statically due to the battery voltage.

I redid the static fuel test. Did or read something wrong the first time. The stactic fuel pressure is 45 psi. Appears fuel system is OK.

Going to start throwing parts at the problem, again :p

Jim

[JMI]

The one sensor (http://www.bimmer.info/forum/showthread.php?t=25309) I did not check.