• Multiple DTCs indicating multiple misfires in various cylinders, and a P0174 indicating a lean condition in bank 2, which I believe is cylinders 2, 4 and 6 on this inline 6 engine.
•Fuel pressure for this make and model should be 50 psi.
•Measuring fuel pressure at the rail, system intact, KOEO - 30psi, pressure holds after pump stops. Goes no higher with multiple keyings. Same reading with KOER.
•Measuring fuel pressure before the rail with rail disconnected, terminating at the gauge - 50psi, pressure does not hold after pump stops. Goes quickly to zero.
•Fuel pressure regulator was in the loop for both measurements above.
•Measuring fuel pressure at the fuel pump, terminating at the gauge - 90 PSI.
This is telling me that the fuel pump is strong, but I cannot understand why the system holds pressure when the system is intact and measuring at the Schrader valve on the fuel rail, and it will not hold pressure with the fuel rail disconnected and the system terminates at the gauge. I also do not understand why the system only pumps to 30psi when system is intact, and pumps to spec at 50psi when measuring before the fuel rail, terminating at the gauge.
If an injector were leaking I might expect the intact system not to hold pressure, unless the injector(s) stop leaking at 30psi. Anyway, I plan to remove the fuel rail tomorrow to check for any leakage with KOEO.
Thanks, that’s pretty much what I did, except I did not use the designated BMW tools, but the correct adapters from a Fuel Pressure Tester kit that comes with just about every adapter known to man.
The 3.5 bar specification in the online BMW manual is equal to 50.7632psi, which I rounded down to an even 50 in my original post, so I seem to be on the right track. I just don’t understand the behavior I detailed in my OP when taking the measurement at different places in the circuit.
If a fuel injector were leaking bad enough to reduce the pressure to 30 psi, you would see fuel spraying on the engine or fuel flooding a cylinder causing a misfire and lot of smoke.
30 psi is too low, there needs to be 50 psi at the fuel rail, at idle and while accelerating. Does the fuel pressure fall below 30 psi while accelerating?
My friend took this car to Siegfried at the local German auto repair shop. Siegfried changed his spark plugs, charged him $600 and sent him out the door, problem unsolved. I would imagine that Siegried had access to the software you described. I am relying on a fuel pressure gauge to help diagnose the problem. The results that I got are detailed in my original post. While I appreciate your attempt to steer me toward software that might aid in diagnosis, I presented my findings using the fuel pressure tester. I was hoping to get some feedback on those findings.
I have not attempted to rig the FPT to be readable with the car being driven. I did try revving the engine while in gear and brakes strongly applied. The pressure did not change.
I don’t know how he made it home with fuel pressure that low, why didn’t he return to the shop after driving a few blocks?
Maybe your fuel pressure gauge is inaccurate, if there is only 30 psi, the vehicle would be barely drivable.
I would like to review the fuel trim freeze frame data for both banks. Is the lean condition common to both banks?
Observe live data, does the lean condition occur at a specific engine speed?
Only P0174 shows, no P0171, so that particular problem might actually be the upstream O2 sensor for bank 2. However, the more immediate problem is P0300, P1351, P1343, P1353, P1345, P1349, On looking at the photos I took of the last OBDII reading I see a P0172, which is new.
I plan to test the fuel pressure again tomorrow, but instead of using the Shrader valve I will break the quick-connect fitting under the hood between the metal fitting from the FPR and the rubber fuel line going to the fuel rail. I would not be surprised if I get a steady 50psi. I suspect that the reading at the Schrader valve might be problematic for some as yet unknown reason.I will post the results tomorrow.
Thanks, I have some MAF sensor cleaner. I can clean it tomorrow, although I am sure that was one of the first things I did. Checking the FP tomorrow as I detailed in my earlier reply to you should dispel any doubt about the true pressure.
Having gotten problematic readings at the Schrader valve on the fuel raiI on this BMW, this morning I measured fuel pressure by teeing into a connection just before the fuel rail. With engine running, fuel pressure read just a hair below 50psi at idle, and very steady. The system held pressure after engine turned off. I do not know what the problem is at the Schrader valve, why it reads only 30psi. I reconfirmed that reading after reading 50psi by teeing into the connection just before the fuel rail. At any rate I am putting aside problems in the fuel delivery and looking into the air side.
I did a smoke test to look for vacuum leaks. I confirmed that smoke was entering the system under 2psi of pressure by removing a plug at the rear left of the intake manifold and saw smoke pouring out. Other than that there was no smoke to be seen on top under the hood, or underneath at the fuel pressure regulator which has a vacuum hose going to it.
At this point I removed the MAF sensor and cleaned it with MAF sensor cleaner. Nothing changed. I will look up how to test the MAF sensor and consider advising my friend to buy a new one if I see anything amiss.
I took pictures of the dynamic readings of the OBDII scantool (cheap basic DTC reader) with engine running. They obviously indicate something is wrong. Will upload soon.
One other measurement from today: vacuum at idle measured 14 PSI. In spite of the fact that I did not see any smoke emanating anywhere during the smoke test, it seems to me that 14 PSI is too low for healthy vacuum at idle. Other than vacuum leaks I wonder what could cause such a low vacuum reading at idle.
That was going to be my first test, but the owner told me that Siegfried at the German auto repair shop did a compression test and found cylinder six to be about 20 pounds lower than the other five, which showed healthy compression. I figured that was not too bad, and proceeded on to test the fuel pressure. Siegfried changed the plugs at that time and I later changed the coils at the owner’s request.
Here are some photos of the datastream after all the fuel pressure measurements were taken, and the MAF sensor was cleaned. Just five or 10 minutes later the datastream shows different readings for FUELSYS1 and FUELSYS2. That photo is included.
Thanks, it certainly won’t take long to do a compression test. In searching for clues to the slew of DTCs that pop up, along with the rough idle, my attention has been drawn to the DISA valve, which I will remove and examine tomorrow.
