Intermittent stalling with a no start condition
We have here a special case of the Mini Flu. This vehicle has been in our shop for the last 6 or so years on and off. Very well serviced.
Recently the customer has brought to our attention that the vehicle occasionally has a lack of power, sometimes stalls and restarts, and sometimes just will not start at all.
Our technician road tested the vehicle with the scan tool attached and it ran fine for several miles with no issues. Suddenly the vehicle stalled completely and the tech noted that the high pressure fuel pump was reading around 80psi. Far lower than the ~1500+ psi that the high pressure pump generates. Being that the high pressure fuel pump is known to fail and the low pressure feed pump also fails often, the technician was sure to watch the low pressure and high pressure scan data.
The technician noted that the low pressure fuel was ~74.5 psi while the high pressure pump was reading the ~80 psi pressure. So, with this information we were capable of sending the vehicle to the dealer to have the high pressure fuel pump swapped out for free under their service campaign for this particular vehicle.
All fine and dandy. The vehicle is towed to the dealer which is less than 5 miles from our shop, and the customer notified me that they had no issue with having the high pressure fuel pump replaced. The dealer tested the high pressure pump and it tested bad. They swapped it out free of charge.
Now comes the fun part.
The customer leaves the Mini dealer and no less than 10 miles away, the vehicle stalls out again. The customer calls me and asks for advice, and also notified me that the Mini dealer is sending their Service Director out to check on the vehicle and will call me once he arrived. Once the Mini Director shows up, he pulls off a panel on the passenger footwell and reveals the JBE. He gives it a good slap and the vehicle starts and drives.
Now I personally give the vehicle a good look over and am attempting to now diagnose the vehicle. I drive the vehicle into the shop and let it idle for about 10 minutes and the vehicle begins to misfire terribly and is certainly choking. Looking at the scan tool data reveals that the high pressure fuel is dipping very low. Notably, the low pressure is reading at 74.5. That seems oddly familiar. Looking at the tech notes on the vehicle, the previous fuel pressure was "~74.5". I graph out the low pressure fuel data and note that the pressure is not moving at all. low pressure fuel is 74.5 precisely for the duration of testing. No amount of turning the car off and on, stepping on the gas, or any other trick to get the pressure to fluctuate would cause that data to move at all.
Checking the power to the pump and I note that there is no power.
Using the "trick" that the dealer used to start the vehicle, I attempted to slap the JBE. And lemme tell ya, I was slappin'. But no results. No power to the pump. Vehicle is running, however it is choking terribly. I supply power to the pump and Viola, the vehicle runs fine.
Turns out, if you run a high pressure fuel pump without fuel, it goes bad. Who woulda thought that both the JBE and the HPFP failed at the same time?
Thank you Mini, for integrating the fuel pump relay onto the circuit board of the fuse box. That'll never go bad right? Obviously your service campaign for the HPFP may be caused by your own faulty electrical design. Also, thank you "low pressure fuel pump sensor" for giving out false pressure data. (a keen eye would have caught a flatline, but we're all human)
I'll save the Service Director's words to the customer about us for another day. Thankfully we are the ones with the customer's trust.
Nice job Bill. This was my response on another forum to a tech who is having the same issue on a Buick that the hpfp has already been replaced on as well. "If so then you need to remove the low pressure feed line at the high pressure pump and check for pressure from the in tank pump. DO NOT T in the fuel gauge because a high pressure pump can actually suck fuel from the tank and make you think…
I've seen scan data show (74.5 PSI) substituted data when the ECM was getting no reading or a false reading. It's important to understand and verify scan data when ever trouble shooting.
Couldn't you just check in-tank pressure KOEO? The HPFP wouldn't be operating then.
Well Done Bill. Thanks for sharing, there's a reason that you client trusts you and not the dealer.
Hi bill, I believe both your tech and the mini tech misdiagnosed the vehicle. I do agree the hpfp is common and also the JBE is also common for the fuel pump relay going bad. I see both all the time. What I believe the issue was is both techs relied on scan data of the pressure sensor and wasn’t confirmed by simply hooking up a gauge to verify. I see these all the time and the first thing I do…