A common reason cars are towed into our auto repair shop is to diagnose an engine that stalls. We start diagnosis by scanning the engine computer. In this case the customer’s car was a 2002 X5 3.0i. We didn’t find any fault codes that would lead us to the cause of the engine stalling. Then we started diagnosing the vehicle. Since it was an older BMW with high miles we wanted to make sure the engine was mechanically sound so we started by putting a socket on the crank pulley and turning the engine by hand to make sure it isn’t binding or has some serious mechanical issues. The engine turned fine so far it seems mechanically sound.
What an engine needs to run
An engine needs three things to run. It needs spark, fuel, and air. So one of those systems was causing the engine stalling issue. The first thing we checked was the air filter and air intake system for obstructions or other issues. All the plastic ducting was clear and the engine was getting a proper reading from the air meter when the engine was temporarily run without stalling. Then we used a spark tester to confirm that the coils were firing properly and there weren’t any frayed wires in the harness that powered the ignition coils. The battery was tested as well and was running great. Finally we moved on to test the fuel system. This model BMW thankfully has a fuel pressure testing port on the fuel rail. We hooked it right up and immediately noticed low fuel pressure. For port injections systems we expect to see about 50 to 60 pounds per square inch of fuel pressure. Also when the engine stalled out the fuel pressure dropped to zero. So we knew that we had to find out what was wrong with the fuel pump. Was it a broken wire? Was the fuel pump bad? Was it a severely clogged fuel filter?
Accessing a fuel pump
Depending on the manufacturer accessing a fuel pump can be a breeze or it can be labor intensive. Some manufacturers install an easy access panel under the back seats or in the trunk. Other manufacturers require you to lower the exhaust and part of the rear suspension to access the fuel pump by dropping the whole gas tank. This can make the repair quite expensive when you are paying a shop as it is labor intensive. Thankfully this BMW X5 has an access panel under the rear seat. We accessed the fuel pump and tested the wiring to make sure it is receiving the proper voltage and the wiring is in good condition. Once the wiring was confirmed to be good we moved on to test the actual fuel pump. The fuel pump was likely a factory original due to the markings on it. Then we confirmed that the fuel pump was barely running and would suddenly stop when voltage was increased. We the repaired the car by installing a new Original Equipment Manufacturer fuel pump assembly and whenever you change the fuel pump you must also clean out the gas tank of any debris and change out the fuel filter.
This blog post goes over a little bit of the process that is used to properly diagnose a problem and not simply change parts at expense of our customers. This shows a little bit of the process we go through to fix any problem the right way the first time. It shows how we have built up our reputation and why our customers keep coming back to us for their automotive repairs. If you have any questions or would like to set an appointment please feel free to contact us at Tolima’s Auto Center.