After diagnosing that the head gasket needed to be replaced in my 2007 VW Passat, I went through the process of pulling off the intake, head, exhaust, turbo and everything else that needed to be removed from the top end.

With it all torn apart, I decided that it was a good time to replace any and all of the parts like water pump, idler pulleys, belts, injectors and so on…. The whole process was very involved, and I took my time getting through each engine system so that I did not miss anything.

Once I had it all put back together the moment of truth was upon me. I turned the key. The car cranked over and fired up for a moment before I heard a loud bang! Terrified because it sounded expensive, I immediately shut the car off, jumped out and found oil gushing from the engine! It turns out that I missed one bolt to torque on the oil cooler bolted to the front of the engine! Very disappointing to say the least.

The bolt was in a very tight space between the radiator fans and intake charge pipe which made it extremely difficult to get to, so I decided to go a step beyond and remove the entire front end from headlight to headlight!

Although it was very frustrating, it did allow me to clean up the oil that splattered all over the front of the engine, and to get a direct view and access to the loose bolt! Eight hours later, I was able to fire the car up, and it ran great after that. Lesson learned, preparing a list of steps would have helped prevent oversights.

Mark in Canada

Air becomes denser and pressure decreases inside tires when the weather turns cold. The solution is to add more air to the tires until the pressure is back up to where it should be. Cold weather also makes the gasoline or diesel in the fuel tank denser, but the fuel pump should not necessarily automatically pump more fuel to maintain warm-weather fuel pressure. The quantity of fuel is important. When fuel becomes denser, the engine needs a smaller volume of it. The engine computer uses signals from temperature and/or pressure sensors to estimate how dense the fuel is and calculate the correct corresponding fuel pump output to help maintain the ideal air/fuel ratio entering the engine (14.7 air to 1 part fuel).

Older fuel injected engines have a fuel line to return any unneeded fuel back to the fuel tank. Newer engines can precisely turn the fuel pump and fuel injectors on/off (duty cycle) so a fuel return line is not needed. This precise metering of fuel falls apart if a sensor (or other fuel system component) breaks. With an incorrect air/fuel ratio, the engine will stumble, have a rough idle, gobble fuel, generate black exhaust and/or set computer trouble codes.

GM Pressure Sensor on Fuel Rail (top left), Ford Fuel Injection Pressure & Temperature Sensor (lower left), Nissan Fuel Temperature Sensor on Fuel Pump Assembly (right)

Fuel injection pressure sensors are on just about every modern engine and are often relatively easy to find and replace on the fuel rail (gasoline and diesel) or fuel pump (diesel). First check what the sensor looks like in the RockAuto.com catalog (found under "Fuel & Air") to make it easier to identify the part on the motor. Consult the vehicle's repair manual (found under "Literature") for specific instructions on how to safely depressurize the system and replace the sensor.

A fuel temperature sensor related trouble code can be more difficult to diagnose and fix because the fuel temperature sensor might be part of the fuel pump assembly in the fuel tank (Nissan), integrated into the fuel injection pressure sensor on the fuel rail (Ford) or be plumbed in somewhere else in the system. The engine may not actually have a dedicated fuel temperature sensor but instead use signals from other temperature sensors (intake charge, coolant...) to estimate fuel temperature. The vehicle's repair manual can help determine if and how fuel temperature is directly measured or estimated. Other computer trouble codes might be related to a fuel temperature related trouble code. For example, if there are both fuel pump and fuel temperature trouble codes, then maybe the fuel pump and fuel temperature sensor are part of the same assembly and/or share electrical connectors/wiring harness.

Tom Taylor,
RockAuto.com

To read more of Tom's articles, click this link and choose from story titles on the Newsletter Archives page.