Hard Start Nightmare

A small issue on a F-150 snowballs into multiple problems

This should have been a straightforward diagnosis, but it ended up being a bit of a nightmare due to incomplete service information and the vehicle having multiple problems. When it comes to drivability and engine performance, rarely do I find more than one issue. I believe in this case it started out as a minor problem that snowballed because the original problem was not addressed by the customer until it affected the way the vehicle ran.

This should have been a straightforward diagnosis, but it ended up being a bit of a nightmare due to incomplete service information and the vehicle having multiple problems.

– Mark Lemay

Extended crank issue

The vehicle in question is a 2015 Ford F-150 pickup with a 5.0L engine. The complaint is an extended crank which we confirmed. The vehicle cranks for about 10 seconds before it fires up and then it runs rough until it goes into closed loop.

I started with a code scan and a look at the data. All four O2 sensors were setting codes for running too rich and the Fuel Alcohol content was set at 69%. (Fig 1).

This would account for the extended crank and the rough running because it the vehicle thought the fuel was 69% alcohol it would over fuel if the tank was full of gasoline with little or no alcohol in it. Since e85 is not available in our area we usually see Fuel Alcohol content around 8 or 9%.

I have run across this on many vehicles and usually resetting the Alcohol content takes care of it. There is a procedure in the manual that describes how to do the reset on this Ford. The procedure is simple, clear the computer’s KAM (keep alive memory) with a scan tool and drive the vehicle until the vehicle learns the new fuel content.

Updates unsuccessful

About 20 minutes of driving according to the procedure. When the data was examined the Flex Fuel Learned PID had changed from learned to not learned but repeated attempts to get the Flex Fuel content to update were unsuccessful. There is a trouble tree procedure if the new Fuel content cannot be learned. This involves some testing of the wiring but if no faults are found the procedure calls for a new PCM.

A new PCM was ordered and installed and the vehicle returned to normal operation, but it would not learn the new Fuel content. The Flex Fuel Learned would not switch over to learned no matter what was tried. (See Fig 2)

At this point it became obvious that there was something else going on here. I did some digging to determine how the vehicle actually calculates the alcohol content of the fuel. Basically, on this vehicle, the PCM waits for a refuelling event (minimum 20% fuel added to the tank) then it watches the O2 sensors after a predetermined amount of time. From this it can estimate the alcohol content. The service manual procedure to reset the alcohol content did not mention anything about putting gas in the vehicle. Once it was determined how the vehicle calculates alcohol content, the O2 sensors were tested and 2 of the 4 failed.

Coated sensors

When the sensors were pulled, they were coated with black soot to the point where you could not see the vent holes. All four O2 sensors were replaced at this point. The vehicle’s fuel tank was filled, and the vehicle was driven again. Within about 15 minutes, the Flex Fuel Learned PID switched over to learned and the vehicle ran and started normally.

In summarizing this nightmare, the vehicle did not need a replacement PCM. The procedure in the manual did not include the information about the vehicle having to see a fuelling event to update the Flex Fuel reading. I think that this started as a bad O2 sensor which over time skewed the Flex Fuel reading. This caused the vehicle to run extremely rich and contaminated the remaining O2 sensors. If the original O2 sensor problem had been addressed, then none of these other issues would have occurred. Lesson learned.