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Engine misfire

This is a post to illustrate how tricky and elusive engine diagnosis can be.

I recently had a vehicle to repair that had a customer complaint of intermittent misfire. The owner stated that this miss was most noticeable at stop lights. The vehicle was a 2003 Ford Escape.

I first drove the car to verify the concern. This took a while and it was by chance that I pulled off the road to allow a following car to get around me when I first noticed the car shake a bit in the way they do when the engine has a miss. I drove around some more, but found the miss was very occasional. I returned to the shop to check for possible causes. Here is a list of what I did for diagnosis:

• Hook up the Ford IDS diagnostic computer and run the PCM self-test to check for codes. I had a P0301 and P0316. Those are misfire codes.
• Run the cylinder balance test. This did not show a problem right away, but eventually on road tests the #1 cylinder showed a drop in the graph indicating a miss.
• Run a fuel injector flow test, which resulted in a pass. All injectors flowed at about the same rate.
• I pulled up the intake plenum and removed the coil and spark plug. I replaced the plug and swapped the coil for one in the front that was easy to get to.
• I did a road test with the cylinder balance graph on and found that #1 still missed, on occasion, at a stop, briefly, then the miss cleared up. Hmmm.

I considered the possibilities; bad fuel, (but why only on one cylinder? Usually, bad fuel affects all cylinders), a sticking valve, (possible, but this problem, in the past, has only appeared in a hot engine coming to a stop from highway speeds. There, a valve stem, which is gummed up from deposits, sticks in the valve guide). I dismissed the sticking valve because of the conditions. A problem with the engine’s Powertrain Control Module? Perhaps the injector driver or the coil driver was cutting out on that cylinder when it got hot. I opened the wiring harness from the PCM to the fuel injectors and coils and looked for any chaffing or cracks etcetera. Everything looked okay.

One more diagnostic step, check the fuel. I had not done this because access to the fuel was difficult. The shop fuel pressure gauge set was old, leaked and didn’t fit this car well.

The minute I saw the appearance of the fuel in a clear container, I realized what was happening.

Caution! Do not put any poisonous substance in a drinking container. Make sure no one will mistakenly drink poison!

(I cut the top off this bottle, removed the label and then discarded the thing right away when I finished taking pictures). 

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There was water in the gasoline. Check out the pictures of gas with and without water. The gas with water contamination appears cloudy and the sample, when left to sit still, lets the water separate and go to the bottom of the container.

This is what was happening in the Escape! The water collected in the fuel rail which feeds the injectors. It just so happens that a slug of water would, when the vehicle was not moving and tipped a bit to the right as when near the curb, collect at the number one cylinder injector. Only that cylinder was affected. The miss only occurred briefly because the small amount of water would be used up and then good gas would replace the water and good performance would reappear. Voila!

I put two bottles of isopropyl alcohol additive in the gas tank, sent the customer on her way, and haven’t heard any more about it.

So, the lesson here is to follow the kiss rule, KISS = keep it simple, stupid.

I have another example of an engine miss caused by unusual circumstances. I will post that one soon.

walt