2016 fiesta SE stalling and rough idling

[ShelbySE]

I have a 2016 Ford Fiesta SE 117k miles, that I’ve been having minor issues with over the past year or so. This morning I was able to drive to the gas station on my way to school (got a coffee, no gas, so not a purge valve issues I don’t think, switched that at 70-80k miles), when I got back in my car it would not start. Took me 4 separate times to get it to turn over and start. I took it straight home and called my mechanic to drop off later today hopefully. Once I was home I was able to start it no issue, and no dash lights came on.

I’m just really stumped as to what it could possibly be. Over the past year I have replaced my spark plugs, ignition coil, battery, did a coolant flush, regular oil changes with no issues. Last week I replaced my fuel injectors as I got a misfire code for the 3rd cylinder. When he replaced the fuel injectors, my mechanic told me wires looked tight and in place. I know I need to switch out my tension belt, I’m just waiting for parts to be delivered. After replacing the fuel injectors, I’m still getting the rough idling (almost the same type of idling with the purge valve issues but not as noticeable, it’s very slight). No weird or concerning smells, fluids etc. Only sound I have notice is the whining of the tension belt the past 3 days.

just wondering if anyone has any advice or went through something similar. After telling my mechanic that it was still rough idling after injector switch, he said he was a little stumped and would need to look into it more. The car is spitting no codes and no pending codes as of Monday, the pending might have changed by now, not sure.

 

[Handy Andy]

I hope he kept the old injectors - for the newer ones might have a different pin size making the issue more noticeable - the mis-fire can occur due to weak pin connections on those injectors. Might want to swap in those older ones to see if that mis-fire is reduced, if that clears up the mis-fire - that takes care of that. Else the Fuel rail could have some dirt or varnish in it. To help, look or search for "Connector Memory" - it may help you understand that technology moves on, but the connectors used are still stuck in time and may not make the best connections on the next set of pins.

However, the fill up condition can make for an expensive repair...Why? That d*mn fuel filler design is made to be convenient as a "no cap" but the seal it forms around the nozzle of some Gas station pump handles - due to vapor capture - are part of this problem.

The filler neck Seal can form a Positive pressure from the gas pump pushing fuel into the tank - which then might make the wet fuel flow into the evap system and it's valve - potentially causing a condition similar to a vapor lock that used to happen on older carbureted cars, only without heat, just the pressure. That pressure can make the fuel pump feel it's in a pressurized system so it won't start to pump because it thinks there's enough pressure to work - only the rest of the system doesn't see any fuel so it starves and won't start - it stalls. All because the evap valve is stuck shut and the fuel can't vent to relieve the pressure.

So the next time you have to fill - is to take a minute or two to let that foam that the system forms in the filling action, settle down and let the vapors vent thru the nozzle to neck seal - the longer you wait to yank out the nozzle the better these results are in getting the pressures balanced - slow down that yank action - the neck has two flaps to provide a secondary spill seal that if wet can make matters worse until the seal dries out.

Might have to take time to use that nozzle to let that pressure out due to diameter of the nozzle and your filler neck diameter - can make the vapor seal the pump will try to capture the vapors from - too tight to escape or let in air to balance the pressures inside the tank. Just stick the nozzle in to get past those two flaps and slowly back it out to let that built up pressure equalize to outside atmospheric pressure.

If you've ever seen a gas can half-filled left out on a hot-day and then brought to a cooler place - the can itself can collapse from the change in vapor pressure and the seal it has is air-tight so it can't balance that pressure to the outside atmospheric (Barometric) pressure so it deforms and looks crushed.

​

So when you drive this tank to empty - keep an eye on your gas gauge for you're going to have to learn how the issues of volume and pressure and density work to form the pressures that affect the level of fuel that gas gauge is trying to show you.

So if you can - don't fill up all the way for the next several cycles to help the EVAP system dry out and re-learn pressures it got choked on from earlier. Put in a little less.

Leave a gap for expansion of air and it's vapors it will have from the tank for next time so it doesn't repeat this - it can get expensive to repair.