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klatoo

Engine stutter / vibration

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I'm not sure the <2% fuel is hybrid specific also. The Atkinson cycle ICE always blows gasoline laden charge back out the intake valve into the intake manifold. Offhand I can't think of how this might get into the oil but there are a lot of hoses and relays and valves involved. Have you checked for any stored DTCs? Ford systems have long monitored misses, uneven-running and even somewhat lowered power from an individual cylinder.

Ask Blackstone if they have comparison fuel content data from another 2013+ FFH.

Edited by lolder

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I suspected that might be true about the gas but the car should not stutter at all. I don't think how often the car stops and starts is it. Here's how it works:

1 The 60+ hp starter motor spins the ICE up to about 1000 rpm in about a 1/4 second when computer calls for the ICE.

2 The spark is turned on

3 Throttle is opened, fuel injection is ramped up as the starter energy and traction motor energy is ramped down.

When the computer calls for the ICE to stop:

4 The fuel injection is ramped down as the traction motor energy is ramped up

5 When the injectors are off, the throttle is kept open for a brief period with the ignition still on and the starter motor keeps the ICE at about 1000 rpm very briefly to purge the intake manifold of air/fuel charge. The throttle closes and the starter motor then stops and the ICE rapidly goes to 0 rpm. Below 1000 rpm there is never any fuel, ignition or much air in the cylinders as the throttle is closed.

 

This is all for emissions and smooth running. The ICE never has combustion below about 1000 rpm for smoothness. When the ICE is started again, the intake manifold is clear and the very first amount of fuel injected produces low emissions combustion. There is almost never any fuel that is not burned stoichiometrically ( chemically perfectly ) during running, starting and stopping.

 

You never hear the ICE "cranking" or going through compression strokes without firing like you do in a non-hybrid.

 

The big difference is the Atkinson ICE closes the intake valve latter in the compression stroke and a lot of fuel/air charge is blown back into the intake manifold. It tends to get the throttle body dirtier quicker. They can be cleaned or replaced.

Edited by lolder

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In these hybrids, the ICEs are always run at almost wide open throttle and the lowest RPM that will yield the desired hp. The spark is advanced as far as possible. This is just shy of the "bucking" that you got in manual transmission cars when you were in too high a gear with too much throttle. It runs that way all of the time. That means the pressure in the cylinders during combustion is always at the same high level whether the rpm is low or high. Higher power is achieved by higher rpm only. Most cars run at half throttle or less so pressures are less unless you floor it. Consistently high pressures could produce more piston ring blow-by which could put more fuel in the crankcase. Since the ICE runs less, there's less of an opportunity for high engine temperatures to evaporate the gas and have it sucked into the intake via the crankcase PCV valve ( if there is one ).

This is my educated guess.

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