Used 2014 Ford Fiesta with ecoboost--should I be using 89 octane instead of 87?

Question

Manual says 87 recommended, but specifically for the ecoboost version, which I have, it adds that 89 "might improve performance."

I've defaulted to 87. However an issue has arisen with the car not starting--it cranks forever, but never starts. This is intermitant. Once it finally does start it starts reliably until we leave the car off for more than 12 hours or so.

A mechanic, based on a code he got, says he thinks the issue is I've been using the wrong grade of fuel and it has messedd with my evaporator or my "turbo". (I admit I don't really know what that means in this context. He pointed to a part of the engine towards the front with three slots in it.)

On this model with this engine, do you use higher grade gas? Does it sound plausible that switching will be necessary to keep this engine-start problem from occurring?

Answer 1

This does not sound like an issue with using 87 octane fuel. The ECU can deal with the lower octane by pulling timing. Yes, 89 will give better performance, but really, if you don't need the performance, it isn't going to hurt anything.

It sounds to me like your fuel pump is losing pressure over time. If the fuel pressure drops too much while its sitting, it can make it very hard to start.

If you have the availability of a fuel pressure gauge, you could test the pressure by attaching it to the fuel rail. If the fuel pressure drops over time by any significance, this could be your issue. The pressure should stay up at full for quite some time. It may experience a small drop, say 5psi or so, but really shouldn't be much more than that.

If you don't have access to a fuel pressure gauge, some car will run the fuel pump at key on. If you were to cycle the key from on to off several time, this will build residual fuel pressure back into the system. Once you've done this several times, you could try starting it. If it starts easier after this, it's most likely your issue.

In either case, a new fuel pump may be in order.