Rattling when accelerating only

SHERADIN22

MEMBER
2016 FORD FOCUS
4 CYL
2WD
AUTOMATIC
67,000 MILES

Hear rattling noise (like rock shaking around) from engine area when accelerating. Noise goes away once I hit third gear, am up to speed, or just idling. Worst when trying to go up a hill. Also lose power (like something isn’t catching or fuel isn’t pushing through) for a few seconds when in first and trying to accelerate uphill. This part happens only when going uphill and only when starting out very occasionally. Car runs and idles fine otherwise. Am I looking at a costly repair?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

This is potentially a large issue. However, if I am correct this sounds like detonation or spark knock.

Basically this is igniting air/fuel at the wrong time. Normally this is caused by poor fuel quality.

There are some other causes but let's start with the easiest things first.

https://www.2carpros.com/articles/engine-has-low-power-output

Here is a video that gives a pretty good overview of this issue:

https://youtu.be/UfqXhnr2Ho4

I want you to run your fuel tank almost empty and then put in 10 gallons of the highest octane fuel you can find from a reputable station (no discount fuel station) . Most places in the US have 93. Clearly it is going to be more expensive but we are just doing this to confirm this is the issue.

Then I want you to go to the auto parts store and buy one bottle of octane booster and add that to the 10 gallons when you fill it up. By the time this 10 gallons is gone, if this issue is caused by poor fuel then it should be gone.