I have an intermitted issue where my 2019 Ecoboost won't start. The starter engages, then immediately stops. Gauges on the dash will twitch for a second. This will happen with the ignition turn or remote start from time to time. It will eventually start.

Brought it to my local dealer, they replaced the starter, but that did not fix my issue. Any thoughts as to what the root cause might be?

 

There are a few grounds I would check. Close to battery, close to PCM by passenger right foot panel. I assume your battery and general cables are in good condition given dealer has looked at it?

 

The dealer replacing the starter without diagnosing the root cause is the classic misdirect. On the 2019 3.5 EcoBoost, that symptom -- starter kicks, immediately stops, gauges twitch -- is almost always a weak ground or a PATS/anti-theft hiccup rather than a starter problem. Check these in order:1. Battery ground to chassis (driver side, under hood) -- clean both contact points, these corrode2. Ground strap from block to chassis -- common on 2019s to get loose3. Have someone scan the BCM for any PATS codes -- if the PCM momentarily thinks the key is invalid it will cut the starter immediately Also worth putting a load tester on the battery if it hasn't been done recently. The 2019 batteries are 7 years old now and a marginal battery will do exactly this.

 

When the Starter engages, the load it's trying to move results in very high Current requirements through all the heavy cables and post connections.
If there is a lose, corroded or faulty connection, a large voltage drop occurs across the Resistance that is present at that time..
At this point a large amount of Heat can be generated at that connection.
If voltage drop is so large, it leaves very little for the Starter needs to move the engine load.
As well, the high heat at the time could results in a good connection >> via melting metal arc << but will happen over and over on an intermittent basis until complete failure occurs.
Good luck.

 

Get your battery tested mang.