I have a 2006 ML350, 120K miles. I've driven it since 2014. .Replaced fuel pump in 2015 ($1100.00). Started having issues around 2019. Car would continuously go dead. Had it in/out shop. Replaced fuel pump ($1200) and battery ($600) in October 2019. Replaced fuel pump AGAIN in September 2021 ($1200.00). In December 2022.....car stranded me. Came outside of a store and it wouldn't start. Had it towed and fusebox replaced ($800.00) AC unit went out in March 2022. Had complete new AC unit put in in June 2022 ($2800.00).

As soon as I picked vehicle up from having AC replaced it NEVER drove well again. I initially thought it was transmission as it ran sluggishly and had a hard time going into different gear (from start up to 35/40) but drove jerkily once past 40 mph. Then it just quit. Had it towed to shop and can't diagnose. Was advised it MAY be ECU but can't guarantee that's the issue. Questions: 1. Could the AC replacement have messed up the engine? 2. From the issues I've described could the ECU be the fix? 3. Given the money I've put into repairs.......is it even worth trying to get it back on the road?

If it wasn't for the brand new AC unit put in less than 90 days ago and all the money I've sand into it for repairs, I'd just trash it. I've already replaced it w/a 2013 ML350

 

You have a W164. You have posted in the W166 section. Try posting in the W164 where owners with experience can help.

Look at the rear taillamp gaskets and look into the rear trunk floor in the spare tire area for water intrusion. This is somewhat common on W164 and causes electrical havoc.

 

If you currently have that many MB, I hope you have a very good independent garage doing the repair work. I personally get second/third opinions/estimates once it becomes recurrent and $$$.

On chassis advice for water intrusion, keep that in mind for any MB you own. Once water gets in (which is not that difficult if the water drainage lines are not clean), they cause all kinds of nasty surprises. Each model/class has a different water entry point, but they exist and must be monitored.

 

Or get rid of them once they approach ~15 years of age. They are designed to fall apart on purpose so it is no longer feasible to service them and keep them on the road.

 

Wait. You spent $600 on a battery?????
That'd be the last time that shop saw my car.

 

I can see it costing that much including labour as they have to take out the front passenger seat among other things, so it does take several hours... but not on the battery (part) alone.

 

No need to remove the passenger seat. In the worst-case scenario the mounted battery is dead, it can be moved into place by using the battery posts under the hood and a battery charger/booster and activating the seats to move them forward.

The Indy changed sis' car battery in 20 min ( I was away ). Here is a video for the W166


Now, I have to admit it is not clear which battery was replaced, say it was the auxiliary battery and no shortcuts were taking (no carpet/panel cutting), it requires a lot more work than the main one