Start-up Bang/'Slow Start'/AGM Battery

[Ecto1]

Check engine mounts. The only way you're going to get "lift" upon a start up event is if 1 or both engine mounts are loose, or deteriorated.

Check the trans mount as well and all the bolts securing the driveshaft to the flanges.


If the problem is not those areas, then as mentioned above the issue may be related to the transmission.

Thx. I checked the trans cross member but it seems fine. I can see the engine mounts but I can't tell if they're loose or damaged. They appear OK but I need to figure out how to watch the engine/drive train when the engine starts but this ridiculous 'smartkey' business simply won't allow the car to start with the hood open. Don't ask me why. Something to do with the security system I suppose.

I'll keep puzzling over it.

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[Ecto1]

FWIW, checking voltage is not a way to find excessive battery loads.

Only the AMP reading will show it, for a starter. Most dime store multi-meters will not be capable.

Series wired

I'll assume the dealer would know if the starter was at fault, loose/noise form the pinion gear & flex plate engagement ?

Even if that were the case rocking does not compute. Does it rock before it fires, or at the same time.

Happens cranking, then turn it over again and it fires up ok_Could be timing related, to much advance, wet cylinder, coming up on the combustion stroke.

I assumed the dealer would know to check the starter & current draw during startup as well but who knows. 2 dealers looked the car over (one prepurchase '179 point' inspection - which I doubt checks very much) and both claim everything starter/battery/alternator is A-OK.

The rocking occurs while the starter is engaged. It stops right after it catches. Not sure if the starter is still turning or not when it quits.

 

[Ecto1]

Post #3 in this thread claims that the start-up bang on the Ecoboob is normal...

https://www.mustang6g.com/forums/threads/auto-trans-quirk.165334/

I'm still going to try to figure out how to watch what the drive train is doing during start up. Mostly because I refuse to be outsmarted by a @$%* key.

 

[Ecto1]

I think I now understand what's going on with the start-up bang & rocking of the car. I spent some time examining the engine mounts & I noticed vacuum lines going to both. I'm sure what's happening at start-up is that there's no vacuum in the engine mounts. Maybe it's normal or maybe there's a leak somewhere. I would expect some check valves or a reserve tank somewhere in the system to assure vacuum at start-up but I didn't see anything obvious. So most likely there's just no vacuum until the car starts and the vacuum pump starts to operate. That's why the bang and the rocking of the car only occur once at start-up. As soon as the vacuum pump starts operating vacuum is applied to the mounts and both symptoms stop.

Does anyone have a diagram of the vacuum system from the pump to the mounts? Or do you know where I can find one?

Thx.

 

[Cheo]

Looks like there's a small vacuum line connected under the mount. Did you check for cracks/leaks? Where the vacuum comes from may be here: https://www.mustangecoboost.net/threads/6th-eco-boost-breather-pipe.23584/

 

[Ecto1]

Looks like there's a small vacuum line connected under the mount. Did you check for cracks/leaks? Where the vacuum comes from may be here: https://www.mustangecoboost.net/threads/6th-eco-boost-breather-pipe.23584/

Thx. That's helpful. I noticed the vacuum system when I was replacing the brake power booster check valve. Apparently there's a vacuum pump located at the top/rear of the engine that creates the vacuum source for the brakes & engine mounts. And any other vacuum operated components under the hood. (Maybe the HVAC system too.) But I hadn't realized at the time that the engine mounts were vacuum operated (or assisted). Now that I realize that they are I suspect this is the source of my 'bang' problems.

I took the car to the dealer as soon as I bought it and they claim this 'symptom' is normal. Not sure why. I still don't think it is. I'll need to 'rent' the vacuum tester again and check the mounts. If I can figure out how to connect the vacuum lines to the mounts.

The car came with 2 & 1/2 months of extended warranty (3rd party) and I'd like to get this sorted out before that expires. If one (or both) of the mounts need replaced I'd like to get a little use out of the warranty.

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