Gas Engine Ground Strap: Provides Ground For?

[Vanagon Nut]

Hi folks.

I realize the strap between transmission and vehicle must supply some kind of ground path to the engine but does the ground strap between engine case and vehicle frame provide a ground path mainly for:

- charging

or

- some of the engine management operation. e.g. coolant sensor.

or

- both

If it's "both", do the tranny and engine ground strap locations some how split the load so to speak? e.g. cranking starter would pull current through the larger ground strap at tranny?


Thanks

Neil.
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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Sodo]

The starter should be grounded directly from one of its two large bolts.
Having starter current cross the interfaces of 4 or 5 old magnesium housings is ludicrous when you think about it for just one second.
Won't the current choose your shiny steel bearings over corroded magnesium siliconed interfaces?
Yes it will, and it will pit your bearings on the way to the front of the transaxle.

See this thread for more discussion of this issue.
Transaxle ground strap - is this really the only engine ground?

It's easy to ground the starter (as it should be). Then removing the front-transaxle ground eliminates starter current traveling across transaxle bearings.

There some sense to grounding the alternator too.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[djkeev]

Hmmm...... not saying it can't happen or won't happen but transaxle bearings being damaged by operating the starter isn't something I've heard of before.

One would think that VW would have addressed such an issue during the fifty/sixty years that they used the nose cone ground strap if it were a real problem.

Adding grounds isn't a bad thing for a weak ground can make all sorts of problems. Starting, operation, lighting, turn signals, etc.

Dave
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http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

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https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[MarkWard]

I’ll wade in. For years VW was happy with a simple ground strap from the chassis to the engine. Starter load, charging, choke, ignition , were all handled easily.

Working for VW when they started having more advanced electronics, weird ground issues started appearing. Adding additional grounds became common place.

My feeling is grounding the starter through the case is fine assuming clean connections. I don’t believe additional grounds are load balancing. It’s more about eliminating resistance.

My TDI has the battery grounded through a cable to the block. My alternator also has a heavy duty ground between the case and negative battery terminal. I also have the original transmission ground strap. Probably overkill but does add some redundancy.

I have fixed other gas engines by direct grounding the cylinder head. Spark plugs love a good ground, and some engines passing grounds through the head fasteners can have issues.
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[Sodo]

[Vanagon Nut]

[AtlasShrugged]

The main engine ground is there for the starter/charging. It completes an electrical circuit from the battery to the starter or alternator and back to the battery negative.

The engine and transmission are completely insulated from the metal chassis+12v battery by the rubber engine and transmission mounts. You really need that big ground!

There is a small long ground from the driver's side cylinder head to the chassis, under the coil. VW wanted to be sure that particular aluminium cylinder head was completely grounded to the chassis/battery. (the rubber head sealing gaskets and "O" rings are good insulators) Probably because of the sensors in the thermostat housing. Those sensors don't routinely need a chassis ground except on the Synro.

[Vanagon Nut]

[crazyvwvanman]

The whole point of the 2.1 having the brown "reference" ground wire for the O2 circuit attach to the engine metal is to make it so the O2 sensor reading isn't dependent on any of the body ground straps. The O2 sensor only has 1 wire to it and uses its threads and metal exhaust system connection to the engine as the other wire. So the brown wire lets the ECU measure the 2 "wires" of the O2 sensor, 1 of the wires being the metal of the exhaust and engine.

It is a fact of physics that there will at times be a voltage difference between the engine metal and the body metal. We should strive to keep this at a minimum by ensuring that the ground straps are in good shape. I like adding a heavy one between the starter bolt and the body. I don't like any other added grounds between the engine and body. I sometimes add a #8 or #6 between the alternator case and the engine metal so the charging amps don't have to go through the WBX alternator mounting brackets that are not always reliable.

I don't want people to add flimsy grounds that could someday cause the van to burn up. That possibility is real.

Mark

[DuncanS]

[Vanagon Nut]

Thanks for that Mark. Ok, I see what you mean re O2 "reference" wire.

With my 50º ABA engine swap, to the best of my recall, all engine management sensor, ECU, etc. grounds connect to the engine block. So, I really need to have a proper braided strap between the engine and body metal as per OE design in the Mk3 Jetta. (and as I have on my 15º ABA swap on the other van). One strap should suffice. It's where I have the current wire connected to the engine that is likely the fault behind my hot start issue. i.e. for that aspect only, wire gauge is likely not the issue.

I'd recently read your warnings regarding ground wire or strap size. The wires I have in place are temporary but I really should've put a proper sized strap in from "day 1" of the conversion.

Neil.

[Vanagon Nut]

[Sodo]

You can check with a voltmeter if there's any voltage between the alternator and the engine block. THat will tell you the state ( at that moment ) if there's any voltage loss. It could be different after a winter.

Test voltage when the battery is "hungry" like 15-25% down, headlights on, wipers running, ventilation fan on high so there's lots of current.

New car, new alternator, new engine block, is gonna have really good conductivity, for many years. After the surfaces of all these parts are "old" with corrosion, paint, or other insulators, there could be losses. Its an “old car thing”.

On some cars, in some environments, a direct, maintained ground strap could be superior. From there on out, you'll know exactly which surfaces (only two locations) need to "maintained" in the future and the original ground path becomes irrelevant.

That's to keep it at 100%. 99%, 98% are still pretty good.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[Vanagon Nut]

This is a minor detail, and likely moot as I didn't do this on my other ABA van which runs ok, but after rebuilding the ABA engine in question, I did not clean the engine alternator bracket mount points at block, and bracket itself, to shiny clean. But any added resistance at those points is likely very small and of no real consequence.

I'll measure voltages, see whats going on. Thanks for pointer on adding current draw while testing.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN