Correcting Porsche's Ground design...am I nuts or on the right track?
04-07-2018, 03:55 PM
#1
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Correcting Porsche's Ground design...am I nuts or on the right track?
As I delve into my first 944 restoration, I am faced with a no start, and a lot of wiring issues, corroded fuses and fuse blocks, rusty relays and so on. I have managed to get the car to turn over now, but am having all sorts of weird things happening, like the battery light is on without the key in the ignition, about 230mA of constant drain on the battery, poor connections on the multiple battery cable connecting points etc.
So I am thinking of simplifying this, being an electronics guy, I am used to having a central ground system, sometimes referred to as "star ground", where everything that needs a ground stems from a central point. The 944's, for reasons I don't understand, grounds from the battery to the frame, relies on the frame to make continuity to another ground block on the firewall, then from there to the engine and so on, many places for corrosion and loss of continuity and voltage drops. I am thinking of running the main battery ground straight from the battery to the engine block, like every other car I have ever owned, and then ensure the block to firewall is perfect and clean of corrosion. Running the starter current thru the frame and multiple studs doesn't make sense to me. The DME and it's sensors all rely on good grounds to have clean stable signals so the better the ground reference, the less potential for noise and extraneous signals to cause problems.
Am I on the right track? Anyone else tried this? Anyone know why Porsche grounded the system the way they did, that could explain it to me?
Cheers
So I am thinking of simplifying this, being an electronics guy, I am used to having a central ground system, sometimes referred to as "star ground", where everything that needs a ground stems from a central point. The 944's, for reasons I don't understand, grounds from the battery to the frame, relies on the frame to make continuity to another ground block on the firewall, then from there to the engine and so on, many places for corrosion and loss of continuity and voltage drops. I am thinking of running the main battery ground straight from the battery to the engine block, like every other car I have ever owned, and then ensure the block to firewall is perfect and clean of corrosion. Running the starter current thru the frame and multiple studs doesn't make sense to me. The DME and it's sensors all rely on good grounds to have clean stable signals so the better the ground reference, the less potential for noise and extraneous signals to cause problems.
Am I on the right track? Anyone else tried this? Anyone know why Porsche grounded the system the way they did, that could explain it to me?
Cheers
04-07-2018, 06:40 PM
#3
Three Wheelin'
I am limited in knowledge in all things electrical , but do know this:
Water cooled Porsches such as our 944s, suffer from 'stray voltage' and it is common for it to affect the coolant in the water jacket, promoting galvanic corrosion.
One of the reasons Porsche recommends coolant change as often as they do.
Doubt me ? Put a probe in the reservoir and take a reading ...... Or, take off the heater core and check for AL flaking collecting inside from the engine passages eroding.
There is a huge amount of redundancy within the layout of Porsche current flow and many folks have found this out seeking to delete wiring while stripping their cars for track duty.
And again, remember the '82-'83 cars differ in wiring from their '84 - '85.1 brothers, and again from '85.2 and up, using a quite primitive fuse block. A lot of power runs thru the headlight switch and failure of this switch has burned many a car to the ground; maybe even more than the fuel line fires on the second series cars due to routing by the manifold.
Water cooled Porsches such as our 944s, suffer from 'stray voltage' and it is common for it to affect the coolant in the water jacket, promoting galvanic corrosion.
One of the reasons Porsche recommends coolant change as often as they do.
Doubt me ? Put a probe in the reservoir and take a reading ...... Or, take off the heater core and check for AL flaking collecting inside from the engine passages eroding.
There is a huge amount of redundancy within the layout of Porsche current flow and many folks have found this out seeking to delete wiring while stripping their cars for track duty.
And again, remember the '82-'83 cars differ in wiring from their '84 - '85.1 brothers, and again from '85.2 and up, using a quite primitive fuse block. A lot of power runs thru the headlight switch and failure of this switch has burned many a car to the ground; maybe even more than the fuel line fires on the second series cars due to routing by the manifold.
04-07-2018, 08:18 PM
#4
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I am limited in knowledge in all things electrical , but do know this:
Water cooled Porsches such as our 944s, suffer from 'stray voltage' and it is common for it to affect the coolant in the water jacket, promoting galvanic corrosion.
One of the reasons Porsche recommends coolant change as often as they do.
Doubt me ? Put a probe in the reservoir and take a reading ...... Or, take off the heater core and check for AL flaking collecting inside from the engine passages eroding.
And again, remember the '82-'83 cars differ in wiring from their '84 - '85.1 brothers, and again from '85.2 and up, using a quite primitive fuse block. A lot of power runs thru the headlight switch and failure of this switch has burned many a car to the ground; maybe even more than the fuel line fires on the second series cars due to routing by the manifold.
Water cooled Porsches such as our 944s, suffer from 'stray voltage' and it is common for it to affect the coolant in the water jacket, promoting galvanic corrosion.
One of the reasons Porsche recommends coolant change as often as they do.
Doubt me ? Put a probe in the reservoir and take a reading ...... Or, take off the heater core and check for AL flaking collecting inside from the engine passages eroding.
And again, remember the '82-'83 cars differ in wiring from their '84 - '85.1 brothers, and again from '85.2 and up, using a quite primitive fuse block. A lot of power runs thru the headlight switch and failure of this switch has burned many a car to the ground; maybe even more than the fuel line fires on the second series cars due to routing by the manifold.
Yes, the fuses, I made a comment in my first thread about this car, wondering why WWII era fuses were still being used in the 80's.
I have cleaned all of the fuse holders, and the fuses, and the relays, and everything else that is under there. Grounds are next on my list. I'm going to run a #1 or 2 cable from the battery, thru the drain port over to the engine block, directly. All new ends on the 3 or 4 12V feeds to the harness, clean all grounds that I can find...then try to start it. Lots to do, thankfully I enjoy this sort of work, it's a hobby for me.Cheers
04-08-2018, 11:26 AM
#5
Rainman
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theres a big honkin ground cable from block to frame dead center behind engine.
and about 8-12" to the passenger side is where the battery ground to chassis cable goes.
you could run a splice to join them...
but remember, the body may be 1/16" steel but it's 5 feet wide which gives more conductor area than almost all AWG wire sizes.
so there's plenty of current flow despite the resistance of the steel vs copper.
and about 8-12" to the passenger side is where the battery ground to chassis cable goes.
you could run a splice to join them...
but remember, the body may be 1/16" steel but it's 5 feet wide which gives more conductor area than almost all AWG wire sizes.
so there's plenty of current flow despite the resistance of the steel vs copper.
04-08-2018, 11:42 AM
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theres a big honkin ground cable from block to frame dead center behind engine.
and about 8-12" to the passenger side is where the battery ground to chassis cable goes.
you could run a splice to join them...
but remember, the body may be 1/16" steel but it's 5 feet wide which gives more conductor area than almost all AWG wire sizes.
so there's plenty of current flow despite the resistance of the steel vs copper.
and about 8-12" to the passenger side is where the battery ground to chassis cable goes.
you could run a splice to join them...
but remember, the body may be 1/16" steel but it's 5 feet wide which gives more conductor area than almost all AWG wire sizes.
so there's plenty of current flow despite the resistance of the steel vs copper.
Cheers
04-08-2018, 02:38 PM
#7
Rennlist Member
When you break any of the electrical connections, use some dielectric grease before reassembling them..helps prevent future corrosion...You can also use electronic cleaner on the connections as well to help clean them, especially the female side of the connectors. I found my car had lotsa corrosion after sitting out in New Hampshire winters in a field for about 10 years.
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04-11-2018, 12:06 PM
#8
Three Wheelin'
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Dielectric grease is suitable to apply AFTER the connection has been made; it inhibits corrosion but if applied before assembly, it also inhibits conduction. I'd use Deoxit as your cleaner for all contact points and possibly some stabilant to improve the conduction.
04-11-2018, 01:15 PM
#9
From working on salt spreaders the best stuff I've seen for terminal protection by far is Permatex battery protector and sealant. It also protects the wire itself too. Without it I've seen the copper wire turn to green power as far back as 3 feet or more from the terminal!
From seeing what salt can do to those trucks, I'm amazed by how many people drive their classic cars on salt covered roads.
From seeing what salt can do to those trucks, I'm amazed by how many people drive their classic cars on salt covered roads.
04-11-2018, 11:00 PM
#10
Rennlist Member
One thing I noticed while cleaning up ground points this past fall, is that the terminal rings are real high quality copper connectors. The irony in this is that the copper terminal rings were in many cases, landed on aluminum. Definitely a recipe for a poor ground connection, given enough time, especially in a wet climate.
04-12-2018, 03:33 AM
#11
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HI guys,
Thanks for all of the excellent info, much appreciated. I have cleaned all of the major ground and power connection points, and had my can of Deoxit present and applied to all connections, everything seems good. I have some special battery paste that we used on all of our batteries when I was a signal maintainer for the railway. 2 different types, one is a thick brown paste, usually put on as the connections are made, the other is a clear thinner paste, dielectric grease in a jar used after the connections are made.
I also would like to know the recommended, if any treatment for the torpedo fuses and holders once they have been cleaned. I would think any of the tin fuses should be replaced with copper to avoid dissimilar metal junctions. Any other recommendations?
Cheers
Thanks for all of the excellent info, much appreciated. I have cleaned all of the major ground and power connection points, and had my can of Deoxit present and applied to all connections, everything seems good. I have some special battery paste that we used on all of our batteries when I was a signal maintainer for the railway. 2 different types, one is a thick brown paste, usually put on as the connections are made, the other is a clear thinner paste, dielectric grease in a jar used after the connections are made.
I also would like to know the recommended, if any treatment for the torpedo fuses and holders once they have been cleaned. I would think any of the tin fuses should be replaced with copper to avoid dissimilar metal junctions. Any other recommendations?
Cheers
04-12-2018, 02:16 PM
#12
Rennlist Member
HI guys,
Thanks for all of the excellent info, much appreciated. I have cleaned all of the major ground and power connection points, and had my can of Deoxit present and applied to all connections, everything seems good. I have some special battery paste that we used on all of our batteries when I was a signal maintainer for the railway. 2 different types, one is a thick brown paste, usually put on as the connections are made, the other is a clear thinner paste, dielectric grease in a jar used after the connections are made.
I also would like to know the recommended, if any treatment for the torpedo fuses and holders once they have been cleaned. I would think any of the tin fuses should be replaced with copper to avoid dissimilar metal junctions. Any other recommendations?
Cheers
Thanks for all of the excellent info, much appreciated. I have cleaned all of the major ground and power connection points, and had my can of Deoxit present and applied to all connections, everything seems good. I have some special battery paste that we used on all of our batteries when I was a signal maintainer for the railway. 2 different types, one is a thick brown paste, usually put on as the connections are made, the other is a clear thinner paste, dielectric grease in a jar used after the connections are made.
I also would like to know the recommended, if any treatment for the torpedo fuses and holders once they have been cleaned. I would think any of the tin fuses should be replaced with copper to avoid dissimilar metal junctions. Any other recommendations?
Cheers
04-12-2018, 02:38 PM
#13
Drifting
If there's a difference in the grounding, perhaps you could update. I believe on my '88 the ground wire from the battery splits with one end connected to the frame nearby and another to the bellhousing? Have to check... but i do know that there are three connections at the bellhousing; one on its own and two on top of each other right beside