dr bob

I think it's possible to go way overboard on wire quality, where a difference of 0.01% isn't going to make a bit of difference in overall performance. I just need to rule out the cable for another 25 years or so. That will be well into the years beyond mine.

The telltale voltage drop did not repeat, and there's a possibility that a ground strap fault was part of what I saw. I'm still replacing both pieces with mildly upgraded parts because it's no more effort.

Aside, I plugged in a 'smart' maintainer with the voltmeter attached, and watched voltage sail past 15 when I pulled the plug. Not so good.

More news when it happens!

txhokie4life

Any updates?

Is it possible to wire in parallel or is a full replacement the best remedy?

I've got an '82 Euro in need of juice.

m

dr bob

Started out on a little two-hour project today, replacing the positive battery cable. A few hard-to-access clamps extended the operation a bit. Forward lower control arm mount had to come off, and it was a bit of a chore getting the new cable to sit perfectly in the body channels. Anyway, four-plus hours later, it's all in but the front section at the cross-member. I need to get a few feet of hose to use as the heat shield where the cable passes under the exhaust, and crimp on the lug.

Unless you are pretty sure that you have a problem with the existing cable, I don't recommend this replacement as PM. The new cable is pretty, it's very fine-strand tinned copper, in 1-gauge, that should be better than what was there originally. Will there be a noticeable difference? Probably not.


The biggest symptom-solver was the new ground strap. Several listers had mentioned that as a likely problem but the meter didn't show it directly. The diagnosis path caused a lot of connection cleaning, a couple new batteries, a new alternator, and finally new cables. I should have listened to those who had passed this way before, and replaced the cheapest/easiest part (ground strap) per their guidance.

The 16" 2ga ground strap from waytekwire is a perfect replacement. I added a sleeve of 1" heat-shrink over the braided part, with an extra section over the area where the braid passes under the edge of the cover. This is a cheap-and-easy replacement that is likely to help many other cars that seem to suffer from low voltage at idle. A weak ground cable keeps the battery from charging completely, but shows OK voltage on the dash gauge with the engine above idle. The undercharged battery shows low gauge voltage at idle. Any of this sound familiar? Start off with the ground cable. Cheaper/faster/easier than a bigger alternator, for instance.

danglerb

Do you think the 16" will be long enough for all models?
http://order.waytekwire.com/productd...016%22%20LONG/

Alan

I used a 19" version of the same but only because I have it connecting to a battery switch at the ground point end. This is a good upgrade and really quite cheap - but you do need to cover it. I used self vulcanizing rubber tape and a thin PVC sleeve over that.

Alan

dr bob

I don't know that the early cars with group 49 batteries would need a different length, but it's possible. The later cars with group 48 battery have a cable that's 15" center-to-center, so the 16" is a perfect match for them. Someone with an earlier car should post the length if theirs is different.

txhokie4life

FWIW,

At IDLE in all cases.

I was seeing 12.5-6V at idle at my jumper post with one electric fan on.
Cleaned up my battery cable and my engine ground wire connections.
Gained about 0.2V but I still didn't feel that was right.

I picked up a new 15" 2 gauge battery ground cable.
Installed it -- fired up the car and now I have 13.7-13.8 at the battery
AND at the jump post with the electric fan running. I forgot to measure at
the battery with the old cable (sorry -- wasn't going to put it back on either :-)

Now I did sag to 13V at the jumper post with my foglamps and exterior lamps
(other than the headlamps on).
And the turn signal does modulate my voltage.

Looking at the Dash and giving it some RPMS with the lights/etc on -- it looked
like I gained some more voltage.

So I don't think I am out of the woods. I also have the engine ground strap to
replace.

But I am much happier now.

lot simpler than the positive cables -- but I'll probably attack them too at some point.

mike

dr bob

Just put the meter on it after a nice mountain drive. With main beams and 100W aux headlights, full interior fan speed, full cooling fan speed, engine idling. 13.8V at the jump post. With everything off and engine idling, 14.1V at the jump post. Engine off and everything settled for 20 mins, battery reads 12.6V.

Dash gauge is reading half a volt lower than the DMM at the jump post. I should have the isolation breaker in a week or two for installation at the CE panel. I'll add test ports for a voltmeter and have CE panel readings to match up with the other readings.

So far, looks great.

Rob Edwards

Been having problems with iffy starter performance in the GT for some time, such that getting the car to start when warm is hit and miss. I swapped the starter for my spare, no joy. Lots of poking around with the multimeter yesterday revealed no real issues, I got 13.7V at the + terminal and the jump post at idle. And these values were unchanged after installing a new battery ground strap. But swapping in the new ground strap greatly improved the cranking speed.

The new factory strap is about a half inch longer than the original, perhaps the replacement is a catch-all for all model years (?)

Not sure how/when/why the old ground strap's distal insulation melted off, perhaps that's the cause? We'll see.

danglerb

Distal? Been hittin the pathology pretty hard lately have we?

Any chance you measured the length during the autopsy?

Rob Edwards

Mike-

Yep, too much work, not enough play.

I did measure the new one, Si.

danglerb

I'm thinking the proximal end got too hot and the shrink shrank and split.

JohnKoaWood

Sorry to jump into the discussion, caught this one on "most recent updates"...

Any 928 owners in the Richmond VA area willing to bring their car to me? I have everything on hand to do these... except the grounding straps...

Please do NOT use welding wire in your car... please please please dont use it... even marine grade is better than welding wire... even if it is marine grade PVC jacketed! (SGX is currently the best, and can be had for under $3 a foot... at least that is what I get my 1/0 SGX for...)

I have an account with Waytek, and have a couple hundred feet of good heat-shrink on hand to sheath them in... just sayin...

Rob Edwards

Build them and they will come.

JohnKoaWood

Well, I can tell you the bits used on other mid 80s Porsches are similar materials, and suffering from the same age related issues...

Specific to the primary power cables, cracked jacket (PVC was the standard in the 80s...), corrosion not only at the cable ends, but also internally within the cables anywhere there is a crack in the 20+ year old PVC jacketed cable, on and on and on..

I have now replaced the cables in a dozen different cars, and yes, they ALL suffer the same shortcomings... I haven't yet done a 928, but I am willing to make it happen..

So come on, someone in or near Richmond (or Virginia for that matter) come on over, I have plenty of space in the garage, and barring any special bits or pieces needed, I can have it knocked out in a day or so... Then just need to cross check across years to verify fitment.. Nothing removed from your car before I am 99% sure that everything is on hand to get it done!