98 S70 voltage drop? Topic is solved

[shegarty]

Hey guys - I have been experiencing a voltage drop on my S70 for a number of years now. It is usually associated with a large current draw kicking in (SAS, A/C, power windows). The drop is only noticeable momentarily usually as a short dimming of the headlights when dark. I still need to check the charging system under load but at idle it produces around 13.8V.

I would like to replace the wiring between the battery & fuse box as well as the main cable to the starter and the alternator to eliminate the possibility to parasitic draw from what is most likely the original wiring. There is noticeable corrosion where the wire meets the positive battery terminal. At this point I am not experiencing any electrical issues but would like to do this as preventative maintenance.

I will likely just make up my own wires with soldered terminals as the wire is relatively cheap. From what I have researched 6Ga should be sufficient (battery to fuse block and battery to starter) but I will probably do 4Ga just because I think I have some leftover from another project. What I cannot find is what gauge of wire runs from the alternator to the starter post (this is the way it is wired, right?) - should I just use 4Ga for that too?

[misha]

2AWG cables are needed for positive battery terminal to starter and from starter to alternator b+.
Also...2AWG(it's 25mm2 EU standard) from negative battery terminal to transmission housing.

Voltage drop test must be performed after driving the car for about 30min and without turning the engine off before testing....when everything under the hood is warmed up,because when you perform a voltage drop test on cold engine or when it's turned off before testing...you will have false reading.

It is because the bad cables show their weakness and resistance climbing up when they are warmed up.
When they cool off....the readings are in spec,but for about 15-30min.

At idle....healthy charging system must have 14-14.2v on these cars without turned on consumers like radio,headlights and heater blower.
13.8-14.2v at idle with headights,radio and heater blower on(except on 4th speed) is indicating that charging system is healthy.

Anything below 13.5v at idle with consumers on is not enough to keep the battery charged.

[shegarty]

AWG cables are needed for positive battery terminal to starter and from starter to alternator b+.
Also...2AWG(it's 25mm2 EU standard) from negative battery terminal to transmission housing.

Thanks for the heads up - not sure where I got 4AWG from ...

Voltage drop test must be performed after driving the car for about 30min and without turning the engine off before testing....when everything under the hood is warmed up,because when you perform a voltage drop test on cold engine or when it's turned off before testing...you will have false reading.

I've performed the test warm and cold on the idling engine and have not noticed any real difference - usually around 13.8. With being a Canadian car I can't test without the headlights on (haven't done the DRL delete mod yet). I will test it again with a few more things running after a longish drive (hard to fit those in these days - we're still in lockdown here) and see where it is at.

[misha]

If you can't drive it for 30min....let it idle for 30min and then perform voltage drop test.

[shegarty]

If you can't drive it for 30min....let it idle for 30min and then perform voltage drop test.

Had it out for a run that was long enough to heat it up (15mins) and it looks like I am going to need to replace the main cable between the battery and starter. When warm, with headlights, rear defrost, seat heater and blower on it only registers 12.8V at the battery. I was able to get a probe on the starter terminal and it registered 13.4V to battery negative meaning a 0.8V drop over that cable. The positive end of the cable at the battery was very hot to the touch. Voltage seems to be consistent over main positive wire to the fuse/relay panel meaning it reads the same from fuse panel to negative as it does from positive to negative on the battery both under load and with all accessories turned off. I would have liked to have been able to go right back to the alternator post to verify that the alternator to starter wire is good but it was way too cramped to get a probe in there. When I am in replacing the main battery/starter wire I will try and rig up a temporary jumper wire that I can access easier when the engine is running.

Thanks for the advice

[misha]

The culprit is almost always(99.9%) the cable from positive battery terminal to starter.

You can add additional 2AWG cable there without removing the old one.

Crimp both sides of a cable with proper crimp connectors and just bolt one end to a starter(there is room for both cables) and the other end to the top of the positive battery terminal.

Just make sure that you disconnect battery while you doing this and re-connect after you finish the job.

That's what i did long time ago.

[abscate]

Don’t buy the aftermarket one if you go for a part, mine lasted one year. Go Volvo here and cry once. Ok, FCP had to cry on this one.

[jreed]

I've got an 850, so the post below won't be directly helpful for your S70, but I had a similar problem with the original positive cable at the battery and also with a short-lived aftermarket replacement. I ended up making my own cable about 7 or 8 years ago and it has been working fine since... no issues noted yet.

viewtopic.php?p=316743

[misha]

Don’t buy the aftermarket one if you go for a part, mine lasted one year. Go Volvo here and cry once. Ok, FCP had to cry on this one.

Make your own....buy 2AWG cable and two crimp connectors.
Use zip-ties to secure it along the route.

[shegarty]

Thanks for all the input folks. I added a parallel 2awg wire from the starter to the battery and now have less than 0.1V drop from starter to battery even when the engine bay is hot. The battery post is no longer hot to the touch either suggesting that all current is now running along the new wire.