Starting Issues 2008 XC90

[RickHaleParker]

Battery Posts - 12.34 - 9.0-9.9 cranking
Battery Cables - 12.34 - 9.0-9.9 cranking

Them numbers tell me the the problem is not at the battery or battery clamps.

Jumping Post (Put negative to ground) - 12.34-6.9-7.6 cranking

When you moved the negative lead to ground you changed the datum, that throws everything off.
However I have cooked up a simpler test that should tell me the same thing.

Get your jumper cables,
1. Hook one of the red clamps to the battery, do not hook up the black clamp.
2. Hook the other red clamp to the jump start stud, do not hook up the black clamp.
3. Crank the engine, if it working good, replace the red battery cable that runs from the battery to the jump start stud.

[Roger_850T]

Looking at your numbers, I agree with RickHaleParker that something is not right, probably in the positive cable from the battery to the jump post. The V8 draws a pretty high current when starting, and wherever the problem is, it's causing that extra 2.1 to 2.2 volt drop.

It looks like the cable is one long wire, I think, although it goes through many little conduits along the way.
I think it's volvo part number 30724664
You might search on the internet for "Volvo 30724664" - that will come up with a number of places you can buy it (about $300), plus more useful, diagrams.

I just went through this on my 850, with the cable corroding on the inside. On that one, I also had a lower voltage when charging, so the battery would not charge very well. With everything on, I had 14V at the alternator, but only ~12.5 at the battery - enough to run everything, but not enough to add any charge to the battery. Thus, I had to make sure I drove with everything off (headlights, blower, etc.) to charge the battery.

I hope this helps!

Roger

[jimmy57]

Voltage drop is done on the same side of circuit. You could check while cranking at batt and get 11.37V and then check at the post at fusebox and get 11.22v. OR you check from pos post to pos post (stud) at fusebox and read .15 V.
You check for batt post to cable terminal by enagaging tarter and using voltmeter lead on post and the other lead on the terminal on cable. "looks clean" is totally meningless. A good connection with a 1/2' layer of acid salt on it is not a source of a problem. A squeaky clean connection on batt post with an oxidation layer can cause enough resistance for a 3 volt loss.

Given all this, since you say it is a V8 it is likely the starter from my experience. The 9 V range while cranking with a good battery is what you see on that starter when a bushing is worn and it has internal drag. More amps from a jump allows it to spin faster with less voltage starvation to the electrical system.

[RickHaleParker]

Cleaned both battery posts and cables, and the positive leads up at the fuse box with no change.

Did you get both ends nice and shiny ... that is clean them down to bare metal? Just a thin layer of oxidation on the surface of the metal is enough to cause the problem your having. This is one thing where you cannot do ... "that looks good enough". Yes, the starting system has so much current, a detail that small can render it inoperative.

Not trying to beat you over the head but that cable is $300 - $600 for a new one, depending on how you acquire it. It would be a shame to shell out that kind of personal cash when it could of been avoided for a few dollars and some elbow grease.

[RickHaleParker]

I agree with RickHaleParker that something is not right, probably in the positive cable from the battery to the jump post.

I can think four things it could be .... if it is that cable.

1. Dirty/damaged battery clamps, his numbers eliminate this one.
2. Dirty/damaged lug at the jump start post, this has not been eliminated.
3. Over current melted copper in the cable and/or cable to lug connections, this has not been eliminated.
4. Sometime in the past somebody replaced the cable with one too small, this has not been eliminated.

[RickHaleParker]

More amps from a jump allows it to spin faster with less voltage starvation to the electrical system.

He tried jump starting at the battery which would increase the available current but no effect. Jumping at the jumper post made a big difference. This tells me the nature of the problem is not a lack of current capacity, the nature of the problem is a lost of Electromotive Force, which is measured in Volts, between the battery and the jump post.

If I'm right about this, running a jumper cable from the positive side of the battery to the jump post will cause the problem to cease. Because the jumper cable would offer a path of less resistance and bypass the defect.

[stljrdnfan]

Hey all, thanks for the posts. Will look into these things tonight.

A couple things. The starter has been replaced already. I'm 99% certain this is an electrical issue.

Yes, I cleaned all connections until they were shiny.

Also, I can jump the vehicle off it's own battery with a 30 ft set of cables I made myself.

I always kind of thought it had to be the cable from the battery to the engine, but have removed the seats and see no damage. However, hearing someone once had corrosion on the inside of the cable is interesting.

[RickHaleParker]

Also, I can jump the vehicle off it's own battery with a 30 ft set of cables I made myself.

That confirms it ... The defect is the a battery cable from the battery or a ground. Try jumping from it's own battery using only the positive lead of your jumpers, that will narrow it down for sure.

You got any more of that cable you used to make your 30' jumper cables, enough to make a new battery cable? It would need to be the same or a bigger gauge then the OEM battery cable.

A quick fit would be to run another cable in parallel with the damaged battery cable, this can be a smaller gauge, it will only need to assist the damaged cable in carrying the current, not carry all the current.

[stljrdnfan]

The cable I have is a larger gauge. It's DC power plant cable for a DCO facility.

I've never tried the positive only, but have gotten it to start running the ground only. But it still doesn't turn over full speed. Problem with a ground issue is that could be anywhere right? Not just on the cable from battery to front. so then the trick becomes finding it.

[RickHaleParker]

Do the one wire self jump start on the positive side and post the results.
Starting motor ground is through the firewall.