Battery earth/ground point

WhiffSmithler · Post by **WhiffSmithler** » 18 Mar 2018, 06:09

Can somebody please tell me where (on a 2007 XC90, so probably all gen 1 XC90s) the negative lead from the battery is earthed (grounded, attached, connected) to the body (or something else that is)?
I follow the black lead off the battery's negative terminal and it runs in between the third row seats and off under the plasticware.
I'd like to clean up all the main electrical connections as I've been having issues starting the car for about six months now. It cranks a bit slow and the first start of the day might take ten or twenty seconds of cranking. It's never actually failed to start, just a bit temperamental about it.
I thought it might be a fuel injector/high pressure pump issue, but the engine isn't that old (~120,000km) unlike the rest of the car (285,000km) and a wise man told me to first clean up all the earth points. I've done the ones in the engine bay near the fuse box, and a couple of others, but there's an elephant in the room that I haven't been able to find so far!
Thanks in advance...

Post by **RickHaleParker** » 18 Mar 2018, 08:04

From what I can see in the wiring diagrams.

Coming of the negative battery cable, the cable runs all the way to the firewall (31/53) without interruptions or electrical junctions. So the one on the firewall (31/53) would be the root "earth" as you call it. From that point the secondary "earths" branch off.

The only other "earth" that might effect the starting system is the one at the left strut tower (31/93).

Lately a lot of XC90 owners have been trouble with the starting system. There seems to be a pattern. If memory serves me correct, they all have the V8. Do you have the V8?

WhiffSmithler · Post by **WhiffSmithler** » 19 Mar 2018, 05:58

Thanks for that imagery and info Rick. I'll go and see what I can find on the firewall near the left wheel arch.
My XC90 is a D5 - not sold in the USA from what I've seen. 2.4L 5cyl common rail diesel.

The person I spoke to was a patrolman for an auto club in my state in Australia and he told me a few stories of vehicles where the earth points were failing because the factory was painting the connection points on the body and relying on a lack of paint inside the thread that the bolt goes into. Not necessarily the problem here, but a bit of corrosion creeping in over a decade or so would be more likely.

WhiffSmithler · Post by **WhiffSmithler** » 19 Mar 2018, 07:16

Okay, so thanks to Rick's diagram that was an easy find. Not quite on the firewall, it's kind of at a junction between the left suspension strut housing and the firewall, directly below a plastic box that shields a bundle of cabin wiring. Hopefully these two photos are helpful. I'll have a go at cleaning it up tomorrow.

WhiffSmithler · Post by **WhiffSmithler** » 22 Mar 2018, 03:11

That bolt is easy enough to see, and getting a socket on to is easy enough, but getting your hand down there to pull it out isn't that easy! The bolt has about 20mm of thread, but only the top 3-4mm is engaged with the bodywork, and these threads were full of white corrosion powder. And yes, the face of the bodywork that the big metal tab on the end of the earth lead is pressed onto was well and truly painted. Even the bolt was somewhat painted!
So I replaced the bolt with a stainless one, cleaned out the female threads in the bodywork, ground the paint off the bodywork with a Dremel with a conical grindstone, and cleaned up the tab too. Put it all back together and (after leaving it unstarted for 24h when symptoms are usually worst) hey presto - no difference! [long, slow, pained groan]
Perhaps Rick can find some more connections for me to clean up where the motor/transmission/?? are connected to the bodywork...

Post by **RickHaleParker** » 22 Mar 2018, 15:40

Even the bolt was somewhat painted!
You want it coated, helps prevent galvanic corrosion.

I'm thinking your problem is not grounds. Bad grounds most of the time will result in no crank or slow crank. From what you wrote your problem does not sound like no crank or slow crank, it sounds like long crank.

It might be fuel pressure:
Try this.
1. Turn key on but do not crank, count the seconds it takes for the fuel pump to stop. Let this be time one.
2. Turn key off, wait 5 seconds.
3. Turn key on but do not crank, count the seconds it takes for the fuel pump to stop. Let this be time two.
4. Turn key off, wait 5 seconds.
5. Turn key on but do not crank, count the seconds it takes for the fuel pump to stop. Let this be time three.
6. Crank the engine, count the count the seconds it takes for the engine to start. Let this be time four.

Post times 1 -4 and any any observations.

WhiffSmithler · Post by **WhiffSmithler** » 25 Mar 2018, 00:45

Thanks Rick.
I had been all set to follow this fuel pressure/supply line of thinking, starting with an injector leak-off test (until I had to call the auto club patrolman after blowing the pipe off the turbo outlet and not being able to get home without a tow - and the patrolman advised me to chase down grounding/electrical connections. I've just driven the car a few hours ago, before seeing your reply, so I'll wait till tomorrow to run the test as described.

Post by **oragex** » 26 Mar 2018, 07:12

Measured the voltage at the battery with the engine on and off? What does it say?

WhiffSmithler · Post by **WhiffSmithler** » 27 Mar 2018, 07:11

Hi Rick,

From ~30 hours ago... Time1: ~12s, Time2: ~9s, Time3: ~9s, Time4: ~2s (which I'd call good/normal)

But it's hard for me to be confident that the first three times are real as I wasn't certain that the sound I was timing was the sound of the fuel pump. There were several other whirring and clicking noises happening in the engine bay (I assumed you meant noise from the high pressure pump, not the fuel tank pump). And I waited more than 5s after switching off, more like 15s, to have those other noises stop. Is there some particular trick or clue to attend to so I can be sure that what I'm timing is the fuel pump? Could I, for instance, hook up a 12V LED to an electrical input on the fuel pump and time its period of being lit up?

And I just went and started it five minutes ago: less than 3s of cranking till kick-over, having not been started for ~30 hours.

Thanks Oragex for your suggestion too. Prior to most recent start battery was 12.65V, back up to 14.15V by the time I got around the back and had the multimeter on it again, and up to 14.30V after one minute of idling. The battery was new 5 months ago and is a traditional lead acid type, not calcium-modified type, as recommended by the auto electrician I took it to for the sake of getting the old battery and alternator tested (and they were cheaper for the battery itself: small plug for Gibbs Auto Electrical in Belconnen, ACT).

I should also say that the poor starting symptoms have been the same with the old glow plugs (3 of 5 dead, other 2 well on their way), some Lucas glow plugs (that I destroyed by testing for too long directly on a car battery to see if they were slow to heat up to red hot), and the current NGK glow plugs which were all 0.5 Ohms at installation less than a month ago.

In January I did a mega road trip in the XC90. Drove Canberra to Perth (~3500km) in six days and had starting problems regularly. Changed the fuel filter, oil and oil filter in Perth a day or two before departure. After a day of driving homewards had no starting problems, which lasted for about a week after getting home. Have wondered if I should just change the fuel filter again (after less than 10,000km)..? I don't recall there being much crud in the fuel drained from the filter bowl.

Thanks again for your advice.

Post by **RickHaleParker** » 27 Mar 2018, 14:39

Time4: ~2s (which I'd call good/normal)

That is what I was looking for more then anything else. The first three times was a fishing for supporting data.
If it starts up better when you give it time between turn on and crank, that is a strong indicator of a fuel delivery problem. Excessive bleed off or excessive build up times.

A more accurate test would be to hook a fuel pressure gage to the fuel rail. Watch the initial pressure and the pressure build up times.