Zel's Fleet Blog - BX, Jag XJ-S, Sinclair C5, Mercedes 208D & 230TE, AC Model 70.

[Zelandeth]

Not content with averaging 13MPG the Jag apparently decided this morning that merely using its fuel wasn't bankrupting me quick enough!



Yep...it was caught dribbling fuel all over the floor.

I had fuelled up in the last hour, our drive slopes slightly downhill towards the camera and it's been quite nice and sunny here so far today.

As such I reckon things have expanded in the tank and it's forced fuel bank out the filler, probably due to a compromised tank vent line (which I've suspected for a while on account of a distinct pong of fuel in the boot). Though I've never noted and excessive pressure/vacuum in there really. It was weeping out around the cap seal itself then draining down the spill line in the filler surround today. Turning the car through 180 degrees so the filler was at the high rather than the low side sorted things.

Obviously only an issue when the tank is really full (so about 3 miles worth of driving then probably!) and on a warm day, but something I'll need to be aware of until I can investigate the venting system properly, and possibly renew the seal in the filler cap as it's a little perished in a couple of spots.

Have to wonder if this happened unknown to me at some point during the random sub-10MPG tank a couple of weeks ago...hard to say as the evidence is gone minutes later!

[xantia_v6]

The tank ventilation system on your car is probably "interesting"... There were a few variants fitted, depending on the year and target market.

Yours probably has a vapour separator can mounted above the right hand end of the tank with about 5 hoses going to it, most being tank vents, but one to drain fuel back to the tank and another being the external vent.

On US market cars the external vent line goes to a carbon canister etc. on UK market cars, until the early 80s, they just vent to atmosphere through a hose that couples into the drain from the boot lid channel. In about 1985, the EU apparently introduced a vapour emission spec, but it was more lax than the US spec. I can't remember if the system has an electric valve with purge to the engine intake, but when the engine is not running, the fuel tank is sealed off, with a pressure relief valve (above the center of the tank IIRC) that lets vapours excape if the tank pressure exceeds about 2psi.

The net effect is that if the tank cap does not seal 100%, it becomes the weakest link and vapours (and potentially fuel) get pushed out past or through the filler cap on a hot day.

[Zelandeth]

The tank ventilation system on your car is probably "interesting".

I never would have expected any differently!

There's always been a strong smell of fuel in the boot so going over the venting system in detail is already on the to do list.

Edit: Plus having cleaned the base carpet it's showed up how grubby the rest of the carpeting in the boot is so it all wants to come out to be cleaned anyway.

[Zelandeth]

Pretty sure we've got a developing issue with either the alternator or the regulator on the Jag. While the light goes out as normal when the engine starts, it doesn't seem to properly start charging until the engine is brought up to around 3000rpm and held there for a couple of seconds. Then the system seems to wake up and start charging properly. It will then stay there until the engine is next stopped. Before that point the system voltage will hover around 13V - so it is still generating power, just at a reduced level. Once the system "wakes up" it jumps up to a normal charging voltage.

Need to do some research on the likely cause and get the necessary things ordered in. At least alternators don't look to be massively expensive if a new one is needed. This one has been rebuilt - but that was back in 1998 so it's not really undue some attention.

I will obviously have a crawl under that corner (I *think* it's relatively accessible from underneath) and get myself covered in oil and clean up the connections to the alternator as it wouldn't be the first time I've fixed odd charging behaviour with naught but jiggling a connection.

I've had a strong recommendation of another classic friendly garage from a friend (having had them have work done on their classic AX(X2), Maserati and chasing gremlins on a P38 Range Rover). I'd really like to cultivate a good working relationship with them for the future (especially as they are willing to do the odd job on bigger things like the van), so think I may well toss the Jag at them to do the brake discs and the belts.

I know they're jobs I can do myself, but I've been struggling to find the time and it seems like a good sort of set of (hopefully!) simple jobs to get my foot in the door with. Can get them to test the alternator while it's in there to.

Got the kit in now to do the timing covers, so that's probably going to be the first big task I get stuck into on my own drive. However it's dependant on a couple of things...One being the weather actually looking decent for a couple of days. Two, having one of the other cars back on the road (either Xantia or Invacar) so I'm not stuck with the van as my only transport! Not that I mind...but the rest of the family look at me funny when I go shopping in it. Oh...and a couple of my regular destinations have 2 metre height barriers at their entrances!

Getting rid of the horrible braking vibration and knowing the belts aren't falling to bits (they are horrendous!) would be really nice in the short term though.

[white exec]

Had a similar indifferent alternator output on my V8 Rover, which usefully had a dash ammeter, so you could see actual charging. Not just at idle, but also at low (light traffic) revs, there was discharge if headlights etc were on. Lucas service centre were familiar with this, and fitted a slightly smaller diameter alternator pulley, which completely cured the problem.

IIRC, at the time, max recommended alt speed was 30,000rpm, so no problem checking that the mod wouldn't cause problems. Lucas said it was not unknown for lazy V8's to suffer this.

A Sealey 75-0-75A clip-on ammeter would allow charging to be monitored. Cheap, and on Amazon.

[Zelandeth]

I've got a clamp meter somewhere. The thing that's making me puzzled and thinking something is amiss (aside from the fact it didn't do it when I got the car) is the fact that you need to provoke it into starting to charge...but it doesn't then drop out at idle again. The voltage does sag a bit as you'd expect, but it picks right up again as soon as the revs rise above idle.

When the system initially wakes up with you manually holding the revs up, you audibly hear the change when the system loads up as it starts properly charging. Sticky brush maybe? Though I'd expect a dead ignition light then and zero output until it kicks in...not just reduced output. It's odd behaviour.

Need to get some proper tests done...

[xantia_v6]

My first guess on your alternator symptoms is that you have a slipping drive belt. The bad news is that you have to remove 3 other belts to change the alternator belt.

I don't know if I am lucky or not, but my XJ-S has its original 1975 alternator, which is one of the VERY rare cars fitted with a Motorola alternator, not Lucas. I would not know where to start to look for parts for that.

[Zelandeth]

Not a bad shout actually... hadn't thought of a belt silently slipping. It's easy to forget they don't always screech.

At least I've got one less belt to argue with as the air con one is currently missing. Have been looking into that a little too, and reckon that just changing the whole compressor (replaced with a reconditioned unit in 2008) rather than just changing the clutch pulley assembly...so may well just go down that road. That way I've got something with a warranty on it rather than spending the best part of a hundred quid on a compressor that's not run in probably a decade...especially as I've already got to take a lot of things in that area apart anyway...

So yeah...let's get the belts changed and see if this odd charging behaviour continues.

[Zelandeth]

Here's a video of the behaviour snapped just now sitting in the Asda car park.

Note that the dash voltmeter reads a couple of volts low.

Comes up to around 13V when the engine starts, sits there until the revs are held at ~3000rpm for a second, then jumps up to the proper 14.4V charging voltage. It will then wander around a bit at lower revs as I'd expect. My ICV is a bit sticky (it's on the list) so the idle speed is a bit low sometimes.

[YouTube]_ZcvQ2Hke_I[/YouTube]

[white exec]

What are lights doing during this voltmeter wandering? Do they jump in brightness, too?
What does an good test-meter show?
How about ammeter reading (for current supplied by alternator)?
Recall that you said there was odd behaviour across all the dash instruments.

[Zelandeth]

The numbers I quoted earlier - initially ~13V, then jumping to 14.4V once the system sorts itself out - are quoted from a digital meter on the battery terminals. While the meter on the dash reads a bit low it tracks accurately proportionally if that makes sense so it's still valid to keep an eye on what things are up to.

Haven't tracked down the clamp meter to do a current reading yet... it's buried somewhere in the garage.

The headlights etc behave much as you'd expect given the meter readings. They do pick up a bit when things sort themselves out (biggest indicator is actually the tone of the HVAC servos), though it's not a massive voltage jump so it's not hugely visible on the headlights.

The wandering at the end of that video clip is more down to low idle than a charging system issue I think! The car trying to idle at 400rpm isn't helping!

It's definitely an actual voltage issue we're seeing, not just an instrumentation glitch.

[white exec]

OK, all understood, Zel.
So likely belt slippage, or the alternator objecting to being asked for meaningful output at such low revs.
What happens voltage-wise if you lift the idle speed to its proper figure, and keep it there?

[Zelandeth]

At the correct idle speed (assuming the rev counter is accurate!) it hovers around 13.5-13.8V. Up to 14.4 by about 1200rpm - which is pretty much what I'd expect from the electrical stuff on a car of this sort of age.

I'll try to grab a better clip tomorrow to more clearly show what it's doing - this one was purely a case of me being bored in the supermarket car park!

It's worth noting that this failure to provide full voltage doesn't seem to be dependent on current draw. It will behave exactly the same when started up after a few hours of driving to if you've started it up for the first time in a few days, so the amount of current being sunk by the charging system doesn't seem to play a huge part.

If you watch carefully in the video you can definitely hear (and see on the revcounter) the point at which the charging system kicks in.

Other than less than stellar access (on an XJ-S, surely not!) is there anything I need to keep in mind while doing the belts? Looked like the adjusters and such were pretty standard setups...just as usual on this car it's a bit hard to actually see what you're looking at as there's so much car in the way. Few folks have suggested removing the bonnet but that's definitely a two man job and I don't have a helper, so we're not going down that road. I do have ramps (assuming I can get the car onto them with how low it is), is this a job which can be done more easily from underneath? To make sure I give it as much opportunity to drop oil up my nose as possible...

[xantia_v6]

It is a while since I have changed the blets, but they are done from above, except the alternator belt which I think is adjusted from below.

On the pre-HE engine, the oil cooler pipes make any access from below to the crank pulley almost impossible, I can't remember if that was slightly improved for the HE (probably not).

[Zelandeth]

On the pre-HE engine, the oil cooler pipes make any access from below to the crank pulley almost impossible, I can't remember if that was slightly improved for the HE (probably not).

Doesn't look exactly access friendly!

We've definitely had our money's worth out of these...