Quessies from a Diesel Dummy

addo · Unread post by **addo** » 17 Aug 2011, 10:24

There are maybe half a dozen diesel Xantias here; the screenshot below is of a Series 1 turbo diesel, with Bosch pump. Engine had been idling for a few minutes on a cooler day. I think the car was a private import.

To my mind, the car is noisy, and possibly running rich (the exhaust smells a bit "sweeter" than many diesels). It's just had a pump rebuild, motor in/out, turbo overhaul and head service. I can't vouch for the quality of any of these tasks, as they were performed by people I don't deal with.

However, as mentioned, besides the noise it takes a bit of churning to start, runs on and seems somewhat sluggish.

Can anyone offer comments on the screenshot (other than "a bit fuzzy")?

Thanks, Adam.

Unread post by **RichardW** » 17 Aug 2011, 12:17

It can't run rich - that's not possible on a diesel. Well, not at idle anyway!

I would suspect that as it is calling for 7.7° advance and is getting 8, that the static advance on the pump is too much. Never looked at one on a lexia though, so it could be rubbish

addo · Unread post by **addo** » 17 Aug 2011, 12:26

So, I agree "rich" is probably not the best word!

Somewhat sooty.

Should the pedal voltage change with gentle depressing of the accelerator, or only with increased load?

DickieG · Unread post by **DickieG** » 17 Aug 2011, 12:34

addo wrote:Should the pedal voltage change with gentle depressing of the accelerator, or only with increased load?

Pedal voltage changes in line with pedal movement, or should do!

IIRC as the engine is accelerated the two advance figure should show roughly parallel figures.

addo · Unread post by **addo** » 17 Aug 2011, 23:28

I didn't notice any appreciable change in the pedal voltage with accelerator travel. Hmm!

MikeT · Unread post by **MikeT** » 18 Aug 2011, 16:02

It's not uncommon for a cold TD to be a bit smokey though they usually clear up as the engines gets up to temp. Although mine idles slightly higher than yours is showing, the fuel output was fluctuating (due to thick veg oil) between 2.7 and 4.7mg so that's probably ok.

IME, the called-for and actual advance timing rarely match as one is always chasing the other but they should be close, allowing for computer lag. ~8 degrees matches mine under those conditions. Lift sensor and egr looks normal also.

The pedal sensor should follow pedal movement. Mine shows 0.5v (idle) to about 4/5volts (WOT) but it's sensitive to fitment and can be "tuned" slightly.

Does the smoke clear once the temp is 80 and above?

addo · Unread post by **addo** » 18 Aug 2011, 23:21

Thank you Mike.

The smoke doesn't linger, and I got the impression a hot start would barely smoke at all. Noisy bugger, it is.

How is the throttle pot adjusted? Is it the one atop the Bosch pump?

Regards, Adam.

MikeT · Unread post by **MikeT** » 19 Aug 2011, 07:52

addo wrote:How is the throttle pot adjusted? Is it the one atop the Bosch pump?

Yes, but I wouldn't recommend adjusting it for the symptoms you describe (not registering pedal position). Instead, I would undo the two bolts securing the whole pot assembly to the pump body and lift it clear. You will see the accelerator shaft is fitted with a two-pronged fitting that locates into the pot underside. It's possible they were misaligned in the slots rather than the holes.

I've not described it very well but it should all become clear when you lift it off.

DickieG · Unread post by **DickieG** » 19 Aug 2011, 08:09

There is a specific setting that the throttle pot should be set to for when the accelerator is in the idle position. I'll have a look at the diagnostic manual and let you know the specific figure when I'm next home.

addo · Unread post by **addo** » 19 Aug 2011, 09:14

Thanks. I don't have any diesel data, so this is all flying by seat-of-the-pants for me.

The car has a standing electrical issue anyhow (either worn alternator or dying battery) so there is some sorting yet.

Unread post by **Dommo** » 19 Aug 2011, 10:04

Sorry, not exactly on topic here, but I don't understand anything to do with the later bosch pumped Xantia, what exactly do all the extra gubbins do?

My earlier Xantia doesn't have most of that stuff however it does have one microswitch that changes over from on/off at about half throttle, I can't tell what it does? I thought it might affect the running of the AC as the AC does turn off when you pull off, but it doesn't seem to be the cause.

Again sorry about the off topic post, just intriegued is all!

DickieG · Unread post by **DickieG** » 19 Aug 2011, 10:15

I believe the additional gubbins are there to give more accurate fuelling/lower emissions, not too sure off the top of my head about the switch on yours but it might well be to turn off the glowplugs post start heating when full throttle is used.

KevMayer · Unread post by **KevMayer** » 19 Aug 2011, 17:46

The throttle potentiometer sends a voltage to the ECU which represents throttle position. Engine speed is another signal back to the ECU. There's a solenoid actuator at the bottom of the Bosch pump which controls pump timing advance.

The timing angle is adjusted by the ECU depending on engine load.

I had a battle with this system on my old Xantia 1.9 turboD