Help rescue my poorly Xantia TDI

[ridds]

Hello all, long time lurker and I only appear to pop up when I need help from those more experienced in the quirky world of Citroen!

My Xantia Diesel Turbo Auto appears to have dropped into some torque limiting function. This started with a slow pullaway in first which had been ongoing for a few weeks.

After a recent more spirited attempt at getting away from a junction (imposing truck!) it now struggles to accelerate in all gears. Reading up on others experiences on here with similar symptoms it appears that the AL4 transmission may be issuing a torque reduction command to the fuel pump and retarding the timing to reduce torque.

The strange thing is the car drives fine, no clunking when changing gear, no transmission slip, there's no excessive black smoke or grey smoke from the exhaust.

The car didn't cost me much but in the last 30k miles (now at 130K) I've replaced the cambelt, water pump, cab heater, changed the trans oil (with the correct Mobil oil) serviced it every 5000 miles In the week before this happened I threw £400 worth of tyres and a battery at it and I'm loathed to let this issue kill it.

I've enquired at Stephens Engineering and they want £900 +VAT exchange for the refurb AL4 and £1440 +VAT to supply and fit.

The car is a 1.9 TDI, Lucas pumped, Auto with Air Con but not cruise control.

So, my questions are.

Does this potential transmission fault show in gear indicator?
Can I bypass the de-torque function?
Where can I find the diesel pump advance valve and can this be tested?

Thanks all in advance. If you need other info let me know.


If the answers to all that is no, has anyone got an AL4 gearbox laying around???

[vborovic]

It seems you've got a problem with the turbo part of the TDI engine, i had the similar experience on the previous '98 Xsara 1.9 TD ... when it occurred, I felt the driving of the car became like pushing the brick on square wheels, no extra power to overtake, when all was working the turbo would start breathing at around 3500 RPM, and when the problem started, it was going with snail speed ... what we did on the car was, well, everything but the kitchen sink ... ...

Never found the exact source of the problem, but we had the turbo taken off, repaired (which later came obvious didn't have the need to be repaired in the first place), rechecked, and reinstalled ... one thing that was found was the EGR valve wasn't working, we got a new one ... and also, we had some other activities with the bosch pump (the yearly test failed due to higher emissions that allowed) so we had done a lot to the car, and in the process the turbo got working, almost with the same way as it stopped working ... we believed that at some point, due to several dismounting/mounting of the parts solved the problem all by itself ... of course, after all that, the car wasn't exactly like before, but it wasn't a brick, and that was the best we could get from it ...

[RichardW]

I agree - sounds more like a boost problem than a gear box problem. I think you have been reading Mandrake's thread about his V6 - the AL4 / TD combo is far less clever, so there is no torque reduction. Check for a split in the small hose that runs from the intercooler piping to the injection pump, and then check that none of the intercooler pipes have fallen off - although you would probably know about this, as it sounds (even more) like a tractor under load Check also that there isn't a load of slack in the throttle cable at the injection pump.

[ridds]

Cheers, I'll have a poke around for the boost compensation hose. All the main boost pipes are on and there's no hiss of escaping air which is why I don't suspect a boost issue.

Throttle cable slack has been checked.

No fault codes in Lexia apart from intermittent coolant temp (ECU) which I have changed out and had no improvement in the problem.

There is torque reduction from the AL4 (pin 5 on the trans ECU) and it is signaled to the fuel pump. The fuel pump then retards the diesel advance to reduce power. This is explained in the AL 4 manual and many other descriptions of the fuel pump electronics.

However, it appears this valve may also control the idle timing and there's no issue with this so I'm not 100% that is the issue either!

The symptoms I have are exactly as Masood had minus the pressure regulation issues.

http://www.frenchcarforum.co.uk/forum/v ... =3&t=23029" onclick="window.open(this.href);return false;

[addo]

Seriously, can you be sure it's not a blocked exhaust? I've abused an AL4 more than anyone else I know (how does three miles of flat towing 2 tonnes up hill and down dale, sound?) - yet it still runs fine on a replaced solenoid pair.

[ridds]

Pretty sure. It was fine one day then after a spirited pullaway from a junction felt as if it had lost about 50% of it's previous torque.

[Mandrake]

No fault codes in Lexia apart from intermittent coolant temp (ECU) which I have changed out and had no improvement in the problem.

There is torque reduction from the AL4 (pin 5 on the trans ECU) and it is signaled to the fuel pump. The fuel pump then retards the diesel advance to reduce power. This is explained in the AL 4 manual and many other descriptions of the fuel pump electronics.

You can stop worrying about the torque reduction signal as a cause of lack of power - it's only activated during an upwards gear change. I actually went as far as monitoring the torque reduction control line on my 4HP20 with an oscilloscope when it was suffering from low power problems and confirmed that it was not related to the torque reduction signal. (In fact it was an engine misfire)

Almost definitely you're looking at an engine problem not a gearbox problem, so I'd follow the advice given regarding turbo pipes etc...

[ridds]

Good to know.

What if it has failed in "reduced torque" position though?

How is the solenoid controlled? +12V to activate normal operation. So if I have a break in the signal then it will be in permanent low torque mode. Or is it wired the other way around?

Bear in mind this is an AL4 on a diesel engine and not a 4HP20 on a V6 petrol engine, I know they could be similar but you can't categorically say it will be the same between engines and gearboxes.

[addo]

If you're talking about the transmission solenoids they are modulated by a 100Hz waveform.

But you don't have a transmission problem at the root of all this, I am quite certain.

You'd be surprised what can cause loss of power and stumbles; one of the sneaky culprits being the rubbish factory battery terminals which go high resistance inside. If your pressurised side of the manifold is all good, and there's not air getting in the fuel, or a blocked fuel filter then you likely have a problem with the turbo or exhaust.

[ridds]

Nope, the fuel pump advance solenoid is the one I'm concerned about.

[ridds]

Well I had a good poke around and you were right!

The boost compensator supply pipe that travels via a solenoid attached to the cam coverhad popped the hose off the back of the valve!

Removed, cleaned and soften the pipes before reattaching again. Quick test drive and all is good!

Thanks all.