Limp mode away from home C8 2.2 HDi 170 auto

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I want my XM back
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Joined: 03 Aug 2020, 14:04

Limp mode away from home C8 2.2 HDi 170 auto

Post by I want my XM back »

Hi. My first post on this forum. From 1994 until 2018 I drove XMs, with just two cars lasting all that time if we ignore the tatty 2.5 diesel that I shouldn't have bought. The V6 XM suffered the standard pipe over back axle problem in 2018 and I wasn't up for repairing due to a back injury. Enter a C8 with about 80k miles and 96k now. It has been good other than replacing the butterfly valve on the front of the engine when the nylon gears stripped and made a lot of noise. Common I believe.

I have searched for an answer to my woes and have learned much but I am desperate for advice. Apologies if I have overlooked a previous solution.

We are based in London but have a bolt hole in Normandy. I'm on drugs for the back injury, they affect immunity so have shielded and was pleased to finally get out of the house to France. Ten days ago the car drove fine London-tunnel-Caen ring road. Off the motorway onto the ring road, then forced to double back immediately due to road works closing the peripherique completely. On the slip road back onto the ring road the wrong way I lost most of the engine power and pulled to the shoulder where the road splits three ways including to Paris on the motorway. There would be few worse places to stop, and with kids in the car. I couldn't make sense of it, thought the (6 speed auto) gearbox had failed and was moving the car back and forth on the hard shoulder. In the end, I realised I had to manually shift and, totally underpowered, I aimed for two lanes over which takes you off the ring road into the suburbs. I've never suffered limp mode before and what hard work that is.

There was no engine light showing until I restarted. Disconnecting the battery didn't help. It was 11pm and my priority was getting the family to safety so I limped 50 miles to the house. 20mph up country hills, 50mph maximum on the flat. Next day ordered a Lexia because my original is helpfully in the UK, took the car down the road and it was still limping with EML on. The day after, still with the engine light on, it drove like normal for five miles of Italian tune up. Came home to get a food shopping list, restarted, limp. Had to take the two seater we have registered in France.

My new Lexia Rev C arrived a couple of days ago. I find it slightly odd that most of the engine faults are logged into the BSI faults log rather than the engine ECU. With my setup, I need Diagbox for the engine but that won''t read the faults log so I turn to Lexia.

Relevant faults in the BSI were 299 turbo pressure below reference and 23E turbo pressure 2 - consistency between 3 sensors. I don't even know what the three sensors are - pressure, pressure 2 and reference (ie expected?).

I don't know to what extent the 2.2 170 twin turbo is different to the other diesels. I worked out, by unplugging, that "turbo pressure" is the sensor on the front of the engine after the butterfly valve I replaced last year. "Turbo pressure 2" is mounted top right of the engine, with a pipe disappearing under the rigid pipe from the EGR valve. I have no idea where that pressure pipe goes. I also worked out that the vacuum solenoid front left of the engine controls the (one?) wastegate valve.

I wouldn't have started at the vacuum solenoid but that seems to be mentioned sometimes with these faults. I fortunately have a Mityvac here so checked the wastegate valve holds vacuum and the vacuum supply to the solenoid is good. I tried cleaning the foam in the separate filter, that disintegrated. I can't find a Pierburg replacement but can see a larger Febi part that will do.

Looking at live data on Lexia one day into testing, I noticed turbo pressure 2 was reading atmospheric, which it didn't seem to when I looked before. This seems something to do with the engine being cold? At this point I should have used the Mityvac pressure mode to check pressure 2 sensor but I looked at the sensor on the front of the engine and thought it the same. If we still had access to PSA parts, I would have realised the two pressure sensors are slightly different - one for tube and one for hole with an O ring. I gently pulled the front sensor (pressure 1?) and it broke, leaving most of its stem and O ring near where the EGR pipe enters the intake. Then I realised it was no use as a substitute, finally tested both sensors with the Mityvac and they seem fine from small to large increases over atmospheric.

To remove the broken pressure 1 sensor stem I will have to remove the butterfly valve so the plastic doesn't go into the intake. To keep going, it's broken anyway, I tried some superglue on the recessed stem and restarted.

Now I've got, revving in the driveway, appearing in this order on the faults log,
P239 Line air inlet turbo pressure not plausible mono turbo - is this due to leaking front sensor?
P129B Turbo2 valve VT2 opens less than setting - pressure sensor or it measures mechanically?
P2563 Positioning of turbo2 valve blocked - pressure sensor thinks it isn't changing?
P23E Consistency between 3 sensors

I am getting readings on turbo pressure (we call this 1?) although lower than reference but they always were and is turbo pressure a fair test when parked rather than under load?

On pressure 2, I was surprised to see that only starts to read when the engine is warm.

I am confused what pressure 2 is connected to, I have no idea where the pipe goes and I think a starting point for access might be to remove the air filter to twin turbo pipe (with breather) but that looks like a lot of fragile plastic if I am chasing the wrong thing.

French dealers are usually better than UK, where I gave up in the 90s. I needed an XM height corrector changing urgently in France and the dealer ten miles away was very good. I would rather work this out for myself, although I feel your experience may be needed as these modern diesels have more components than I am used to.

I feel a fool for breaking the front pressure sensor, but it is meant to come out and is likely trapped by aluminium corrosion. The DIY car parts market in France is years behind the UK, lucky if they even ship next day never mind have it in your hands. I have ordered the two pressure sensors and the vacuum solenoid, not because I believe they are all needed but it is so slow getting parts here. Is this anything to do with sensors, or should I be looking at EGR (at least ticks on test activate) or turbo or perhaps put some LHM into it?

Good to have yet another Citroen that's "nice when it's going".

Thoughts? Help. Thanks. Help again.

Chris
Last edited by I want my XM back on 03 Aug 2020, 15:33, edited 1 time in total.

Hell Razor5543
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by Hell Razor5543 »

Hi, and :welc: to the Forum. I LOVE the Avatar name! I am not going to be able to offer any advice, other than (if you need any parts) to contact the forum member citroenxm, who seems to have a Citroen gold mine.

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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by I want my XM back »

Hell Razor5543 wrote:
03 Aug 2020, 15:27
Hi, and :welc: to the Forum.
Thanks James.

Does anybody please have an explanation of how this twin turbo 170 works and all its valves / sensors? Is there an agreed way of testing these electrovalves in situ? Four apparently according to the French at post 288. Then at post 291, after replacing all the valves the problem is still there,

https://www.forum-peugeot.com/Forum/thr ... 73/page-10

I wonder whether one of the three smaller on/off electrovalves is stealing the vacuum. Does that explain no turbo 2 pressure when cold, is it related to recirc? Not that I know what pressure sensor 2 is looking at.

Like opening Pandora's box, having any Citroen start to misbehave then researching how common the fault is. Another web site has a twin turbo (C5) owner in France with code 299 with posters saying change the waste gate electrovalve. He comments better to take the XM, because at least the 130 horses are there all the time unlike the twin turbo 170 where you might get half that.

Should I source a manual if possible, continue to mend, send to the dealer, bonfire? Four valves for the turbo, and all their associated pipework. All buried.

Chris

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GiveMeABreak
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by GiveMeABreak »

Chris, pop your VIN up and I can probably dig something up on this engine for you.

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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by I want my XM back »

VF7**************[VIN obfuscated, can be read by forum staff]

Thanks, I have seen and understood the sticky about contributions to PSA access. Quite reasonable, particularly as time given.

I can see the other three valves front right of the engine, access would be great without the EGR pipe. Plus the flex of the EGR pipe is at the front so not useful, think you have to reach into the depths under the dash and remove from the EGR.

Two on/off vac valves that are obvious and, hidden from view behind them, I think a proportional valve with integrated filter because I can't see a separate filter like the wastegate one.

It would be better to have the valves on the body, but I guess they want an engine complete ready to drop into a car.

Certainly on the French DIY sites they seem to copy the dealer scatter gun approach of changing many things at once.

Chris

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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by GiveMeABreak »

Sitting comfortably Chris: Here you go :-D

I can provide the following for you which may help with the workings of the Turbos on this engine, but as you've already mentioned, if you need any parts info that will cover you for up to 2 years, please do follow the donation link in the table below.
A response to your question by a forum admin will require detailed vehicle information that requires you to have made a current contribution to the Forum.
Donate

Further Information

DW12BTED4 Engine Turbo Specifics:

Special features:
4 cylinders, 16 valves
Direct injection turbocharged by 2 parallel sequential turbochargers
4 turbocharging control electrovalves
air/air heat exchanger(cooling of the turbocharged air)
An exhaust gas recycling device (EGR)
An electric EGR electrovalve with position copy
A low pressure circuit fitted with a transfer pump incorporated in the high pressure pump
A third generation system of filtration of pollutant particles (FAP)

Fixed geometry parallel sequential dual turbocharger

he parallel sequential turbocharging system is based on the use of 2 fixed geometry turbochargers.
The dual turbocharger permits turbocharging of the engine with air:
Turbocharger 1 operates for the low engine speed phases
Turbochargers 1 and 2 operate for the high engine speed phases
C8 Turbo A.PNG
T1: turbocharger 1.
T2: turbocharger 2.
(8) Turbocharger turbine isolation valve 2 (VT2).
(10) Pressure regulation valve "Waste Gate" (VT1).
(18) Turbocharger 2 (Vrec) compressor air recirculation valve.
(21) Turbocharger 2 (VC2) compressor isolation valve.
turbocharger12
makeGARETTGARETT
Type of geometryNot flashingNot flashing
Type of turbochargerGT14GT12
Maximum speed of rotation(rpm)250 000270 000
The DW12BTED4 engine turbocharging principle is based on the use of 2 fixed geometry turbochargers which can operate in single turbocharger mode or in dual turbocharger mode.
The turbocharging system is controlled by 4 pneumatic valves, which are themselves controlled by 4 solenoid valves.
C8 Turbo B.PNG
(8) Turbocharger turbine isolation valve 2 (VT2).
(10) Pressure regulation valve "Waste Gate" (VT1).
(18) Turbocharger 2 (Vrec) compressor air recirculation valve.
(21) Turbocharger 2 (VC2) compressor isolation valve.
(24) vacuum pump.
(25) Vacuum reservoir.
(26) Solenoid valve VT2: Device for control of the valve (VT2).
(27) Solenoid valve VT1: Device for control of the valve "Waste Gate" (VT1).
(28) Solenoid valve VC2: Device for control of the valve (VC2).
(29) Solenoid valve Vrec: Device for control of the air recirculation valve (Vrec).

Operation of the turbocharging system

The turbocharging system is controlled by 4 valves (pneumatic actuators).
2 "All or Nothing" (TOR) valves located on the inlet air circuit of turbocharger 2 including:
"Vrec": Turbocharger 2 compressor air recirculation valve, which makes it possible to cause compressor 1 to operate outside its pumping zone when turbocharger 2 comes into operation
"VC2": Turbocharger 2 compressor isolation valve

2 "proportional" valves located on the air exhaust circuit:
"VT1": "Waste Gate" valve permitting regulation of the exhaust gas in parallel with the turbine of turbocharger 1
"VT2": Turbocharger 2 turbine isolation valve permitting the gradual start of rotation of turbocharger 2

The valves are activated by means of a vacuum.
This vacuum is provided by the solenoid valves (pneumatic control) which are controlled by the engine ECU and supplied with vacuum by the vacuum reserve.
The operation of the dual turbocharger system is divided into several phases :
Single turbocharger mode with "Waste Gate" regulation (zone limited by the EGR zone)
Single turbocharger mode with VT2 regulation (transitional phase permitting the start of rotation of turbocharger 2 to limit thermal impacts and guarantee comfort during the transitions)
Dual turbocharger mode with "Waste Gate" regulation


Approximate limits of the operating zones:
C8 Turbo C.PNG
c: Non-regulated single turbocharger zone.
d: Single turbocharger with "Waste Gate" regulation zone.
e: Transition or single turbocharger with VT2 regulation zone.
F: Dual turbocharger zone.
G: Torque (Nm).
H: Engine speed (rpm).

Key:0
LineDesignation
PinkStart of switch to transition or limit of switch from 2T to 1T
GreenLimit of switch to transition 1T to 2T
Dotted line : GreenEnd of the VT2 regulated single turbocharger mode
Dotted line : BlueSwitching limit for a forced transition from 1T to 2T
Dotted line : BlackSwitching limit for a forced transition from 2T to 1T
RedEngine operating zone limit
Hatched zonesOperating zones which are prohibited in single turbocharger mode (Accessible in dual turbocharger mode)
The zone outlined in green is a compromise zone, it imposes operation in 1T mode even though the consumption would require operation in 2T mode. The operating mode chosen in this zone therefore depends on the operation of the engine (stable, acceleration, ...) and the requirement sensed by the driver.

During sharp acceleration, the transition is delayed until the forced limits corresponding to the limits of operation of the compressors.
There are two types of transition depending on the discharge of the turbocharger.
During a transition, the VT2 valve regulates the turbocharging pressure without being fully open. The transition is referred to as "normal". The transition time is between 500 ms and 1 second.

If the pre-rotation of turbocharger 2 has not begun at the time of the transition, the transition is referred to as "forced transition".

Note: The zones represented do not correspond to the operation during sharp acceleration.
C8 Turbo D.PNG
Key.
O: valve open.
F: Valve closed.
1T: Single turbocharger mode.
1T-2T: Transition from the single turbocharger mode to the dual turbocharger mode.
2T: Dual turbocharger mode.
2T-1T: Transition from the dual turbocharger mode to the single turbocharger mode.
colourvalveDesignation
BlackVT2Turbocharger turbine isolation valve
RedVT1 or WG"Waste Gate" valve
BlueVrecTurbocharger 2 compressor air recirculation valve
GreenVC2Turbocharger 2 compressor isolation valve
Flow chart: 1 mode - turbocharger

Note: You'll need to click the images to magnify them to see flow direction arrows
C8 Turbo E.PNG
Air circulation (as per arrows):
  • J: Exhaust gas
  • K: Exhaust gas + air
  • L: Air
The VC2 turbocharger isolation valve is closed and the "Vrec" air recirculation valve is open permitting isolation of the turbocharger 2 compressor.
The VT2 turbocharger isolation valve is closed permitting isolation of the turbocharger 2 turbine.
The VT1 "Waste Gate" valve regulates the exhaust gas.

Note: The diagram is only a symbolic representation of the air supply function.

C8 Turbo F.PNG
Flow chart: 1T-2T transition mode or 1T mode with VT2 regulation

Air circulation (as per arrows):
  • J Exhaust gas
  • K: Exhaust gas + air
  • L Air
The VC2 turbocharger isolation valve is closed and the "Vrec" air recirculation valve is open permitting the start of rotation and the isolation of turbocharger 2.
The VT2 valve opens gradually permitting opening of the turbocharger 2 turbine exhaust air circuit.
The VT1 "Waste Gate" valve closes gradually then again regulates the exhaust gas.

Note: The diagram is only a symbolic representation of the air supply function.

Flow chart: Dual turbocharger mode
C8 Turbo G.PNG
Air circulation (as per arrows) :
  • J: Exhaust gas
  • K: Exhaust gas + air
  • L: Air
The VC2 turbocharger isolation valve is open and the "Vrec" air recirculation valve is open permitting normal operation of turbocharger 2.
The VT2 valve is open providing the supply for the turbine of turbocharger 2.
The VT1 "Waste Gate" valve regulates the exhaust gas.

Note: The diagram is only a symbolic representation of the air supply function.

Phases of operation

Transitions

Transitions graph.
C8 Turbo H.PNG
Key
M: Engine speed(rpm).
N: Turbocharger pressure.

Solid blue line: Switch from single turbocharger to dual turbocharger mode from 0 to 1000 m.
Solid red line: Switch from single turbocharger to dual turbocharger mode at 1500 m.
Dotted blue line: Switch from dual turbocharger to single turbocharger mode from 0 to 1000 m.
Dotted red line: Switch from dual turbocharger to single turbocharger mode at 1500 m.

Depending on the engine speed and the boost pressure reference value, the engine ECU gives the order to switch to single turbocharger/dual turbocharger transition or to dual turbocharger/single turbocharger transition.
The transition switch graph differs in relation to the altitude (Atmospheric pressure).
The order to switch to dual turbocharger is also given when a system fault is recognised by the pressure sensor downstream of the turbocharger 2 compressor (Example : VC2 valve open).
The transition may be suspended in the event of sharp acceleration. The rapid increase in torque means that the transition must take place as late as possible. The transition takes place when the compressor enters the forced transition zone.
A single turbocharger/dual turbocharger transition may be requested depending on the use of the engine.
A dual turbocharger/single turbocharger transition may be requested if sharp acceleration is detected to improve the low engine speed low load performance in dual turbocharger mode.

Regulation

Depending on the engine speed and the boost pressure reference value, the engine ECU gives the order to switch the regulation from the "Waste Gate" valve to the VT2 valve or from the VT2 valve to the "Waste Gate" valve.
The order to switch from VT2 valve regulation to "Waste Gate" regulation may be given if a C2 downstream pressure sensor fault is recognised.

Internal diagnostics

The calculation of the reduced flow and the calculation of the compression rate makes it possible to identify whether compressors 1 and 2 are in a critical zone (oil leak, over-revving and pumping).

Forced transition

A request for forced transition to the dual turbocharger is issued if compressor 1 has an "oil leak" or "over-revving" status or following sharp acceleration. The rapid increase in torque means that the transition must take place as late as possible. The transition takes place when the compressor enters the forced transition zone.
A request for forced transition to the single turbocharger is issued if compressors 1 and 2 are at the "pumping" status.
The forced transition has special synchronisations, the opening time of the valves thus permitting offsetting to the limit of the switch to transition zone.
In order to delay the transition phase and permit the forced transition phase, the engine ECU delays the control of the Vrec and VT2 valves.
In order to extend the transition phase, the engine ECU controls VT2 and allows a period of time to elapse before controlling the Vrec valve.
The forced transition control phase lasts 500 ms.

Note: The pumping, oil leak and over-revving statuses are detected by the "Internal diagnostics" function.

Back-up mode

The diagnostics function incorporated in the engine ECU permits activation of the emergency strategies associated with the detection of faults:
  • Detection of a positive loop difference relating to the position of the VT2 valve. The engine ECU forces the dual turbocharger mode prohibiting the single turbocharger with VT2 regulation mode and requests a reduced flow.
  • Detection of a negative loop difference relating to the position of the VT2 valve. The engine ECU forces the dual turbocharger mode prohibiting the single turbocharger with VT2 regulation mode and requests a reduced flow.
  • Detection of a malfunction in the measurement of the pressure after the turbocharger 2 compressor. The strategy prohibits the single turbocharger with VT2 regulation mode and deactivates the forced transitions from dual turbocharger mode to single turbocharger mode.
  • Detection of a malfunction in the measurement of engine inlet pressure. The engine ECU deactivates the forced transitions from single turbocharger mode to dual turbocharger mode and requests a reduced flow.
  • Detection of a malfunction resulting in a significant increase in the pressure after the compressor 2. The engine ECU forces the dual turbocharger mode prohibiting the single turbocharger with VT2 regulation mode and requests a reduced flow.
  • Detection of over-revving of compressors 1 and/or 2 in 2T mode. The engine ECU requests the reduced flow

I want my XM back
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by I want my XM back »

That's great Marc. I will donate later this evening. Now we just need to find the boffin who wrote that and ask how that relates to real world fault codes.

When I have read it another few times, it should help me work out whether my atmospheric readings of turbo pressure 2 make sense and whether that is related to the fault I am chasing. The Diagbox live update does show turbo state, which I guess ties in with the modes described. I know pressure sensor 2 seems sound and the main sensor was okay before I snapped it off and await a replacement. I don't know how to tell whether the feed to sensor 2 is leaky or whether the fault is real with valves or the turbo itself. It almost needs a self test routine to work out whether faults are measurement or control, could have been possible one would have thought. The system seems quite fault tolerant, perhaps explaining how you can lose much of the power without the EML coming on.

I've been dialling back the clutch bite point on the wife's C4GP for 7 years. Auto adjusts to the point of dangerous pulling onto roundabouts, manual adjust on Lexia makes it like new. I would like to meet the experts who designed that. Probably the same people as designed this turbo.

For anyone reading this later, I was wrong about the variable vacuum control that is behind the two on/off controls on the front right of the engine. It appears the same 9661960380 as the valve that sits on its own front left of the engine. The filter is dead obvious when you trace the pipework with a finger, on the left side of the oil filler and below the EGR pipe. I haven't confirmed the part number on the valve itself, just looks the same.

Edited because I was referring to the single valve on the left as waste gate control. The diagram from Marc above and a note in a French forum explain that waste gate is the hidden variable valve in the group of three. So I haven't tested vacuum on the waste gate diaphragm. The single one I checked is VT2 which spins up the second turbo. My fault said low pressure 2 so it could be that single valve, or maybe the main waste gate control tends to trigger pressure 2 even though both sides of the turbo are affected. Or the two on/off valves. Take your pick really.

The French might have more of these engines as they seem to write about them a lot. Plenty of references to changing all four vacuum valves and the car being transformed. Should have ordered more valves.

Chris

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Doo
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by Doo »

Looks like fun! I imagine the small turbo spins up at idle to around 2k rpm then opens the wastegate after the big turbo takes over. That would be your atmospheric reading. They only work together for a very short period so one will almost always be spinning for nothing while the other is working. That's my take on it.

Heat and oil takes it's toll on these valves...

jml
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by jml »

Hi Chris,
Sorry to hear of your problems. I too have a C8 2.2HDi 170 Auto - there are only about 100 left in the UK.
I’m a mechanic by background but have been pretty much off the spanners for almost 40 years and I’m sorry to say that much of the modern stuff leaves me totally baffled.
I have downloaded hundreds and hundreds of pages from Citroen service and have all of the pages that Marc has shown above. I have read these time and time again but, unlike yourself, I am still not much wiser.
Anyway, mine has been so good - now at 161,000 miles - that I am determined to do all I can to keep it going for as long as I can (besides there’s nothing modern that appeals to me). Well, bearing in mind my comment earlier about so few being left, when I saw the opportunity a while ago to buy a complete engine, auto box and all ancilliaries, I jumped at it. I’ve totally dismantled the engine and stored all of the components in case I ever need anything.
Well, the point of my post is to say if photos of any parts could help then just ask and if you end up totally stuck for anything then I may be able to help - just praying that whatever component it is doesn’t fail on mine straight afterwards !
I too had to change the air ‘doser’ valve on the front of the engine like you, but at over 140,000 miles, and it was only thanks to the helpful guys on here that I identified what was wrong.
Good luck and PM me if you think I might be able to help.
Cheers
Julian

I want my XM back
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Re: Limp mode away from home C8 2.2 HDi 170 auto

Post by I want my XM back »

Julian,

Thanks for your reply and everything you say is interesting, hopefully we can both keep ours going and share what we learn along the way. Yes, it is a special car, found mine by complete fluke. Chap in banking bought it used for his kids' nanny. Nanny was let go, and the C8.

Slow to reply because I haven't logged in all day, got an email first thing saying my Yakarouler package was on the way (a day late) and I didn't want to miss the delivery so was lingering by the front door.

Worked on it most of the day, it's going again and better than ever. I don't remember it pulling this well even when I bought it two years ago. Flat out, snatching the next gear and off it goes again. I haven't done much in the end but I have theories. Otherwise I haven't mended anything and it will limp tomorrow.

Will share more in due course.

Chris