11 replies to this topic

[martinroger]

Back for a second "photo-tutorial". Direct access to the pictures is HERE.

 

LY36 started developing intermittent lambda sensor issues a while back. Every 60-80ish miles I would get a micro-interruption of the postcat lambda sensor that would trigger a MIL on the dashboard. I tried linking this to either vibrations, humidity, potholes, or something. I couldn't find any other cause than a faulty sensor or wiring.

Upon switching the diffuser for a TAT one, I saw that the lambda wires looked tatty, so I decided to change the postcat sensor and see how it goes from there. You can find the postcat sensor for £20-25 easily, be careful to not be mistaken with the pre-cat sensor. Part number is 9201421 , or item 7 on here.

 

The procedure to change the lambda sensor is not exceptional on the VX compared to other cars, but things can start to go sideways if - like me and so many before me - that pesky little dude has decided to be stuck.

 

HEALTH AND SAFETY WARNING - You will be working upside down, possibly partially under the car. By all means :
- Wear gloves, you may be late on your tetanos vaccination 

- When jacking the car up, either do not work underneath or do not leave the car on the jack. USE AXLE STANDS IF YOU NEED TO GO DOWN ON HER.

- Wear protective eyewear, even if you then look like a dork like me. ESPECIALLY IF YOU HAVE TO USE A BUTANE TORCH

- IF USING A TORCH, have a friend or roommate not very far in case things go awry. Fire extinguishers get you extra points.

- BEER GOGGLES DO NOT QUALIFY AS PROTECTIVE EYEWEAR

 

Step 1 : Prepping the tools

In addition to all the PPE I mentioned in the part in bold up there, here is an outline of the tools you may need to undertake this task :

• A 22mm spanner, possibly a flared one
• A breaker bar
• WD40 or PB Blaster
• An 8mm spanner or socket
• A cruciform screwdriver
• Allen keys
• Zip ties
• A wheel nut remover
• A jack (and a hockey puck in my case)
• A replacement lambda sensor
• A wire cutter
• A butane or butane/propane torch in case the sensor is REALLY stuck
• A small hammer

This should cover most of your needs for this operation.

 

Step 2 : positioning your VX

 

This step is very personal... I like to first balance the rear wheels on two pairs of brick. It allows me to slide my standard height jack in an easier manner with the hockey puck on top, and also it lets me have easier access to the diffuser's screws without actually removing the wheels/jacking up the car.

With crazy fingers you could do everything without removing the N/S/R wheel and wheel arch... but I don't have crazy finger.

 

 

[martinroger]

Step 3 : removing the rear diffuser

 

This is the easy bit (and I got a bit trigger-happy with the camera, sorry !). Putting it back on will not be as easy

There are 5 8mm bolts towards the rear, 2 larger button socket head bolts on the wishbone mounting points, and two small cruciform screws in the side trim that need to be removed. Whichever order you follow, make sure you support the diffuser at all times in order not to bend it.

 

The rear 8mm bolts : 

 

The front button head bolt : 

 

The diffuser and its L-bar, removed and set against the brick wall :

 

[martinroger]

STEP 4 : Getting the lambda sensor unstuck

 

The lambda sensor you want to get to can be found after the cat (the bulge in the exhaust line) and features a flat connector that is in the left rearmost quarter of the engine bay, next to the wheel arch. Here is the guy (notice the smug look): 

 

 

There are a number of ways to unseize a probably-seized lambda sensor. It is just my advice, but you should try things in this order : 

 

- First just use the 22mm spanner (or special lambda socket and ratchet ) and try to undo the little guy.

- That usually fails. Your second best shot then becomes using a breaker bar to gain leverage ...

- And it may not suffice for you as it did not for me. You may then position the spanner neatly against the sensor and gently tap on the spanner with a light hammer to "break" the seizing between the threads.

- At this stage your frustration may be growing. Have a coffee, and whip out your favourite can of either WD40 or PB Blaster (or duck grease... whatever greases your oars). Soak everything and let it penetrate (ah ah ah). After that, repeat the steps I just mentioned, see if the product did anything.

 

Then you may find yourself in a situation similar to mine : you have a stubborn sensor, it is really not moving and/or you really need to go back to the gym. It is then fair game to WHIP OUT THE BURNING FLAMES FROM HE.. wait no. It is fair game to get your favourite workshop butane torch. Or propane. Or mix. As long as it makes high temperatures.

All the while being careful with it, start heating up the threaded stub in which the sensor is bolted, all the while trying to avoid heating the sensor too much.

Make sure you do not set anything on fire and that most of the flame is directed in the firewall area.

Once the exhaust stub is starting to faintly glow cherry red (no pictures of this... I didn't feel manly enough to handle both camera AND torch under the car), put the torch away and spray a drop or two of WD40 on the sensor but not on the stub. This should cool it quickly and make it shrink while the exhaust stub is still hot. (You may not need to do this, but the smoke it makes is very cool and I like its smell).
Grab the spanner, be wary of hot bits and just undo the sensor, which should now move with many creaks and squeaks.

 

Note the cool smoke :

 

 

[martinroger]

Step 5 : Removing the culprit

 

While paying attention to the hot bits you just unleashed burning hell onto, remove the lambda sensor completely. It is a good idea at this stage to wait for the exhaust to cool back down to near-ambient temperatures and to run a thread chaser in it to clean any debris. 

 

I also like to cut the wires at this stage to get the sensor a bit more easily, as unscrewing it twists the wire. Extra points for dramatic lightning of the tools at this stage.

 

The culprit : 

 

 

The dramatic wire cutters : 

 

 

 

[martinroger]

Step 6 : Removing the N/S/R wheel and wheel arch while things cool down

 

Start by opening the engine bay to get some light in there. Then loosen the wheel nuts using your favourite tool to do so (unlike what is pictured, you should use nylon-covered 17 and 19mm sockets).

 

 

Then jack the car up. I personally like to use a hockey puck to spread the load and then I aim for the chassis beam and crossmember corner that is roughly at the level of the door handles. When jacking up keep an eye on the puck to make sure nothing gets pushed in. No need to jack up high in this case, just enough to free the wheel.

 

The hockey puck (and imprint of the chassis beams) :

 

 

Once the wheel is out, undo the wheel arch liner - I don't have pictures of this because mine are a bad example : they are holding in there without any screw or rivet because the rawl nuts are either gone or buried under years of grime... but it should be fairly straightforward anyway. Be careful when extracting the arch liner.

 

It is also a good opportunity to check you hub carrier bolts, toe links, brake pads, wheel bearing, ABS wiring (like mine that is really looking like crap for instance).

 

 

[martinroger]

Step 7 : locate the wiring, and remove it

 

At this stage you will see a thin loom running along the edge of the wheel arch liner towards the rear of the car : 

 

 

Guess what ... it is your lambda sensor wiring. Remove the arch liner if it is not already done and cut up all the zip ties securing the wiring (if there are any left... in my case one was broken and stuck behind the arch liner).

 

You will now have very good access to the flat connector of the lambda sensor and you should be able to extract all of it very easily :

 

 

 

 

[martinroger]

Step 8 : screw it in, put everything back together, reset the error codes

 

Check that the exhaust isn't hot anymore. It should be warm to touch. If not, have another foamy one on the house.

 

Start by threading the sensor back in the pipe. Make sure the threads are clean on the exhaust, and covered in anti-seize grease on the sensor (it may come pre-coated). 

While threading in, pay attention to the wiring, to make sure it doesn't entangle itself too much. 

 

 

 

There is probably a recommended torque for the sensor, but alas you may be in a similar case to mine : impossible to get a torqued ratchet in place, no special socket for the sensor either. If you are fine with it then, just liberally tighten (enough, but not too much) until the pipes start moving around a bit.

 

Once this is done, re-route the wiring as it was before, securing it with zip ties to avoid rubbing and burning on the heat shields. 

Re-connect, secure the connector with a zip-tie (make sure the latch clips in, on the connector).

Put the arch liner and wheel back in place, tighten wheel bolts, and unjack the car on the bricks, gently.

 

Grab your favourite OBD scanner (in this case ODB fusion), put the key on ignition but don't start the engine, and reset any DTC or Freeze Frame that triggers the MIL.

Once this is done, turn the engine one and let it go to tick-over to make sure that the ECU starts using the postcat lambda, like in the below picture (fuel system 1 status 2).

 

 

Congratulate yourself, go to the pub, and witness France barely being beaten by England in the 6 nations while having a beer. Have mixed feelings between the loss and the fact you fixed that damn lambda sensor issue.

 

 

[smiley]

Very good.

 

If you're ever back in that area: Have a look at your abs wiring, and make sure it's tywraped away from your tyre, as it allready started eating in. Put some heat wrap over your ubend. It's allready melting away your mudguard

[martinroger]

Very good.

 

If you're ever back in that area: Have a look at your abs wiring, and make sure it's tywraped away from your tyre, as it allready started eating in. Put some heat wrap over your ubend. It's allready melting away your mudguard

 

Thanks ! 

 

I need to redo the ABS wiring completely on all four corners. The gap in the protection sleeve and blue tape you see is from a previous owner's repair with simple electrical dominos. I have some superseal connectors and a lot of good heatshrink tubing, I just need to find the correct gauge wire to make some waterproof extensions.

 

Agree with you on the U-Bend... thing is it has been that way for ages and the mudguard is done melting now. But you're right, I should wrap it anyway !

[oblomov]

 

Agree with you on the U-Bend... thing is it has been that way for ages and the mudguard is done melting now. But you're right, I should wrap it anyway !

 

 

Nice review, like the sense of humour.  My liner is that way too, been like that since I had the car but never gets any worse.  

[smiley]

The liner is showing effects, but could get to other areas also.

There is a reason the oem bend has a shield.

 

There was a callback in the early days for the rears that were not heat treated.

Edited by smiley, 05 February 2017 - 01:16 PM.

[martinroger]

The liner is showing effects, but could get to other areas also. There is a reason the oem bend has a shield.   There was a callback in the early days for the rears that were not heat treated.

There is really not much there else apart from the lambda loom and then the clam... but you're right, I probably should heat shield this.