G60 smoking ... Lamda probe, wiring or ECU hose??

[Andy T 0]

Right, I fitted a new master cylinder to the C on friday night. I unclipped the Lambda probe wiring from holding clip on the bulkhead to give me some room. I spilt some brake fluid in the engine bay so I flushed it away gently using a hosepipe.

 

I took it out for a spin and the car drove fine. Saturday morning it was great for 20 mins, but then half an hour later I started it up, and it was chugging at idle. Five mins later it would hardly drive and was spurting out black smoke! :(

 

I drove it straight back home at this point. I unplugged the lambda probe wiring loom from the connector on the rear engine mount - there was a little water inside and the pins were slightly corroded.

 

Today I cleaned up the contacts on both sides of the connector and sprayed them with WD40 to get any water out. I also unscrewed the earthing wire from the loom to the earthing point near the connector, it was pretty corroded so I cleaned both contact points up. I then checked continuity from the earthing point to the battery -ive, all ok.

 

After doing this I took the car for a spin. It ran absolutely perfectly 8) at least it did for eight minutes, then it started to splutter and kick out black smoke again. The oil temp had just reached 72° when it started going wrong, could it be temperature related?

 

I have read posts about disconnecting the lambda sensor, I tried it and it did seem to run better. I have not tried taping up the WOT switch yet, shall I do this and still run the car until I can get the problem sorted?

 

Has anybody got any ideas on what it could be? have I disturbed something when working on the car, or is it just a coincidence? The car has always ran perfectly in the past. Could it be a wiring/fuse problem, or has the lambda sensor gone?

 

Also, will I have done any damage to the platinum plugs/lambda probe/cat by driving it like this? I only drove it for about 4 miles at low speeds.

 

Cheers for any help.

[Andy T 0]

Taped up the WOT switch this morning, its just hunted at idle and still put out black smoke! Disconnected the lambda sensor loom instead, and runs fine & drives well.

 

Drove it seven miles home carefully with no problems or black smoke, is it safe to run it with no lambda sensor until i can get it fixed?

[Supercharged 2]

You didn't plug it in the wrong was did you??

[Andy T 0]

You mean did I plug it in the wrong way? no, its shaped so that it will only fit one way.

 

Just took it on the motorway and the MPG is much improved with no lambda sensor, 45 MPG!!! :?:

 

I guess im gonna have to remove it to check the wiring, and condition of the probe...

[Supercharged 2]

I meant the wiring... I think its posible to plug it in the wrong way round...?

[Andy T 0]

:?: not sure what you mean..... the plug/socket in the wiring loom mounted to the rear engine mount can only be plugged together 1 way... kinda like this on the socket -

 

[ 1 2 3 [ 4 ] ] so '1' on the 'plug' can't be plugged into '4' if you get my drift.

 

reading some other threads it sounds like it could be a broken/bad wire somewhere in the loom 'probe side' so I think i'll have to remove it all from the car to inspect it properly. I just hope the loom on the engine bay/fusebox side is ok!

 

The probe is probably the original unit so maybe it needs changing after 90k miles...

 

cheers

[Andy T 0]

Did some more circuit testing today -

 

Most of the readings were as expected, but not sure about the purple wire on the loom side - e.g.

 

Probe side -____White l White l Brown l Black

 

Loom side -____Red/White l Brown l Black l Purple

 

 

Red/White & Brown had good continuity to earth, black had none, and purple had just 3volts (was using 12v tester) ??

 

I've read that the purple wire sends the signal to the ECU, so should it have a poor continuity to earth, if one at all ???? also the loom earthing point on the engine bracket had about 1.4ohm resistance when measured from the battery negative, is that ok? (the engine block & cyl. head had the same resistance)

 

Next I removed the Lambda probe from the cat (cheers VW for making it so bloody hard to get a spanner on!!) the probe part was pretty black.

 

It was a proper VAG unit and the correct part number, stamped 05/92 (date of manufacture?) it looks like it could be the original unit but it is cleaner on the outside than I expected? The wiring was all good, no breaks or damage to the insulation/alu hose.

 

I also checked out the braided ECU hose to the inlet manifold. it looked ok, it had been rubbing on the soft silver coloured wiring protection on the bulkhead a little bit but I don't think it had worn through the braiding.

 

Any idea's? shall I get a new lambda probe on it first, or will it get damaged it if it turns out to be another problem?

 

Cheers and sorry for the waffle!

[Timo. 0]

Right here goes. I have just had a lot of problems with my lambda probe and the fatal black smoke. Check the voltage across the two white wires when the engine is running. These are the heater wires for the lambda probe. volatge should be battery voltage (12 volts +) . Then check the volatge of the across the black and brown (probe side). Engine must be up to operating temperature and has been running for at least 2 minutes (The engine doesn't use the signal from the probe until 2 minutes after starting). The voltage should be between 0.1 and 0.9 volts. It should flucuate between these values.

 

Timo.

[Andy T 0]

I checked for 12v across the heater wires and it was okay, but I didn't check for the signal voltage and its off the car now. Is it worth just plugging it in to check this or will I get duff readings from atmosphere!?

 

I think i'm going to replace the probe anyway with a genuine item and also replace the ECU to TB hose, hopefully it will be okay then!

[Timo. 0]

Probe needs to be on the car as it measures fuel/oxygen ratio. Or something along those lines. No point in testing it off the car. I would be inclined to put it back on and test it. Its not the cheapest thing to replace, especially if you find it wasn't the problem!

 

Timo.

[Andy T 0]

Cheers. Just noticed that Euro car parts sell a lambda probe tester for £17, not sure how it works though or if the probe has to be on the car and working or not.

 

After 200 miles of driving with no lambda sensor, i'm getting 35mpg instead of the usual 28/29! so maybe it was due for replacement anyway...

[Andy T 0]

Car all sorted now 8) running like a dream.

 

Replaced the lambda probe (was 12 years old) and renewed the 1 metre long ECU to Throttle body vacuum hose (was very flimsy at the TB end, measured 990mm (shrinkage?) also had wear patches all over it!

 

Also wired an additional earth from the lambda earthing point on the rear engine mount, up to the stud on the suspension tower that the ABS wheel sensor plug mounts to using 36amp cable - now getting 0.2 ohms resistance on the earth circuit as opposed to 1.3 ohms through the rear engine bracket. It looks neat and and almost stock!

 

Guess I betterstart to renew/clean all the major earth straps/points :?

[kongo127 0]

Nice one Andy! :)