Lamda sensor voltage reading

[Jimm218]

Hey,

I've been having a bit of trouble with a miss fire on my 4.2. Plugged in the computer and it has a fault with Lambda 2. Cleared the faults and then fired her up. Discovered that i keep getting a voltage of 1.83V and the MIL light comes on.

Does this mean the Lamda sensor is broken? Id have expected a low voltage in that case.

Thoughts, ideas and suggestions please.

Thanks

Jimm

[tvrgit]

Jimm218 said:

Hey,

I've been having a bit of trouble with a miss fire on my 4.2. Plugged in the computer and it has a fault with Lambda 2. Cleared the faults and then fired her up. Discovered that i keep getting a voltage of 1.83V and the MIL light comes on.

Does this mean the Lamda sensor is broken? Id have expected a low voltage in that case.

Thoughts, ideas and suggestions please.

Thanks

Jimm

I had a very similar problem - the sensor has three wires, one of which is a feed and the other is a signal. I can't remember if the other is earth or a pre-heater or whatever - but anyway, mine had a cosntant reading and the MIL light was on. Turned out to be the connectors (they sit on top of the bellhousing) - one was packed with dielectric (waterproof) grease, the other wasn't - the second one was duff. Cleaned the connector, added grease, sorted. Worth a try before you buy a new sensor.

[Tanguero]

Or that bank that the sensor is on is running rich enough to max out the sensor.

[Jimm218]

I'll have a look for the connector. Are we looking at a from beneath or from above procedure? I have fairly small hands and long arms!

What would cause it to run that rich on that bank? It is showing no other faults.

[tvrgit]

The connectors are accessible (just) from above. You'll probably need to remove the fuel rail though, just to get your hands down between the cylinder head and the bulkhead.

If you go to my web site http://www.tvrgit.com and select "previous diary pages" on the left, then go to 6 July this year, you'll see an explanation and some photos of what I had to do.

[Tanguero]

You should be able to get to the connector from above, though its a bit of a stretch. You need to remove the battery cover panel and with a torch you can probably see the plugs down either side of the bellhousing.

A misfire on one cylinder will pump enough unburned fuel into the exhaust to max out the lamda sensor. Though it it more likely to be a connector problem and that is easier to check first. I ended up replacing the connectors with properly waterproof AMP ones.

[Jimm218]

Ok that sounds reasonable enough. I'll get in there and see what I can find. Thanks for the how to as well.

If that doesn't cure it I'll start going through the ignition system on that bank. On thing I have noticed is that it is an intermittent fault. Some times it does it sometimes it doesn't. When the sensor isn't giving an off the scale reading it seams to give a similar reading to the other sensor and the adaptives are a couple of percent.

I'll keep everyone informed of progress! Just hope there is some, its hard working in the dark.

[Tanguero]

The great lamda sensor chicken and egg game. Is the missfire causing the lamda to max out or is the dodgy lamda sensor causing the misfire?

[Jimm218]

Still not sorted this

It got worse. I tried to come home from work last week and it ran so rough that it stalled about 6 times (i live 3 miles from work) on the way. In the end it rolled on to the drive.

Plugged it in to look at the codes and there were faults everywhere. Lambdas, AFR, Crank sensor, water temp control, t-pots. The whole damn lot!

Cleared the faults. Tried to fire it up and it wouldn't kick over. Found the nearside lambda connector cracked it open and it looked ok. Sprayed it with some electrical contact spray to keep the water out and worked it a few times. Car still wouldn't fire. Tried alsorts of batteries off different cars and still would not fire. Just going click. Fuel pump seems to prime then wait a min or so and prime again. There are clicks of relays to accompany this. We finally jumped it earlier to day which brough it to life, sort of.

The airbox on the nearside was off the car but everything else in place. Ran like s***. Idle was around 600rpm. ECU showed crank fault, and Lambda 1 and 2. AFR both BAD. MIL light coming on and off. Cleared faults and the car warmed up a bit. Crank sensor fault disappeared. Lambdas both Fault and AFR bad on both sides.

So whats up? Have we done something silly by running with out the airbox? Does it need to see a certain air pressure across both the airboxes? I'm kinda running out of ideas and am bored of working in the dark and rain! Can anyone help at all?

[mikesr]

Faults appearing everywhere is often a symptom of water in the ECU connector.

[ridds]

Yep, I'd say damp ECU as well. Likely if the car is used a lot and with the recent poor weather.

[Peppe]

If it isn´t water in the ECU connector, check the HT leads. Bad HT leads can give you a lot of noise in the sensor signals. I would start by checking the HT leads on the bank that had the high lambda reading.

[Jimm218]

SORTED!

Thanks everyone. Took the ECU connector apart and got drowned in coolant. Will have to be more careful topping her up next time.

Running sweet as a nut now.

[ridds]

Some cars have coolant pipes inside the car above the ECU so have a check up there.