MIL help...... again!

[tejr]

So its happened again, this time i was able to get the laptop connected to the ECU while the MIL light was still on...

I'm getting both Lambda's coming up as a fault and weirdly one throttle pot is totally off (which was replaced about a year ago)..

If i d/c the bad throttle pot idle jumps back up to where it should be (ie, not 500-600rpm)but both lambda's show up as faults showing 1.8v constantly.. sometimes the bank with the d/c throttle pot will jump back to "ok" and then "disabled" for the lambda control..

Yesterday the car was near perfect after having its 1000mile run in service and decats! today I give it a wash and it does this to me Was looking forward to a run with the decats as it sounds gorgeous! Btw, I'm very careful of how I wash the car, i try not to let any water drip into the bonnet..

I've had a look at the wiring under the bonnet and it looks dry (just a few drips on the coil packs, nothing major) and the ECU is bone dry inside..

It must be water getting in somewhere to throw off both lambdas and a throttle pot?!

With T-pot on the driver side bank d/c -




iirc, this was with the t-pot re-connected

Edited by tejr on Sunday 4th December 13:30

Edited by tejr on Sunday 4th December 13:31

[mikesr]

Have you checked the ECU?
It is possible for water to track down inside the harness and emerge in the ECU connector.

[tejr]

Yeah that was one of the first things I checked, the inside of the ECU was dry. I took apart the connector also and theres no moisture from what I can see in the connections themselves, though some connections do look a bit green from corrosion, but nothing major..

I'm sure its water but I just can't figure out where its gotten in and where its causing the havoc!

So annoying! all i want to do it take it out for a drive after patiently putting 1000miles on it since the rebuild!

[Tanguero]

When I had exactly these symptoms, I tracked it down to water getting into the lambda sensor connectors. I replaced them with properly waterproof AMP one and haven't had the problem since

[tejr]

Things are slowly but surely getting worse! I thought maybe I have two seperate issues with water in the lambda wiring and a dodgy t-pot (as previously when I had the MIL light on the car would idle, and when I had the issue a few weeks back of low idle there was no MIL light, now I have both!)

However, I went out there to see if I could swap the T-pot wiring over to rule out the (water in) wiring or the t-pot itself, but it seems now BOTH t-pots are reading 30-50% at idle! So the car will barely idle..

Also, in addition to before, "water temp" and "dthrottle" were bouncing between "ok" and "no control"

Anyone local willing to lend a hand?

I've no idea where to go from here, its too dark to do anything now but I can't see any water anywhere I think it would cause such havoc..







ps. would a shorted out lambda read 1.8v or 0v?

Edited by tejr on Sunday 4th December 16:48

[tejr]

Ok, I've been looking at the ECU wiring diagram here -



And assuming TPS = Throttle pot, then maybe if there was water somewhere and it shorted lambda1 and 2, the next in line would be t-pot 2 ,and then t-pot 1.. ?? Although I would have thought a shorted out T-pot would read 95%(full throttle?)

Is there another connector/harness that leads to the ecu somewhere else that might be in harms way? One that carries both tpots and lambda signals?

Edited by tejr on Sunday 4th December 17:36

[Peppe]

On the early Cerberas there is a connector underneath the coolant expansion tank. The connector is between the ECU and the engine loom in the electric diagram. It is common that water come in the connector and causes a lot of problems with the engine.

[tejr]

Thanks for the info!

Is it inside the cabin or in the engine bay?

[N4 FTW]

Peppe said:

On the early Cerberas there is a connector underneath the coolant expansion tank. The connector is between the ECU and the engine loom in the electric diagram. It is common that water come in the connector and causes a lot of problems with the engine.

This may be the issue I have too, is it directly under the expansion tank?

[tejr]

By the way, if anyone has a pic or a diagram that would be good If I get a chance to have a look tonight it might be a bit tricky fumbling around in the dark with a torch!

Theres no way the water is going to evaporate away itself in <4'C temperatures

if I get there first I'll post a pic..

[Peppe]

The connector is in the engine bay, follow the engine loom and there should be a connector before the loom goes in to the cabin.
On newer cars the connector is moved in to the cabin, then you will find it in the passenger footwell. It is a 19 way connector (J10 in the diagrams).

Edited by Peppe on Monday 5th December 20:13

[tejr]

Many thanks for the info Peppe Is it easy to reach?

[tejr]

With the car not running should the water temp show "no control"?

Good news is I've now only got lambda 1 showing 1.8v, lambda 2 is down to 1v (normal for engine off?) and both throttles are showing the correct signals (~19%)...

There is no engine loom connector either in the cabin or under the expansion tank though? So I've no idea what is wet? I can see the 'even' lambda plug with a torch and from the outside atleast it looks very dry... can't see the odd bank.. (which is lambda 1 and which is lambda 2?)

[Peppe]

I found my connector (J10)on the side of the footweel, behind the carpet where you get to the hinges for the door. The best way to know if it is the right connector is to check the colors and the gauges on the wires that go into the connector. When checking in the diagrams I can see that the only signal that goes through this connector which has anything to do with the sensors you have problems with, is the heating for the lambdas.

Some older Cerberas with the 941ECU have a bulkhead connector that can cause a lot of trouble, sounds as yours doesn´t have that connector. My Cerbera is a 1999 sp6 and it doesn´t have the bulkhead connector, so it must be earlier than 1999. If you look att the diagram that use to come together with the diagnostic software you can see the bulkhead connector up to the left. Most Cerberas have these wires going straight to the engine without a connector.

[tejr]

No, I don't think it has this connector either. I followed the ecu cable by feel up to the bulk head and could not feel for a connector, and there is definitely nothing under the expansion tank...

Any idea what other connectors bunch the throttle and lamdas sensors together? Im going to try and waterproof as mamy connectors as I can on the weekend..

[Peppe]

If you don´t have the bulkhead connector, it is just the connectors at the sensors and the ECU.

I would check all minus connections between the battery - chassis - engine - ECU. I had a bad connection between the battery and the earth point under the dash that gave some strange readings from some sensors.

Try to measure how the 5 volt feed to the throttle pot, it should be steady with the car of and started and very close to 5 volts. If not steady you have a problem with the ECU. There is a topic about this in the SP6 forum.