An unwelcome ECU connector suprise

[falling-out-with-my-car]

apologies for bringing this to the forefront again but I am having engine management problems similar to the original poster
with my 1998 S2 xantia 1.9TD SX estate XUD9.
I am now tempted to lift the ecu plug and have a look at it as the lift sensor checks out on the ohm meter.
although as Jim says this can be a bit hit and miss without a lexia, however I would like to know I had covered every base before I commit to buying expensive injectors.
This maybe a daft question but do I need to allow the electrical system to discharge with the battery disconnected before removing the ecu plug for a minimum amount of time like you would with the airbag system, or do I just disconnect the battery live and leave the earth connected? and secondly can someone please advise as to where I might find my return line restrictor as I have been running on dewatered wvo and diesel mixed? many thanks
Nigel.

[addo]

Don't worry about the battery disconnection - just unplug the ECU connector.

[CitroJim]

Nigel, no need to disconnect the main ECU connector for the Needle Lift Sensor. It has it's own two-pin plug located on the RH end of the cylinder head. This plug can be a cause of problems in it's own right. It's the perfect access point for checking the resistance of the sensor.

Personally, when disconnecting any ECU connectors I always disconnect the battery.

[falling-out-with-my-car]

Jim,

Thanks I have tested the resistance on the lift sensor with ignition off and it reads 111 ohms so at a guess Maybe its alright?
I am interested in this ecu plug fault found by another member of the FCF I have been down some very bumpy roads in the last three days and the engine management light has been flashing on an off staying on for a few seconds and going off again sporadically so I am guessing that it may well be a wire somewhere.
can anyone confirm if the 1998 S2 xantia 1.9td had these TDC plugs over the gearbox please?
I shall disconnect the battery when unplugging the ECU.

one final thought does the ECU remember the fault and need to be reset after a repair has been done?

sorry so much to ask I am still learning after seven years of owning my xantia.

Thanks in advance

Nigel.

[CitroJim]

Hi Nigel, sorry for the delay in responding to this and your PM. I've been strictly forum read-only today at the salt-mine

That the sensor reads OK continuity-wise does not mean it's good. Only a Lexia can prove it 100% good. Also, the TDC sensor on the top of the bellhousing could be duff too although they rarely fail.

The ECU needs both signals as it calculates the time difference between the two to judge timing.

One test is to unplug each in turn and see if the rev counter stops counting revs. Either the NLS or TDC sensor will make the rev counter function. You should, if everything is good, hear a distinct change in engine note on disconnecting either sensor as the timing goes off and awry. No change means generally the sensor (or pump - see later) is duff.

I believe, but can't be certain, that the EML will go off once the fault is clear although the fault code will remain stored. The EML will hang on for a time on startup to let you know there's faults stored.

All the above is really hard to do and can be non-conclusive. Try to get it on a Lexia and then you can see precisely what's happening. On live data you'll see the timing value the ECU desires and how good the pump has been at achieving it. Both desired and actual values should be identical.

I warn you that I have seen a case or two where the electronics have been fine but the pump has got itself stuck. Usually because of excessive wear in the timing device or because the fine hydraulic passages that control it are blocked. Your pump may be a victim of WVO if the electronics seem OK.

[cachaciero]

I always assemble all my connectors with a liberal application of Wax Oyl and apply liberally around the assembled connector, pretty well guaranteed to keep moisture out and keeps rubber boots etc. supple for not a lot of cost.


cachaciero

[Rhothgar]

It's funny how 17 years on this post is actually becoming more relevant!

I was searching for the forum members' views on di-electric grease and stumbled on this post.

As some will know I had a corroded ECU pin issue back in 2019 which I found and resolved.

Just wondering if this ACF50 is really as wonderful as it suggests. I maybe could do with searching for a little tool that will gently clean up ECU terminals before applying some ACF50.

For general use, body earths etceteras what about cleaning up, spraying with ACF50 on contact surfaces, reconnecting, spraying again, letting it dry and then putting a layer of Vaseline over. Probably not needed but thinking belt and braces.

[CitroJim]

ACF 50 is the dog's doo-dahs for rust treatment and proofing Roger but I'd not put it anywhere electrical connectors of any sort...

Ditto WD-40 and every other kind of snake oil and snake grease.

All I ever use is a small smear of electronics-grade silicone grease after a clean-up - if necessary - with electronics grade contact cleaner such as Servisol.

For earth terminals and the like, clean them up until they're shiny - Scotchbrite is your friend - and then coat in silicone grease. Vaseline is OK for temporary use but will rapidly deteriorate when exposed to air.