Engine/ Fuel Management Electronics

[Candles]

The symptoms are consistent with the suggestion above of a failed Coolant Temp Sensor (CTS) but you need to check with ElanScan to see, or it may throw up a fault code for it:

Paperclip Test

There is a way of checking the sender with a multimeter, but you need to be a little bit handy:



Candles

[GeoffSmith]

I've got a gut feeling that this is the CTS. I know this is well off topic, nothing to do with ElanScan and will probably get move into some backwater to get forgotten, but here goes........

My Polo had become troublesome to start from cold and got worse each day. Spark and fuel seemed fine and the strange thing was that it would crank over for a couple of minutes without so much as a cough before finally struggling to very weak running but quite frequently stalled. After about 30 seconds of lumpy idle however, it picked up and ran fine.

I'd found an OBDII reader similar to ElanScan but not having an OBDII interface (similar to the ElanScan interface) I was stuck. Thinking about it logically, I deducted that the CTS had failed by going leaky or presenting a lower resistance than normal to the ECU. This would make the ECU think the engine was warm and would be most apparent at cold temperatures when the CTS resistance was at its highest (see Candles' post on CTS resistance above and is previous post on the formula for parallel resistance: 1/R=1/R1+1/R2). When the engine is cold, it relies on the ECU to enrich the mixture (pulling the choke out Pinky ). I decided that cranking it over and over eventually built up enough fuel that it could eventually struggle into life but still the mixture was too weak for a decent idle until....... the O2 sensor had warmed up sufficiently. As the ECU detected the O2 sensor signal, the car goes into closed loop control and the ECU then adjusted for the lean mix and the car ran fine. Although the CTS was out of specification, it did not throw up a CEL as the CTS signal was still within the expected range

The way I proved it on the Polo was by disconnecting the CTS to make the ECU think the brass monkey's balls were dropping. It immediately sprang into life but the exhaust fumes were a bit black as one might expect. Letting it run for 30s allowed the O2 sensor to come online and I plugged the CTS back in.

An OBDII reader would have highlighted the problem to me immediately as would ElanScan if this is your problem. The Polo and my S2 have the advantage of having an O2 sensor, but the SE hasn't so a consistently lumpy performance is to be expected.

It might be worth you disconnecting the CTS (read this to see what you're looking for) to see if you can get it started any better.

[rip]

Scanned earlier today.
The ECU is seeing a coolant temp of -40.
CTS is showing as faulty, but the fault first occurred after a minor repair to the coolant expansion tank.
Could a wire have been disturbed, or is the sensor at fault?

[GeoffSmith]

Pound to a pinch of s**t, the wiring has been broken somewhere. Open circuit = very cold.

[Candles]

Probably still unplugged. Check by the CAS:



Bit fiddly to get in there but possible!

Candles.

[rip]

Thanks for the pic, candles. That end looked ok. I hope the wire has not been broken elsewhere because it is tied together with a load of others.

[a5gcd]

Scanned earlier today.
The ECU is seeing a coolant temp of -40.

This occurs if the CTS is disconnected or faulty showing an open circuit.

I have recently replaced mine with an Intermotor equivalent part number 55511 from my local Factors at £20 inc.

[GeoffSmith]

Geoff,

Are you certain it has the same characteristics as Candles' post at the top of the page? If it is, where have you been hiding? The CTS has the same characteristics as the Stevens Esprit and a couple of them are off the road due to lack of CTS.

Geoff

[a5gcd]

Geoff

This is an equivalent to the GM/Isusu 8-25036979-0 quoted on WikiLEC. It is used in the Vauxhall/Opel Monterey 3.2 V6 among others. It plugs straight in. Intermotor are part of Standard Motor Products based at Nottingham, see http://partfinder.smpeurope.com/index.h ... alue=55511 .

I tried to get a spec sheet from them but couldn't so I checked the temp/resistance characteristics and they seemed near enough. I put it in, checked it with ElanScan and all was OK. See scans attached.

Bromsgrove Motor Factors (at Worcester) sell it at £20 inc

Geoff

[hilda]

Hi.

I've been away which is why there has been a delay.
Problem now solved, it was the Coolant Temp. Sensor which has been replaced
Thanks for all the help.

John

[GeoffSmith]

:SMUG BASTARD SMILEY:

Glad you got it sorted John.

[Candles]

Smart ass. Good work.