T4 telling lies?

vitesse · 7th August 2021, 14:51

Having a bit of a love / hate relationship with my now mobile T4. Went to try and help a local 1.8T owner whose car will idle on 3 cylinders but not on 4, doesn’t seem to matter which cylinder he disables.
Good comp. fuel pressure 4.2 bar, no fault codes except for the standard P1520. So I explore a bit and while exploring the engine management a new error report pops-up telling us there’s an open circuit between one of the ignition coils and the ECM.
Moment of joy, that must be it, packed the T4 in its granny trolley and went home. Few hours later the joy evaporated: the owner had checked for continuity and the circuit was fine.

Now why is the T4 telling us one thing and reality another?

Ps. If like this owner you have a Kmaps ECM and the T4 wants you to update the software don’t as it’ll wipe the map, luckily checked first before taking chances.

Regards

Phil-T4 · 7th August 2021, 19:30

Continuity of the circuit is one thing but can it carry the required current?
Say if 19 of the 20 strands in a wire are broken, it will still show continuity but will be useless.

PS never seen that type of error before, it maybe unique to the K-Maps ecu.

stevestrat · 7th August 2021, 19:35

Quote:

Originally Posted by Phil-T4

PS never seen that type of error before, it maybe unique to the K-Maps ecu.

Would it be worthwhile contacting Kmaps?

Yorkshire GOC · 7th August 2021, 19:37

Quote:

Originally Posted by vitesse

Having a bit of a love / hate relationship with my now mobile T4. Went to try and help a local 1.8T owner whose car will idle on 3 cylinders but not on 4, doesn’t seem to matter which cylinder he disables.
Good comp. fuel pressure 4.2 bar, no fault codes except for the standard P1520. So I explore a bit and while exploring the engine management a new error report pops-up telling us there’s an open circuit between one of the ignition coils and the ECM.
Moment of joy, that must be it, packed the T4 in its granny trolley and went home. Few hours later the joy evaporated: the owner had checked for continuity and the circuit was fine.

Now why is the T4 telling us one thing and reality another?

Ps. If like this owner you have a Kmaps ECM and the T4 wants you to update the software don’t as it’ll wipe the map, luckily checked first before taking chances.

Regards

I would give the Kmaps guys a call -they have always been helpful - and they are as i understand it the original ECU MGR Team.

vitesse · 7th August 2021, 21:13

Many thanks for the replies, especially the note about carrying the current and the simple explanation which of course I never considered.

I wrote to Kmaps earlier today and received a very prompt reply confirming that I was correct in not proceeding with the update as per T4 request. I'll have another word with them concerning this error message.

Thanks again

Lovel · 8th August 2021, 08:55

If you are absolutely sure about the continuity that it can be eliminated, perhaps a closer look for any pushed pins/connectors would be next?

Failing that I would suggest a slave Mems which can be virginised or if you remove the eeprom from the original can be swapped over. It’s not unknown for a mems component to fail although would be rare. I have seen only one fail but it was related to the fuel pump not stopping.

WillyHeckaslike · 8th August 2021, 09:42

The wiring under the throttle body can rub through and so that area is a known source of electrical-based problems.. The wires for the coil packs are routed via that area so I would give it a thorough inspection together with the multi connector which is also there - is the multi connector closed properly and locked? I would disconnect it and reconnect it after having a close look at the contacts for anything untoward.

How old are the plugs? Although they might appear to be ok the insulators are known to break down as they age and become leaky giving rise to running/starting problems. Weird and unfathomable electrical problems can sometimes be traced to a bad earth, is the main engine/gearbox to chassis earth ok?

vitesse · 8th August 2021, 09:51

Quote:

Originally Posted by Lovel

If you are absolutely sure about the continuity that it can be eliminated, perhaps a closer look for any pushed pins/connectors would be next?

Failing that I would suggest a slave Mems which can be virginised or if you remove the eeprom from the original can be swapped over. It’s not unknown for a mems component to fail although would be rare. I have seen only one fail but it was related to the fuel pump not stopping.

Thanks for the input. The owner bought a Kmaps as the original ECM was suspect due to burnt and corroded crank sensor wiring, but no improvement with the Kmap's.

I'll tell him about the pins, but I believe the next step would be to bridge the two connectors with a length of cable and see if things improve. Something is causing the engine to only run on three and suspect wiring between the ECM and one of the two coils sounds logical, at least to me.

Finger crossed ...

vitesse · 8th August 2021, 09:58

Quote:

Originally Posted by WillyHeckaslike

The wiring under the throttle body can rub through and so that area is a known source of electrical-based problems.. The wires for the coil packs are routed via that area so I would give it a thorough inspection together with the multi connector which is also there - is the multi connector closed properly and locked? I would disconnect it and reconnect it after having a close look at the contacts for anything untoward.

How old are the plugs? Although they might appear to be ok the insulators are known to break down as they age and become leaky giving rise to running/starting problems. Weird and unfathomable electrical problems can sometimes be traced to a bad earth, is the main engine/gearbox to chassis earth ok?

Thanks for the reply, I believe the plugs are new. The owner has disconnected/ reconnected/cleaned every connector he's found within the engine bay, lifted the fuse box, and checked earthing points. Our hopes now lie with a wiring fault between the ECM and the second coil. Unfortunately he bought the car as a non-runner and despite various repairs to the EWS & crank sensor wiring he has yet to see the car running.

But hopefully ...

WillyHeckaslike · 8th August 2021, 18:24

The wiring fault identified by your T4 although intermittent does arouse suspicion given your running problem. The faulty wire identified is coloured black/white and runs from contact 26 of the ECU connector to contact 15 of the multi connector under the throttle body. From contact 15 of the multi connector it then runs to contact 2 of ignition coil 1. That last run to the coil is the the one that is prone to chafing and if any damage is evident you might not be able to spot it until you ease the wire out of the black convoluted conduit which houses it and other wires.

7th August 2021, 14:51	#1
vitesse I really should get out more....... Rover 75 Saloon Join Date: Jul 2011 Location: Gävle Posts: 2,528 Thanks: 395 Thanked 823 Times in 652 Posts	T4 telling lies? Having a bit of a love / hate relationship with my now mobile T4. Went to try and help a local 1.8T owner whose car will idle on 3 cylinders but not on 4, doesn’t seem to matter which cylinder he disables. Good comp. fuel pressure 4.2 bar, no fault codes except for the standard P1520. So I explore a bit and while exploring the engine management a new error report pops-up telling us there’s an open circuit between one of the ignition coils and the ECM. Moment of joy, that must be it, packed the T4 in its granny trolley and went home. Few hours later the joy evaporated: the owner had checked for continuity and the circuit was fine. Now why is the T4 telling us one thing and reality another? Ps. If like this owner you have a Kmaps ECM and the T4 wants you to update the software don’t as it’ll wipe the map, luckily checked first before taking chances. Regards

7th August 2021, 19:30	#2
Phil-T4 I really should get out more....... MG ZT-T, Rover 75 Tourer Join Date: Mar 2011 Location: Olney Posts: 2,969 Thanks: 245 Thanked 1,088 Times in 657 Posts	Continuity of the circuit is one thing but can it carry the required current? Say if 19 of the 20 strands in a wire are broken, it will still show continuity but will be useless. PS never seen that type of error before, it maybe unique to the K-Maps ecu.

7th August 2021, 21:13	#5
vitesse I really should get out more....... Rover 75 Saloon Join Date: Jul 2011 Location: Gävle Posts: 2,528 Thanks: 395 Thanked 823 Times in 652 Posts	Many thanks for the replies, especially the note about carrying the current and the simple explanation which of course I never considered. I wrote to Kmaps earlier today and received a very prompt reply confirming that I was correct in not proceeding with the update as per T4 request. I'll have another word with them concerning this error message. Thanks again

8th August 2021, 08:55	#6
Lovel I really should get out more....... P6B, L550, Imp, F56, Commando Join Date: Nov 2006 Location: Aberdeenshire Posts: 2,886 Thanks: 352 Thanked 677 Times in 440 Posts	If you are absolutely sure about the continuity that it can be eliminated, perhaps a closer look for any pushed pins/connectors would be next? Failing that I would suggest a slave Mems which can be virginised or if you remove the eeprom from the original can be swapped over. It’s not unknown for a mems component to fail although would be rare. I have seen only one fail but it was related to the fuel pump not stopping.

8th August 2021, 09:42	#7
WillyHeckaslike This is my second home Rovers 75 & 25 Join Date: Oct 2010 Location: Wearside Posts: 4,522 Thanks: 543 Thanked 709 Times in 511 Posts	The wiring under the throttle body can rub through and so that area is a known source of electrical-based problems.. The wires for the coil packs are routed via that area so I would give it a thorough inspection together with the multi connector which is also there - is the multi connector closed properly and locked? I would disconnect it and reconnect it after having a close look at the contacts for anything untoward. How old are the plugs? Although they might appear to be ok the insulators are known to break down as they age and become leaky giving rise to running/starting problems. Weird and unfathomable electrical problems can sometimes be traced to a bad earth, is the main engine/gearbox to chassis earth ok?

8th August 2021, 18:24	#10
WillyHeckaslike This is my second home Rovers 75 & 25 Join Date: Oct 2010 Location: Wearside Posts: 4,522 Thanks: 543 Thanked 709 Times in 511 Posts	The wiring fault identified by your T4 although intermittent does arouse suspicion given your running problem. The faulty wire identified is coloured black/white and runs from contact 26 of the ECU connector to contact 15 of the multi connector under the throttle body. From contact 15 of the multi connector it then runs to contact 2 of ignition coil 1. That last run to the coil is the the one that is prone to chafing and if any damage is evident you might not be able to spot it until you ease the wire out of the black convoluted conduit which houses it and other wires.