ECU to fuel pump relay earth fault - diagnosis at last!

mkilpatr · 16th December 2022, 14:41

So, a local auto electrician has /finally/ found the fault with my Rover 75 1.8T that began cutting out or not starting. The other garage was no use in that respect and I've lost a lot of time. As the car has only a couple of days left on its 3-month warranty I'm calling them right now to register the issue.

He has identified the problem as a faulty earth connection between the ECU and the fuel pump relay. Nothing to do with the relay itself, the crank/camshaft sensors, the fuel pump or the silly magic orange clip. He had to fit a current clamp and a triggered oscilloscope to the circut and wait for the engine to cut out (which it didn't do at all at first but eventually did this morning, at last).

How many people have experienced this problem in the past and had to deal with it? I can't recall if someone mentioned it in one of my earlier threads as a possibility.How painful might this be in the worst scenario?

If the ECU itself is damaged (water ingress?0 rather than it just being a problem with its connector, how difficult is this?

Michael

Yorkshire GOC · 16th December 2022, 14:49

It is the diesel ECU that is prone to water damage as it is not sealed to enable the barometric pressure sensor to function. The petrol ECU's are sealed and so are not prone to water damage.

mkilpatr · 16th December 2022, 14:54

The auto electrician said something similar so he must have experienced something with the diesel versions in the past and is aware that they are different from the petrol versions (I think he said the diesels have a Bosch ECU).

However, his testing showed that it's the earth connection between the ECU and fuel pump relay. Are you suggesting, then, that this is far more likely to be a wiring fault or the connection to the ECU but not an internal ECU fault? Should I treat that as slightly better news?

Michael

vitesse · 16th December 2022, 15:48

Snap! Sounds remarkable similar to a fault I've got on my V6 (https://www.the75andztclub.co.uk/for...d.php?t=321896) and yet when I substitute another ECM the fault doesn't appear, other ones appear instead.

As yet unresolved as it's too cold to play in my unheated garage, the outside temperature is around minus 20c.

Good luck

Ducati750cc · 16th December 2022, 16:29

Quote:

Originally Posted by mkilpatr

So, a local auto electrician has /finally/ found the fault with my Rover 75 1.8T that began cutting out or not starting. The other garage was no use in that respect and I've lost a lot of time. As the car has only a couple of days left on its 3-month warranty I'm calling them right now to register the issue.

He has identified the problem as a faulty earth connection between the ECU and the fuel pump relay. Nothing to do with the relay itself, the crank/camshaft sensors, the fuel pump or the silly magic orange clip. He had to fit a current clamp and a triggered oscilloscope to the circut and wait for the engine to cut out (which it didn't do at all at first but eventually did this morning, at last).

How many people have experienced this problem in the past and had to deal with it? I can't recall if someone mentioned it in one of my earlier threads as a possibility.How painful might this be in the worst scenario?

If the ECU itself is damaged (water ingress?0 rather than it just being a problem with its connector, how difficult is this?

Michael

So he has diagnosed the fault as being the loss of an earth between the ECU and relay.

Did he give any idea if the fault was within the ECU ? in the ECU connections to the ECU wiring plug ? or between the ECU wiring plug and somewhere within the loom to the relay ?

mkilpatr · 16th December 2022, 22:15

Further investigation such as whether the ECU is damaged or whether it's a bad connection at the connector or a wiring problem will have to wait until Monday, unfortunately. I'm hoping the answer, whatever it is, is sufficiently obvious when he gets the time to look under the scuttle.

FLYING BANANA · 17th December 2022, 06:41

On my 1.8t the fault was found to be the actual relay itself, three pins live in, live out and earth. But the earth wasn’t earthing all the time.

Again was a old school auto electrician to find the fault. Banana has been ok ever since.

mkilpatr · 17th December 2022, 11:26

I woke feeling puzzled by all this as I've been told that the ECU provides a switched ground not a switched positive to the pump relay. Actually, I can't see how he can have determined a fault yet because the ECU would cut off the earth to the relay if a fault elsewhere made it believe the engine isn't running or shouldn't be running. Also, after previous cutting-out, it was clear that the pump was running as it should for a couple of seconds with the ignition switch in position two before cranking the engine but the engine would not subsequently fire up on cranking the starter (until I had waited for ten to twenty minutes). That doesn't really suggest a fault in that relay circuit, does it?

SD1too · 18th December 2022, 13:14

Quote:

Originally Posted by mkilpatr

... I've been told that the ECU provides a switched ground not a switched positive to the pump relay.

Yes, that is correct.

Quote:

Originally Posted by mkilpatr

... it was clear that the pump was running as it should for a couple of seconds with the ignition switch in position two before cranking the engine but the engine would not subsequently fire up on cranking the starter (until I had waited for ten to twenty minutes). That doesn't really suggest a fault in that relay circuit, does it?

No Michael and that is crucial new evidence.

When the engine is cranked by the starter motor the ECM receives a signal from the crankshaft position sensor. The fuel pump relay is then energised. If this signal is not present or if it disappears whilst driving, the engine will stop.

Simon

mkilpatr · 20th December 2022, 08:46

"But it won't be the sensor, as no new errors appeared on the ECU" said my local garage and "if it's internittent, it won't be a sensor dying from heatsoak so I'm going on a wild goose chase" says the auto electrician.

I think I'm surrounded by buffoons who just refuse to eliminate a simple problem and easily replace a sensor or two and instead make up all sorts of nonsense. And people on the online forums repeatedly going on about the orange clip despite me having said I inspected the fuel filter and it's rock solid.

Its quite ridiculous. I should have listened when someone suggested the camshaft/crankshaft sensors as a possibility two weeks ago and just renewed the damned things myself to see what happened. What would that have wasted? £100?

Michael

16th December 2022, 14:41	#1
mkilpatr Regular poster Rover 75 Saloon Join Date: Sep 2022 Location: Cambridge Posts: 42 Thanks: 1 Thanked 0 Times in 0 Posts	ECU to fuel pump relay earth fault - diagnosis at last! So, a local auto electrician has /finally/ found the fault with my Rover 75 1.8T that began cutting out or not starting. The other garage was no use in that respect and I've lost a lot of time. As the car has only a couple of days left on its 3-month warranty I'm calling them right now to register the issue. He has identified the problem as a faulty earth connection between the ECU and the fuel pump relay. Nothing to do with the relay itself, the crank/camshaft sensors, the fuel pump or the silly magic orange clip. He had to fit a current clamp and a triggered oscilloscope to the circut and wait for the engine to cut out (which it didn't do at all at first but eventually did this morning, at last). How many people have experienced this problem in the past and had to deal with it? I can't recall if someone mentioned it in one of my earlier threads as a possibility.How painful might this be in the worst scenario? If the ECU itself is damaged (water ingress?0 rather than it just being a problem with its connector, how difficult is this? Michael

16th December 2022, 14:49	#2
Yorkshire GOC I really should get out more....... Rover 75 connoisseur se v6 auto Join Date: May 2014 Location: Hull Posts: 2,085 Thanks: 1,842 Thanked 623 Times in 469 Posts	It is the diesel ECU that is prone to water damage as it is not sealed to enable the barometric pressure sensor to function. The petrol ECU's are sealed and so are not prone to water damage. __________________ She came off the Longbridge Line on 20-05-2003 The Silver Machine was the 13th of 160 Rover 75's to come off the production line that day and is the 100th of 527 Starlight Silver Rover 75 2.5 V6 Connoisseur SE Auto saloons listed in the build records produced world wide.

17th December 2022, 06:41	#7
FLYING BANANA Moderator/Club Shop MG ZT 1.8t+. No.3 of 4 in Sunspot Yellow & Ford Fiesta in Black. Join Date: Aug 2010 Location: Rattler Farm Posts: 22,639 Thanks: 9,270 Thanked 15,645 Times in 6,806 Posts	On my 1.8t the fault was found to be the actual relay itself, three pins live in, live out and earth. But the earth wasn’t earthing all the time. Again was a old school auto electrician to find the fault. Banana has been ok ever since. __________________ 233,730 onen hag oll

16th December 2022, 14:54	#3
mkilpatr Regular poster Rover 75 Saloon Join Date: Sep 2022 Location: Cambridge Posts: 42 Thanks: 1 Thanked 0 Times in 0 Posts	The auto electrician said something similar so he must have experienced something with the diesel versions in the past and is aware that they are different from the petrol versions (I think he said the diesels have a Bosch ECU). However, his testing showed that it's the earth connection between the ECU and fuel pump relay. Are you suggesting, then, that this is far more likely to be a wiring fault or the connection to the ECU but not an internal ECU fault? Should I treat that as slightly better news? Michael

16th December 2022, 15:48	#4
vitesse I really should get out more....... Rover 75 Saloon Join Date: Jul 2011 Location: Gävle Posts: 2,559 Thanks: 395 Thanked 823 Times in 652 Posts	Snap! Sounds remarkable similar to a fault I've got on my V6 (https://www.the75andztclub.co.uk/for...d.php?t=321896) and yet when I substitute another ECM the fault doesn't appear, other ones appear instead. As yet unresolved as it's too cold to play in my unheated garage, the outside temperature is around minus 20c. Good luck

16th December 2022, 22:15	#6
mkilpatr Regular poster Rover 75 Saloon Join Date: Sep 2022 Location: Cambridge Posts: 42 Thanks: 1 Thanked 0 Times in 0 Posts	Further investigation such as whether the ECU is damaged or whether it's a bad connection at the connector or a wiring problem will have to wait until Monday, unfortunately. I'm hoping the answer, whatever it is, is sufficiently obvious when he gets the time to look under the scuttle.

17th December 2022, 11:26	#8
mkilpatr Regular poster Rover 75 Saloon Join Date: Sep 2022 Location: Cambridge Posts: 42 Thanks: 1 Thanked 0 Times in 0 Posts	I woke feeling puzzled by all this as I've been told that the ECU provides a switched ground not a switched positive to the pump relay. Actually, I can't see how he can have determined a fault yet because the ECU would cut off the earth to the relay if a fault elsewhere made it believe the engine isn't running or shouldn't be running. Also, after previous cutting-out, it was clear that the pump was running as it should for a couple of seconds with the ignition switch in position two before cranking the engine but the engine would not subsequently fire up on cranking the starter (until I had waited for ten to twenty minutes). That doesn't really suggest a fault in that relay circuit, does it?

20th December 2022, 08:46	#10
mkilpatr Regular poster Rover 75 Saloon Join Date: Sep 2022 Location: Cambridge Posts: 42 Thanks: 1 Thanked 0 Times in 0 Posts	"But it won't be the sensor, as no new errors appeared on the ECU" said my local garage and "if it's internittent, it won't be a sensor dying from heatsoak so I'm going on a wild goose chase" says the auto electrician. I think I'm surrounded by buffoons who just refuse to eliminate a simple problem and easily replace a sensor or two and instead make up all sorts of nonsense. And people on the online forums repeatedly going on about the orange clip despite me having said I inspected the fuel filter and it's rock solid. Its quite ridiculous. I should have listened when someone suggested the camshaft/crankshaft sensors as a possibility two weeks ago and just renewed the damned things myself to see what happened. What would that have wasted? £100? Michael