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Discussion Starter · #1 ·
Howdy all, I’m new to this forum and I have a problem with my P reg MG F, and hopefully a solution too!

It’s the old battery drain problem. The battery goes flat in about a week. Its charging up ok but something is draining it while the car is standing idle. I’ve found that if I disconnect a battery lead, wait a few seconds and then reconnect it the battery does not go flat. So what I guess is happening is that the ECU is staying on and draining the battery and by taking a lead off I’m basically resetting it which stops the drain.

A new ECU is going to be rather expensive and as I understand it will need fitting by a dealer as it needs to be programmed to match the car.

So here’s the plan…

I’m thinking of building a separate circuit to detect when I switch the engine off, wait for 10 mins then reset the ECU by cutting power to it for a few seconds. I’m fine with building electric gadgets but not that knowledgeable about car electrics. So here’s a few questions:

First off I need a signal from the car to tell whether the engine is on or off. I was thinking there must be something easily accessible at the back of the radio but if there’s anything better someone knows of then that would be helpful.

Second, I don’t want to do the reset on all the electrics of the car just the ECU. There’s 2 fuses both of which say ECU and are rated at 15amps does anyone know which one would reset it? I could try pulling one at a time but as it takes a week for the battery to go flat this would take a while.

Lastly, anything else I’ve not though of. Is this likely to set the alarm off etc.
 

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Discussion Starter · #3 ·
IKWYM about the sticking relay thats what I'd hoped it was but doing the power off reset thing suggests to me that its more than just a physical sticking problem. If turning off the power to a realy and turning it back on causes it to start behaving then it seems to me that the problem is that the ECU is still powering the relay when it shouldn't. If the relay was just stuck then I dont think powering off and then on would affect it.

I've had a search through the archives but cant seem to find any definitive solution to this seemingly common problem. Most threads seem to end with "i'll do some tests and let you know....." :-(
 

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I was just wondering about the alarm system. I don't know how inter reliant all the components are. If you were going to go this way then a simpler solution would be a remote battery isolator wired into the circuits that you need to isolate.

Introducing things like this into the equation can cause safety problems. What if your "homemade" solution fails while you are doing 70 mph on a motorway, or if you are overtaking. You are introducing another point of failure into the circuit.

May be worth getting it looked at at a "rover garage" to see if they can do anything relatively cheaply.

If you want to change your ECU then they can be got off ebay or from breakers, but as you say it may have to be fitted/programmed by a garage. Of course, buying second hand can bring the same, or other problems. Just as an example, there is a YF 1.8 one on ebay at the moment for £65.
 

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Hope you can sort something as mine still doing same after week,iv'e spent half hour looking through archives for this relay prob and fix, if anyone finds or know please let us know,and good luck Wildgoose im'e same boat as you :) Dave
 

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Discussion Starter · #6 ·
You raise a good point about the safety aspect. The gadget I had in mind and in fact have assembled this afternoon isn't entirely homemade and I have a reasonable level of confidence in its reliability. Its based on one of these http://www.rev-ed.co.uk/docs/AXE020.pdf

I've programmed it to detect whether the engine is on or not and after a 10 minute delay to send a reset signal. Whenever the engine is on it goes into an idle state so it cant send the reset signal. Thats the theory anyway and it works fine here on my workbench, how it works in real life though is another matter.

I'd love to take the car to a Rover Garage but I have absolutely no confidence whatsoever in my local one here in Ipswich. I did try a non-rover garage who I usually use for other work on the car but they kept the car for a full day and couldn't find the cause of the drain.
 

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I posted this a little while ago. Not greatly usefull, but shows there is a common problem. Have yet to discover what is causing it.

http://fp.remmington.plus.com/rover.html

Maybe a safer way to wire your project would be a normally closed relay supplying the ECU which would wait 30 seconds and then be held open for 10-20 seconds after you have switched your engine off. This would reset the ECU each time you switched the engine off but would not affect the normal operation if the circuit failed as the relay would stay closed.
 

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Howdy all, I’m new to this forum and I have a problem with my P reg MG F, and hopefully a solution too!

It’s the old battery drain problem. The battery goes flat in about a week. Its charging up ok but something is draining it while the car is standing idle. I’ve found that if I disconnect a battery lead, wait a few seconds and then reconnect it the battery does not go flat. So what I guess is happening is that the ECU is staying on and draining the battery and by taking a lead off I’m basically resetting it which stops the drain.

A new ECU is going to be rather expensive and as I understand it will need fitting by a dealer as it needs to be programmed to match the car.

So here’s the plan…

I’m thinking of building a separate circuit to detect when I switch the engine off, wait for 10 mins then reset the ECU by cutting power to it for a few seconds. I’m fine with building electric gadgets but not that knowledgeable about car electrics. So here’s a few questions:

First off I need a signal from the car to tell whether the engine is on or off. I was thinking there must be something easily accessible at the back of the radio but if there’s anything better someone knows of then that would be helpful.

Second, I don’t want to do the reset on all the electrics of the car just the ECU. There’s 2 fuses both of which say ECU and are rated at 15amps does anyone know which one would reset it? I could try pulling one at a time but as it takes a week for the battery to go flat this would take a while.

Lastly, anything else I’ve not though of. Is this likely to set the alarm off etc.
Seems a lot of trouble to go to, just to treat the symptom and not the cause...

Have you checked the usual suspects??...

Boot lid switch not turning the boot light off.
Wiring loom to left hand boot-lid hinge.
Door micro-swithes
Also have you tried checking the drain with a multi-meter then pulling each fuse in turn to see if it makes any difference to the drain?.
 

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Sorry to jump in here again on this one,
Mark, done top 3 still have bottom one to try,Dave

Have you checked the usual suspects??...

Boot lid switch not turning the boot light off. yes ok
Wiring loom to left hand boot-lid hinge. yes ok
Door micro-swithes yes ok

Also have you tried checking the drain with a multi-meter then pulling each fuse in turn to see if it makes any difference to the drain?. Not yet
 

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There really is tons about this subject in the MG Enthusiasts BBS archives ( http://www.mgcars.org.uk/ ). Here's one the replies giving details about a sticking relay -

Like Brian says, check the archive for threads which contain the words Battery and Drain.

There is a relay box mounted underneath the MEMS unit on the rear engine compartment wall (wall between engine and boot). It is black. A relay inside this box is possibly stuck on. The relay is supposed to remain on for about nine minutes after the car has been switched off so that the radiator fans can cool the rads and the engine compartment fan can cool the engine compartment, if necessary. The relay also supplies other components and it is this drain of current that you could be experiencing.

The MEMS relay unit is replaceable and also repairable as I found out on mine. To start with you could try giving the unit a sharp tap with a screwdriver to try to release the relay. I opened mine up and adjusted and cleaned the relay contacts and have had no problems since (18 months). I believe a new unit would have been about £35.

Hope this helps
 

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Discussion Starter · #11 ·
Nice idea about the relay thats usually on and toggles to off CJJ, that's the kind of thing I had in mind. Ideally the circuit will wait 10 mins after you switch off the ignition to allow for any cooling fan action then trigger it for a short burst of 10 secs off-time then allow it to power back up again. Now all I need to figure out is how to trigger the circuit, i.e. where on the car I can find a signal which changes or a contact which closes when you turn the ignition off.

Thanks for looking up that post on mgcars.org Stafainn but I'm still not convinced the problem is with the relay itself. If it were just sticking then I wouldn't expect cutting power to reset it, I'd imagine that when the power came back on it would still be stuck IYSWIM.
 

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just one thing I thought I'd mention.

Recently I had an intermittent (sic) battery drain..
did all the usual test...

when testing the car when on.. the battery was getting it's charge and usual and when off it wasn't getting a drain.

I thought it would be ECU, but in fact it turned out to be the alternator..

What was happening is every now and again it would actually draw from the battery instead of charge, only when the car was off....

It took three days of testing at a local garage (and over £200.00 in fees) whittle it down to that..

I then went and changed the alternator and robert's my mothers brother...
 

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Sorry to jump in here again on this one,
Mark, done top 3 still have bottom one to try,Dave

Have you checked the usual suspects??...

Boot lid switch not turning the boot light off. yes ok
Wiring loom to left hand boot-lid hinge. yes ok
Door micro-swithes yes ok

Also have you tried checking the drain with a multi-meter then pulling each fuse in turn to see if it makes any difference to the drain?. Not yet
Best to pull one end of the fuse out and insert a meter on DC current in series with the fuse.
 

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FYI...

I can supply M.E.M.S 1.6 & 1.9 (Most K-series between 1992 and 1999/2000) for £75.00 plus v.a.t. These are recon units with 6 months warranty. I can also code the units without the need for the car to be here. If you send me your old unit (the yare exchange anyway) i can extract the security code and input it into the new unit. This is free of charge if you buy a unit from us.
If you did not want to do it this way, i can supply a fully decoded unit which you can either get the garage to fit and code or i can supply instructions to get the car running without the need for re-coding. This only works on our units though bear in mind.

I will need the MKC or MNE number you have on your existing unit, i can then tell you if i have anything in stock. If i do not have anything i can normally repair your old one within 48 hours for the same price. There is £6.50 postage to UK mainland to send them out.

Hope this helps.
 

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Discussion Starter · #16 ·
A little bit more testing.

Yesterday I did a test to reassure myself that is was definitely the ECU which was causing the drain. I managed to connect an ammeter in series with the battery and measured a drain of 0.47 amps. I then pulled one of the two ECU fuses (far left) and nothing changed so I pulled the other one (next to far left) and the reading went down to 0.02 amps After reinserting the fuse the current drain stayed at 0.02 amps.

If anyone else wants to try this measurement its important to know how to get your ammeter connected without disconnecting the battery. If you disconnect the battery and break the circuit to connect the ammeter then the ECU will reset so when you connect your ammeter the fault wont be there to measure. I did this by:

  • Disconnect one battery lead
  • Wrap a piece of wire firmly around the base of the battery terminal and leave the end dangling
  • reconnect the battery lead
  • Start the engine
  • Stop the engine
  • I left mine for about 20 mins as the ECU is supposed to stay powered for a while, about 10 mins I think
  • Clip one crocodile lead to the piece of wire from step 2
  • Clip the other crocodile lead to the battery lead
  • Disconnect the battery lead from the battery terminal
  • You now have an ammeter in series and the circuit was never broken so the fault should still show up.

I’ve not made any real progress with the reset gadget I mentioned before and I’m starting to have second thoughts about it. I’m sure it will work but if I can just swap out the ECU for about £100 then I think that would be safer all round. Plus if I sell the car its not really fair that someone else has to drive around with my modifications under the hood.

Slashformayor, from the description of the current drain above, does this sound like a faulty ECU to you, the kind of thing one of your recon units would fix?
 

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I would test it like this.

Put your ammeter in series to the battery so you can see the drain.
Start the engine
Stop the engine
Keep your eye on the ammeter for 5 mins
You should have that drain of 0.47 amps for 5 mins until the ECU drops out.
If, after 5 min, it is still 0.47 amps i would get the ECU tested
If it drops to 0.02 amps then the ECU is fine.

You can actually time it!
The ECU will stay live for EXACTLY 5 mins after the ignition is turned off! Set your stopwatch by it. If it does not drop out after 5 mins leave it for a further 2 min or so, just to prove a point.

By taking the fuse out you were cutting the ECU's feed off anyway, so that would have not tested it fully, as you cannot tell if the ECU was staying live or not.
 

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Rover 75 Battery Drain

My brother had the battery drain problem with his 02 reg "75". He changed the battery and the problem appears to have gone away for the time being. My brother in law reckons it is a fault in the Alternator, probably one of the diodes gone down, allowing a drain. You used to be able to buy a refurb kit for alternators !!! probably not not. Hope this helps.
 

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I have been struggling with the same problem for weeks. There is a constant battery drain of 0.42 Amps (well beyond 5-10 mins).

I have checked the following:-
  • Bonnet light is going off
  • Boot light is going off
  • Boot lid wiring (LHS) seems OK
  • Door locks seem to be working OK
  • Battery earth strap making good contact (must check engine strap!)
  • The car will Lock & Superlock normally on the blip
  • I have had the ECU swapped for a known good one (no change)
  • I have changed the ECU relay pack (no difference)
I took the lid off the old ECU relay pack and connected it up to the wiring loom. There is one relay still energised which must be the ECU Master Relay. Breaking these contacts allows the ECU to drop out proving it is the ECU staying on permanently.

There must be one of the sensors making the ECU stay on. I pulled the connector on the engine bay sensor and the fan came on so I assume this is OK.

Anything else I can try - this is driving me nuts.

Given the number of people grumbling about the problem, someone must have solved it. Please let us know how you did it. I cannot believe there are hundreds of MGF owners like me; scared to go away for 2 days without a charger plugged in :-(

Reg
 
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