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MG MGF Technical - Power Relay Board

Just had to replace a small circuit board known as
"Power Relay" board. About a tenner's worth of components - a few electrolytics, a comparator and a big trasnistor - costing 160 quid, plus the labour was quite a bit as
it took a while to locate the fault and then replace the
part.

I'd initially thought it had been a more traditional
ignition problem - like the time Eastern Rover cross threaded one of the plugs and left it half screwed in.

This time the main symptom was intermittant misfiring and occasional loss of power. One of the capacitors is fried to a crisp. At one point it felt like I had only two
cylinders joining in and the engine sounded like it was
gasping for breath.

It's fine now, but I'm a bit annoyed at the very crude and cheap looking board of dubious design quality that I didn't even know was there until yesterday.
Also there are two LEDs on the board - which can't be seen when fitted, so I'm not sure why they're there. The only thing I can think of is that this board was originally designed for another purpose (probably the
glove box light on a Maestro ... ;-)

How many more of these things are there I wonder?

I see you can get a replacement 3-rd party ECU, and I wondered if
it still relied on all these satellite boards.

Chris

Where is this board located?

Bruce
Bruce Caldwell

It's behind the dash on the nearside - I think - I'll
have to check exactly where with the mechanic I use.

I've got the board on my desk here. All that's left of
one of the capacitors is a melted crisp, and that's destroyed a few of the surrounding components.

I think its function is to interface various sensors to
the ECU, so if it sends back false readings, the ECU gets
its knickers in a twist.

On my car there was a burning smell in the cab one day coming home from work, which I couldn't trace and
eventually assumed came from outside,
which was then followed by allsorts of intermittant
power loss at different revs. The worst being what felt like
only two cylinders firing for about 5 miniutes one
morning, with a sound like air being sucked in hard through the side vents. I thought it was going to pack up altogether when it suddenly started firing normally for no apparent reason.

Performance was noticably poor, with higher fuel
consumption, but for the most part felt like typical LT ignition problems, but I could find nothing obvisouly wrong,so I had to take it to my mechanic to have a look with the proper equipment.





Chris

Are you talking about the MEMS relay pack - black formed wedge shaped box, with two multi-connectors on the end?

If so then it's in the engine bay, right behind the MEMS.
Will Munns


Hmm ... I'll have to have a word and check to see where
this one was. I thought he said it was in the front - I certainly smelled the cab it when it burnt out.

Is there still no haynes manual available - or is there
any more information about how this works available anywhere? as I am in the dark, although I have always been able to trust the guy who does the work on my cars, so I assume he's telling me the right thing ....

I'll double check with him.
Chris

Thanks for sharing this info Chris.
Another interesting question could be: "can we visually check this board, or do we need to open a seales box?"

Cheers,
Erik

>> Also there are two LEDs on the board - which can't be seen when fitted, so I'm not sure why they're there. <<

Was it re-cycled from an 80's HiFi? LOL Seriously though, the LEDs perhaps provide some kind of diagnostic function???
Rob Bell


I'll find out exactly where he pulled it out from.

He's always been a good mechanic, but I don't
think he always uses the same technical terms for the electronics - I don't know what they are either as I have been unable to find any information about it myself. He always gives me all the invoices from the
parts he orders and it just appears listed as "power relay board" with a code number.

Also I could have got the wrong end of the stick (again) when I thought he
said it was behind the dash - he may have meant/said bulkhead - I was still reeling abit from the shock. I had been hoping it was something quite cheap.

I know that it took him quite a while to find
the problem, due to the intermittant nature of the
symptoms and that he also called in some help from a guy who specialises in K-series engine diagnostics after his own equipment didn't detect anything wrong at first.

Problem is that I use the car every day for a 100 mile round trip commute and I have to get things fixed quickly and there's never time to shop around and look for cheaper options.I'm on about 130,000 miles now, and I do
use a bit of oil, but it's doesn't run too bad. (My sierra used to use about 2 litres of oil a week).
I will have to consider getting a recon engine and spending a of money on it versus buying another car in
about a years time.

Will is probably right in his reply above that it is next to the MEMS,(if I actually think about it, it makes no sense for it to be in the front of the car) in which case you can probably open the box and take a look. On mine there is no doubt about what the problem is as there is a huge melted black mess in the middle of the board. If there's a way to post a jpeg I can send a in a snap to the BBS.

If I had another car to drive while this one's off the road, I could possibly have
repaired this board, by looking at another non-burntout one, and replacing three capacitors and a couple of resistors, but I still don't know what caused this to happen in the first place.

Cheers

Chris


Chris

The inly at the front is the MFU ?
http://www.mgfcar.de/MFU/index.htm

No LED, or capacitor.

Main Relay looks like this:
http://www.mgfcar.de/mems1.9/dcp_1554.jpg

and MEMS like that:
http://www.mgfcar.de/mems1.9/index.htm

There are more boards at Steptronic MGF.
Dieter K.


Well, that's funny - it's not any of those pictured. I will hopefully get a reply from my mechanic tommorrow about where he pulled this out.

I hope he hasn't just given me a bit out of an old
metro and spun me a yarn! Although I have used him for
four or five years (and on my mileage I have three or four services a year) and he's never, ever ripped me off, so I've no reason to suspect he's not telling the
truth.

I'll take a photo tonight and post it somewhere it
can be seen and send the URL.

I'm beginning to worry now, that nobody has heard of this, and wonder if I have been given the oil pressure indicator out of a Lada and then simply charged loads for a new set of plugs ... obviously this could happen, but not with someone you use regularly?

This board actually looks like a power supply - it has
an L2610CV - a 10V voltage regulator, a voltage comparator IC (2901DP) and a few caps and resistors.
The voltage regulator part is common in car instrumentation apparently.



Chris

find me very curious :)
Looking forward to seeing a picture.
10V is not common with the MGF (IMO). 5V gets supplied by MEMS ECU to all engine sensors.
Dieter K.

Hello Chris,

Have you got any reply from your mechanic, I am really looking forward as my friend has similar problems with his car and is starting to get a little desperate after donating a serious sum of money to his local dealer without solving the problem...


Regards,

Marten
marten

Any news Chris?

I think you got us all very curious.
Spyros Papageorghiou

This thread was discussed between 19/12/2003 and 24/12/2003

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