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MG MGF Technical - Interesting symptoms

My 2002 MGF has started to hesitate slightly when under load at low speeds.

I have a Brown & Gammons water level sensor kit fitted. When the car falters, the alarm sounds sporadically, as if it is going through its self test sequence, which it does every time the ignition is switched on.

This is not being caused by the float mechanism, as I have completely disconnected the sensor and the problem persists.

It's not the physical motion of the car which is causing the alarm to go off, as I've replicated the movement and everything is OK.

It's as if the fault is causing the water level sensor control unit to see intermittent disconnections and re-connections of power to it.

My initial thoughts are that something in the HT system is causing the hesitation and at the same time, producing a spike in the car's electrical system, which the water sensor unit is detecting.

I'm planning to take it to a local garage, which has a diagnostic computer, to see if that throws anything up.

Any ideas would be welcome.
Sam Murray

Sounds like the volts across the battery are dropping.
Check the alternator is not giving low output when the fault appears.
Gary Luxon

Run 2 cables from the battery to the cockpit and either connect to a 12v battery or multimeter. When alarm sounds check brightness of bulb / multimeter to see if there is any change.

Good to see you've still got the F Sam, mine's still under cover in the driveway, 3 years after HGF. Need to get that fixed at some point, considering all the other bits that've probably siezed it'll be a little project for me.
Leigh Reid

Thanks Leigh.

Yep, she's still looking as good as she did the day I took her out of the box.

Hope you get your back on the road soon.

:-)
Sam Murray

hows it starting in the damp sam?
Leigh Reid

No problems starting at all.

Also runs fine most of the time. Just seems to "hyter" if I drive slowly with a bit of load on the engine.
Sam Murray

sam, if it's the 1.8 mpi, dizzy cap and rotor would be the obvious place to start.
Leigh Reid

Agreed, but why would it set off the coolant low alarm???
Sam Murray

So, I took the old girl to a local dealer who plugged it into their magic computer, which diagnosed faulty MAP and air temperature sensors.

Bits on order.

:-)
Sam Murray

Doh!

Took the car to the garage to have the MAP sensor changed.

"It'll take a hour", the man said, so I went for a walk with the dog.

Returned to find nothing had been done, because they have to drop the manifold and didn't have enough time.

I despair!
Sam Murray

So, the computer said that the MAP and air temp sensors were faulty. Garage thought air temp fault reading was due to MAP sensor fault.

However, they discovered that there is no MAP sensor fitted to my car. Reset all fault codes, which did not re-appear.

After a brief test drive, the mechanic diagnosed condensation in the fuel lines. Put some gas treatment and fuel cleaner into the petrol tank and took it for a blast.

Now going like a dream.

I can only think that this is due to the car doing a very low mileage and sitting around for most of the winter.

The moral of the story...never trust a computer.

Still can't explain why this affected my low coolant alarm, which also now works perfectly.

Sam Murray

Spoke too soon.

Low Coolant Alarm still going off intermittently.

Emails Brown & Gammons to see if I can get the ECU only, as I suspect it to be the culprit.

No reply after 2 days.
Sam Murray

I cannot comment on the B&G problem but the diagnostics are hopeless, as you found out.

I cured hesitation under load by changing plug leads for a set of silicone leads
Brian Highe

It sounds as if you are losing the 12V feed to the alarm box which sounds purely electrical. For an electrical fault to be causing hesitation it would point the finger at either the alternator, battery or their connections. Of these the alternator would be most likely, perhaps the bearings trying to seize?
I would also like another ECU if you get any luck with B&G!
Charless

Since fuel treatment was added, the car runs much better. With only slight hesitations now and again, but only used half a tank of fuel, so will reserve judgement until I have used it all.

If there's still a problem, I will replace the HT leads as you suggest Brian.

I agree that the low coolant alarm seems to be momentarily losing it's 12 volt feed.
Since it seemed to be linked to the hesitation problem, I thought it might be ignition related, causing a spike in the 12v supply.

According the diagnostic computer, no miss-firing is being detected by the engine's management system.

I also suspected a bad earth or battery connection, but surely that would affect other electrical components such as instruments etc.

B&G did get back to me and offered to provide me with a replacement low alarm ECU for £39.95 + VAT.
Sam Murray

This thread was discussed between 19/07/2013 and 30/09/2013

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