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MG MGF Technical - It won't fire! Why?

My 1.8 MGF has always been an excellent starter. However, I had not run it for several weeks and the battery was flat. When tested it was knackered and I have fitted a new one. The engine cranks, there is petrol in the bores and a spark at the plugs. What is it that is stopping it running? I'm totally confused. Help!
Geoff Smart

The only thing I can think of is the engine management system. Are you sure the battery was knackered, it could be the same root cause problem.
DW Staniforth

If the ECU was kaput I doubt there would be any spark. Having said that, a dying battery can occasionally 'confuse' an ECU, so disconnecting the new battery & leaving for an hour before re-connecting might be worth a try, although admittedly I'd be rather surprised if that worked...

Evidence of fuel in the cylinders may not necessarily mean the correct fuelling is going in. Do you hear the pump priming when you turn on the ignition? After a sustained period of cranking, can you smell unburnt fuel from the exhaust?

The prime suspect in the case of an engine refusing to start after several weeks of inactivity is damp. Is the spark strong, i.e. bright blueish, or orange? A dose of electrical contact spray on every contact in the ignition circuit would be my first step, then the same with the brown coolant temperature sensor & the throttle position sensor.

Was the old battery likely to have died of simple old age, or do you suspect there may be a drain going on somewhere?
bandit

Thanks for the responses.The 'old' battery was purchased earlier this year and as it would not hold charge was this week replaced under warranty. The car does with its alarm system, clock etc. gradually drain the battery when standing.
I confirm blue spark at plugs ,hear pump starting sequence when turning on ignition and strong smell of petrol after cranking. Have sprayed WD40 liberally and replaced what looked like a dodgy rotor arm. Still the saga continues and I can't drive the b.car. Oh, I also found the inertia switch which seemed ok. I can't drive it to the garage to ask 'what is it?'! Any more ideas please?
Geoff Smart

Other sensors that feed the ECU for fuelling/timing are the crank sensor & intake air temperature. I'd inspect all the sensor connections and check all the copper pins & blades and thoroughly clean off any sign of oxidation or corrosion, i.e. until they're shiny, and sluicing with electrical contact spray (WD40 deals with damp ok, but contact spray will restore connections & result in a better connection)

Perhaps worth looking into whether there is a mobile auto electrician that can read the ECU parameters - generally when there's a problem with one of the inputs the ECU requires it'll show up on a scanner. Still, it would be a major coincidence if a sensor has properly died, I'd still put a poor connection somewhere at the top of the list of suspects.
bandit

Does your car have ecu fed immobiliser? Mine has been bypassed by best of british. If your ecu has an immobilser,have you reactivated it. To reactivate it connect car battery.point key fob in the direction of imm warning light,press padlock sign on key fob 3 times ,the 5as box in your car should start clicking and warning will flash quickly ,the lamp should then slow flash,then press blank button on key fob the warning should go on ,put key in ignition turn key,fuel pump should prime .turn key to start starter motor engine should fire up.I
simon connolly

Should read warning should go out ,warning means warning lamp. I cannot edit thread
simon connolly

Thank you for your thoughts Simon. The immobiliser appears ok and does as you advise but still the car will not start. Have today bought some Easystart which I shall try tomorrow morning (weather permitting - the car is outside). Hopefully this product will produce a bang! I shall hopefully have more time to recheck everything tomorrow and then report on what happens.
Geoff Smart

Hi Geoff,

If the crankshaft sensor is duff then the timings will be all wrong, e.g. the spark is not occurring on the power stroke.

I'm probably barking up the wrong tree here. Hopefully, someone with more knowledge of the "mems" electronics will give some input.

willyphixitt
W A Nixson

Do not use easy start ,my dad used it on a london cab fitted with an austin 2.2 diesel back in the 70s it got to stage even in summer the engine would not start without it.the engine became addicted to it.an aa man said the violent detonation caused by the easy start in his opinion had damaged the piston crowns thus lowering compression.what do you guys think?
simon connolly

Geoff check out this site

http://homepage.swissonline.ch/TomsSeven/Navigation2/Map.htm#
simon connolly

Simon thanks to you and all the others for your inputs. That Toms Seven site is very informative re the engine management system and its gizmos and hopefully will help me resolve matters. Its' 1015hours and still too wet. The engine is dripping with condensation so I am going to need patience whilst it dries up a little before I start trying again. Meantime, I've put the battery on charge to keep it topped up.
Geoff Smart

B---er the rain!
Geoff Smart

Thank you all for your help and suggestions. Despite yesterdays rain there were one or two pauses in the deluge during which I cleaned the connectors on the sensors,regapped the plugs, copious amounts of wd40. I had also had the new battery on charge overnight and first turn of the key (without Easystart)it started, alleluia! Smiling again!
Geoff Smart

Well done
simon connolly

Good result!

I make it a habit of giving any connector that I suspect suffered from moisture ingress a coat of engine lacquer over the outside surfaces. It'll need a firmer pull to disconnect if the need arises, but well worth the added protection.
bandit

This thread was discussed between 18/11/2009 and 24/11/2009

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