MG TF 160 won't turn over

[danielt]

I have a 2002 MG TF 160 and I seem to have caused the electronics to refuse start the engine.

It started with a blown fuse 8 (side/tail lights LH, number plate lights, interior illumination, glove box light). Changing the fuse brought back all the expected items, but I decided to investigate the cause and at the same time fix my blower fan coils. I have looked for insulation damaged by the sharps bits behind the radio and also the wiring in the boot. I've not found anything obvious.

I confess that I did this all without disconnecting the battery (unwise I know).

I've also checked all fuses in the driver-side fuse box with a multimeter and the fuses under the bonnet are all fine.

So I removed the centre console and illuminated centre console side panels without breakage plus the glove box.

The renewed blower fan coils went in without problem and all 3 fan speeds now work. I reconnected everything except for the glove box light but have left all the removed panels unfitted.

I have tested that everything you can switch on does work so lights, indicators, windows, electric mirror etc all work.

The problem is the car now refuses to do anything on ignition switch position III (turn the engine). I get a glowing oil temperature light, a small negative deflection on the oil temp gauge and no sounds whatsoever. I've tried with the lights on to see if I get a dimming showing that current is being pulled for the started, but the lights remain bright.

The key fob locks and unlocks as expected and I've tried the four-times lock and unlock sequence.

So I'd be grateful of any suggestions.

One thing I suspect (but I could be wrong) is that the cables to the oil temperature gauge and the clock were under a lot of tension, as I wrestled the centre console off. I've taken off most of the insulation tape for the oil temperature gauge and the clock cable bundles, but can't find any snapped cables. However the oil temperature light comes on when I try to start the car, so could this mean I've broken a connection to the oil temp gauge (and also the ECU)? The plug connector into the oil temp gauge looks fine, with no pins pulled out from the back, but I haven't tested it with a meter.

I can add some pictures if useful.

Best regards,

Daniel

[talkingcars]

Hi and welcome to the forum

Sorry to hear of your problems. Have you checked the wiring around the boot hinge and the ECU?

James

[danielt]

Thanks James,

The boot hinge wiring looks to be in order, but I know I need to unwrap it from the insulating tape to know for sure. A short there would make the fuse 8 pop I'm sure. Currently it's not popping fuse 8.

On the ECU wiring is there something in particular I should look for?

Also do you know if the car has a disconnected oil temp gauge, if this will cause a fail? From various other threads it looks like there is an oil temp gauge to ECU connection so I'm thinking if this is broken, could that cause the ECU to stop the starting?

Best regards,

Daniel

[talkingcars]

The hinge wiring can through up all sorts of strange seemingly unrelated problems.

The only reason a disconnected oil temp gauge would cause a problem is if it was shorting out somewhere.

[danielt]

Thanks James,

I'll investigate further the boot hinge wiring and look under the insulation tape where there's maximum bend. I'm not sure if the oil temp sensor cable gets bent with the boot opening so I'll check that also. I believe it's an NU cable.

Best regards,

Daniel

[RobboMC]

Just a dumb thought - it may not be connected to your work.
It could just be coincidence that it happened at the same time.

Perhaps check the starter motor wiring and the earths and work backwards from there.
Your symptoms suggest to me a broken starter motor wire or spade terminal. Our car
was like this after we fitted the new engine and it took forever to find the break which was hidden inside
some heavy insulation.

[danielt]

Thanks Robbo,

I haven't checked the starter motor wiring yet, but I did recharge the battery (made no difference) and checked also the single 80A fuse on the engine. So now every fuse on the car has been tested with a meter.

In the engine bay I could hear a very quiet but high pitched tone like a capacitor being charged in a flashgun. I hear this with the no key in the ignition. So I'm not sure if that is a symptom of the failure.

[danielt]

One thing I didn't mention is that when the ignition key is turned, I don't even hear a click from the starter solenoid. The only reaction is the illumination of the oil temperature light. But I will be checking the starter wiring today.

[jonaf]

Do the symptoms change if you disconnect the spade contact from the starter solenoid? Or supply 12V directly to the terminal?

[danielt]

Thanks to all for the various suggestions.

Here's what I've found today.

1. There is +ve 12v supply to the 80A fuse in the engine compartment verified with a 12v bulb on a lead to negative earth.
2. There is +ve 12v supply to the solenoid in the engine compartment also verified with a 12v bulb on a lead to negative earth.
3. I've wiggled the connectors to the starter and solenoid and none appear significantly corroded.
4. Suspecting the earthing of the engine from perhaps a corroded engine earth strap (I couldn't see it) I tried a supplemental earth by using jump leads - one end to an earth point and the other to a gearbox case bolt.
5. I took off the ignition switch cover and unplugged, examined and re-plugged the ignition switch connections. I didn't notice a loom behind the switch, but it's a 2002 so might be early enough to have the problematic switch.
6. I have no power to the glove compartment light. All fuses are in order and everything else on that circuit works, but I wonder if a short here caused the fuse 8 failure which is why I started the dismantling and seemed to have caused the non-starting.

So I am still getting total silence when twisting the ignition key (no relay or solenoid noise) and an illuminating high oil temperature light. Does anyone know if there is a relay that drives the solenoid power or is there a direct connection from the ignition switch to the ignition solenoid?

[talkingcars]

Using a bulb will only show there is sufficiant current to light the bulb which could be much lower than 12v, you really need some sort of volt meter, they are only a few pounds from a DIY warehouse or somewhere like screw fix. A battery only needs to dip to 8v to be too low to start the car.

Do the dash lights dim when you turn the key to position 3?

[danielt]

I have several voltmeters so will check tomorrow.

On the current drain test (looking for dimming lights etc) there is nothing observed when turning the ignition key. It is like there is no extra current drain at all when turning the key.

[danielt]

Thanks to all for the many helpful suggestions.

The problem is now solved!

Here's the issue and others may be similarly misinformed by the owner's handbook.

My owner's handbook on page 104 shows the main fuse box specification with a satellite fuse box on the right of the main driver's side fusebox. The lowest fuse is shown as F24 Heater Blower. This fuse I borrowed to replace a blown F8 for my initial investigations. I thought this was a good idea as the heater blower is a standalone non-critical component.

Today I decided to check everything again as the car still wouldn't start. I also found some more fuses so added a fuse to F24.

Then the car started as normal!

The reason is that the F24 position shown in the handbook is not actually heater blower - it looks like it should be F19 Engine Management. And it is is shown on the fuse box door chart as START.

So the moral of the story is a) be guided by the fuse charts in the car not the handbook and b) don't try to trace any electrical problems without each and every fuse in place and tested working.

[talkingcars]

Good news, please you are sorted.