15 replies to this topic

[1984mini25]

998 70k, 65d electronic dizzy timed to 8 degrees, vac advance disconnected as had been for the last 6 years with no problems.

 

Last month the mini started misfiring, almost as if the ignition was temporarily being switched off with the alternator light coming on below 2000 rpm. Worse with the choke out needed to keep it above 2k and close to undriveable. As it also cuts out when the clutch is depressed when coming to a stop with the choke in/engine warm. Where the engine goes completely silent (so no warning) and the alternator light comes on and restarts instantly on the key.

 

Started on morning of mot. Witch after a hill start with lots of choke to keep it above 2k and stop it from stalling/ misfiring causing lots of blue smoke (probably bore wash) it cleared once warm. Passed mot with 2.3% CO and 317 ppm HC, but has been undriveable since.

 

Have so far done the plugs, leads looked ok, new dizzy carp and rotor, new ignition module, borrowed working coil from other mini, and checked the wiring and connectors. Reconnected vac advance witch had been disconnected for last 6 years, thought it was “fixed” until the carb was dumping fuel out of the overflow.

 

So have also stripped and cleaned the carb, renewed the gaskets, relapped and adjusted the needle valve, replaced the fuel pump to carb line doing away with inline filter. Fixed the sticking choke after the carb was refitted, stripped dizzy, sprayed innards and refitted. Only for it to still be doing it as before.

 

Recap, it idles all day fine, revved between idle and 2k misfiring/cutting out (but still running) alternator light on, above 2k all as normal right up to 5.5k.

Edited by 1984mini25, 10 October 2015 - 10:31 PM.

[Shifty]

Low voltage at the coil?  The leccy dizzys are sensitive to voltage, try turning the lights on and seeing if the miss gets worse.

[1984mini25]

Just been out and done some voltage measurements at the battery and coil with it both off and running.

 

Battery, 11.91 volts but still starts the car perfectly fine. Running, 14.15 volts and rising and voltage at the coil while running, 13.14 volts.

Edited by 1984mini25, 11 October 2015 - 12:32 PM.

[ACDodd]

Use no ballast wire and use a 1 to 1.5 ohm coil. What you describe is classic of wrong coil or ballast feed problems.

Ac

[1984mini25]

I removed all of the pink ballast wiring and chucked in it the bin when I first fitted this ignition back in 07. Then fed a direct 12 volt feed from no1 of the fuse box (four fuse type) and have been using the GCL143 coil ever since.

[72clubman]

I'd be doing a compression test. Mine did almost exactly this, turns out it'd blown the head gasket between cylinders 2 and 3.

Joe

[1984mini25]

That's something to consider, but it's not using any coolant or oil and neither are mixing with each other. I had also thought about doing the tappets, just simply because I'm running out of simple things it could be.

[CityEPete]

Coolant loss and mayo won't happen if it's blowing between cylinders. Compression test next before you alter anything as it will either show up a fault or confirm it is ok.

As the voltage is low at rest I'd see what a known good battery does, if it's goosed it could be hiding the problem.

[72clubman]

Exactly as city Pete said. A blow between cylinders will not show any contamination of coolant. The misfire is the compressing cylinder blowing back through the next cylinder on intake. As the revs get over 2k the time duration is much smaller so you don't notice as much.

I the same as you figured it was something small and spent a week messing with timing a fueling. But a compression test revealed this.
Once diagnosed I had the gasket replaced in a few hours.


If it's battery related, which isn't beyond the realms of possibility, I'd be checking the battery earth strap and the engine earth strap. Do a resistance test to check it's actually doing its job. My engine strap looked in perfect health, but actually had an internal break so wasn't doing its job.


Joe

Edited by 72clubman, 11 October 2015 - 07:39 PM.

[1984mini25]

As the voltage is low at rest I'd see what a known good battery does, if it's goosed it could be hiding the problem.

 

It's looking like I'll need a new battery anyway, if a little peeved as the battery is less than 24 months old and I though the Exide batteries were supposed to be decent. As I've taken it off the car and have had it on a full charge today and its still only showing 12.2volts.

 

Although I'm still surprised the 11.9 volts taken at the battery was enough to start the car as normal, with no signs of struggling to turn over etc.

[CityEPete]

Batteries are one of those things that last longer if you use the car regularly, many motorcyclists have to fit a new battery each spring which is daft when an optimate is £30 and will keep things ok for years and a motorcycle battery can be £100 a pop!

Edited by CityEPete, 12 October 2015 - 09:10 AM.

[CityEPete]

If you take the battery to a proper place they will test it for you, there is more than just voltage to it plus there's the calibration of you meter etc.

[1984mini25]

Spent another day on it while the battery was left on a trickle charge, although it still only holds just under half. Removed and cleaned up the braided engine earth strap and refitted. Also 'borrowed' the earth strap from my other mini and fitted that on the thermostat housing to bulkhead. Removed all of the wiring on the starter solenoid (inner wing type) cleaned up all the connections and refitted, also did the single one on the starter while I was at it. Took apart and cleaned up the innards of the alternator plug. Cleaned up the battery connectors in the boot including the earth point to the boot floor. Replaced both terminals on no1 of the fuse box. Took it for a short drive up and back down the street and it was still doing it, although not nearly as badly as it has been. So I then readjusted the tappets and checked them over just to make sure, leaned off the mixture 2 flats and it seams to have cured it.

[spiguy]

I would also wonder about the calibration of the meter before condemning the battery. Maybe check a brand new 1.5V AA cell with it, should read 1.6V on a brand new decent make cell. My dad was chasing issues on his car for a while as he thought his alternator was outputting too high a voltage, turned out to be an error in the meter.

[1984mini25]

Just tried the above on a fresh AA straight out of the packet and its showing 1.65 volts.