Electric trickery - the prince of darkness strikes again!

[squeezer]

Hi,

Not sure if anyone can help me with this one but I'm having problems with my 2500TC. When the lights (halogen conversion) are on and/or the electric fan cuts in, the engine falters and sometimes stalls (only when ticking over). The electric fan runs from a direct fused feed from the battery and all of the new auxilliary circuits are running on an ign controlled relay. I have a high output alternator and sports coil fitted (both have made no difference to the problem). Ignition is by Lumenition (wired through a toad immobiliser). I'ts not too bad at the moment because I don't use the lights that often but I'll be struggling come winter time...

The car runs fine otherwise and is not too bad on fuel...

Regards

James

[Alec]

Hello James,

do you have a voltmeter fitted, if so what is the voltage at tick over?
What speed is the tickover?
The other ting that can give odd effects is the state of the main earth strap(s)?

Alec

[Mike Stevens]

Hi,

Not sure if anyone can help me with this one but I'm having problems with my 2500TC. When the lights (halogen conversion) are on and/or the electric fan cuts in, the engine falters and sometimes stalls (only when ticking over). The electric fan runs from a direct fused feed from the battery and all of the new auxilliary circuits are running on an ign controlled relay. I have a high output alternator and sports coil fitted (both have made no difference to the problem). Ignition is by Lumenition (wired through a toad immobiliser). I'ts not too bad at the moment because I don't use the lights that often but I'll be struggling come winter time...

The car runs fine otherwise and is not too bad on fuel...

Regards

James

Hi James,

This is probably due to the increased electrical load on the alternator at tickover. In fact, a high output alternator is likely to make it worse! When the battery is fully charged, there is very little load on the alternator, and you've set the tickover at that load. With lights etc switched on, the load increases and this has to come from the engine which will slow down a bit.

Now, it shouldn't stall - I would have expected - but what speed do you have the tickover set to? You may have to increase it a bit to allow a bit more engine power output for the increased alternator load at tickover.

I once had a GT6 with an electric fan. Tickover on those was never very smooth, especially when hot and when the fan cut in, I iften had to catch the revs on the throttle and blip it to clear the excess mixture!

Cheers,
Mike.

[Alec]

hello Mike,

my feeling is that the battery should supply the load at tickover, hence the voltage question and also the reference to the earth strap. If the alternator is powering the load then something is not quite right?

Alec

[squeezer]

Gents,

Tick-over is set at around 800 rpm. The earth strap is in good condition but I will remove the connection to the strut top and clean this up tonight. As for the voltage - I'll check that tonight on the way home though I do know at cruising speeds the voltage reads 14.5v. Funny you mention the lumpy idle as it's fitted with a witor cam which I believe is based on the gt6 fitment.

Regards

James

[Alec]

Hello James,

tickover and running voltage seem OK, I'd be interested in the idle voltage when you get a chance?

Alec

[squeezer]

OK,

I ran the car (without the lights on) and measured the voltage at the + terminal of the coil to be 9.3 volts. At the feed side of the lumenition it was 14.1v. When the fan cut in these dropped to around 8.5v and 12v respectively (to me this should still be enough). The engine ran unevenly and eventually stalled. I checked the earth strap. There is one running from the engine at the coil fixing bracket to the battery -ve terminal. From the battery end of the earth strap there is a short narrower run to the strut fixing bolt. These are all clean. There doesn't seem to be a main earth strap anywhere else - I don't know if ther should be one. I have just been out in the car (father in-law droped off at the pub) and the car cut out dead at tickover with the lights on (no fan operating). It did this twice and restarted instantly. I'll check the rest of the earths tomorrow but i have to admit to being stumped by this one...

Regards

James

[Alec]

Hello James,

that is the standard earth connection on some Triumph models.

Would you clarify if it is an engine cooling fan (which can be quite a high load) or the heater fan?
The latter should not draw very much current so shouldn't really affect the voltage that much. If you have 12 volts at tickover that sounds low.
However it is worth doing volt drop checks at various parts of the circuits, e.g. alternator body to battery negative? body to battery negative etc with a decent load on to highlight possible poor connections. Incidentally the most obvious check is the fan belt tension and condition?

Alec

[David Withers]

I can't really add much to this as, unlike Alec and Mike, I'm not very good on electrickery.

All I'll say is that with some cars fitted with low mass flywheels, like the Peugeot 205GTi, switching on the lights could reduce the engine idle speed quite noticeably. However I've never experienced this on a big Triumph with its heavy flywheel etc.

James, I assume the flywheel on your car hasn't been lightened?

[Alec]

Hello David,

the line I'm following is that the battery is the main source of power rather than the alternator, Certainly battery voltage droops with load, droop being dependent on the load itself, hence the ballast ignition system as the voltage drops by a few volts on cranking (albeit drawing 100, or more amps.). At idle the alternator should be generating above nominal battery voltage and the increased load should not really impact the alternator as the battery should feed the load?
As James said that it cranks up OK I suspect that the turret earth connection is poor?

Alec