Terravent
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| posted on 6/5/03 at 09:40 PM |
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Rover 414 SLi
I have a K plated Rover 414 SLI that will not start from cold on the key. It will bump start instantly when cold and starts without problem once the
engine is warm. Can anybody shed any light on what might be wrong please. Recent new parts include starter motor, battery, exhaust (non-cat) plugs,
leads, cap.
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craig1410
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| posted on 6/5/03 at 10:56 PM |
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Hi,
It looks like you've covered the main suspects already. If it wasn't for the fact it starts when hot on the key then I'd certainly
suspect the ballast resistor (if fitted) or more precisely the connection from the starter motor to the coil side of the ballast resistor(via a relay
or diode). This could still be the problem because it would mean that the coil wouldn't be getting a boost when cranking as it should.
In case you don't know about the ballast resistor principle it works like this:
The coil is designed to run on between 6 and 9 volts and the resistor drops the battery voltage from 12 V to this reduced voltage when the engine is
running normally.
However, when cranking, the starter load drops battery voltage to about 9V usually, even with a good battery, and to ensure a strong spark the ballast
resistor is bypassed by feeding the full battery voltage (reduced due to cranking load) to the coil. This must be done via an isolation mechanism such
as a relay to avoid the ignition circuit feeding the starter when not cranking. Check the relay or diode and all the connections related to it.
If the above mechanism had failed then you might indeed find that bump starting was fine but cold cranking (when battery power is lowest and engine
friction highest) is reducing voltage too far to create a good spark. Check coil voltage from Earth to the +ve terminal with ignition on but not
cranking and then watch it while cranking. It shouldn't drop much and may even increase voltage slightly. If it drops significantly under
cranking then it points to the ballast resistor.
Also, check your spark plug gaps since if they are too wide then more coil voltage will be required to jump the gap but they'd have to be way
off to cause this problem on their own.
Another less likely possibility is a problem with the crank sensor (gap too wide) which might mean the sensor only picks up the crank pulses when the
RPM is higher such as during a bump start. This is common with inductive sensors, especially in ABS braking systems, where the gap is crucial to low
RPM sensing.
I hope this helps,
Craig.
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craig1410
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| posted on 6/5/03 at 10:58 PM |
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BTW, I've got a Haynes manual for the Rover 214/414 in my garage so I can help you to debug the connections if required. My Wife has a 214Si (L
Reg) so I can trace wires and give you voltage readings as well if it comes to that.
Cheers,
Craig.
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jollygreengiant
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| posted on 8/5/03 at 09:54 PM |
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Could also be a fualty temp sensor telling the engine it hot (lean mixture), when its cold (rich mixture for starting). If the sensor is telling the
ECU that its hot, when its actually cold then your chances of starting could be severly reduced.
Also Rover ECU's are reknown for dry joints and all-sorts of of starting/running problems.
But it still doesn't hurt to check balast resister and earths first.
Hope this helps. Enjoy.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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craig1410
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| posted on 8/5/03 at 10:00 PM |
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Yes I thought of that too but given that it starts okay if bumped when cold then I though the ballast resistor was more likely.
Cheers,
Craig.
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craig1410
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| posted on 9/5/03 at 12:11 PM |
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Hi Syd,
He said in his original note that he'd changed the battery which makes it unlikely (though not impossible...) that the battery is faulty. One
thing might be worth checking are the heavy earths from battery to body and starter/engine. He could put a voltmeter between the starter earth and
battery earth and check that the voltage is as close to zero as possible. I'm not sure what voltage you'd expect but if it's any
more than about 250mV (I guess) then the earths aren't as good as they should be.
Tarravent, does the engine crank at a reasonable speed when cold or does it labour? If it is labouring then it might indicate bad earths (or feeds)
and/or a bad battery. If it cranks in a spritely manner then it's more likely to be sensors or ballast res. as discussed.
BTW, please put us out of our misery if you do find the solution 
Cheers,
Craig.
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