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Re: [Mgs] '80 MGB: Faulty coil and fuel pump

To: "Mark Wise" <>, <>
Subject: Re: [Mgs] '80 MGB: Faulty coil and fuel pump
From: "Paul Hunt" <>
Date: Fri, 16 Apr 2010 09:26:44 +0100
A coil needs both voltage to it and changing current through it to work, the 
implication is that you have only checked the former.  Do you have points or 
the original electronic ignition system?  Points and the original Opus 45DE4 
system (although a 1980 wouldn't originally have had that) can be checked 
statically but the 45DM4 can only be checked dynamically.  For the first two 
turn the engine until it is coming up towards top dead centre on any piston 
and at any time before about 10 degrees BTDC the points should be closed and 
the 45DE4 module powering the coil.  This is checked by monitoring the 
coil -ve terminal (white/black) and making sure it is changing between 12v 
and 0v i.e. a ground as the points close/module energises the coil.  At the 
same time check that there is still voltage on the coil +ve, about 6v in the 
case of a 1980 with ballasted ignition.

If the coil -ve stays at 12v then the circuit through the points is open 
(wire to points, burnt points, distributor ground wire), or the electronic 
module is faulty.

If it stays at 0v, check the +ve, and if that is switching between 12v and 
0v then there is a bad-connection back through the ballast resistance and 
ignition relay.  If it's at 0v all the time it is open-circuit.  If it's 
staying at 6v, but goes up to 12v when you remove the wires from the 
coil -ve then there is a short-circuit from the points or module.  If it 
stays at 12v as you turn the engine then the coil primary is open-circuit.

The 45DM4 only gives a short pulse of duration controlled energy to the coil 
as the engine is turning, rather than the on and off points being controlled 
by crank angle, so these voltage changes will only be momentary at the 
trigger points and not static while the engine is static.  The static 
condition i.e. crank not being turned for a 45DM4 should always be 12v on 
both coil +ve and -ve.

An SU pump not working can be either not clicking at all if the points are 
burnt or solenoid burnt out, or just clicking once if the points are stuck 
together because of a spike and pit, or if the movement of the solenoid is 
not sufficient to throw the points open.  Check there is 12v to the pump 
measured between the two spades on the pump, not just between the 12v spade 
and a body ground.


----- Original Message ----- 
> Problem #1: there is no charge coming from the coil to the plugs, but
> there is power going to the coil.
> Problem #2: the fuel pump isn't pumping. 
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