[Mgs] MGA , no start, no spark

[W. David Houser]

Thank you all very much...problem was the coil after all.
Dave Houser
On Mar 21, 2010, at 12:28 AM, Barney Gaylord wrote:

> Always do the diagnostic work before throwing money at it.
> Basic stuff first, start here:
> Spark and fuel curcuits: http://mgaguru.com/mgtech/electric/circ_i.htm
>
> Grab test light.  Switch on.
>    A3 = light  ---  If not, fix the fee wire.
>    SW = light  ---  If not, fix the fee wire.
>    CB = no light when points closed  ---  If light, no ground  
> through distributor.
>        Broken flex wire (2 of them), or loose base clamp.
>    CB = light when points are open  ---  If not, shorting across  
> points in distributor.
>        Common wiring error, points wire shorted to ground on screw  
> post.
>    Points of course must open and close.
>
> Use ohm meter.
> Check resistance in coil, SW to CB.
>    3.2 ohms = good
>    1.6 ohms = wrong coil
>    50 mega ohms (open circuit) = bad coil.
> Check resistance, distriutor side terminal to engine block with  
> points closed.
>    Near 0 ohms is good.
>   >1/4 ohm (250 mili ohm or more) = burned points.
>
> If that checks out, then check for spark at coil HT wire (not plug  
> wires).
> Very weak spark from coil = bad condenser
> No spark out of coil = bad coil
> Spark from coil but no spark at any plugs = bad rotor or broken  
> center contact in cap.
>
> Spark on some plugs, not others = fault of cap or HT wires or plugs.
>    Check for spark on each HT wire to engine bolt (not thorugh plugs).
>    Some wires no spark, check resistance of wires end to end.
>          0 ohms = solid wire, good
>        ~5000 ohms per foot of length = resistor wire, good
>        ~50 mega ohms (open circuit) = bad wire or bad end connectors.
>    Check resistance of plugs from top connector to center electrode.
>        0 ohms = solid plug, good
>        ~3000 ohms, resistor plug, good
>        6,000 ohms or more = resistor plug, faulty
>
> If that's okay, then spark on some plugs but not others = bad cap.
>  Check resistance of each post inside to outside.
>        0 ohms = good post.
>        50 mega ohms = corroded aluminum post
>            Repalce cap.  Try to buy one with copper posts.
>    If posts asre good, visual check inside of cap
>        Crack or tracking inside of cap = bad cap.
>
> If you haven't got it yet, read these pages:
> Coil Testing: http://mgaguru.com/mgtech/ignition/ig108.htm
> Ignition Trouble Shooting: http://mgaguru.com/mgtech/ignition/ 
> ig106.htm
>
> After all of that, call back about either success or failure.
>
> -----------------------------------------
> At 12:58 PM 3/20/2010 -0400, W. David Houser wrote:
>> ....
>> .... replaced coil, no change. .... switch on, fuel pump works,  
>> lights, getting gas...no spark out of coil....
>> ....
>> Car ran finecoming into garage and then  it didn't.
>> ....