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Re: [Mgs] MGA , no start, no spark

To: "W. David Houser" <>, <>
Subject: Re: [Mgs] MGA , no start, no spark
From: Barney Gaylord <>
Date: Sat, 20 Mar 2010 23:28:36 -0500
Always do the diagnostic work before throwing money at it.
Basic stuff first, start here:
Spark and fuel curcuits:

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:
Ignition Trouble Shooting:

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 spark out of coil....
>Car ran finecoming into garage and then  it didn't.
Suggested annual donation  $12.75

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