Fouled plug, injector problem - exhaust manifold crack?

[Robert Abatecola <robert@xxxxxxxxx>]

My Spider has not been running too well lately.  Idle is rough and 
there's noticeably less power than normal during acceleration. 
There's a hint of misfire (I think) at all RPM.

During trouble shooting I discovered that the exhaust manifold is 
cracked at #4.  I also found that #4 plug is black and wet. 
Compression is about 165, 160, 160, 150.  If I disconnect the plug to 
the #4 injector while the engine is idling, the engine continues to 
run as if I had not pulled the plug.  All other injector plugs cause 
a drastic change in idle when pulled.

I'm not sure what my next step should be.  The exhaust manifold 
clearly has to be replaced.  But other indications tell me that the 
#4 injector might be bad.

Can the cracked manifold cause the plug fouling and apparent injector 
problem?  How can I confirm if the injector really is bad?

Thanks!
--

 -Robert Abatecola, San Jose, CA
  1985 GTV6
  1987 Spider Quadrifoglio
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