Porsche 924 The Porsche 924 was produced from 1976 to 1988 was a two-door, 2+2 seat sports car coupe.

87 924S cold misfire

  #1  
Old 08-23-2007, 09:17 PM
Thread Starter
Join Date: Aug 2007
Posts: 1
Default 87 924S cold misfire

Hi all,

I have an 87 924S in my shop that is rather maddening. It starts fine, but within 3 seconds or so drops cyl #3, and then misses until the engine reaches operating temp. The owner replaced plugs, wires, dist cap/rotor, coil, fuel filter, fuel inj temp sensor, idle air control motor, etc. That made no change. I have checked compression on all cyls, hot and cold, no problems. Leakdown tests fine. Spark output is fine. Cam timing on. Fuel pressure is good. Switched fuel injectors, no change. Lifted fuel rail with injectors, all spray equally when cranking. Checked spark timing on each cylinder with timing light, all at correct time. Found no vacuum leaks. Substituted known good airflow meter, no change. Cam lobes look fine. Pulse width on adjacent injectors the same. Everything seems to check out fine, but it still misses on that cylinder until it warms up. Why??? I'm open to suggestions. Thanks for any thoughts..
 
  #2  
Old 10-14-2007, 03:54 PM
Join Date: Oct 2007
Posts: 2
Default RE: 87 924S cold misfire

did you find the problem? Mine has a problem where it tends to want to stall when I move the accelerator pedal when it's idling from acold start - if you pressin more it catches - light tip-ins are a probelms though.
Steve
 
  #3  
Old 10-14-2007, 03:55 PM
Join Date: Oct 2007
Posts: 2
Default RE: 87 924S cold misfire

did you find the problem? Mine has a problem where it tends to want to stall when I move the accelerator pedal when it's idling from acold start - if you pressin more it catches - light tip-ins are a probelms though.
Steve
 
  #4  
Old 10-14-2007, 07:09 PM
Join Date: Oct 2007
Posts: 4
Default RE: 87 924S cold misfire

Are you sure its misfiring number 3? just a question. It could still be the injectors even if they sprayed equally, i would say change them around the 4 cylinders and see if #3 still misfires. Then try it with the plugs too. If it is still number 3, its something inside the motor. If it changes, It is one of the injectors or plugs. But you said if leak down and compression are fine i doubt its internal. But, there maybe some gunk on one of the valves that only happens to hang it up after the engine has gas in it or is firing, then the leakdown test wouldnt catch it. Im used to the supra, with the inline 6, so it sucks more with 6 cylinders to diagnose!
 
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