Crank ,no spark condition

Joe Diagnostician Midland, Texas Posted   Latest  
Question
Driveability
1981 Porsche 928 4.5L (A) 3-spd (722.1)—WP0JA0928BS821263
Crank / No Start

This vehicle is a 1981 Porsche 928 v8 4.5l with a crank no start condition a fellow tech replaced the v belts and parked the vehicle. The following morning the owner of the shop went to move the car and experienced a no start Condition. I checked for spark at the ignition coil no spark present. I checked battery feed at the ignition coil 4.5 V KOEC. I also checked Powers and grounds at the ignition control Module And crank signal all checked good I noticed two ballast resistors near the coil i couldn’t find any wiring diagrams on Alldata or Identifix so I’m reaching out for further direction on this 81 thank you.

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Francisco Diagnostician
Vienna, Virginia
Francisco Default
 

I would check any wires close to the belts!!

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Obie Technician
Spokane, Washington
Obie Default
 

For any serious diag you will need an accurate wiring (current flow) diagram. That car has a history of wiring issues, up to and including fires. Start with basics. Check all the fuses for condition, position and corrosion. The fuse/relay box is under the passenger foot support. Check for fuel pump while cranking. There are a couple relays that can cause no start. Be sure the diagram you use…

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Joseph Diagnostician
San Antonio, Texas
Joseph Default
 

Make sure the vehicle is not in clear flood mode. Even though the vehicle is an early 80's design, Porsche is known for pushing new technology early. Clear flood mode will turn off ignition and fuel circuits. I'm not a Porsche guy and don't know the fuel setup on this car, but due you smell raw fuel coming out the tail pipe when cranking? Good luck

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Joe Diagnostician
Midland, Texas
Joe Default
 

hello thank you to all for your knowledge I thought about the clear flood as well. this vehicle is equipped with two micro switches on the throttle one for idle and the other is for full throttle. i checked both switches especially the idle contact switch which test ok, so I steered away from that. I scoped powers and grounds at the transistor ignition unit (ignitor) as well as the vrs signal…

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