Goal: Build a laptop-based data-acquisition system to diagnose transient rich-running condition on Maserati passenger car with non-OBD fuel-injection system.

Discussion:

Most fuel injected vehicles are easily diagnosed with a "code-scanner" thanks to on-board diagnostics (OBDII). However, this older exotic had no such system.  The problem was particularly difficult to diagnose because it was transient (only occurred during deceleration, when the fuel delivery should be cut off), and because typical problems (leaking injectors, bad O2 sensor, vacuum leaks, bad wiring, etc.) had already been eliminated.  A means was needed to measure what the system was doing during the conditions where the problem occurred.

Solution:

• Found and purchased low-cost 4-channel data-acquisition module.
   
• Built buffer circuits between vehicle ECU and DAQ module for:
   
  • Manifold pressure
  • Engine RPM
  • Fuel injector pulse width
  • Throttle position
  • Lambda (O2) sensor output
  • Coolant temperature
  • ECU supply voltage
     
• Drive cycles showed that in decel conditions (closed throttle), the fuel injection system was correctly cutting off fuel, yet the O2 sensor continued to report a rich exhaust stream.
  
  
   
• With fuel injection system eliminated, attention was turned to more obscure causes.  Problem was found to be faulty evaporative emissions canister, which was allowing fuel vapors from the tank to be drawn in through the purge lines during high manifold vacuum.  Replacement of this component solved the problem.