Technical Information
 Tech Tip 
Ford Courier/Mazda Bravo Running Rich.....
Recently we have struck a number of situations where Ford Courier/Mazda Bravo 2.6 Litre MPI Petrol engines have been running excessively rich, more often than not the fault was especially evident after the head had been off the vehicle.

After Investigation and carrying out all the basic system checks including checking a cam timing, fuel pressure and flow etc, it was found that the injector duty cycle was excessive and was consistent with that of a cold engine where cold start enrichment would be evident.

Resistance and voltage checks of both the air temp sensor and the coolant temp sensor were carried out however showed no fault with both sensors operating within specification. Back at the ECU the same resistance and voltage checks were carried out at the relevant ECU Terminals, ECU 2Q for coolant temp and ECU 2L for air temp. All the tests were carried out with the vehicle at operation temperature therefore the coolant temp sensor should have been reading a low resistance corresponding with an engine temperature of approximately 90 degrees and the air temp sensor reading should have been reading a temperature of approximately 20 degrees which is the equivalent of a higher resistance. However this was not the case, when checked at the ECU the air temp sensor was reading a much lower resistance (hotter temperature) than that of the coolant temp sensor which was reading a high resistance (colder temperature). How could it be that with a hot engine the air temp sensor is reading 90 degrees and the coolant temp sensor is only reading 20 degrees at the ECU? After closer inspection it was found that on reassembly of the engine after the head had been off the vehicle that the coolant temp sensor wiring and the air temp sensoring wiring had been refitted back to front therefore giving the ECU misleading information about coolant temperature and causing the vehicle to run rich. This could be a very easy mistake to make as both air temp and coolant temp sensors use the same style of electric plug and both have extremely similar wiring colours.

Air temp sensoring wiring: Brown with black trace and straight green

Coolant temp sensoring wiring: Brown with black trace and green with white trace.