BA Falcon missing at idle and underload


Ford Falcon BA XR8 5.4L 4 valves per cylinder 2004


The vehicle drove into the workshop running the vehicle was running ok, but a miss was noticable at idle, the vehicle was then test driven to confirm the customer complaint that it hesistates and misses during takeoff.

Diagnosis: 3 hours

Firstly the Falcon Series usually do not show up a check engine light very often, but can still have a few codes present and will still help in tracking down the problem and give a base line to start from.

Once the fault codes where check we found BA-XR8-Fault-Code-Read-out

  1. P0171 – system too lean bank1 (above amx threshold)
  2. P2105 – If no related DTC’s are set record the ERR_FR Quiz & ERR_2_Quiz Values in the Warranty Replace the PCM
  3. U1900 Can Communication Bus Fault – Receive Error.

Great lets start from here but nothing about the vehicle missing. The engine covers were removed and visual inspection showed that 2 coils had allready been replaced, Bingo looks like it could be another faulty coil, we decided to check all the ignition coils for Maximum output, we did find 2 suspect coils and marked them for replacement, during this time we found Cylinder 3 has a full missfire, and spark was present at 30KV. Time to remove the spark plugs, we checked the spark plugs to our shock the spark plug gaps where WAY to Large, the largest being 1.9mm Gap (never have we seen a gap this large before) the standard Gap for this engine is 1.5mm, This is the reason the the Ignition coil failing. Knowing this,  we didn’t have the spark plug part number on hand we adjusted the gaps on the spark plugs, refitted the Igntion coils in loose and started the engine, the engine misfire was now smoother but a misfire was now only on one cylinder. CYL3ba-falcon-xr8-Spark-plug-gap

Tests that had been carried out

  1. Compression test. (all around 155-170) ok
  2. cylinder leakage test on CYL2 & 3 0% leakage.
  3. Inside bore scope to visually inspect the valves, dirty seats and slight coked up but ok visually.

At this stage we where shaking our heads thinking ok a full misfire and there is no engine mechanical faults, this is not normal.

Remembering back to the first fault code P0171 We decided to check long term fuel trims to find the long term fuel trim bank1 at 30% + whilst Bank 2,  2%+, this was where the problem lied, a Smoke test confirmed that the vacuum lines underneath the throttle body where leaking, again not having the parts on hand we blocked them and started the engine,  no change. whilst the plenum chamber was removed we decided to quickly remove the injectors and bench test, just so we knew where we where working from. all injectors tested good 110cc over 20 sec. Great but this did not help us at all.

We then got out the Vacuum Gauge to test for sticky valves, to our disbelief, the manifold vacuum was better than expected at 21 inches, the vehicle was now ready to get serious, the Pico Scope was pulled out to test the Injection Pattern, and a pattern was found, the cylinder 2 was then tested which was ok, but we noticed that the duration was different, on cyl 2 duration of approx 3-4 ms on cyl 3 1ms injector duration, an no advancement of injector duration during acceleration. the video will help to understand this part mentioned above.

Bingo the Problem was found, but not fixed just yet, we had to confirm that the P2105 Fault was actually To replace the ECM, as knowing this code is specific to throttle control, which made us think differently as the vehicle idled perfectly.

Now to test what could be wrong with the ECU outputs, we have seen cylinder misfires due to bad reluctor teeth on crankshafts in segments so before condemning the ECU Injector Driver, testing the Inputs was necessary.





After spending a few hours on testing, The spark plugs where replaced and 2 new ignition coils fitted, ________________ this was also done the Vehicles KAM memory was reset, which resets the long and short term fuel trims a test drive was conducted and the condition of the oxygen sensors was performed. ___________