Have you checked the fuel trim readings for bank 1 with a scan tool?This can be helpful for misfire diagnosis.
The only way to test an ECM is to replace it unfortunately,basically eliminate everything else first.Here is the procedure to balance test the fuel injector's.
Fuel Injector Balance Test with Tech 2 Circuit Description
The scan tool first energizes the fuel pump and then the injectors for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.
Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gauge. Place the towel in an approved container when the connection of the fuel pressure gauge is complete.
The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to Hot Soak fuel boiling.
The fuel pressure should be within the specified range. If the fuel pressure is not within the specified range, go to Fuel System Diagnosis.
The fuel pressure should reach a steady value. If the fuel pressure does not reach a steady value, go to Fuel System Diagnosis.
If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check
Did you perform the Fuel Injector Coil Test Procedure?
Go to Step 3
Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F)
Is the engine coolant temperature above the specified value?
Go to Step 4
Go to Step 5
Allow the engine to cool below the specified value.
Is the engine coolant temperature below the specified value?
Important: The fuel pump will run for approximately 2 seconds. Repeat step 8 as necessary in order to achieve the highest possible fuel pressure.
Is the fuel pressure within the specified limits?
284-325 kPa (41-47 psi)
Go to Step 6
Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F)
After the fuel pump stops, the fuel pressure may vary slightly, then should hold steady.
Does the fuel pressure remain constant within the specified value?
Go to Step 7
Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by the specified value?
10 kPa (1.5 psi)
Go to Step 8
Go to Symptoms
Notice: Do not repeat any portion of this test before running the engine in order to prevent the engine from flooding.
Re-test any fuel injector that does not meet the specification. Refer to the procedure in step 7.
Does any fuel injector still have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by the specified value?
Go to Step 9
Replace the faulty fuel injectors. Refer to Fuel Injector Replacement .
Is the replacement complete?
No I have never seen this type complaint and I have lots of experience on that model.I had one strange intermittent northstar misfire that ended up being very small pieces of the plastic intake manifold coming apart inside the intake plenum hanging up the valves.That one ended up costing me an engine.Here is the only TSB related to your problem.
PI01748A: 4.6L LD8 , L37 and 4.0L , L47 Engine Rough Idle - kw body calibration camshaft code DTC EGR intake leak lean manifold MIL miss misfire PCM - (Feb 20, 2004)
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Some 2000 and early built 2001 model year Cadillac Deville, Eldorado, Seville with 4.6L (LD8, L37) engines or 2001 Oldsmobile Aurora with 4.0L (L47) engine, may exhibit a condition of rough idle with no PCM DTC and no driveability complaints
The camshafts must be replaced (part numbers are listed below) on all 2000 vehicles with 4.6L (LD8) (L37) Engines and the early built 2001 vehicles (see broadcast codes listed below) with 4.0L (L47) OR 4.6L (LD8) (L37) Engines. For a 2001 vehicle, you must verify that it has the early cam profile by reading the 3 alpha characters of the broadcast code listed on the tag attached to the passengers side of the engine's rear cam cover. The Broadcast Codes for early 2001 engines are:
Seville, Deville Applications:
ENGINE VIN CODE Y KMA
ENGINE VIN CODE 9 KKA
ENGINE VIN CODE Y KCA
ENGINE VIN CODE 9 KBA
ENGINE VIN CODE C KYA
Camshaft Service Part Numbers:
4.6L (LD8) VIN CODE Y AND 4.0L (L47) VIN CODE C CAMSHAFT SERVICE PART NUMBERS;
12570331 RH EXH
12570332 LH INT
12570333 RH INT
12570334 LH EXH
4.6 (L37) VIN CODE 9 CAMSHAFT SERVICE PART NUMBERS;
12570335 RH INT
12570336 LH INT
12570337 RH EXH
12570338 LH EXH
NOTE: the Camshaft Service Part Number information can also be found on page 7 of the July 2001 GM Tech Link Volume, No. 7
SPECIAL NOTE: If you are having difficulty setting the mechanical timing on the rear bank exhaust camshaft. SI and the Service Manual instructs you to set the exhaust camshaft gear so that the stamping "RE" is in the 12 o' clock position. It has been found the "RE" stamping is located in the incorrect position on the exhaust camshaft gear. The correct positioning of the Exhaust Camshaft is when the camshaft dowel pin is in the 12 o' clock position. and the Exhaust Camshaft gear "RE" stamping is in the 9 o' clock position .
Once all 4 camshafts have been installed, the calibration must be updated. The dealer must contact TECHLINE and tell them that the camshafts on the vehicle have been replaced, and they will give the Dealer a VCI number to install the correct calibration. Techline must be contacted each time so that they have a record of when a camshaft change occurred on each vehicle. This will ensure that future calibration for that vehicle will be correct.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.
(00 01 CADILLAC DEVILLE, SEVILLE, KB, ELDORADO, EB, 4.6L (LD8 , L37) ENGINE) and 01 OLDSMOBILE AURORA 4.0L (L47) ENGINE)
hope get a chance to do some testing on the car this weekend and will keep you posted