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[Marks DTM Calib]

misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification.

Its not, the crank sensor can only give crank position info, cam sensor is required to give cylinder cycle info. Key need for a cam sensor is to support sequential injection and cylinder specific ignition (so not so important on the 2.5/3.0 where its a wasted spark setup but is used for the sequential injection), without it, cylinder specific miss fires can not be determinde.

With crank sensor alone you can not determine which cylinder is next to fire on a four stroke engine so you would have to block fire injectors and spark (as per limp mode with 4k rpm limit in the event of a cam sensor fault, 2.0 owners will know this one more than V6's where the cam sensor is mega reliable)

Missfire detection is via knock sensor, ecu fires the cylinder spark, knock sensor listens for firing....no firing, miss fire (after x number of sequential missfires).

All simples 

[Webby the Bear]

Hi,

Just to add my thoughts..

When I was hunting for a fuel consumption/lack of perfprmace issue I did the following...

Exhaust leak test
Vacuum leak test
Voltage leak test
Stuck caliper checked for (in neutral and roll. If free to roll no stuck caliper/pads)
Swap out MAF (if live data shows low maf readings)
Clean EGR
Disspac replace
Oil in plug wells (if so replace CC gaskets...in middle of doing that too)
Compression test
Batt. Voltage test
Loose plugs check
Multirams (check for movement at approx 4000RPM)... Buy Gunson Lo-Gauge (vacuum leak) for rear multiram to check vacuum
Injectors tested
Buy and replace CTS
Check timing
Test Thermostat
O2 sensors (if bad on live data replace)

I've listed these in terms of money... i.e. first things done first are cheapest/no cost

[dbug]

misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification.

OBD1 codes for GM are
12 System normal
13 oxygen sensor circuit open
14 coolant sensor high resistance or shorted
15 coolant sensor circuit low or open
16 direct ignition system (DIS) fault in circuit
17 cam position sensor fault
18 crank or cam sensor error
19 crank sensor circuit fault
21 tps sensor out of range
22 tps sensor signal voltage low
23 intake air temp sensor out of range, low
24 vehicle speed (vss) sensor circuit fault
25 air temp sensor sensor out of range, high
26 quad-driver module (computer) circuit #1 fault
27 quad-driver module (computer) 2nd gear circuit
28 quad-driver module (computer) circuit #2 fault
29 quad driver module (computer) 4th gear circuit
31 cam position sensor fault
32 egr circuit fault
33 map sensor signal out of range, high
34 map sensor signal out of range, low
35 idle air control sensor circuit fault
36 ignition system circuit error
38 brake input circuit fault
39 clutch input circuit fault
41 cam sensor circuit fault, igntion control circuit fault
42 electronic spark timing (EST) circuit grounded
43 knock sensor
or electronic spark control circuit fault
44 oxygen sensor lean exhaust
45 oxygen sensor rich exhaust
46 pass-key II circuit or ps.pressure switch circuit fault
47 pcm-bcm data circuit
48 misfire diagnosis
51 calibration error, mem-cal, ecm or eeprom failure
52 engine oil temperature circuit, low temperature indicated
53 battery voltage error or egr or pass-key II circuit
54 egr system failure or fuel pump circuit low voltage
55 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage
56 quad-driver module #2 circuit
57 boost control problem
58 vehicle anti-theft system fuel enable circuit
61 a/c system performance or degraded oxygen sensor signal
62 engine oil temperature high temperature indicated
63 oxygen sensor right side circuit open or map sensor out of range
64 oxygen sensor right side lean exhaust indicated
65 oxygen sensor right side rich exhaust indicated
66 a/c pressure sensor circuit low pressure
67 a/c pressure sensor circuit or a/c clutch circuit failure
68 a/c compressor relay circuit failure
69 a/c clutch circuit head pressure high
70 a/c refrigerant pressure circuit high
71 a/c evaporator temperature sensor circuit low
72 gear selector switch circuit
73 a/c evaporator temperature circuit high
75 digital egr #1 solenoid error
76 digital egr #2 solenoid error
77 digital egr #3 solenoid error
79 vehicle speed sensor (vss) circuit signal high
80 vehicle speed sensor (vss) circuit signal low
81 brake input circuit fault
82 ignition control (IC) 3X signal error
85 prom error
86 analog/digital ecm error
87 eeprom error
99 power management

GM codes for Mototronic 2.8.1 (ie 2.5 & 3.0 V6) run from 10 to 145 - your list is incomplete!

Misfire detection is NOT via crank sensor - this is positional only! 
Trust this is clear now   

[dbdb]

Misfire detection is via the crank sensor have a read http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

The knock sensor is to detect pre detonation, no spark = no detonation at all.  So why anyone would think the knock sensor is involved I do not know, there will be no knock if there is no spark.

[Michael2.6]

Reading this post with interest                                 

a lot of good points but calm down lads and play nice

[TheBoy]

To definatively clarify things here:

2.5 and 3.0 UK spec Omegas use Motronic 2.8.1 or 2.8.3 ECUs (depending on age). These have no misfire detection. They are not OBDII compliant, or EOBD (the euro version of OBDII). They are proprietry. 2.5 and 3.0l Omegas finished production at end of MY 2000, with 2.6/3.2 (with OBDII/EOBD compliant Motronic 3.1.1 ECUs) coming in MY2001.

A cam sensor, on any engine, is a requirement to ascertain which is the firing cylinder. A crank sensor simply cannot do this. Not possible. Ever. At best, a crank sensor can be used out which pair of cylinders are in which position (eg, TDC), but not which of those 2 is just starting induction stroke and which is starting firing stroke. The cam sensor is needed for this.

It makes perfect sense to use the knock sensors, if fitted, for misfire detection.

[pirate]

ive had this happen with old oil and filter blockage in autobox,changed oil and filters sorted and had no fault codes that i remember she had full service history but gearbox had never been opened .

[dbug]

Misfire detection is via the crank sensor have a read http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

The knock sensor is to detect pre detonation, no spark = no detonation at all.  So why anyone would think the knock sensor is involved I do not know, there will be no knock if there is no spark.

Had a read - thats OBDII.

Quote from pdf -"When misfire occurs the crankshaft actually slows down and this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification."  As stated crank sensor cannot identify which cylinder(s) is/are misfiring.

Repeat 2.5 & 3.0 V6 are NOT OBDII. 

[cem_devecioglu]

"When misfire occurs the crankshaft actually slows down and
this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification"
 
yep.. as said above by admins, there is no way the ecu to identify which cylinder missfires by crankshaft sensor alone..

[dbdb]

"When misfire occurs the crankshaft actually slows down and
this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification"
 
yep.. as said above by admins, there is no way the ecu to identify which cylinder missfires by crankshaft sensor alone..

yep as I said "misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification."

And to clarify what the artricle I referenced says if read in full and not quoted selectively  "Cylinder misfire is calculated by the PCM through the Crankshaft Sensor input." http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

[dbug]

"When misfire occurs the crankshaft actually slows down and
this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification"
 
yep.. as said above by admins, there is no way the ecu to identify which cylinder missfires by crankshaft sensor alone..

yep as I said "misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification."

And to clarify what the artricle I referenced says if read in full and not quoted selectively  "Cylinder misfire is calculated by the PCM through the Crankshaft Sensor input." http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

At the end of the day mate the OP has a 2.5V6, and your suggestion of removing a plug lead to force a fault code is totally incorrect.  You then posted OBDII fault codes which are not relevent to that engine as it is not OBDII compliant, and misfires on that engine do not throw a code. 
You just seem intent to argue with all and sundry, including two highly respected OOF experts (I don't include myself as one of these) who know more about these cars than you'll ever know.  None of this goes any way to assisting the member who is asking for help in diagnosing and fixing his problem.

[Marks DTM Calib]

"When misfire occurs the crankshaft actually slows down and
this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification"
 
yep.. as said above by admins, there is no way the ecu to identify which cylinder missfires by crankshaft sensor alone..

yep as I said "misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification."

And to clarify what the artricle I referenced says if read in full and not quoted selectively  "Cylinder misfire is calculated by the PCM through the Crankshaft Sensor input." http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

And I am telling you that miss fire detection on the Motronic setup is via the knock sensor but your to bloody minded to listen

[Kevin Wood]

I'm not sure why we're arguing about misfire detection anyway. The one thing that nobody can refute is that it's not even implemented on the OP's car.

[cem_devecioglu]

"When misfire occurs the crankshaft actually slows down and
this change in RPM is sensed by the PCM, which also uses the Camshaft sensor for cylinder identification"
 
yep.. as said above by admins, there is no way the ecu to identify which cylinder missfires by crankshaft sensor alone..

yep as I said "misfire detection is via the crank sensor,  the camshaft sensor is used for cylinder identification."

And to clarify what the artricle I referenced says if read in full and not quoted selectively  "Cylinder misfire is calculated by the PCM through the Crankshaft Sensor input." http://www.magnaflow.com/07techtips/TechBulletin/TB80011.pdf 

[Andy H]

Apologies for prolonging the off topic rambling but
misfire detection can be sensed either by
1. using the knock detectors to sense a normal firing pulse (as opposed to the larger signal given by a pre-ignition or knock) (as already stated this is the method used by EOBD compliant Omegas)
2. by sensing the angular acceleration of the crank by use of the crank sensor. The ECU knows which cylinder it wanted to fire because it has access to the cam position sensor. I am pretty certain that VW have used this method of misfire detection but as already stated THIS IS NOT THE METHOD USED IN THE OMEGA.