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[minerwilly]

Hi everybody, I'm a new Omega owner and really need some help!

I bought a 1998 2.5 V6 Auto just over a week ago. On the short test drive that I took, everything seemed absolutely fine, but then as soon as I had to do any real distance (driving the thirty five miles home from work) everything went to pot.

For a start, it turns out both cats had collapsed and were causing the exhaust to overheat and sending burning material out from the rear end. This I'm not too worried about. I've temporarily removed the cats completely and installed straight pipes. Obviously I'll replace them before the MOT.

What is more worrying is the fact that when driving, after the first couple of miles (or less if up hill and the engine is under load), the car seems to go into some kind of limp mode and loses all its power. There's a lot under the bonnet, and as a newcomer to these cars I'm not in a great position to start making potentially expensive assumptions about what the problem is.

I've checked the ECU for error codes and there are none at all, which was a bit of a surprise to say the least.

I really need to get this car up and running as soon as possible because I have a seventy mile a day round trip to work and back! Also, I've spent as much as I can afford on the car in the first place, so I'm at a point where I have no choice but to see it through. Apart from this loss of power, the rest of the car is great, but the way it is at the moment it's undrivable!

Any help or advice would be very gratefully received.

Cheers.

Marc

[TheBoy]

Does the EML ever come on (either when driving or initially when turning on ignition)?

Crikey, just looked up your location, as my Scottish geography is bad

[minerwilly]

Yep, I'm as far north as you can get without leaving the mainland

The EML did come on a couple of times when the cats were in but hasn't come on since I took them out. Having said that I haven't driven it far since then.

Thanks for replying.

[TheBoy]

Hmmm, the last decatted Omega I drove ran down on power as well, but no sudden, massive power losses, just generally down a bit on power.

Is it just down on power, or is it actually misfiring? Misfires with no codes = check HT side of things

[minerwilly]

No misfire, it just feels limited.

It was doing this before I took the cats out as well though. My instinct tells me that it's the ECU acting on wrong information, but I have no experience of these cars at all so I will bow to the opinions of you guys.

Marc

[cem_devecioglu]

"Also, I've spent as much as I can afford on the car in the first place, so I'm at a point where I have no choice but to see it through"
 
Willy, before spending any extra, let it be checked by a mobile mechanic and he may be able to tell you other hidden expenses..
 
those cars are cheap for a reason.. and if yours are badly abused by previous owners , it will be good for your wallet to learn whats coming next before its too late.. sorry , but I feel necessity to warn you  
 
ps: do you know the history of car/prevous owner.. any service papers, cambelt, head gasket etc etc.. ?

[TheBoy]

Check multirams are working - think its described in our Maintenence Guides section, although that normally affects low down power...

[minerwilly]

It's actually a well looked after car. 80k on the clock, everything works, nice clean engine, mechanics all fine. The ash tray hasn't even had a cigarette in it.

It's had two previous owners and sailed through its last MOT. It should hopefully be a good car when I get this power issue sorted.

What are the multirams if you don't mind me asking?

Cheers.

[cem_devecioglu]

It's actually a well looked after car. 80k on the clock, everything works, nice clean engine, mechanics all fine. The ash tray hasn't even had a cigarette in it.

It's had two previous owners and sailed through its last MOT. It should hopefully be a good car when I get this power issue sorted.

What are the multirams if you don't mind me asking?

Cheers.

glad to hear those.. 

[TheBoy]

Multirams are a pair of valves in the intake to change the intake length, to flatten the torque curve (Omega is a heavy car, so the standard peaky torque curve is not so drivable).

[minerwilly]

Cheers, that makes sense. I'll have a look at the pages on them and get them checked.

It would be great if I can just find the problem and get it fixed before I get sacked

Marc

[Andy H]

I wonder if the original fault that caused the cats to self destruct is still present.

If I have understood correctly the thing that damages cats is unburnt fuel so looking for a misfire or overfueling.

[minerwilly]

It could well be over fuelling. Cats only have a limited life anyway though, and as a 98 car, I wasn't that surprised they were dead.

If it was over fuelling what do you think the cause and cure would be?

[TheBoy]

If you have access to equipment to read live data, what are MAF readings at idle, 2000rpm, and idle and partial load trims for both banks.

[Kevin Wood]

For the cats to fail in a spectacular way there needs to be excessive unburnt fuel in the exhaust, so I'd suspect either a misfire or overfuelling.

Worth checking that the little rubber pipes in the SAI system which feed air to each exhaust manifold are still present, IMHO. They are unlikely to have survived the cats blocking and, if they've perished, they will be letting air into the exhausts before the lambda sensors and upsetting the closed loop mixture control, which might well explain why it's sluggish.

[cem_devecioglu]

in addition to above (MAF check), I would also recommend 3 checks..
 
cambelt timing, DIS pack condition(there are some tests in youtube that you can apply yourself also)  and very close inspection of head gasket area both rear and front (above the alternator is a candidate).. 
 
ps: dont trust compression tests alone as mostly fire rings stay intact.. and coolant loss can be minimal.. and mileage not that important , as time with old coolant also kills the gaskets..

[minerwilly]

Keep em coming people. This is all starting to sound like great advice.

Could the head gaskets be responsible for this if they were failing?

I'll get all of these bits looked at as soon as I can. Hopefully if I can get past the initial issue of getting my car working, I might actually become a contributor on here instead of an advice leech

I'll report back when I have more information.

Thanks again everybody.

[cem_devecioglu]

Could the head gaskets be responsible for this if they were failing?

may be yes, may be no but I can bet , you wont wait long

[Rods2]

Is the going into limp mode consistent or does it happen randomly. If randomly it could be a failing crank sensor. I had this with the autobox occasionally going into limp mode as it was failing and it then started cutting the engine out when hot. I did not get any engine management codes when this happened.

Fitting a new crank sensor, which cost just over £50 with a trade card cured my problems. Only use a genuine Vauxhall sensor. As you have a 2.5l, I know a member had issues where there are two types of sensor for this engine, but they produced a guide which is in the maintenance guides section.

[dbdb]

I'm surprised the cats went at 80K/15 years, my 98 v6 had fine cats at 200K  when it was scrapped last year on other issues.  So presumably there is a causing problem. 

Do check the simple and cheap things first eg fuel filter.

Also surprised there are no error codes especially as the EML did come on.  Maybe check it is all working by forcing a fault eg disconnect a spark plug lead for a very short period.

[dbug]

Disconnecting a plug lead on a 2.5V6 won't necessariy throw a fault code

[andy_driver]

i had a problem once with the ecu coolent temp sensor the car would run ok then all of a sudden it over rev and over fuel and cut tempermental it was fitted a new sensor and it was on the other hand the past few months my car was really lumpy on idle and fuel wasnt great at all and sounded rough and slow every so slighty what i found was that after unblocking my heater matrix the problem was cured because were the ecu temp sensor sits in the coolent bridge the outlet pipe that comes out of the matrix goes back to the coolent bridge the temp sensor was getting proper hat water in stead of look warm getting wrong signal in turn cause low power the car is running great and fuel consumption is better cause the sensor is sending the right signals before the ecu was thinking the car was cold and still giving out loads of fuel how does the heater feel in your car .

[dbdb]

Disconnecting a plug lead on a 2.5V6 won't necessariy throw a fault code

P0300 Random/multiple cylinder misfire detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
No fault will always throw a code but with OBDII misfire detection is pretty good, primary info is from the crank sensor. 

[dbug]

Disconnecting a plug lead on a 2.5V6 won't necessariy throw a fault code

P0300 Random/multiple cylinder misfire detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
No fault will always throw a code but with OBDII misfire detection is pretty good, primary info is from the crank sensor.

Above are codes for Mototronic ME 3.11 which is fitted to dbw motors (2.6 & 3.2V6) - the 2.5 and 3.0 V6 uses the Mototronic 2.8.1 - different codes and misfires not recognised or coded

[dbdb]

Above are codes for Mototronic ME 3.11 which is fitted to dbw motors (2.6 & 3.2V6) - the 2.5 and 3.0 V6 uses the Mototronic 2.8.1 - different codes and misfires not recognised or coded

They are OBDII codes, they are industry standard, mandatory for all cars from 1996 (US) and Jan 2001 (Europe).  All cars meaning every make sold.  Not proprietary to Motomoronic let alone to certain models of Motromoronic.   

[dbug]

Read the maintenance guides mate

Non dbw Omegas are not OBDII compliant!!

If you don't believe me look here at TBs post #1 http://oldsite.omegaowners.com/forum/YaBB.pl?num=1176839367/0

[cem_devecioglu]

i had a problem once with the ecu coolent temp sensor the car would run ok then all of a sudden it over rev and over fuel and cut tempermental it was fitted a new sensor and it was on the other hand the past few months my car was really lumpy on idle and fuel wasnt great at all and sounded rough and slow every so slighty what i found was that after unblocking my heater matrix the problem was cured because were the ecu temp sensor sits in the coolent bridge the outlet pipe that comes out of the matrix goes back to the coolent bridge the temp sensor was getting proper hat water in stead of look warm getting wrong signal in turn cause low power the car is running great and fuel consumption is better cause the sensor is sending the right signals before the ecu was thinking the car was cold and still giving out loads of fuel how does the heater feel in your car .

yep.. coolant temp sensor is a likely candidate for over fueling..
 
but I still doubt car have other issues..

[cem_devecioglu]

Read the maintenance guides mate

Non dbw Omegas are not OBDII compliant!!

If you don't believe me look here at TBs post #1 http://oldsite.omegaowners.com/forum/YaBB.pl?num=1176839367/0

agreed..

[Marks DTM Calib]

Disconnecting a plug lead on a 2.5V6 won't necessariy throw a fault code

P0300 Random/multiple cylinder misfire detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
No fault will always throw a code but with OBDII misfire detection is pretty good, primary info is from the crank sensor.

Miss fire detection is mostly via the knock sensor based on cam sensor input as to which cylinder is finring next e.g. Fire cylinder 4, fire detected via knock sensor - all good. No firing detected for x consecutive firings then raise code.

The 2.5 and 3.0 do NOT support miss fire detection. 

[dbdb]

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

[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.

[dbdb]

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.

Well that's amazingly clever of Vauxhall since knock sensors were only first proposed for misfire detection in academic papers in March 2002, the only two methods at that time being crank speed and ionisation current through the plug.

[dbug]

Just give up gracefully, you're now just being arumentative for arguments sake, and none of this is helping the OP.  He has a 98 2.5V6 and mifire detection is not available on his car.  This originally started because you gave the OP incorrect advice re his car

Your posts are becoming boring now

[Kevin Wood]

Yes, indeed. Let's get back to trying to help the OP.

A couple of more things occurred to me:

Coolant temperature sensor: If this has failed the ECU might think it's got a cold engine, hence it deteriorates as it warms up, runs rich, and may have been what destroyed the cats.

Lambda sensors: These start to control mixture as the engine comes up to temperature. Any leak in the exhaust upstream of them (hence my earlier point about the SAI pipes) or tired sensors, will have an impact here (although I'd expect a code to be  stored). As the car has no cats, there's no harm in disconnecting the lambda sensors, accepting that there'll be codes related to that, but in doing so, forcing the system into open loop. If it drives better, that's an indication that the exhaust / lambda sensors are the culprit.

If that doesn't help, reconnect and try it with the MAF sensor disconnected instead.

Might be worth trying it with the EGR valve blanked off with a sheet of metal too.

Plus check the basics - plugs, leads, DIS pack. Cut it immediately after a run and see if the plug condition varies between cylinders perhaps?

[dbug]

Checked back exhaust box clear and not blocked/partially blocked?  Some members have had this in the past, with significant power loss

[Webby the Bear]

All things that I listed to check... although I think it may have been overlooked following the topic getting heated 

[Kevin Wood]

Yes, wouldn't be surprised to find he's gone to find a more helpful forum now.

[Michael2.6]

The only person on this forum that can answer this post correctly and end it is TB

[TheBoy]

The only person on this forum that can answer this post correctly and end it is TB

There are many people on this site who are far cleverer than I will ever be. 2 of them have already posted on this thread.


Poor running, with no codes, and fuel trims and MAF reading in normal range, I'd always suggest checking HT in first instance.

Obviously not everyone can read live data on pre EOBD Omegas, so trying with MAF disconnected and then Lamdas disconnected (and MAF plugged back in) is a way of getting a feel for what might be happening within the ECU. Caution has to be paid to cat health normally when doing this though, esp playing with lamdas.

[Webby the Bear]

The only person on this forum that can answer this post correctly and end it is TB

There are many people on this site who are far cleverer than I will ever be. 2 of them have already posted on this thread.


Poor running, with no codes, and fuel trims and MAF reading in normal range, I'd always suggest checking HT in first instance.

Obviously not everyone can read live data on pre EOBD Omegas, so trying with MAF disconnected and then Lamdas disconnected (and MAF plugged back in) is a way of getting a feel for what might be happening within the ECU. Caution has to be paid to cat health normally when doing this though, esp playing with lamdas.

I never knew you thought of me so highly 

[dbug]

The only person on this forum that can answer this post correctly and end it is TB

There are many people on this site who are far cleverer than I will ever be. 2 of them have already posted on this thread.


Poor running, with no codes, and fuel trims and MAF reading in normal range, I'd always suggest checking HT in first instance.

Obviously not everyone can read live data on pre EOBD Omegas, so trying with MAF disconnected and then Lamdas disconnected (and MAF plugged back in) is a way of getting a feel for what might be happening within the ECU. Caution has to be paid to cat health normally when doing this though, esp playing with lamdas.

I never knew you thought of me so highly 

Sorry mate think he means dbdb   Don't be upset though Webs

[Webby the Bear]

The only person on this forum that can answer this post correctly and end it is TB

There are many people on this site who are far cleverer than I will ever be. 2 of them have already posted on this thread.


Poor running, with no codes, and fuel trims and MAF reading in normal range, I'd always suggest checking HT in first instance.

Obviously not everyone can read live data on pre EOBD Omegas, so trying with MAF disconnected and then Lamdas disconnected (and MAF plugged back in) is a way of getting a feel for what might be happening within the ECU. Caution has to be paid to cat health normally when doing this though, esp playing with lamdas.

I never knew you thought of me so highly 

Sorry mate think he means dbdb   Don't be upset though Webs

 

can I have this on one of OOFs welcome messages....

''Webby the Bear is officially more intelligent than The Fat Shadow'' 

[dbdb]

In amongst the personal attacks and frankly 'technical crap' there have been sound and helpful posts on this. I wouldn't normally post again and frankly won't answer the posts 'playing the man not the ball'  but there is one that only Kevin and Webby have mentioned (plus FS with his HT) and is relatively easy and cheap to check/fix.

Burnt out cats as someone else said are likely the result of unburnt fuel.  Unburnt fuel would be the result of the much discussed misfires.  So check all the spark plugs as a high priority.  It's a bit of a pain on the pre facelift v6 mind.

[minerwilly]

Right everybody, sorry I've been mysteriously absent, but I've been away on business.

I've managed to find the problem and luckily it's perfectly logical and inexpensive.

I ended up driving the thing to work a couple of times earlier in the week through absolute necessity, and although it was as rough as it was before, it got a little bit better the more I drove it. I've now been driving it all week and it's pretty much fine.

Through my astonishing powers of deduction, I'm pretty sure that when the cats collapsed they choked the cylinders, valves, and plugs with exhaust gases which condensed and covered them in carbon. I think that was the problem that caused the loss of power (which I guess would have translated to random misfiring), and simply giving the car a good run has burned off any deposits that were causing the problem in the first place.

Obviously there is possibly still the underlying problem that caused them to disintegrate in the first place, but that should be a fairly easy thing to track down, and whilst it will do nothing for the fuel economy, at least the car is drivable. I'm really glad that I seem to have got to the bottom of the problem, and even more happy that it was nothing expensive. This weekend will see a change of plugs and full oil change for the engine and the gearbox.

Thanks for all of the good advice and even the bickering, because I've learned a lot about the car through it all. Hopefully given a little time I'll be able to contribute too.

Cheers.

Marc