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Jun 23, 2009 17:27:36 GMT
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Bit of a techy modern question this but worth a shot...
My old man has a 2001 Vauxhall Omega. Occasionally when starting, the fault light will come on (the car with the spanner through it) and the car will run a little strange - I'm fairly sure it's in Limp Mode.
Now, if you turn the ignition off and then re-start the car will be fine and running properly. The fault only occurs every now and then.
What I suspect is that the ECU is getting a bad signal from one of the sensors when it does its "pre-flight check" and the ECU then goes into limp mode with average values inserted (for example, coolant temp), hence the slightly bad running when cold.
So I got an OBD2 reader and plugged it in, scanned it... No codes. I read that the ECU only logs DTC codes after 30-60 seconds of the car running with the fault. As I had instructed my dad to re-start the car when it didn't start correctly, the ECU obviously wasn't logging the fault code. So next time it happened, he just let the car run for a few minutes.
Scanned the ECU... no codes.
I'm a bit baffled... anyone have any idea?
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Jun 23, 2009 18:41:46 GMT
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welcome to my world quite a few vauxhalls are the same some you cant even read so I'm affraid the stealer bekons
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97 volvo 940 turbo wagon 87 fiat strada abarth 78 gs1000 82 katana 1100 84 gsx1100 efe
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Jun 23, 2009 19:30:36 GMT
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welcome to my world quite a few vauxhalls are the same some you cant even read so I'm affraid the stealer bekons Thanks Russ (I think?! ;D) I thought OBD2 meant that all ECU's had to be readable by law? The reader hooks up to it fine, I can do a drive cycle check and all that... I've even pulled two pending codes from it but neither seem related and I think they're just daft things that the ECU thinks are faults (System voltage and engine torque signal) - those clear after a while. If the fault gets worse I suppose a main stealer is the only option... I'll keep trying find a code after each time it acts up though.
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Jun 23, 2009 19:51:09 GMT
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the mrs has a 56 plat zaf and we have had the spanner sign up for ages and the turbo etc all work fine!
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Jun 23, 2009 19:53:08 GMT
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yes its russ and mine conects and sometimes nothing even if you disconect sensors it doesnt pick up a fault strange all that elastictrickory
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97 volvo 940 turbo wagon 87 fiat strada abarth 78 gs1000 82 katana 1100 84 gsx1100 efe
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froggy
Posted a lot
Posts: 1,099
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Jun 23, 2009 20:00:47 GMT
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if its ecotec check all the breather hoses and clean the egr valve . just because your code reader said no codes doesnt mean they arent there,a proper scanner will pick up a lot of what these cheap ones cant.
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Jun 23, 2009 21:12:40 GMT
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With fault codes the ECU has to 'notice' a fault for a certain length of time. For example, a crank sensor might have a fault but the ECU will only record it as one if it happens for at least 5 revolutions. An oxygen sensor may only throw up a code if it fails to switch a minimum amount of times over a second or so. You get the idea.
I saw a similar fault happen once (and only once!) The rev counter seemed to be getting a surge/interference on start up which gave the instrument panel a fault code which the engine ecu picked up! We sorted it by soldering a diode into the ecu to instrument panel wire. Think it was a bit of a one off problem though!
If its the Ecotec, by far the most common fault when I worked at Vauxhall was the Idle air control valve but when it broke the car would have a rough idle or cut out. Rarely would it bring up a code (kinda the opposite of your problem!) Idle air control valves fail far less in Omegas though for some reason! Next on the list was Crank sensors. They would bring up a code and put the car on limp mode (wont rev above 4000) with no other symptoms. Sometmes the sensor would fail and sometimes the wire would fall against the exhaust manifold. Another common on is the camshaft sensor. It too would throw up a code without any other symptoms. sometimes if you replaced the camshaft or crankshaft sensor one week in a week or so the code for the other would appear as the signal from the new sensor would be much stronger/clearer and the ecu would assume the other sensor was malfunctioning.
Personally, I'd check the crank pulley. Crank pulley dampers wear and seperate. As this causes the engine to go out of balance it may be just enough to flex the crank to fool the crank sensor on start up or under load.
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Jun 23, 2009 21:50:16 GMT
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Thanks guys . It's the 2.2 litre - is that Ecotec? I had the airflow sensor out and cleaned it some time back but it wasn't dirty at all... just did it incase the breathers had chucked curse word all over it. I think he'll have to just give it some time and see if things get any worse / better. At the moment it's just a small inconvenience. I just didn't want him to take it to a dealership and have them throw expensive parts at it until it goes away... they like doing that! ;D
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Torquesport
Part of things
Astras all the way!
Posts: 453
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