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Discussion Starter #1
Can anyone help? My 1996 155 V6 has just developed a misfire at 3500 rpm whether its hot or cold. It's quite violent but is a consistant misfire, by that i mean it doesn't vary its cycle, the time between misfires is the same (does that make sense?). To me it seems like the rev limiter but at 3000rpm lower than it should be!. Over the last couple of days it has also developed a tendancy to increase the idle on it's own. It idles at 1000 rpm then sometimes starts to increase upto 2000rpm again hot or cold.! I have also noticed that it does feel very very slighltly hesitant on acceleration from low revs. Isn't it typical as I'm trying to sell it! Maybe the car is telling me it doesn't want to go! Any help/advice greatly appreciated.
Cheers
Chris.
 
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I would have said lambda, but the lambda doesn't function when the engine is cold due to the "choke" enrichment.

It sounds like the car is missing on 1 cylinder only if I understand your description properly.
Maybe a duff plug or lead ??? Oil in one of the plug wells ???
The rising idle will probably be the engine trying to burn off the fuel from the misfire as it will probably give a "rich" signal to the lambda.
When my Silverstone was running rich, the revs would rise at idle as it tried to burn off the excess fuel it was detecting.
 

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Discussion Starter #4
Chaps, thanks for the info. I have left the car unused most of the day and have just been up the road in it and found it will rev upto about 5000 rpm before the misfire starts. Does that add more wait to the arguement that Lambda is the cause of the problem? If so can i test this? Can I get a replacement easily (no doubt costing a fortune!) and if so where from?
Cheers
Chris
 

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Discussion Starter #5
Another update! Jumped in the car this morning, stone cold no misfire! but as soon as it started to warm up the misfire reappeared? Is it looking more like Lambda??? Can I confirm this using the diagnostic self test which I think the car has??? If so anyone know how to do it? If it is the Lambda do I need a genuine Alfa part or is there a cheaper/universal alternative? Ta.
 

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There's cheaper universal ones (OE is about £90) but for the sake of £30-£40 once every 10 years, the OE one gets my vote.

Ralf S.
 

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I don't think I'd even bother testing it- classic lambda symptoms. Just ask Marlon which lambda fits your car. Don't worry about genuine parts, stuff boxed under Bosch or NGK is the same or better. (Just make sure its the correct parts listing!) :)
 

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Discussion Starter #8
Thanks ally.


Marlon, have you got any manufacturer/part number details for non OE Lambda's? Is it relatively straight forward to fit?
 

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Ralf S. said:
There's cheaper universal ones (OE is about £90) but for the sake of £30-£40 once every 10 years, the OE one gets my vote.

Ralf S.
The 'cheap' ones that cost about £30 less are not cheap at all they are the same bosch sensor that is on all 4 wire OE sensors. My friend works in a bosch distributor motor parts shop and he says that the only difference between the OE and the 'cheap universal' is that instead of the OE plugs you get a waterproof connector block to connect your old sensor plugs to. I got one for mine and its great. :D

its a bit of a fiddle to fit mind, you try threading the sensor behind the V6 with an extra connector block on the wire!! :mad:
 
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lodgey47 said:
Thanks ally.


Marlon, have you got any manufacturer/part number details for non OE Lambda's? Is it relatively straight forward to fit?
I'll have a look for the box..sure I've still got it.
I got an NGK sensor for the V6 and cost about £40. It wasn't universal but a direct fit. It's easy to change. Once under the car, use a spanner to remove the old one. I think it's a 19mm, or 21mm...can't remember. The connection is at the bulkhead round about the brake fluid resovoir (the plugs are normally underneath it.
 

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Discussion Starter #12
New Lambda fitted............ still misfires!!!!! Arrrrrggghhh! Now only happens at around 4000 rpm though instead of 3000 but just as violent! so some improvement. I'm going to check plugs and leads later but if one of these was breaking down surely it would misfire from 0 rpm and not be as violent? The only thing I can think of that I've done recently is drain the coolent by removing top and bottom hose and renewed. According to the Alfa service manual I have on CD you should bleed water system by running the car upto temperature with the expansion bottle top off then top up when cold which I did. Any more ideas??????? :confused:
 
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it still sounds to me like you have water stuck in somewhere. Like I say it happened to my V6 after I Gunked the engine and used a hose (although very carefully to avoid plug wells etc). After a couple of days of repeated starting and revving and letting reach temp etc it suddenly cured itself and hasn't returned. Like you, I found at first it "limited" at about 3000rpm, then rose to 4K, then 5K and eventually revved right up to redline.

There is a timing sensor or something which sits at the flywheel. You can see it from underneath or if you remove the panel in the wheel arch liner. I'm sure someone had a problem with this about a year ago after water getting into it and caused the same problems. Seems strange as it must get wet while driving anyway, but they said water had got into it. So they dried it off with a hairdrier and it worked :confused:
 

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Discussion Starter #14
Marlon you are bang on!!!! The misfire is now cured. The problem was caused by water in the connector block of the rpm/timing sensor. The connector sits under the expansion bottle and when I changed the coolant water must have found its way in and caused the misfire. I dried it out, a little WD 40 and hey presto the car fly's again!! Yipee!!!.
To everyone thanks very much for your help. Greatly appreciated!
Chris
 

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I was going to add "check the TDC sensor" (mine gave your symptoms before it died altogether) but you beat me to it! Doh! :D

Ralf S.
 
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