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Sudden Missfire VS V6

JoshSvc

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Working on a VS V6 at the moment that has developed a sudden engine problem, initially it was missing under hard acceleration, then it had problems starting and would missfire badly, when it starts it idles fine but if u touch the pedal it will bog down, if u push through that it will rev.

Disconnecting the MAF did make it run better, but it wont even start now.

The fuel filter is fine i was thinking maybe fuel pump as i cant hear it priming, the spark plugs are new.

No logged codes

Any ideas?...
 

soop

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Try another MAF?
Replace the spark plugs, leads and coils.

If that doesn't work check the cat is intact and change the o2 sensor.
 

Brett_jjj

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Replace the sparkplugs and plug leads if they are old,and if theres still no difference,it might be 1 of the 3 ignition coils thats faulty.These coils will sometimes idle and run ok,but break down when the engine is put under load,which then causes it to misfire and splutter etc.If all the coils are a couple of years or more old, then its best to replace all 3 coils at the same time if 1 is found to be buggered.
 

JoshSvc

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Spark plugs are brand new, i'll try and test the coils. Would the coils cause the car not to start though?
 

Brett_jjj

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The CAS (Crank Angle Sensor) will also cause a similar problem with misfiring and not starting,and its very common for it to stuff up too.
 

soop

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Will generally cause an issue all the way through the range though. Not just under load.
My money is on coils.
 

JoshSvc

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I'll try and borrow a coil tomorrow, are the coils the same as VR?
 

Brett_jjj

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Yeah,you would think it should still attempt to start though,unless more than one coil has gone at the same time, or the DFI module under the coils is stuffed.Id try some other coils, and then if theres no difference,then look at the CAS,also a faulty CAS will sometimes not log an error code either,so it can be hard to track it down if its causing problems.Most people just replace the CAS anyway if they are having problems of this nature and cant find the cause..
 

JoshSvc

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Ok i swapped the coils around and the car started instantly, but still with a big miss, it has started to give an oily smell and some slight smoke is coming from the back of the inlet manifold, so i'm tipping that the inlet manifold gasket has shat itself, letting water into the fuel system causing the problems
 
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