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Discussion Starter #1
Greetings to the board,

My car has a condition that seems to be deteriorating over time in that it's not always running on all cylinders.

Engine was mapped five years ago, yet we had to cut the mapping session short because an oil leakage from the rear turbo oil return was dripping down onto the downpipe, constituting a fire hazard. At that point we agreed to let the engine run a little rich in order to provide a little safety margin.

During the first half year or so after the mapping session the car ran perfectly, in fact it ran so good I even hesitated having the job done properly and thereby saving some money. About a year after the mapping session the car would sometimes - perhaps one time out of ten - not start on all cylinders, but this usually fixed itself within a few minutes on idle.

I then sold the car and last year bought it back, the owner in between only drove it some ten miles in total during the four years he owned it, so I basically got the car back exactly as the day I sold it. The issue was still the same, that most of the time it ran good but sometimes it didn't.

Then I started using the car on a daily basis during last autumn, for about a month, and the issue started to deteriorate. Nowadays it never starts on all six cylinders, and most of the time it will not fix itself after a few minutes of idling or not even 5-10 minutes of calm driving.

Knowing that the engine was mapped to run a bit rich, and painfully aware of the intermittent exhaust bangs, I suspected the plugs might have been fouled and so changed them. Voila, the car the ran perfect again - until the third time I tried to start it, when it would not run on all six once more.

I've checked all the plugs for spark, it's there on all six. I've also checked all injectors for fuel, it's also there on all six accounts. I did a compression test, and even though I forgot to note down the exact figures they were all very close to each other.

Question now is what could be at fault here? Since the issues disappeared temporarily with new plugs, I figured that either spark is too weak or there is simply too much fuel smothering the spark. What could cause this, since map is still unchanged and all things bar a new set of plugs are as equal as the day the car came off the dyno?

Could the O2 sensors be packing up, causing the car to run even richer than before? My next move would probably be to invest in either a set of Splitfire coilpacks or a new set of O2 sensors, or perhaps both, before shipping the car off to a new mapping session, but I'd like to check with more knowledgable people on here before I spend some hard-earned cash.

I'd be very grateful for all and any assistance on this matter.
 

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The o2 sensors don't start giving feedback to the ecu that quickly.
Unplug one coil at a time until you find which cylinder is dead. You'll notice by that the engine runs the same when you unplug it.
Try moving that coil to another cylinder.
If the problem moves with the coil then it's the coil. If not, it's not the coil.
Check the wiring and plug to that coil. Nothing changes?
Then move the injector and see If the problem follows the injector.
 

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The o2 sensors don't start giving feedback to the ecu that quickly.
Unplug one coil at a time until you find which cylinder is dead. You'll notice by that the engine runs the same when you unplug it.
Try moving that coil to another cylinder.
If the problem moves with the coil then it's the coil. If not, it's not the coil.
Check the wiring and plug to that coil. Nothing changes?
Then move the injector and see If the problem follows the injector.
Do this!

Could also be the ignition leads for the coilpacks. Also push down on top of all the injector plugs, maybe they are loose. I though i had a dead cylinder after mapping and it was the plug loose!
 

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Discussion Starter #5
Problem was easily solved in the end, it proved to be two faulty ignition coils. For once I got lucky and found a full set of six coils for sale not far from me (only about 20 BNR34 in Sweden so lucky indeed), so now the car is running great again.
 
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