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jmfecon

R51 running a little rough

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Hello everybody,

 

My R51 (2006, V6 Petrol) is running a little rough ultimately, like if 1 or 2 cylinders are failing.

 

A little backstory: A while ago this issue started, and happened only after some time with the car running, when it reaches the working temperature. My first thought was to blame the spark plugs, so I changed them. In fact, a trusty mechanic did it.

 

It did not worked.

 

The mechanic suspected of the fuel injection system, because it was not throwing any codes, so we discarded the coils. So, he took all injectors off, 3 were declared dead and replaced and the remaining ones were cleaned and all of them equalized.

 

It did not worked. In fact the problem only got worse.

 

Then we discovered that the cats were clogged. Not so unsual for a 15 year old car running on brazilian E25. Fixed that. Also changed the fuel pump and some hoses and fuel tank was cleaned.

 

Still, it is not working totally fine. Sometimes in idle, like when stopped at traffic light, I feel it suddenly working fine, as if the issue has disapeared, to come back 1 or 2 minutes later. Sometimes it works fine.

 

I ran out of ideas, actually.

 

Anyone has exeprienced something like that? Any help is appreciated.

 

Best regards

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Failing as it warms up makes me suspect a sensor or other electronic component flaking out. Position sensor, maybe? I'd say coil pack but I'd expect that to code. If you have a scanner that can read pending codes, see if it's got any of those. I would also check the fuel trims with the scanner to see if anything's obviously weird there that could indicate an air or fuel issue.

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11 hours ago, Slartibartfast said:

Failing as it warms up makes me suspect a sensor or other electronic component flaking out. Position sensor, maybe? I'd say coil pack but I'd expect that to code. If you have a scanner that can read pending codes, see if it's got any of those. I would also check the fuel trims with the scanner to see if anything's obviously weird there that could indicate an air or fuel issue.

Thanks for the reply.

 

I think that any sensors would trigger a code or would make the engine stall.

 

When the Crankshaft Position Sensor failed the engine died at random, and gave me an error (P0340 I think)

 

No codes at the scanner. Mine doesn't read the sensors live data. Will try to get one to read and try to get any clue for that.

 

Also I would have a suspicion on the harness. But honestly would not like to even think in this possibilty.

Edited by jmfecon
Add some information

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It happens that @Slartibartfast was sort of right: the coil was the culprit. Well one of them.

 

It happens that one or two of them were failing, but not completely. Better that it was this. Replace all three of the right bank, and the car runs fine now. Will replace the left bank soon.

 

Thanks mate!

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Good to hear you got it! Intermittent failures can be a pain to track down.

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