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RPM Stumbles after revving

Old 08-03-2018, 07:23 AM
  #11  
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Just done another ECU idle relearn procedure and then attached my code reader again. My Short term fuel trim is reading - 3% to 18% fluctuating, and my Long term fuel trim is reading around 10.9%. ( Obviously something wrong.)
This means that my engine is running rich and the ecu is compensating. Plugs look ok.

With this newly acquired info from the video shown in an earlier post I am hedging my way towards buying a new O2 sensor (Pre Cat)

Keep you posted, anyone following this.

Last edited by Snakecharmer; 08-03-2018 at 07:41 AM.
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Old 08-03-2018, 07:44 AM
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Buy the pair for peace of mind!
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Old 08-03-2018, 01:32 PM
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Check the condition of the coil packs and do a resistance check. All for free!
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Old 08-03-2018, 11:11 PM
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Having had some dialog with Mat ( the guy who did the video ) he is absolutely convinced it is not a sensor as the ecu is compensating for rich fuel, so they are working. His suspicion is a fuel regulator problem
( remember my short term fuel trim is reading a - 18% variable ) and watching his video explains why. Even if there are other issues electrical there is still a constant fuel problem to be addressed. I am learning
an amazing amount here as how to read and understand my Launch CreaderVII+. I have removed my air filter to great effect. Must be worse than I thought. Next job has to be to check my fuel pressure.


Last edited by Snakecharmer; 08-03-2018 at 11:21 PM.
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Old 08-09-2018, 09:02 AM
  #15  
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Very unlikely to be fuel pressure.

Whats your primary 02 voltage doing at idle? If it’s not cycling fairly quickly from 0-1v it would be top of my list. They normally start to fail and give a low voltage to the ecu, which then adds more fuel to compensate.... which makes it rich and the erratic reading causes poor idle.
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Old 08-09-2018, 09:04 AM
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Originally Posted by nomadicS2k View Post
Buy the pair for peace of mind!
You only need the front / primary one. The secondary one in the cat has no influence on fuel control.
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Old 08-10-2018, 01:02 AM
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OK. I changed the air filter (although the original looked fine) and the rev drop when returning to idle is now cured. "Whoopeee" However, my short term fuel trim (although better) is now at -7% Surely the 02 sensors must be working
to accommodate this via the ecu. The engine runs sweeter and it feels like I have a little more power but the diagnosis goes on. Just been quoted £200 for an O2 sensor which I am reluctant to spend if it is not conclusive. I suppose
I must invest in a fuel pressure tester next?
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Old 08-10-2018, 06:05 AM
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If your needing to replace primary might as well go wideband,just got one myself but not installed yet.
https://www.s2ki.com/forums/uk-irela.../#post23583038
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Old 08-11-2018, 04:25 AM
  #19  
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Thanks for the info. I think I will keep the car stock just now.
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