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Eric, Automotive Repair Shop Manager
Category: UK Car
Satisfied Customers: 32049
Experience:  Automotive Repair Shop Manager, Technician/JA Mentor
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I have a Peugeot 407, 2.0L petrol EW10J4 engine. It runs

Customer Question

Hi, I have a Peugeot 407, 2.0L petrol EW10J4 engine. It runs fine when warm. But when cold it starts and runs Ok for the first 1/2 to 1 minute and after that it idles rough until it warms up. It seems to run very rich. Upstream o2 sensors has been replaced recently. When diagnosed there are no faults found! Please advice.
Submitted: 1 year ago.
Category: UK Car
Expert:  Eric replied 1 year ago.


I am sorry that you have not been helped yet. I just came online and saw your question.

Ok, most commonly this is due to either the ect(engine coolant temperature) sensor having an incorrect reading when cold and first started, which will cause it to run rich until warmed up, or the fuel pump leaking back. The ect sensor should be tested for correct reading when cold and fuel pressure checked for holding pressure after sitting overnight

Customer: replied 1 year ago.
Hi Erik,
Thank you for your response. As you mentioned I also suspected the ECT as an obvious culprit and I replaced it a while ago. That did not make any difference. However, your suspicion about the fuel leak back is something very interesting. This is something that not only did not come to my mind but also none of the technicians / mechanics that I have spoken to mentioned! I am going to check the fuel pressure and see how well it holds the pressure following the engine is switched off. I will send you a feed back as soon as I have the result.Thank youLeo Sritharan
Expert:  Eric replied 1 year ago.


ok, sounds good.