[Shepp8989]

Hi

After some advice because I’m completely stumped for the past year I’ve been running dreamscience Txx map with a full turbo back system from Milltek with no issues whatsoever however a couple months ago I changed the exhaust for something a bit louder went with a Kms thunderstorm only issue I’m having is when the car is running at idle say if you’re parked at a traffic lights or something for a few minutes the car goes into limp mode and you only notice it after you drive away if I clear the code it does come back after a while but only at idle when car is moving it’s fine no issue at all the mechanic thinks it seems to be an issue with the map but if that was the case surely it would of happened on the Milltek system so any advice is appreciated

Thanks

 

[Alb]

An Induction leak is the most likely reason for this.

 

[Shepp8989]

When you say induction leak do you mean like a pipe or something is not sealed properly ?

I thought it might be the exhaust gaskets has I forgot to get a new set and had to reuse the old ones

 

[Alb]

Yes, look carefully at all the joints from the MAF onward.
Minor leaks aren't always obvious on a visual inspection though so it may be worth having a smoke test done also.
It only takes a small amount of unmetered air to upset the AFR.

 

[Shepp8989]

OK thanks it's due in the garage end of the week so will get a smoke test done the only codes it came up with were too lean at idle bank 1 and o2 sensor to slow to respond so I thought something exhaust related as all this started to happen since changing it

 

[teflonbilly]

I think the change of exhaust is a bit of a coincidence to the fault. As Alb says it could be an intake leak but I would also be checking the upstream O2 sensor itself.

They switch extremely fast between high and low voltage so unless it's flatlining (completely unresponsive) you likely won't be able to diagnose it via OBD because the interface is too slow. An autoelectrician with an oscillioscope probably could, but for the cost of the diagnosis it's almost worth just buying a new one anyway especially if it's done a fair mileage.

 

[Shepp8989]

The car has done 71000 so do you think it's worth putting new o2 sensors on then has I'm not sure how long they usually last

 

[teflonbilly]

The car has done 71000 so do you think it's worth putting new o2 sensors on then has I'm not sure how long they usually last

I'd make sure you eliminate any intake leaks first before spending money, but 71,000 miles isn't massively high in my opinion.

If you do need to replace it you would only need one sensor and they are quite expensive from Ford (£250). I think the OE supplier is Bosch on the ST and they can be bought for about £80. It's exactly the same as you get from a dealer except no Ford or Volvo logos on it.

 

[Shepp8989]

Ah I see well I'll try the intake leaks first any particular pipe or area thats common on these ? my mates got a smoke detector at his garage so maybe that will reveal something its weird it only happens when the cars stationary for a while when at speed its fine

 

[NigelStap]

Smoke testing is easy for any garage and is a good starting point. Don't just start throwing new sensors at the car.

 

[Shepp8989]

I forgot to mention that when it idles there is a strong smell of fumes or fuel I know it has a decat but seems to be more noticeable and the revs tend to fluctuate a little where in the past they have usually been steady and when putting your foot down ther car at certain revs feels like it's missing or like it has the odd hiccup at certain revs

 

[Dabhand16]

I forgot to mention that when it idles there is a strong smell of fumes or fuel

If you can smell fuel on tick over the thread title is wrong. That is running rich - not lean.

Is this from the exhaust? If not you might have a fuel leak.

 

[NigelStap]

GET A SMOKE TEST DONE!

You need to rule out air leaks.

 

[teflonbilly]

If you can smell fuel on tick over the thread title is wrong. That is running rich - not lean.

Is this from the exhaust? If not you might have a fuel leak.

A faulty sensor readout incorrectly reporting a lean condition will lead to a rich mixture as the engine management adds more fuel to try to compensate.