MK6 Fiesta Lambda Fast Idle Test

[HenryV]

Hi folks,

I'm considering a new project and (if I proceed) will endeavour to keep this post updated

As with my other projects, I don't take on these jobs to save money. I just like a challenge.

Yesterday, my beloved 2005 MK6 failed her Lambda Fast Idle test

I've done a limited amount of research today and here's my thoughts/observations:

 

She's done 119 350 miles and hasn't had any emission issues before

Seems to run & idle fine

Still has original cat & lambda sensors

As I understand it a lambda sensor is an oxygen sensor

The reading on the emissions report is too high and thus out of range (I'll post the report on here soon along with last years pass report)

This leads me to presume that the engine is running/reading lean

There is no warning light illuminated on the dash

I've scanned for any fault codes with OBD2. No codes

If the infamous lambda sensor/s was faulty then surely there'd be a warning light/code?

Spark plugs have done 14 000. (admittedly, I haven't inspected them yet)

Air filter has done 45 000 miles (I'll check it) but the first did 74 000 and was fine. I doubt that'll be the cause

Engine hasn't lost any oil and shows no signs of oil burn

I haven't researched the MAF sensor yet

 

So, my initial suspicion is on the cat/manifold assembly, which is sill the original one (119 000 miles & 16 years)

If it is corroded/leaking, could this be allowing excessive air/oxygen into the system, resulting in a lean reading?

Any informed comment/advice on here will be very welcome indeed 😉

Does anyone know if the manifold bolts/nuts are a nightmare on the Zetec, as they often are on other engines?

Best regards,

H..

 

 

 

 

 

 

 

[Wobbla]

Don't know about the bolts on the manifold but i do hope you proceed as i'm looking forward to see how you tackle this one. I read your older post about the abs and it is fantastic. The abs light on my Fiesta has come on.

[HenryV]

Wobbla,

I replied to your message the other day. Please check your inbox.

[HenryV]

This is the 2021 lamda fail report;

[HenryV]

...and last years pass report..

[HenryV]

I started my attempt at this job today but I now suspect that I'm misleading myself. I'm now thinking that the problem is an exhaust leak after both the manifold/cat & lambda sensors.

I'll (as always) post my failings as well as my successes;

I put the car on ramps...

...and removed the airbox...

...to give me a view of the manifold top heat shield...

 

 

 

 

[HenryV]

...Air filter isn't too bad...

...Spark plugs next...

...nowt too bad with the plugs either...

 

 

...

[HenryV]

...when I saw the condition of the heat shield bolts, I knew this was a gonna be trouble;

 

...they're supposed to be undone by an 8mm socket but the bolts are (of course with car manufacturers who seem to be allergic to stainless steel) seriously corroded and ceased.

I called it a day...

 

 

[HenryV]

...and did some more research;

I found an article on emission faults by an apparently well informed fella.

Amongst his reckonings was this paragraph;

'An air leak after the lambda sensor, i.e. exhaust silencer/joint etc leak, will cause the O2 reading to be high and all the rest to be normal. If the air leak is before the lambda sensor, i.e. manifold/ down pipe, then a diluted exhaust gas will be monitored by the lambda. This will cause an inaccurate reading at the ECU, which will, in turn, cause extra fuel to be injected by the injection system, which will effect the CO, HC and lambda readings. The amount that these readings are out will obviously depend upon the quantity air being introduced into the exhaust. Often you will find that the CO and HC readings can remain normal due to the catalytic converter cleaning them up. This can be very difficult to diagnose, as above a pre-cat emission test pipe would be a great help but is not always available.'

It seems to make sense to me because this year:

My lambda reading was high

My CO was zero (as it was last year)

My HC reading was much lower this year than it was last year

No warning light on the instrument cluster

Could my exhaust be leaking after the lambda sensors?

More O2 than last year (Oxygen/air)

Less HC (fuel)

No warning light on the dash

I'm going to (gonna) check the post cat exhaust for leaks next.

I'll keep you posted...

 

[HenryV]

I checked the exhaust and couldn't find any leaks.

I plugged Forscan/ELM327 into the OBD2 socket and found nothing unusual.

I wasn't about to start using guesswork and swapping parts, so I admitted defeat on this project and went to a garage recommended by my brother;

The gent at the garage lived up to my brothers recommendation and soon identified the problem,

It was a split crankcase breather hose (Ford part 1761516);

 

 

After replacing the hose, he MOT'd the car and here's the emissions report;

Regards,

H

 

[DaveT70]

That air filter is dirty, I'd replace it anyway