Mondeo Emissions MOT failure and overheated engine

The CO should be around 1.5% with no cat at all.

Yep , if you've got 9% CO then then the O2 sensor's knackered & possibly the MAF as well

That's your best strategy. Check the oil and water after a few minutes, then after every journey for the next few days. Keep one eye on the temperature gauge too. You might have been lucky.

If you take it into a garage and tell your story, they'll just sell you a new head without lifting the bonnet.

Good luck.

Thanks DP,

I'll probably do a compression test too just to make sure there's no damage in the bores and keep my fingers crossed that I am just damned lucky.

Cheers, Mark

Thanks Mike, Dave and Duncan - this helps a lot.

I have an "el cheepo" fault code reader from Halfords which queries the ECU. Will the faulty sensors be recorded as failing or perhaps are there other ways of checking the sensors for correct operation?

Many thanks, Mark

A failed o2 sensor alone will not create 9+% co! It's only a fuel trimming device! A failed one with a stuck 'go-rich' rich signal would generate (pre cat) a co of about 3.5-4% no more.

The OP's MAF has failed or the ECU thinks its still stone cold- look at the CTS.

Tim..

Well, I've used the fault finder to check the stored error codes (I have no manual for the tester so followed the basic procedure in the Haynes Manual). The code which were reported are :

Finally, does anyone have a manual for a 4152 Gunsons Fault Finder that they can email me as this would be a huge, huge help? I've mailed Gunsons sales department, but I don't know what the turnaround time will be from them.

Thanks all, Mark

Well the oxygen sensor appears to be working, that's what it should say. Check the water temperature sensor as well.

Hi Mark, I have the same tester but have also lost the manual. But then again I did find the haynes manual far better than the booklet that came with the fault finder, it is far more comprehensive and mondeo specific. As for the oxygen sensor I just replaced mine with a universal one from the local motor factor, comes with all the crimps and heat shrink tubing, just cut the plug off the old one and connect all up, job done. For the first time in 18 months my car is now clear of fault codes. The universal sensor was £28. Compared to Fords £86, me very happy. :-)

Hi Tim,

Apologies if this gets posted twice (being at work, I'm limited to google which seemed to lose the last post).

Right, we seem to have come full circle (which is good). Is this level of CO and HC normal(ish) for a cold engine?

A coolent pipe failed completely on the way home from the MOT station dropping all coolant. What's to say that this didn't start during the emissions test resulting in the problem that I am seeing now?

I think that I'll make good the pipe and have a new emissions check to see the outcome before persuing this further.

Many thanks, Mark

Hi John, I agree that the manual is more comprehensive - I'd just forgotten the bits about when to turn the tester off. I think after the ignition retains the ECU memory.

I'd emailed gunsons this morning and was extremely suprised to have a reply within the hour and a new manual in the post. I'm not particularly used to good customer service, but this certainly beat my expectations ;-)

Thanks, Mark

Yes. The water temperature sensor has a much greater effect than the air one.

If you've got a DVM, measure the resistance of the water temperature sensor both cold and then hot. I've not got the figures for your car, but I'd expect something like 3000 ohms cold, 200 hot.

Thanks Dave,

I'll try this today. I've replaced the rusted though steel pipe with

Many thanks, Mark

Well, the car started and ran OK. No mixing of oil and water yet, but it's only been running 20 minutes, so I won't hold my breath ;-)

Now, being rather excited by the fact that the engine sounded OK and no severe knocking, I fougot to measure the CTR and probably sis it after 5 minutes running :( this gave a reading of approx 16K initially and 2.5K hot - the manual states approx 35-40K at 20degrees, 1.9-2.5K at 100degrees and 1.0 to 1.3K at 120degrees.

This sounds OK to me bearing in mind that it was idling on the drive and not been for a run. Do you agree?

Thanks, Mark