Mondeo Lambda Reading and headlights

A bad earth is most common or a failed heater supply. Check your two earths with engine running back to -ve battery terminal. Look for less than 100mV. Its often a good idea to make a permanant earth back to the battery anyways from the lambda socket on rad cover to get the value down as low as possible. Only use soldered and heat shrinked joints....

Other than that, you have to look for another reason that is preventing the ECU entering closed loop operation...

Tim..

Well, the car failed again :(

CO now 2.68% Lambda 0.929

When the lambda could not be read, the CO was low 0.12% I think. Would changing the lambda sensor have such an adverse marked affect?

help.....please.....

Mark

It's probably worth getting the fault codes out of it, any EEcIV reader should do.

Thanks Tim,

I'll check this tomorrow. Would the heater supply be important? I thought that this is only important when the engine is cold......

I like the idea of a permanent earth. I'll probably run some heavy duty cable back to the battery to give minimum resistance.

So, the ECU is not entering closed loop? This is good (in a bad sort of way) - I have a gunsons emissions tester, so if I can get the emissions back down, I should have an idea of what is causing it.

Many, many thanks, Mark

Thanks Duncan,

Once I find my tester (I only had it a few days ago), I'll read what the brain has to say.

Cheers, Mark

Some regular 7.5 amp wire is quite sufficient as it will be passing neligable current- its the resistance you need to get down low through the use of good joints...

The heater is important as it also keeps the sensor hot enough to keep switching at idle...

From your original post you dont mention the o2 sensor switching at all so I can only assume the ecu isnt entering closed loop control. Your next check should be to see if the o2 sensor is capable of measuring a change in oxygen content by 'manually' making the engine go rich and lean and observing the voltage generated. Introducing a vacuum leak by pulling off a vacuum connection at the inlet manifold (at fast idle) should see the volts drop low (indicating go rich to the ecu) and applying an unlit blow torch into the intake should see it go high.

Tim..

Odds on the lamda sensor connections somewhere.

Nice one, thanks. I'll try this as soon as I can.

You previously mentioned that I should look for less than 100mV drop across the sensor. The previous sensor gave me 20mV, but the new one 300mV - so perhaps the original was OK :(

However, as this is the last thing that I "played" with, I'll start there ;)

Thanks, Mark

Well, I have the ECU codes....

113 - Intake air temperature sensor 118 - CTS, normal operating temperature not reached (the engine was pretty hot though, but I measured the CTR resistance and it was 3K, so perhaps it was not fully up to temperature) 157 - Air mass meter 172 - Oxygen sensor, mixture too weak????

I've looked through the circuit diagram for commonalities between all of them and there really doesn't seem to be one.

Cheers, Mark

No, I was talking about voltage drop across the sensor earth and the negative battery terminal indicating there is resistance in the factory wiring for whatever reason.

I was *not* talking about the o2 sensor voltage output across its signal wire and earth, which should range from ~200mv to 850mv at about 1hz or better witch the system in closed loop running...

Tim..

Intake air temp sensor is part of the MAF- check across pins err 5 and 6. (will have to check that) At 10 deg C you should have ~55kohms. 50 deg C -

10kohms. 100 degC - 2 kohms.

CTS- Is the engine reaching operating temp- 100degs C or so. Obvisouly if it cant (thermostat) the ecu will never enter closed loop! it wont enter it anyways under 60degrees. obvously the ECU needs to be fed the correct temp from the CTS- same resistances apply as the charge air temp sensor.

157- discount this at the moment- you probably checked the codes with the engine stopped...

172- mixture too weak - this could be a vacuum leak, but delete all the codes and solve their problems before coming back to this.

Tim..

Sorry Tim,

I misread your previous post and now see that you mean. I will check this as any volt drop on an earth lead is not good.

So, it looks like my old sensor was way off the mark, so that is good news. From memory, the update seemed to be about one per second as you say.

Many thanks, Mark

You really are damned smart aren't you ... wish my MOT tester knew all of this without saying "Change the CAT!" ;-)

As for the Air Intake temperature sensor, the manual shows it as being seperate to the MAF - perhaps this is different on later models, but the figures are in the manual so I will check these. The annoying thing is that prior to changing the Lambda sensor, all codes were OK.

The engine seemed hot enough, but I'm not really sure now. I made the MOT station re-test when I called them as I assumed the figures were due to the engine being too cold. They assured me that they warmed it up sufficiently on re-test, but the figures were really not much better. Their tester did not measure oil temp - is this normal?

At some stage, I needed to remove the battery lead to work on the steering column (the adjuster had too much play due to no locknut), so could the ECU not have re-learnt the settings correctly?

Thanks Tim, I really appreciate you sharing your knowledge with me (and the rest of 'em)...

Cheers, Mark

Check the connecter to the CTS, if it's high resistance then your engine won't go into closed loop,

won't go into closed loop,

Hi Duncan,

I removed the connector and the fan started up, so I guess that the connection is OK, I guess that I just need to check the resistance of the unit.

What are the chances of the thermostat being duff, or perhaps an air-lock at that point?

Cheers, Mark

Could be but if the CTS is reading under 3K I wouldn't expect to see engine temperature not achieved. To be honest I suspect sods law has come to get you & there's a couple of problems each of which makes diagnosing the others difficult. You can always run it till it's hot & stick a 1K8 resistor in the CTS socket, if you've still got engine temperature not achieved then the cables probably at fault. You can idiot check the intake air temperature with a normal thermometer, & as it's running weak the old unlit propane torch trick (with obvious care) should identify any air leaks.

engine temperature not achieved. To be honest I suspect sods law has come to get you & there's a couple of problems each of which makes diagnosing the others difficult. You can always run it till it's hot & stick a 1K8 resistor in the CTS socket, if you've still got engine temperature not achieved then the cables probably at fault. You can idiot check the intake air temperature with a normal thermometer, & as it's running weak the old unlit propane torch trick (with obvious care) should identify any air leaks.

Hi Duncan,

I checked the sensor resistance last night at what I thought was hot and it read 3K4, so it was either not hot enough or something is amis around there.

I'll try the 1K8 resistor to see if this makes a significant difference.

Many thanks, Mark

engine temperature not achieved. To be honest I suspect sods law has come to get you & there's a couple of problems each of which makes diagnosing the others difficult. You can always run it till it's hot & stick a 1K8 resistor in the CTS socket, if you've still got engine temperature not achieved then the cables probably at fault. You can idiot check the intake air temperature with a normal thermometer, & as it's running weak the old unlit propane torch trick (with obvious care) should identify any air leaks.

Thanks Duncan,

When I measured the CTS last night, is was over 3K (something like

3K4) so perhaps something is amis there.

I'll try the 1K8 resistor to see the effect.

Many thanks, Mark

Hi Tim

Not a very good idea at all, you will create a ground loop that could cause other problems like reducing the ECU's susceptibility to electrical noise, all peripheral grounds should go direct to the ECU.