Please can someone help?

I,ve just had an IVA on my MK Indy and it failed on 4 things; protruding bolt not covered, petrol cap not tethered, Speedo reading lower than true speed all of which I know how to fix. However the 4th is the failure of idle emissions test. The test recorded 8.12% CO and 1390ppm HC. Lamda was ok

I am running a 1993 - 2 litre mondeo - off a pre-Pats EEC IV. I am not using EGR, Canister purge valve or speed sensor and unfortunately I removed the test plug because I did not think I would need it (Probably need to put it back)

By the way the engine runs quite smoothly.

During the idle test I took the vacuum hose off the pressure control valve and CO and HC fell to within the limits, so I thought OK faulty valve. I can fix that at home

Well it does not appear to be faulty as I've now checked it. The valve is set at 270 Kpa (~39.5 PSI) so with pump on, engine not running, pressure in rail rises to 3 Bar (44.1 PSI). With engine at idle pressure in fuel rail is 2.15 Bar, Vac in inlet manifold is 19.5 In Hg (.661Bar) and stays relatively constant when I rev. Therefore I believe I am getting a constant differential pressure across the injectors of 2.811 Bar (41.32PSI) which appears to be about right. Also pressures meet the spec given in the Haynes Manual.

The fuel pump is from a cavalier and appears to deliver flow and pressure as required.

I have checked Vac from the output just after the throttle body and at the outlet for the breather to the sump and both are ok (~20 In Hg)

I have also checked injector resistance and they are all ok. They are 948F B2B C 2480, I have another set of 948F B2B's but they have a second code of D 2480. Does the C and D have any significance. Cannot find anything on intranet

I have checked the output from the air mass meter and I am getting a reading which at idle jumps between 0.8 volts DC and about 1.2 Volts DC, and rises as I rev engine.

Removing the Vac hose to the pressure control valve increased the differential pressure across the injector to around 50 PSI which means I believe I should be over fueling but clearly not as the CO and HC reduced.

An help or other ideas of things to check will be most welcome

Regards

Dave

Is the engine reaching full running temperature? ISTR a shade over 90cc
The high HC is probably due to incomplete combustion or misfires due whatever is causing the high CO

I never had to do deal with any engine management problems on these engines but I would start by looking at the lambda output and lambda heater circuit operation. Old lambda probes or probes where heater circuit is u/s often only start to "swtich" high to low and back at fast idle rpm at idle they can flat line. You can back for be the lambda sensor plug with model makers "T pins and look to see if the sensor is going high to low on a digital multi-meter - although an ocilloscope is the tool of choice. The lambda output should switch high and low and back at least once per second. On a digital volt meter this will be random voltages between O.2 and 0.8 volts on an oscilloscope it looks a very jaggy sign wave.

If the voltage is flat below about 0.45 volts then it is telling the computer to make the mixture richer, to test try introducing propane or carb cleaner aafter the MAF and if the output voltage dosen't increase towards 0.8 volts the sensor is dead, but check the sensor heater circuit before changing the sensor as it needs the heater to work particularly at low RPM.

If the sensor is reading high ie somewhere near 0.8 volts then it is reporting a rich mixture to the computer, you can check the sensor response by inducing a vacuum leak the output voltage should fall towards 0.2 volts.

Thanks

Will have a look at this tomorrow

Regards

Dave