The dreaded emissions test

The true test of the work done on the engine is an emissions test unfortunately we have a problem

 

 



 

The Co2 is 10x what it should be and Lambda is 0.91 where the limit is 0.97. It looks like the control loop that sets these parameters is not working. More updates to follow.

Update 22/03/16

Looks like there is problem with the EMS/ecu, the signal from the O2 sensor is being corrupted with the O2 heater power. I need to remove the EMS/ecu module first. Volvo have a special tool but it is expensive and the only ones I can find are off shore.

 

I found this design for a tool on ref: sweedspeed.com: http://www.matthewsvolvosite.com/forums/viewtopic.php?t=57066

 

I decided to make one of these:

 

 

The next issue is the EMS wiring diagram, found this on sweedspeed:

Why I think the ECU is faulty?

I have a Sealey VS925 Lambda Simulator/analyser. The purpose of such device is exactly the application we have here. The ECU monitors the O2 sensor and if the cat is to run at the correct temperature the air fuel mixture should be unity and held within very tight parameters. The O2 sensor or Lambda sensor puts out + 0.5V when this mixture is correct. However there is a control loop set up by the ECU with adjusting the fuel air mixture by measuring the Mass Air Flow and adjusting the mixture to keep the Lambda within range 0 to +1V. At idle the signal is a 1Hz sign wave crossing the 0.5V level about once per second. The tester can inject +/- 0.5V to test the ECU response.

 

 

 In the case of our V70 the O2 signal is +3.75Vand stuck there. I had to check this with a multimeter as it is outwith the range of the analyser. An error code from the ECU indicates the  long term fuel mixture is too week. The lambda is in fact too rich as indicated by the Gas analyser results. This is the ECU trying to square the impossible circle.

 

I have checked the ECU wiring and all the connections are correct. The only time the 3.75V goes away is 5 minutes after engine switch off.

 

 

 

 Unfortunately I cannot identify the ECU part number from the outside, the label is unreadable however I hope this image may identify the part.

The internals of the ecu electronics look factory fresh despite the outside can being corroded slightly.

Update 27/03/16

The purpose of todays measurements was to see if the 3.75V was a signal from the ECU or some noise generated within or without the ecu. In my mind it could be caused by noise from the O2 heater (possibly) if it were pulse width modulated. Some manufacturers of ECU do this trick.

I connected up an old oscilloscope I had in the workshop to the O2 signal and there is no noise just a constant 3.75Vdc. So the incorrect signal must be from the ecu and in fact must be a blown input stage.

I will phone the ECU repair man (The ECU Doctor) in the morning.

 

 Update 12/06/2016

Well I had to give up on my home diagnostics the ECU is not available on ebay (with lock and key) and neither is any repair service available at a reasonable cost. I am not entirely sure the ECU is in fact faulty. We decided to get the help of an expert The Krypton Garage in Blackburn. Krypton (Steven) has all the Volvo approved diagnostic kit.

The key issue was the O2 sensor. The one I obtained from ebay was not the correct one. You must use an O2 sensor matched to the ecu there are several different types for that model year. The incorrect O2 sensor did not deliver obvious symptoms and Steven did a good job tracking this down. It appears Volvo use a current driven wide band sensor that does not give a voltage variation at the input to the ecu, hence my confusion.

Also replaced during the diagnostics was the MAF sensor and VVT solenoid in an attempt to get better performance although I am not convinced it has made that  dramatic a difference. However good enough for a Rome adventure.

Another issue is was the persistent oil leak which returned and caused intermittent sparks from the coil packs. I finally nailed that, the rocker cover bolts were loose.

All in all this is a lesson in what can go wrong with a modern car when they get older and fail the emissions test. I spoke to a garage friend and in normal circumstances this car would have been scrapped as the time spent and cost would normally be prohibative.