Help - my lambda probe won't work

[New S Wales 2010]

After months of smooth running my V6 petrol (not LPG converted) has develped a rough idle and mis-firing. All smooth when started from cold, but starts to mis-fire as soon as it warms up. Also fine under power (over 2-3 k revs) but drop down to idle and the mis-fires kick in again. Everything points to a lean running problem (a short squirt of carburettor cleaner on the air intake settles it down for a short time, but then back to mis-fires again afterwards.

Thought this might point to the lambda probe, so changed it for a universal 2-wire probe (spliced wires white to white and black to blue). No improvement, and have now had it checked by a mobile tuning service. Confirms the new probe isn't working (shows almost zero volts), neither is the old one which I took off. A spare 4 wire probe he had on the van still only got to about 0.24 volts output when the mix was really rich.

With no proper input from the lambda probe the ECU seems to be lost, most of the time it defaults to running lean on idle, causing sporadic mis-fires on most of the cylinders (chug, chug, chug out of the exhaust ). Once we seemed to flip it into feeding rich, at which point the running was of course smooth, but emissions went when way over the top. In either condition none of the lambda probes fitted were giving the correct level of output.

Stuck for ideas now. As the lambda probe is a two wire sensor is it possible that it's not getting hot enough ? (Could be the universal sensor I bought new needs a higher temperature than the Mazda original ?) My engineer's only suggestion was to fit a four wire sensor and connect the heater feeds to a 12 volt supply - a solution he has used in the past successfully on Mx5's that would not pass the emissions test. Any ideas would be very welcome at this stage as I am going mad with frustraion after 5 hours on it this afternoon ! She used to run so smoothly before this too!

PS. Diagnostic revealed one fault code "Variable resonance induction system (VIRS) solenoid #1 malfunction" but I have no clue what this refers to, or whether it has any relevance to the lean running condition.

[Rhinoman]

If you have a fault code then the ECU is unlikely to go into closed loop mode so you won't see the lambda sensor switch.
If you're vehicle is designed for a 2-wire sensor then you shouldn't run a 4-wire sensor as it will run too hot; running directly from a 12V supply is also not a good idea, the heater should only be switched on once there is some heat in the exhaust or the inrush current and sudden change of temperature may cause the ceramic heating element to crack.
You need to fix the fault first then do further diagnostics if necessary.

[g8dhe]

The VRIS solenoid is one of these 4 solenoids shown on the diagram http://lushprojects.com/bongopartsmk2/c ... o=.html#19
however I haven't been able to work out which is which, the diagram below is the electrical wiring B4-14/15/16/17 ;
http://www.g8dhe.net/bwm/bwmanualp.htm?1997/Page_40
There all part of the EGR system on the V6.

[cheffy34]

Yip ive had that fault code valve was goosed when i tested it, replaced it, it then worked but did it solve my problem ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,



NO

The vris solanoid is no2 18-741c if that helps

Dar

[New S Wales 2010]

Thanks for the input guys. Am now thinking the lambda may not be faulty at all (will maybe try to bench test this morning with a propane torch to prove the point).

The fault code could mean that the EGR is not closing / fully-closing on idle, effectively creating a vacuum leak. This would cause lean running with misfires on idle AND a low output from the lambda. Can anyone suggest how to test whether the EGR is fully closed on idle ?

Also, if it is the EGR, any advice on where to get the new solenoid and how to fit ?

[helen&tony]

Hi
I don't know about the V6, as I have a diesel...but...quite a few blank the EGR off on the diesel , and I did mine some years back..very worthwhile! I'm afraid you'll have to ask V6 owners.
By the way...I'm rather envious regarding the V6....I would like one!
Cheers
Helen

[g8dhe]

The vris solanoid is no2 18-741c if that helps

It helps me! You don't know which the others are or where the info is listed by any chance ?

Ah hang on there are TWO 18-741C devices one belongs to 18-740A and the other 18-740B which is the VRIS can you remember ?

[cheffy34]

The vris solanoid is no2 18-741c if that helps

It helps me! You don't know which the others are or where the info is listed by any chance ?

Ah hang on there are TWO 18-741C devices one belongs to 18-740A and the other 18-740B which is the VRIS can you remember ?

740B IS VRIS

740A is same solanoid just has breather on a diff nipple the solanoid is common to 323, 626, mazda 2 amongst a long list of others but you try getting a second hand one £80 from vospers

740A is PRC solenoid valve

Hope it helps

Dar

[g8dhe]

Excellent, yes it does help, I'm hoping once I get sufficient info to make it worth while to provide links between the Bongo Wiring Diagrams and the mechanical diagrams in the Lush projects site so we link the two sets of diagrams together! But there are a lot of items to identify before is worth putting the links in place......

[cheffy34]

Glad to be able to help Ive had my van for a fair few years now and have had some intimite times , never had to send it away to get repaired untill recently when ALLANS sorted it for me cause i lost interest.

if i can help in anyway feel free to give me a pm dude


THANK GOD FOR ALLANS IN PLYMOUTH