Anyone understand petrol emissions?

[Simon Jones]

Took the Bongo for an MOT today and it failed on a leaky rear shocker which is fair enough. Due to time constraints, I'd run out of LPG so had it tested on petrol. It just squeaked thru on the emissions with the Lambda reading being just on the upper limit. As seen from the results below, the CO and HC figures are very comfortably under the limits. A quick bit of research indicates this is running lean (which I would have thought would have been a positive thing from an emissions perspective) and is typically caused by a leaky exhaust. The tester said there was no evidence of a leak so I'm wondering if anyone has any suggestions of what else to check. Another possible option is a problem with the temperature sensor (ECU not gauge) although the rad fans cut in and out as expected.

During my LPG service, it was noted that combustion was not 100% and there was some very slight 'popping' on fast idle. It's had complete overhaul of the ignition system so that in theory is all good. I did buy a spare Lambda sensor a while back which I've never fitted. When hooked up to the LPG diagnostics, we could see the signal from the sensor was alternating as expected. Should I fit the new one and see if it makes any difference?

[BongoBongo123]

I had an issue where my 1997 petrol car just scraped through this year (I posted on here about it being a bit worried), despite being well under last year and only traveled merely 4,500 miles in between (with a full filter/oil service as well a few weeks before the MOT). The guy seemed to suggest problematic sensor which could feedback to the engine and change the mixture. It is somewhat confusing and above my head but I find it worrying because as a "lay man" when it comes to ECU's and sensors they seem to be able to make anything up prior to a proper diagnostics. He also said CAT convertor might be on the way out. so all of this is conjecture. Out of pure interest relative to your mention of a leaky exhaust there has been suggestion when I have had new tyres put on.....the tyre changer said is your exhaust blowing as I rolled the car into the bay ? And it does seem to have a slightly different tone of late.

I find it very strange that one year things are way lower than required to pass then you are on the margin for a failure. I hope you suss it out Simon even if this post was not much help.

Here is my old thread:

http://igmaynard.co.uk/bongo/forum/view ... =2&t=67207

In a nutsell : "Idle pass (0.02 to 0.48 !!!!) " Max permissible 0.50... so now within 0.02 of a FAIL on idle.

[Simon Jones]

I think there's a relationship between the low CO & the high lambda so I need to see how to tip the balance the other way. I'm pretty sure I had some decent fuel in the tank although one thing to be mindful of when running on LPG is that the petrol is only used on initial startup so can take many weeks / months to get used up during which time it can become 'stale'. I tend to chuck some Redex in there with each fill up to keep it fresh.

Interestingly, they did ask me if I had a manual override to control the rad fans as they did not come on when expected. Part of the problem is the use of a Mason alarm which extends the range of the gauge so the needle runs much higher than normal. Normally, the needle at 2 o'clock position would mean the fans would have kicked in, but this is not the case with a Mason alarm. Despite the 3 digital temp gauges I have showing what was happening, they were relying on when the fans cut to determine that it was at the correct operating temperature. This seems like a very unscientific approach. I'd previously given the van a good run on the way to the test centre, but it then sat outside cooling down for 20 mins while they faffed around. Low engine temperature will result in the lambda readings being incorrect.

A duff cat is another possible cause, but I'd like to rule out the cheaper options first.

[mikexgough]

The usual suspects have been mentioned for the "early" Cat vehicles.... Lambda and Temp sensor... On many of these I find you have trouble tracking down the exact cause of any issues/faults unlike the later OBD2 motors... But all is not lost as there are fewer parts to fault find or replace....
I'd check your vac hoses....just in case as a split or damaged one can make the reading lean.... if not... Lambda and or Temp Sensor, but I guess you have already changed the temp sensor with your cooling system service work you have done.
Not being familiar with the Mazda V6.... has it a MAF sensor?.... might need a clean

[scanner]

I thought that according to the Low Emissions Zone people in London (and elsewhere) petrols didn't have any emissions, only the nasty smelly diesels

It just goes to show that petrols are getting as complicated and difficult to keep in tune as sophisticated modern diesels, but all the powers that be worry about, are the diesels.

Strange that as my 170,000 mile diesel had emissions that didn't register on the meter at the last MOT.

[BongoBongo123]

Not to derail the topic too far off but the LEZ seems suspect to me as well. I can see 3 y.o, diesels with mass plumes of black sooty smoke and I see 100pct clear exhaust from my Bongo. It's fine to have a brand new commercial (company owned) diesel and floor it into iron filings within 3 years but a sensibly driven old diesel gets stuck with not being allowed in or £2,000 of specialist work needing doing. Who has not seen the black plumes coming out of old black taxis and buses ? Lucky the Bongo is exempt.

I actually heard 3-4 months back that there might be a £10.00 charge on older petrol engined vehicles coming into force in London the not too distant. So where there is money to be made....

[Simon Jones]

The usual suspects have been mentioned for the "early" Cat vehicles.... Lambda and Temp sensor... On many of these I find you have trouble tracking down the exact cause of any issues/faults unlike the later OBD2 motors... But all is not lost as there are fewer parts to fault find or replace....
I'd check your vac hoses....just in case as a split or damaged one can make the reading lean.... if not... Lambda and or Temp Sensor, but I guess you have already changed the temp sensor with your cooling system service work you have done.
Not being familiar with the Mazda V6.... has it a MAF sensor?.... might need a clean

Thanks Mike for the feedback. I'll check the vac hoses as you suggest. Temp sensor for ECU not changed, but I'll check it as per engine manual. It does have a MAF which I've cleaned with an aerosol of non-residue electronic cleaner. I'm tempted to replace the lambda with one I've already bought as I can always swap it back if it makes no difference.

At last LPG service, it took a great deal of tweaks to get it run correctly. When it was all setup to 'text book' settings it ran like an absolute dog & in the end the mapping had to be wiped & it was all done on the fly with me driving while the chap was sat in the passenger seat fine-tuning it. As the emissions have been problematic on gas & petrol would tend to rule out the fuel type, but could be ignition or ECU / control related. The ECU for the LPG takes its feed from the main ECU so if a sensor input was awry, it would affect either fuel.

The thing is that it runs very well on gas or petrol so no actual symptoms of a fault which you'd perhaps expect if it was running too lean. For next MOT I'll get it tested on gas to see if that makes a difference.

[New Forest Terrier]

No great scientific understanding understanding of this but on the 2013 MOT my V6 with LPG, initially failed on emissions on LPG. A total shock because the emissions had always been fine. I took it back to the LPG installers. They tested it on their machine found the emissions fine, but gave it a tune up anyway. I took it back to the MOT test station and they claimed it had failed again on LPG but had just squeaked through when the turned it over to petrol. Various dire warnings about this being its last MOT pass as it deteriorated so much.

For the 2014 MOT I took it to a Bongo friendly garage. I had done nothing to it in the year, apart from an oil change. I just wanted details of what seemed an inevitable failure. It went straight through with no emissions problems. According to the LPG installer there is apparently a trick to getting a petrol Bongo past its emissions test especially the earlier ones. The Lambda kicks in with a delay after it appears to be at the correct temperature. You wait and the emissions will suddenly drop. At that point it is ready to test. The LPG place knew that and so did the Bongo friendly place where it had been tested more recently. The other MOT station got a pass by luck as they were testing too soon. The final pass being on petrol simply meant it was changed from LPG at the point the emissions were about to fall. Changing the Lambda does not speed things up.

The only other possibility was that the testing machine had not been set up correctly the one time.

[goodlucktrev]

I put my Bongo registration number into the TFL site and it said NO ENTRY £500 Fine will be charged if I enter London LEZ ??? !!!!!!!!!!!! 1998 2.5 Diesel

[Tony x]

I do hope you get lots of useful advice here Simon - You're always thorough when it comes to helping others out.

[francophile1947]

I put my Bongo registration number into the TFL site and it said NO ENTRY £500 Fine will be charged if I enter London LEZ ??? !!!!!!!!!!!! 1998 2.5 Diesel

It should be exempt - see this thread for details of how to deal with your problem http://www.igmaynard.co.uk/bongo/forum/ ... =1&t=51519