Emissions - totally lost! - MG-Rover.org Forums
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post #1 of 23 (permalink) Old 15-04-2017, 10:57 Thread Starter
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Emissions - totally lost!

Hi all,

I've been trying to help out my Dad with our '96 MGF VVC which has failed its MOT on emissions. So far, we have changed:
  • Lamda
  • MAP sensor
  • Coolant temp sensor
  • Wiring harness

The emissions at the last test were as follows:
  • CO, second fast idle - 5.2
  • Hydrocarbon second fast idle - 3579
  • CO natural idle - 4.8
  • Lamda second fast idle - 0.749
  • CO fast idle - 1.86

So in effect, everything failed on the second fast idle and natural idle, only the CO on the fast idle test.

Everything runs fine on the car, although smells rich at idle.

We just got hold of a Pscan, with the following errors:
  • map2 low fault
  • fuel temp high fault
  • VIS/VVT drive fault

From what I understood, the first two errors can be ignored as the VVC doesn't have those sensors, but not sure about the VIS/VVT drive fault error.

We're completely lost, so I've attached the live data when we started the car up this morning. We've yet to warm it up and see what the values are there, but wondering if anyone can help us take a step in the right direction and see if anything seems wildly incorrect there.









Thanks for any insights!
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post #2 of 23 (permalink) Old 15-04-2017, 11:37
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post #3 of 23 (permalink) Old 15-04-2017, 12:03
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The most obvious candidate with an emissions failure is the catalytic converter .

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post #4 of 23 (permalink) Old 15-04-2017, 12:39 Thread Starter
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Apologies for the lack of images - I realised immediately after I posted that I used the wrong code!

Links to the images below.

https://www.dropbox.com/s/3tuuiqrobj...153_n.png?dl=0

https://www.dropbox.com/s/9f1shpzxzs...629_n.png?dl=0

https://www.dropbox.com/s/oh80l1y1lo...238_n.png?dl=0

https://www.dropbox.com/s/cy3fuanybp...470_n.png?dl=0

It has a new cat, so can't be that.
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post #5 of 23 (permalink) Old 15-04-2017, 13:21
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Air filter condition?

Misfiring?

Checked the timing?

One of those photos shows the Oxygen sensors as 'Inactive' - that could be a clue.

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post #6 of 23 (permalink) Old 15-04-2017, 13:24
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I may be wrong but is there not a coolant sensor which drives the gauge and another that sends info to the ecu to control the mixture?

Did you change the right one?

As I said, I may be completely wrong but at least I tried to be helpful!
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post #7 of 23 (permalink) Old 15-04-2017, 13:47 Thread Starter
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We've check all of the obvious things (Dad's a mechanic so not entirely without knowledge ), but can't seem to get to the bottom of anything. We're not sure why the o2 sensor is inactive, given we've changed it to a new one, and the temperature on the lambda seems to change. That said, we've tested it hot and the voltage isn't changing at all, even if the sensor itself feels as if it's working.
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post #8 of 23 (permalink) Old 15-04-2017, 14:17
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It looks to me as though your new Lambda sensor is not switching correctly.
Being a 'F you only have one sensor, so take notice of the one listed as number 1 bank and ignore the bank 2 readings. With the PSCAN connected monitor the bank one sensor, it should be active and not inactive. Look at the switching voltage with the engine running, it should toggle from about 0.1v to 1.1v if i remember correctly. If the sensor is not showing as active it usually means there is a huge air leak in the exhaust system somewhere ( manifold or joint of sensor or joint before cat) or the sensor or its wiring is faulty. If the sensor is not toggling it will make the ECU over fuel the engine and give you the high emissions.
It is quite easy to damage the sensor, especially if you do it with the engine in place and are maneuvering the downpipe around in such a tight space.
PM me your private email and i will send you an excel scan of my good PSCAN results for an MGF VVC.
Nigel
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post #9 of 23 (permalink) Old 15-04-2017, 14:22
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Quote:
Originally Posted by MGNeuro View Post
We've check all of the obvious things (Dad's a mechanic so not entirely without knowledge ), but can't seem to get to the bottom of anything. We're not sure why the o2 sensor is inactive, given we've changed it to a new one, and the temperature on the lambda seems to change. That said, we've tested it hot and the voltage isn't changing at all, even if the sensor itself feels as if it's working.
First rule (as I am sure your Dad will tell you), dont trust anything, even brand new parts...

I've had brand new Bosch and NGK spark plugs straight out of the box not working before. And of course you wouldn't call them cheap pattern parts.

On the subject of spark plugs, what condition and colour are yours? Are they wet with fuel by any chance?

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post #10 of 23 (permalink) Old 15-04-2017, 18:25
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you say you have changed the lamba sensor..
what manufacturer made it , i beleieve some have had problems when fitting cheap / mid price ones ,our cars dont seem to like them and cause some strange problems with them fitted .
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post #11 of 23 (permalink) Old 16-04-2017, 07:53 Thread Starter
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Thanks for all the help, guys. It does seem like it's something to do with the lambda then (how frustrating!). We'll do some more digging and let you know.

Spark plugs were all fine when we checked, so we'll start with the lambda (again!), and keep going from there.
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post #12 of 23 (permalink) Old 16-04-2017, 07:55
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Quote:
Originally Posted by johnan View Post
I may be wrong but is there not a coolant sensor which drives the gauge and another that sends info to the ecu to control the mixture?

Did you change the right one?

As I said, I may be completely wrong but at least I tried to be helpful!
Blue for the dash gauge, brown for the ECU (black on the later cars).

The pscan will show what the ECU sensor is reading.

My mk1 VVC failed one MOT on emissions due to a slight leak on the exhaust manifold to down pipe joint, I had changed the exhaust the MOT before and asked the garage to nib up the bolts on this joint but they hadn't allowing the gasket to burn through.
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post #13 of 23 (permalink) Old 16-04-2017, 08:02
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Just looked at the screen shots - the coolant is a little low at 79-80, to be fully up to temp it should be nearer 88'+, also the oil is only showing 30' but I'm not sure the MEMS 2.0 actually has an oil temp input except to the dash gauge.

I'd be tempted to take the car for an Italian tune up, get it storming hot before testing again.
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post #14 of 23 (permalink) Old 16-04-2017, 09:20 Thread Starter
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Thanks again for all the help!

Ok, so today we tried with a different lambda sensor and car warmed up:
  • Voltage is now fluctuating around 0.3-0.4v with the car idling
  • When we block the exhaust up, voltage goes right down to around 0.1v
  • Revving takes the voltage up beyond 0.7-0.8
  • Pscan still shows the o2 sensor bank as inactive
  • Fuelling is at 100%
  • Every now and again, the sensor state changes to active for a split second, and fuelling went down to 99.5%!

We've checked the exhaust and can't hear/feel any obvious leaks, although Dad's out there tightening everything up just to be sure.

There's also a strange, brief hissing sound just after we switch the car off. No idea!
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post #15 of 23 (permalink) Old 16-04-2017, 09:32
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Seems like lambda is still not working. Can you check wiring to lambda sensor for split or bare wires which are preventing sensor operation coming to ECU?
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post #16 of 23 (permalink) Old 16-04-2017, 10:00 Thread Starter
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Another update: Dad's taken off the exhaust manifold, removed the gasket and there's an oil leak directly above the exhaust manifold. Both sides of the gasket are soaked in oil. Is it possible that it could be pulling oil into the exhaust system, causing the high HCs?
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post #17 of 23 (permalink) Old 16-04-2017, 10:11
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High HC's are normally caused by unburnt fuel in the exhaust. Have you checked or changed any parts on the ignition side i.e. plugs, leads, coil(s), dizzy, rotor arm etc?

perhaps oil being dragged through could also have the same effect, not sure on that one though.

Edit: sorry just noticed you are working on a VVC, so forget the dizzy cap and rotor.

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post #18 of 23 (permalink) Old 16-04-2017, 11:15
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My very early MGF doesn't have a Lambda sensor, it caused confusion at the last MOT as it couldn't pass the test, we got it through in the end.
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post #19 of 23 (permalink) Old 16-04-2017, 12:32
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I do not think the oil leak would be causing such high readings as it would have to get into the combustion chamber to do this.
Have a spray around the inlet manifold area with WD40 and see if the idle rpm changes. That would indicate an air leak which the ECU will try to correct with extra fuel.
Nigel
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post #20 of 23 (permalink) Old 16-04-2017, 14:15
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Quote:
Originally Posted by JoCoLo View Post
My very early MGF doesn't have a Lambda sensor, it caused confusion at the last MOT as it couldn't pass the test, we got it through in the end.
It should, all versions of MEMS right back to 1992 should have at least one.
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