MOT failure fun

I have a history of tracked data on my MGF VVC (Mems 2J) using Pscan. I can see straight away some differences.

When oil and water temp > 85 C and at idle of 875rpm (quick extraction of the norms {note that for several readings, the norm can be an either or} but should be enough for you to decipher even without headings)

4 ° 0.6V Closed On Alternates Alternates Neutral Alternates Alternates Alternates 30 Kpa 26 steps 875rpm 0rpm 0kph 85°C 85°C Varies Varies N.A 13.4V okay okay okay 2-3mS 2-3mS 720.0° 2.5ms 0.9ms 0.7-1.0 V NA NA Active/inactive NA 225.0° 225.0° 717.6° 221.5.° Active Not active Closed Not cranking Started Not stopped Active/not active Active/not active On Off OFF at 98 degrees OFF at 60 degrees On NA 0-100%

The sensor on coolant temp for the ECU is a different sensor to that used for the temp gauge. I have an issue at the moment where the gauge is reading normal but the ECU coolant reading is very different once the temp gauge reaches normal. As both sensors are right next to each other, I am assuming at this stage that the ECU coolant sensor needs replacing.

Thanks for taking the time to post that data but I can't work out what is what.

Coolant sensor seems fine as it starts the same as ambient and go up. I have tried pulling it off and I can hear the radiator fan kick in then.

Iain.

Hi,

I have added as an attachment, the full Pscan live data file if anybody wants to have a look using a spreadsheet, tab delimited seems to work.

I noticed two things :
"Cylinder 1 misfire count" - sometimes says 1 or 2 but also 256 or 512.
Downstream O2 sensor reads higher voltages than the Upstream sensor reads, that can't be right even if there was no Cat!

Today I looked Ignition because of misfire values.
No tracing visable in the dark.
Pulled boots off coils - little bit of white corrosion - cleaned off with alcohol,
Swapped positions over of coil 1 and 2. Misfire in live data stayed on cylinder 1.
Checked spark plugs. When I first put them in I could not find my gapping tool so trusted the factory preset - all at 1mm except cylinder 1 which was 0.8mm - regapped to 1mm, Don't think it made any difference but I ran last live data before this.
Noticed wires to coil packs have been played with.


Performed a compression test,
Cylinder 4 - 14 bar (200psi)
Cylinder 3 - 12 bar (175psi)
Cylinder 2 - 15 bar (220psi)
Cylinder 1 - 15 bar (220psi)

Took a phone video of exhaust sound but it appears too big to attach.

An air pipe is hanging off the air box, don''t think it makes a difference though.


Swore at a group of Ravens in the tree overhead.

Forgot to include, I put a sheet of paper up near exhaust pipe for a few mins too see if there was any soot. Just a bit of rust from pipe edge.

Are you making any progress?

I've had a look at the data file but as it's the first time I've played with this type of data, I'm not going to make any bold statements! However, there are a couple of basic questions I'd like covered.
Are the plugs in the pictures in order of the cyl's they came from with 1 to the right and 4 on the left?
Do you know why cyl's 3 & 4 are showing ? in the misfire column and is it related to the reduced compression tests?

I think I might start looking at a head gasket or valve fault on Cyl 3.

Michael

Hi,

Thanks for the reply

The photo of sparks plugs are the old ones i took out when I changed them a few months ago, don't think they are in order. If I get time in the next couple of days I'll photo the new ones.

Did the compression again recently after dumping fuel system cleaner in and from warm cly 3 is 14% down on the others. No signs of head gasket going, emptied all the coolent out when I did the cambelt/water pump and S/S underfloor pipe and it was really clean. I did not try putting any oil in the cylinder to see if it improved.

The ECU does not give readings on cylinders 3 and 4 only 1 and 2 apperently so Pscan can not read what is not there so gives a ?. The misfire count data seems screwed up, always seems to be one of three values so I have ignored it now.

I can't remember what the exhaust smelled like after failing on massivly high CO but I would expect to smell petrol if there was incomplete combustion. I came near too death sniffing the exhausts of all three cars recently - lol.
VW T4 camper smelled of exhaust but has no cat anyway.
Astra smelled of nothing but is a much newer car.
MG TF smelled of exhaust like the T4 but a bit stonger, no petrol or sulphur smell.

Did a live scan after fuel system clean, new upstream sensor and coolant sensor from Rimmer Bros and it seems better. See attached - just the fuel correction and both o2 sensors. The fuel correction(I think this is the short term fuel trim) is only fluctuating a few percent either way from 100% and the O2 sensor seem to be doing the right thing, upsteam fluctuating and downstream staying mostly steady on the higher side. The cat is using the O2.

Hoping that means the fuel trim error is gone and the cat is ok still. I have cleared the error but I need to let it run a good few times to see if it comes back.
Praying it was a dicky injector cuasing overfueling and the cleaner fixed it.

If not...

Maybe a valve on cylinder 3 like you said or too high fuel pressure in the rail (I've checked the vacuum hose to the FPR). I have checked for vacuum leaks all over with smoke from a vape box and a hose connected to the breather. Also double checked the cambelt I did for timing - all good.

If it was a leak in the exhaust manifold I would have thought it would have been picked up on the MOT.

Written a letter to Santa asking for my car to work - that will do it.

Car passed the MOT last week. YAAAAAAAHHHH.

Emissions went from too high to read to pass. Only thing was a binding rear brake. Bit fed up working on the car so I brought a recon caliper rather than dicking about with new seals etc.

Same MOT tester and garage but advisories :-

Last MOT rear discs worn etc. Slight play on inner steering joint.

This MOT all discs worn etc.

About a month apart and off the road the front discs have worn and the slight play in the steering has magically fixed itself!


If anybody has the same problem, I don't know for sure what fixed it.
Apart from testing nearly everything and cleaning here and there I did three things.
Changed upstream O2 sensor because Pscan results indicated it had a low switching frequency but new one read the same.
Changed coolant temp sensor because it was cheap and easy. Seemed the same.
Last thing I did was add some Snake Oil and that actually got results to my disgust.

Anybody guess what it was?

MGFs seem to suffer from emissions issues. Clean air filters and a bottle of Redex in the fuel help (you can feel the difference in smoothness quite soon afterwards) but the one thing that you can work out from all the MOT histories is that cars that cover a decent mileage suffer the least from excessive emissions. Run a tankful of fuel through the engine in the week before the test and give it plenty of welly!