Erratic running

http://www.ukmgparts.com
Ask the Gurus - Use this board to discuss problems or technical issues you have with your MGF/TF - there's always an expert around to help you!

Moderator: Committee Members

Forum rules
Not many rules really, this board being aimed at technical issues, it shouldn't fall foul (hopefully) of some of the more personal issues that can affect forums.

Rule 1 - Is that you need to think very carefully before posting anything technical or asking anything technical relating to the security system of the car - See 'Security Issues' sticky for more info.

Rule 2 - We (MGF Register) do not support copyright infringement and therefore references to CD ROM, PDF versions or paper copies of the workshop manual (for instance) should not be posted on the forum. We don't want to get into trouble and we'd rather sell you a genuine hard copy through our Regalia shop anyway! :)

Because advice is honestly and freely given in this technical section, much of it will be amateur experienced based, so any information is given in good faith and is not guaranteed as correct.
Post Reply
Konighaus
Posts: 7
Joined: Tue Jun 27, 2017 2:51 pm
MGF Register Region: Somerset & Dorset

Erratic running

Post by Konighaus » Sun Aug 13, 2017 1:18 pm

I am now becoming desperate, I have a problem where the car starts easily and runs well, then if left idling will start hunting, but I can put my foot down and the engine runs normally. Or you can be driving and you get kangaroo petrol, she may stop but will restart immediately or eventually will just clear and goes really well. I have no warning lights on.
So far I have; new plugs, coil packs, fuel and air filters, cam. sensor, air control valve, catalytic converter, LAMDA rear sensor, removed fuel pump and checked all clean.
I have had it on the reader many times, nothing of interest, many times due to me removing sensors and the faults always clear. There is one fault which is a speed sensor which has come up on the last visit I don't know where or what this is but the garage do not think this will cause the fault. All this and the problem persists.
Any ideas please, desperate now!

User avatar
nigelandjo
Committee Member & Regional Rep
Posts: 4908
Joined: Tue Oct 09, 2007 9:44 pm
MGF Register Region: Somerset & Dorset
Model of Car: TF85th,TF135,Trophy
Location: Berrow
Contact:

Re: Erratic running

Post by nigelandjo » Sun Aug 13, 2017 9:54 pm

Air leak on the inlet manifold?
Nigel May
Vice Chairman, Somerset & Dorset Regional Rep, Membership Secretary, Registrar & Archivist
Email: somerset.dorset@mgfregister.org
members@mgfregister.org

MGCC Members register here: https://mgfregister.org/?page_id=319

MrT
Posts: 27
Joined: Sun Nov 10, 2013 8:02 pm
MGF Register Region: East Anglia
Model of Car: 1996 MGF VVC

Re: Erratic running

Post by MrT » Mon Aug 21, 2017 2:51 pm

I have been struggling with similar problems on my '96 VVC. When the engine was cold and for about the first 15 miles or so, it wasn't too bad. At higher revs and wider throttle it seemed fine but if I got stuck in traffic the car was almost undriveable. If I stopped the engine for 10 minutes it would drive perfectly again for a few miles. I had already changed most of the items you listed.

I wondered about the inlet air temperature sensor and while Googling for the location of it I came across a post on a forum that suggested that above 3000rpm and more than half throttle the temperature sensor was not used. That seemed to fit the problems I had. I fitted a new sensor last week and since then I have not experienced any misfires (only done about 100 miles since) and the engine idles a lot more smoothly. I tried blasting along a duel carriageway then into town in traffic and it was perfect, where it would definitely have misfired before. The odd thing is that both sensors measured the same resistance when I compared them so I'm not sure why the new one seems to have fixed the problem.

User avatar
Bazzajay
Posts: 257
Joined: Wed Jan 04, 2017 8:29 pm
MGF Register Region: South Coast
Model of Car: Wedgwood SE 1800i
Location: Shanklin, Isle of Wight

Re: Erratic running

Post by Bazzajay » Mon Aug 21, 2017 4:18 pm

Could have been a corroded connection and unplugging it and plugging the new one in restored the connectivity. When you have problems involving electrical or electronic components it's always worth checking the connectivity and cleaning the terminals as a first step.
Barrie

2000 MGF Wedgwood SE 1800i
2002 Peugeot Partner Quiksilver

MrT
Posts: 27
Joined: Sun Nov 10, 2013 8:02 pm
MGF Register Region: East Anglia
Model of Car: 1996 MGF VVC

Re: Erratic running

Post by MrT » Mon Aug 21, 2017 8:39 pm

I usually do check connections (i'm an electrical engineer), however this sensor is easy to see but hard to reach so I thought I'd get a replacement so I only had to do the job once.

User avatar
Bazzajay
Posts: 257
Joined: Wed Jan 04, 2017 8:29 pm
MGF Register Region: South Coast
Model of Car: Wedgwood SE 1800i
Location: Shanklin, Isle of Wight

Re: Erratic running

Post by Bazzajay » Mon Aug 21, 2017 11:54 pm

Trust me to try to advise someone more qualified than I!!
Barrie

2000 MGF Wedgwood SE 1800i
2002 Peugeot Partner Quiksilver

User avatar
Reckless Rat
Posts: 1887
Joined: Tue Apr 01, 2008 9:01 am
MGF Register Region: Europe
Model of Car: 97 1.8mpi in BRG
Location: South of France - in the Gard.

Re: Erratic running

Post by Reckless Rat » Tue Aug 22, 2017 8:19 am

Have you considered the coolant temperature sensor - the one that goes to the ECU? If it's not working correctly it could be overfuelling and sooting the plugs.

User avatar
talkingcars
Posts: 5766
Joined: Tue Mar 09, 2010 10:44 pm
MGF Register Region: South East
Model of Car: mk1 VVC
Location: West Sussex
Contact:

Re: Erratic running

Post by talkingcars » Tue Aug 22, 2017 7:30 pm

Easy way to check the ECU temp sensor is to read the coolant temp via the OBD port, it should be between 88 and 110' when the gauge shows just under half way.

Depending on the ECU it will be black or brown, don't swap colours.

If you unplug it the radiator fan should come on.
Home to black Alfa 159 3.2 V6 Q4, blue MGZR160, green MGF VVC and grey MGF 1.8i, and red MG Maestro T16.

MGF chatting on the Register and at http://www.the-t-bar.com

Post Reply