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97 Mpi - Spluttering When Warmed Up - Maybe


Best Answer awpainter , 10 December 2020 - 11:28 AM

All sorted now thanks everyone.  Was down to an exhaust leak around the cat.

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#1 awpainter

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Posted 25 November 2020 - 06:09 PM

New member but long time sufferer.  18 years after I last had a Mini I got bored in lockdown and after months of searching found myself a half decent 97 mpi.

 

She runs fine, doesn't appear down on power or anything like that but I believe I am noticing some spluttering from the back end once warmed up.  Having trawled the forums with varying suggesting I can advise that she has no erratic revs, she seems to sit pretty nicely with no ups and downs, again no holding of revs when revved.  Manifold is seated correctly, tight on the gasket, cannot find any leaks.  Tappets have been checked/adjusted for good measure.  Recent woks includes; service, oil, filter, new plugs along with leads.  Leaky gear selector seal replaced.  Oil temp sender replaced. New alternator.  New backbox.  She is mechanically standard under the bonnet apart from a few shiny bits.

 

I'm new to the mpi and if I'm totally honest a bit rusty with my mini knowledge especially the mpi but given that she appears to be running completely fine I now find myself wondering:

 

A - Is it just my ears, I guess not?

B - Do I have a slight misfire or just a bit of a rough idle?

 

Have taken a video to show what I mean. Video shows start up from cold, as expected she runs the higher rpm for the first minute or so to warm up but...

 

At around the 2:40 mark you can hear what I mean.

 

 

Would appreciate someone with better ears than me having a listen in and your views and if I'm going mad.

 

AP



#2 MiniMadRacer

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Posted 25 November 2020 - 07:49 PM

I am no SPI or MPI expert but it could be as theen gine gets up to Temp the mixture is not right.. have you had it plugged in to check the Lambda and the water temp sender



#3 Quinlan minor

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Posted 25 November 2020 - 08:04 PM

Start it and drive it, as per the Handbook.

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#4 awpainter

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Posted 25 November 2020 - 08:05 PM

I haven't yet. That's next but I need someone locally with a reader. Have put a request in the reader sticky thread.

If by chance anyone in the Midlands or surrounding areas has one and is willing to let me pop along I would be extremely grateful.

#5 awpainter

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Posted 25 November 2020 - 08:07 PM

The start it and drive it approach, something I am very familiar with ?

It seems to do this regardless.

#6 Brent

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Posted 04 December 2020 - 08:03 AM

Had a problem with my MPI for ages, it would run perfectly and then have a misfire driving along. The next day it would be OK. Changed various sensors on the engine and it would be fine for a while but the misfire would re-appear. Solved the problem now by putting an earth strap from the bodywork to the engine. There was a technical bulletin dated 03/99 which referred to lumpy running due to a poor soldered connection (I only have the technical bulletin in German!)



#7 pete l

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Posted 04 December 2020 - 02:10 PM

There's already an eath strap going from the body to the engine. 



#8 awpainter

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Posted 04 December 2020 - 05:02 PM

Had a problem with my MPI for ages, it would run perfectly and then have a misfire driving along. The next day it would be OK. Changed various sensors on the engine and it would be fine for a while but the misfire would re-appear. Solved the problem now by putting an earth strap from the bodywork to the engine. There was a technical bulletin dated 03/99 which referred to lumpy running due to a poor soldered connection (I only have the technical bulletin in German!)

 

I'd be happy to take a copy if thats ok? Nothing Google translate can't help with :)



#9 Wazzah

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Posted 07 December 2020 - 11:37 PM

Just a couple of ideas for you to consider.

  • Dodgy crank angle sensors are effected by heat.
  • As the purge valve circuit opens (once the engine has warmed up and above a certain rpm which escapes me atm.) vacuum leaks downstream of the valve can effect the ECU which could result in air fuel mixture change to a rich condition.
  • Crap can accumulate in the fuel hose between the fuel tank and the in line filter.

Regards Waz.



#10 Alice Dooper

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Posted 09 December 2020 - 10:50 PM

Had a problem with my MPI for ages, it would run perfectly and then have a misfire driving along. The next day it would be OK. Changed various sensors on the engine and it would be fine for a while but the misfire would re-appear. Solved the problem now by putting an earth strap from the bodywork to the engine. There was a technical bulletin dated 03/99 which referred to lumpy running due to a poor soldered connection (I only have the technical bulletin in German!)

I had some poor running issues and had heard MPI’s are very needy for a good earth connection.  Simple job sticking another on and it did run better.

something I have learned with several cars and several problems - first step is a code reader session.  Second - don’t replace sensors unless you need to and it’s a genuine one.  I had a lot of issues with emissions and fuel economy, had some daft readings from 2 separate brand new Lambda sensors - sorted when I swapped in a proper Bosch original.  Third - an exhaust emissions test running from cold to hot might tell a bit too.



#11 awpainter

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Posted 10 December 2020 - 11:28 AM   Best Answer

All sorted now thanks everyone.  Was down to an exhaust leak around the cat.






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