Test coil-on-plug, MAF and Temp sender?

  1. My model of MX-5 is: 1.8 NBFL Turbocharged
  2. I’m based near: Chelmsford
  3. I’m looking for technical help or recommendations on: Testing engine electrical components

Hi All

Im trying to identify and cure a misfire I encounter most obviously whilst cruising. It was previously an occasional miss, but seems to have become more frequent. Car pulls great when accelerating, but seems to stutter with light or constant throttle application. I think it’s killed my cat too as i needed a favour to get through the last MOT.

Research suggests these symptoms can occur with failing COPs(Im running the standard items), MAF and Temp thermister.

Is there any way of testing these items other than to replace them? In particularly the coils are expensive and as my car only has 35k on the clock, there is probably a lot of life left in whichever components arent failing. spark plugs and leads are presumed to be good as they’ve <5k miles on them.

Many thanks

Ben

I had a similar problem with my old Vextra, it turned out to be a new spark plug actually going high resistance, so a weak spark was giving misses on lean mixture and/or maximum advance.

They easy way to check this is in the dark. Open the bonnet, run the engine, look carefully at coil packs and leads, the faulty HT will be escaping in little (or maybe not so little) blue sparks to other places than through the plug. If no blues then it’s something else.

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Thanks Richard,

Thats certainly worth a shot I guess to rule out plugs.

Ben

I’m still no closer to fixing this.

I’ve had the plugs out and all were quite black and fuelly. As I understand it this would seem to rule out coils, leads and plugs.

When I plug my laptop in I can see the AFR readings cycle from 13 to 20 every second or so when trying to hold a constant throttle at say 2500 and the revs drop then recover rhythmically.

Anyone got any ideas please?

Ben