Mk3 2.0 Misfire.

Technical Area Engine, Transmission, Exhaust etc
2

Hi Folks. Please help. Hopefully this is in the correct forum area.

My 2006 2.0i Mk3 Sport runs badly until it reaches normal operating temp then it is fine. I also have an engine management warning light staying on which my garage says is coded as a knock sensor issue but they tell me there is no knocking and I haven’t heard any pinking (same thing, yes?). They have reset the ECU but the light still comes on. If the sensor is faulty it will cost a bomb to get at and replace, apparently.

Strangely, this started after a recent mot test. Has someone screwed my car up? The car has had very little use and additionally sat in my garage for 7 months. In my 10 years of ownership it has never previously missed a beat.

I have sprayed the electrics with WD40 on the advice of my retired AA man pal, the idea being to start with the basics. I have filled up with high octane fuel, added redex and given it a bit of welly - to no avail.

I have not yet removed the engine cover to examine the plugs and leads etc. Truth be told, I don’t know how to remove the cover although it can’t be difficult. I can’t find this on the forum. Time to get a Haines manual, eh?

Any advice or information saving me ££££££s would be much appreciated. Over to you folks.

 

3

LIFT the cover straight up and check for damp/water around the plugs, it would be my starting point especially if you’ve just given it a good wash.

4

remove and clean plugs but I suspect a faulty injector.

https://www.youtube.com/watch?v=SMSSyeugyX4

 

5

I have had the car serviced as required and parts repaired as necessary although without looking through invoices I couldn’t be specify what’s been replaced.
Are you thinking plugs? Re the engine cover, what screws/nuts do I remove before lifting it straight up?

6

Thanks so far guys. I’ll look at the link Raymond.

7

https://forum.miata.net/vb/showthread.php?t=287477

8

for what they cost, it would be worth investing in a cheap OBD2 reader, so you can read and erase the error codes yourself.

They only cost about £15

 

Also, here’s my little cheat.

If you suspect a cylinder not firing, a very easy way to determine which one is as follows.

 

With the engine stone cold, pop the bonnet.

Start the car, and let it idle for no more than about 10 seconds and switch off

Now carefully, feel the exhaust manifold.

The cylinder which is misfiring, will be evident by a temperature difference in the exhaust manifold.

One of those laser temperature readers would be ideal, but fingers suffice, so long as your’e careful.

It’s unlikely to take your skin off after 10 seconds running, but just be aware that it has potential to get hot quickly.

9

Just check under the engine cover first, myself and at least one other member have had rodents set up home under there. As you say the car has been laid up a while in the garage, these little blighters will chew through most things including wiring. The cover just pulls off upwards.

 

10

Thanks MickAP and Keat63. I’ll have a look under the engine cover, maybe take the plugs out to check and spray WD40 on cables etc.
Does anybody think that the mot test just before these problems is related to the ECU light (knock sensor code) and cold misfire?
Anyway, I reckon it’s a sticking injector. Easy DIY?
Re your “little cheat”, Keat63, the car ticks over ok when cold so that may not work. The car only stutters when accelerating
with a cold engine. It clears shortly after normal running temp is reached.

I’m becoming obsessed! Does anyone else get like this with car problems?

11

I am now linking my knock sensor problem to the poor cold running. Having read a bit more on this forum and elsewhere, I have found out that a knock sensor retards the ignition when it detects knocking/pinking simply by picking up the vibration of preignition through the engine block. As knocking is usually audible, and given that I have not heard any, then presumably the sensor is faulty, retarding the ignition unnecessarily and causing the stuttering acceleration. Perhaps some other sensor overrides the knock sensor once normal running temperature has been reached and so the car runs well. I have also read that an engine could be damaged by a faulty knock sensor. The garage told me I could safely drive with the ECU light on but now I’m not so sure. Maybe I need to bite the bullet and get the sensor changed after having the voltage across  it checked. There should be none when it has been disconnected.

12

The wee car is going to the garage on Friday. I am told that a faulty Coil Pack can show up as a Knock Sensor issue code.
This is a place I’ve used before and been satisfied with their work, but they are a bit more pricy. They will run a full diagnostic first and contact me with the result.

If I’m lucky my labour charge will be a good bit less. (Knock sensor remove/replace = 3.5 hr. job)
Fingers crossed!
I’ll report on the outcome.

13

Well, folks, the problem was indeed due to a faulty knock sensor.
The guys had to remove the inlet manifold and other parts to get at it, so quite a lengthy job as reflected in the labour charges.
The car is running as she should once again! I will be using it much more often now as I have finally learnt that not running the car has actually cost me money over the years (duh!) in replacing all the brake discs twice, calipers, a rear wheel bearing and now the knock sensor. And only 29k miles at 10 years old.
Thanks for the kind replies to my post.