Running on 2 cylinders / failing coil packs

Technical Area Engine, Transmission, Exhaust etc
2

Hi all,

1995 1.8 NA

A cry for help  I am at a loss as to what to do next, initially my NA had a failed coil pack about a year ago, usual symptoms, new coil pack in and all fine. 

Then about 2 months ago (about 2k miles later) the symptoms showed again. This time I changed the HT leads. Slight improvement then no luck. Then changed the coil pack again, slight improvement then no luck. Yesterday I put a new set of plugs in and replaced the engine earth. Improved then after about 2 miles I have the symptoms of a failed coil pack again (running on cylinders 2&3 only, red hot catalytic converter, no power etc).

 

In short:

  • New HT leads

  • On 3rd coil pack

  • New engine ground

  • New spark plugs

  • New pre cat sensor (as I put a new exhaust on it for the last MOT)

 

One issue that I need to get round to doing is changing the water pump as it is leaking slightly but cant think that this is causing all these issues? 

 

I simply don’t know what to do next save for calling a scrap yard! Does anyone have any ideas of what I can try next? I’m seriously thinking of breaking the poor thing for parts. 

 

Thanks, 

 

James (an almost MX5 previous owner)

3

The scrappy will love you forever.

And then have a good snigger perhaps.

I would.

He’ll likely plug it into the OBD sensor box provided Wink figure out the issue, fix it, and flog it for a nice wedge.

If…you kept the original coil pack you will see they are two sets of two on a common metal chassis.

Easily unbolted, so trial and error has perhaps you’ll nail it cheaply insofar it’s unlikely the entire pack failed…just one out of one the twin packs

Or perhaps not.

PM me if not and I’ll take the poor old thing off you no worries.Wink 

Anyway, Rhino is here…and he will either nail it or…flog you a good pack at a decent price.

4

Hi James

That’s not what’s needed at this time of the year!

Have you interrogated the diagnostic box under the bonnet(top, right) with an led to see if there are any error codes stored?

May also be worth taking a look at the ecu.

There aren’t that many components to check - ECU, Coilpack, CAS, MAF sensor… If the plugs and leads are good there may be an issue with the wiring, perhaps low tension that joins the 3 pin/4 pin. Occasionally the CAS plug wiring, close to the plug goes bad too.

Tell us where you are - someone in the area might pop round to assist.     

5

And…these days the injection wiring looms are beginning to wilt & split.

Forgot that one…especially at pots 1 & 2.

6

Thanks both, 

I’ll keep you in mind Scottishfiver, you may just get a good deal!! A you say will go over it and try a bit of trial and error. 

Rhino, I’m over in Cheadle, Manchester… have just bought a code reader so will check it when it arrives in a couple of days, could be wiring, bad connection somewhere, will keep on at it but if there’s anyone in the area that may be able to pop over that would be great. 

7

Exactly what code reader have you purchased there is only one that will work with the pre 2000 cars. All others do not talk pre 2000 MX5.

This one.

http://www.mx5tech.co.uk/home.aspx

8

My guess is a faulty Cam angle sensor but do not buy one try one that you know that works.

9

Thanks Drumtochty, I bought one from autolinkmx5 the LED type, I’ll have a look at your link if it doesn’t work. 

 

Is it the camshaft of crankshaft sensor you suggested changing? I’ve read a bit on these but can’t figure out which one I should be changing!

 

Cheers, James 

10

Would help if I read your post correctly! Cam angle sensor is what I’ll look at.

Do you think if this was faulty it would cause it to run on 2 cylinders?

11

Solved! (I think at least)!

Thank you all for your help especially Drumtochty I seem to have got to the bottom of this. I set about testing other things that could have been wrong with the car (ECU, CAS etc), neither seemed to be the problem. Turns out that I had bought a cheap coil pack from ebay which failed. It could have been something to do with poor spark plugs, HT leads or earth straps which I changed a few weeks ago, none seemed to be bad but I changed them anyway to make sure. You are probably all more knowledgeable than me but from what I understand if any of these parts had been weak then the coil pack would have been under too much resistance, the chips internally got hot and failed.

Interestingly enough I googled the part number of the coil pack and the below link came up on a bulk-buy website, Chinese manufactured and likely to be very poor quality at between $20 and $28 so beware of buying cheap coil packs of ebay as this is probably where they come from.

https://www.alibaba.com/product-detail/Ignition-Coil-for-MAZDA-MX5-NB_685129479.html

I have written a brief fault finding below for anyone else experiencing ignition problems:

Coil pack test - swap over connector to coil pack from ECU together with HT leads. If one pair of cylinders didn’t fire and now the other pair don’t then it is likely that the coil pack that has failed 

OBD - check any faults from this, it’s located on the passenger side, you can either make a tester up from an LED, resistors and wires or buy one

CAS (cam angle sensor, next to coil pack) - can cause misfire if not reading properly, if the coil packs are working correctly after doing the test above then this could be a cause. The CAS takes a reading from 1&4 and 2&3 separately so if one bank of cylinders isn’t firing correctly then it could be this, read Drumtochty’s note on this forum: https://www.mx5oc.co.uk/forum/yaf_postst114571_Mk1-Non-start-1-6-baffled.aspx 

ECU - This is located in the passenger footwell, check that this isn’t sitting in water or damp, this is could also be another cause of misfire

Earth straps - the main one from the engine on a 1.8 is on the passenger side, check this isn’t corroded, an easy replacement anyway especially as the car is over 20 years old. There are also other earths running from parts of the ignition to the engine, I can help find these if anyone needs a hand

HT leads - swap with replacements each one, pull out and test if cylinder stops firing 

Spark plugs - check gap, if more than 1.3mm then replace, can cause the coil pack to fail as creating extra resistance 

If anyone needs a hand I’m happy to share more of my own experience to help figure it out

12

Pleased to hear it is sorted James.

Coilpack issues do not produce an error code on the MK1 diagnostics and would usually be an issue with cylinders 1 & 4 or 2 & 3. Very unlikely to have a failure on both coil units at the same time and have a car that runs. A 1995 UK spec MK1 likely to have the readily available and cheap three pin(low tension) coilpack as opposed to the earlier 4 pin coilpack fitted to pre factory immobiliser MK1 and Eunos(pre 1995) cars 

MK1/Eunos 1.6 and 1.8 CAS control cam pulse and crank pulse.There is a single sensor for each so a failure will cause a non start.         

13

Not in all cases, they can be a real pain and work intermittently I have found.

14

The sensors are micro electronics so I would not expect, nor have encountered an intermittent fault with these. In theory they either work or they don’t.

Does not mean it’s not possible and in that respect I would appreciate it if anyone with a CAS with intermittent fault send the unit to me at my expense for testing. I will test the unit on the bench and on my car(1.6) and send back to you. Drum if you have one of these hanging around let me know.