Jump to content

Engine Missfire


Recommended Posts

Eurgh. What an annoying day!

I developed an intermittent misfire on my Zetec blacktop early last week. Literally seemed to miss for a second whilst cruising.  Then fine for a minute or so, then a second of mis again.

Rather than mess on I replaced the coil pack, leads and plugs.  Difficult to tell if it resolved it but took the car for a drive and it seemed to be fine. Great. 

Driving along tonight at 60mph it starts missing and losing power, pull over and limp home.  Gradually it lost more and more power (but no change in note) then it finally gave up and is constantly missing - it sounded like a motor bike.  Had to get towed home :(

Where would you guys start? I am thinking compression test first, assuming that’s OK what next? Can I test the coil connector easily enough with a multimeter?

I hope not too much damage has been done :(

Edited by danielbrookes
Link to comment
Share on other sites

Thanks I’ll take a look. I hadn’t even considered the crank sensor I was concentrating on spark and/or fuel injectors.  Hopefully tomorrow I can reproduce the issue (it was idling rough as a dog and misfiring like mad earlier).  I am sure I cought the wiring when replacing the alternator bracket because I remember thinking I need to be careful. Fingers crossed it’s an easy fix.

Link to comment
Share on other sites

I had a year of misfire issues - I changed almost EVERYTHING; plugs, coil pack, crank sensor, HT leads, added fuel filters, replaced fuel lines - nada.

Finally found it - loose wire on the TPS sensor. Every time the loose wire disconnected for a few milliseconds, the ECU thought I was shutting off the throttle, so it cut the fuel to the injectors, hence the misfire (I'm guessing that what was happening). Since that, it's been fine for 2 months and 2000 miles round the Alps 😁 (touch wood etc)


If you've got an Emerald ECU (?), it has a very useful data logger which you can drive along with a laptop connected and it shows you various (configurable) parameters. One is throttle position, which is how I found my problem - when it misfired, instead of being a straight line, I had a jagged graph of peaks and troughs. Details here:



Edited by nelmo
Link to comment
Share on other sites

Thanks, I was logging at the time and one of the things I logged was TPS - unfortunately that looks fine, but will check again.

Started the car for first time after I got towed yesterday and same problem.  Looking at the positives that’s good, it’s constant.

Checked wiring to Crank sensor, seems fine 2v to red and negative is earthed correctly.  The actual sensor could be faulty - RPM reads consistsly.

Plugs 1+4 look perfect as you would expect for new plugs, after only 10 miles both 3+2 are full of soot.  I wonder if it’s one of the coil driver wires.



Edited by danielbrookes
Link to comment
Share on other sites

Hi, are they not sooty because of the misfiring? Induction is supercharger to GBS plenum.

From what I have read the firing order is 1-4 and 2-3.  The pins on the coil pack, I thought the centre was 12v and then either side is the driver for cylinders 1-4 and 2-3 (as per attached).  If that’s correct then surely only 1-4 and 2-3 can fire at the same time?

Hope my ramblings make sense.

PNG image.png

Link to comment
Share on other sites

Firing *order* is 1-3-4-2, coil packs usually have 2 banks and fire every other cylinder (so, given that firing order, one side of the coil will do 1+4 and the other will do 3+2 - this gives the coil the best time to 'recharge' between firings). Wasted spark means each plug will fire on both of the upstrokes (ie. the compression stroke, which is obviously the key one, but they also fire on the exhaust stroke too - this isn't intended to perform any useful function but obviously it does mean if you have unburnt fuel in there on the exhaust stroke, the spark could potentially still ignite/burn something - this is useful to remember when chasing popping/banging and so forth).

Link to comment
Share on other sites

Ahh OK that makes sense. With my symptoms then, would it still suggest there is an issue with the side of the coil that fires cylinder 2+3? Considering I have already changed the coil, leads and plug next step would be wiring?

If I were to unplug coil and crank engine over, would a multimeter show 12v on each pin as it “fires”?

Link to comment
Share on other sites

Well, fouled plugs could be a number of things (oil for example) unrelated to the coil/wiring but, if you feel that 2+3 could be an indicator, then a quick idea would be to swap the pins of the coil over so that the banks of the coil are swapped over - then, if the issue of fouled plugs moves to 1+4 you've discovered that it's something related to the coil or the trigger wiring to it.

I would look to the Emerald logging approach again, but log a shedload of stuff this time. It might take a couple of attempts logging different things, but intermittent is good because you can then spot if something changes between the "running good" and "running bad" sections of your drive. Things I would be on the look out for :

Battery : any massive change in voltage would be a good indicator of a problem
Engine speed : essential reference to the other values
Ign Advance : so we can see what the ignition advance is doing
Inj duration : so we can see what the fueling is doing
Inj timing : so we can check nothing weird is going on with injection timing
MAP if you're using it
Lambda O2 : will help us spot moments of lean/rich which might correlate against something else

If nothing appears on the logs, then it would suggest something more physical with in engine induction/wiring, something degrading with heat maybe, or a bad connection such as loose earth strap, some sensor intrinsic to the operation of the engine (crank, tps, MAF, MAP, water temp, air temp, etc)... or air leak/etc but I'm not a forced induction expert to be fair.

edit: You can save the log to a file (Data Logger -> Data -> Save to file) then share it with me and I can take a look-see if you want... better than a picture ;)

Edited by brumster
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...
Test Footer