Anyway

Seriously we have done a head gasket replacement on this Ka. It was a runner when it came in but now it just cranks until it attempts to fire, at which point it stops cranking. I think the starter is ECU controlled & this is why it stops cranking when the PCM assumes it has fired up.

Anyway tests done thus far.....

Scan revealed no DTC's
Good CMP CKP captures taken (no good reference to compare against unfortunately)
Fuel pressure good.
Valve timing checked & rechecked
Injector rail removed & sequential injection confirmed. (hopefully confirming correct cam/crank relationship)
Compressions not tested, but it sounds right & no cause to doubt it.
Weak spark observed on all plugs.
New coil pack, HT lead & plug tried (in stock & quick to prove a point)
Ignition primary on both coils scoped & the following capture taken...........

It seems pretty obvious to me that there is an ignition issue with this, but I can’t explain what I am seeing in the capture. There is a second grounding of the primary circuit very shortly after the main firing event.

Any input guy's. Dont be shy!

Cheers all

Dave (Hill)

I found this image in the archives.......

Hard to be sure from the detail in that image, but it looks similar to what I have got.

HMmmm

Back to the drawing board!

Cheers

Dave (Hill)

EDIS ICMs respond to the rising SAPW signal generated by the PCM and fire the coil. Many PCMs incorporate software that can fire the spark plugs multiple times at idle and low rpms. This feature is commonly known as repetitive spark. If the rpm is low enough, there is sufficient time to charge the coil and fire the sparkplugs two or even three times. This repetitive spark software in the PCM can be calibrated on or off, and can be calibrated to work below a specified rpm, therefore, each vehicle application may be different. In general, most vehicle applications use this feature, fire the plugs a maximum of three times and restrict operation to 1800 rpm or less. This feature was first introduced on the 1990 Escort.

David (Davies)

Thanks for that snippet of info, very interesting! A nice fella called Tim Bowkett suggested last night that this "dual trigger" capture was infact normal. I didn't know it was such a widely used technology though.

Anyway armed with the understanding that the capture I had made was not actually a problem, I decided to retrace my earlier diagnostic steps. As suggested also by Tim, I took the opinion that the coil energy was being discharged straight to ground. It appears that I may have been a bit a little hurried in my decision that the spark I saw when I tried a new coil, lead & plug was weak. So I tried a new set of plugs in it today.

How deeply embarrassing! It started straight up, nice & clean on all four. My excuse is that I was thrown off course by the unusual capture. Sorry to waste your time folks. & well done Derek!

It is strange that it was a runner when it came in to us. I am wondering if the plugs were contaminated when the machine shop skimmed the head. Maybe the machining fluid had left a conductive residue on the plugs? Any thoughts?

Here is the way it looked when running……….

Here is a known good crank/Cam reference signal.........

Same again but a little closer..........

Hopefully others have learned a little too.

Cheers all

Dave (Hill)

Thanks mate! We would usually present a head for repairs with common sense measures taken. These Duratec heads have all the important workings tucked well away. Having said that, I would normally replace the spark plugs on a job like this, but the customer pleaded poverty, as he has recently had a service & a clutch fitted. Also his cam shaft was well past its best & he asked us to re fit it!

As is often the case, trying to do the customer a favour & save em a couple of quid, has caused me to spend time chasing a fault. At least it revealed some new info hey! (to me at least)

Cheers

Dave (Hill)

Tony

Refitting the original plugs is one thing, but to reassemble it without a thorough cleaning would be tantamount to negligence.

I may have cut a small corner in re-using his old plugs, granted! But all components are cleaned in a standard parts washer & then pressure washed, followed shortly by a thorough drying.

I am guessing that the plugs may have been coated with something that was not water-soluble during the skim process.

Dave (Hill)

Conductivity is a strange thing. I remember my old foreman telling tales of tricks played on mechanics, like drawing a pencil mark down the side of a rotor arm. It's nearly invisible but enough to give the HT an easier route to ground.

An interesting experiment I use to demonstrate these subtle properties is to wire up a workshop lead lamp (12 volt) & with the feed wire cut & wires exposed & dipped into a glass of tap water (so that the fluid is the only elecrical path). The lamp fails to illuminate. Just one teaspoon of salt added is enough to alter the conductivity of the water enough to pass sufficient current to light the bulb.

What’s the relevance I hear you cry (NOT)……… All that moisture, that is often thrown up during winter months has a generous quantity of salt suspended within it. Once settled upon the various electrical systems, it can expose weaknesses that otherwise would go unnoticed.

slightly off topic, but hey hoe!

Cheers all

Dave (Hill)

Sorry, I've only just read your post today otherwise I would have responded sooner.

Having in a previous job spent a lot of time analysing Ford secondary ignition waveforms I was going to say that I thought the traces showed a shorting problem, so given that you had replaced coil and leads would only point to a plug issue.

Also as mentioned already you are seeing the Ford multi-strike / repetitive spark system in action. I have in the past seen the EDIS module create upto 4 spark events on each cylinder, albeit in lab conditions.

Cheers

Sean