Car came in with engine misfire, which only occurs from cold and last a few seconds, but if the engine is accelerated during the misfire, it clears and does not return. I've tried previously to upload PS data files but they are too big, hence I need to know how to cut sections of the recording for uploading.

Tests I've done...

A fault code read initially did not record any P codes only recording network codes. I exchanged the vehicle battery because another garage put a lead acid battery on. Since putting a silver calcium battery on the network codes have never returned.

When the engine misfired after this battery change fault codes PO303-00 cylinder 3 misfire detected, P2303-14 ignition coil primary "B" control circuit low, and P2300-14 ignition coil "A" control circuit low was recorded.

I started by completing the following tests...

Engine relative compression, all along the waveform the maximum peaks of current demand are all even.

Engine cranking compression tests using the WPS 500x. All compressions are approximately the same. A running compression test using the WPS does not show any obvious faults.

A crankcase test using the WPS500x does not show an increase in negative pressure at idle, nor does the crankcase pressure increase above atmospheric when the engine is accelerated.

Inlet manifold depression per cylinder records approximately 22" vacuum.

I could not see anything obvious, moving on...

I used the Power Probe to measure the resistance of the electrical wiring regarding the ignition circuits, and using the HOT SHOT function the wiring was loaded and passed. I tested the wiring several times and found no obvious faults.

I sent the ECU in for testing and after a week received a phone call saying thye tested the ECU, which recorded 1 ohm and nothing was wrong! I didn't go into it with them but a resistance test is not a load test and my confidence in the ECU being okay is sketchy?

Using the scope I tested the ignition coils power supply underload, which drops to about 30 mV. I've used two amps clamps on the ignition primary circuits and never once seen both circuits provide even current demands. On the latest recordings I can see current demands of 6A and 4A, also when the power transistor switches off in the ECU, and the current demand is switched off, the current goes negative as low as minus 7A. I'm not convinced that is correct and could be showing a poor power transistor operation, which can't be tested using an ohms test alone.

When the engine has misfired and I've managed to capture it on the scope, I've seen the ignition circuit secondary voltage significantly reduced, which has caused me to keep focused on the ignition system operation.

The injectors operation by comparisons allo look the same, but at some point I did remove the injectors and carryout a flow test. I was not convinced I liked what I was seeing! When the car drives there is no noticeable power loss, but the fuel spray didn't look brilliant? In fact the only test not performed is the fuel pressure, but because of the ignition voltage failing I didn't think the injector circuit would have an effect on that!

The other question I asked myself was, why if the injector circuits have a problem should the ECU record fault codes for the ignition and not the injection system?

I've reached the point that the only test left to complete is the fuel pressure test, and if that records okay, I'm not sure then which direction to go?

I found a Snap On write up on the internet with a very similar problem to mine, and their conclusion was the ECU, which fixed it when the exchanged it. A colleague of mine advised he'd had the same problem with the same company testing the ECUs and after several attempts at testing the ECU on his behalf and finding no faults, he purchased another ECU, which he then said fixed his problem.

I'm at a cross roads and not sure which direction to head off in now?

Anyone else had this problem with these Fiestas!!

Thanks for reading.

Hi.
.
To begin with, you need to close the issues with current consumption by coils and injectors.
The easiest way to do this is by comparing the current consumed.
To do this, you need to check the signals of consumption current on the common power wire of the coils and on the common power wire of the injectors.
This can be done either on the appropriate fuse, or on the wire in the motor harness.
When the question is closed, you will return to compression in cylinders.
Since this is what can cause such a defect.
.
There are many examples from practice when a malfunction in compression causes a similar defect.
On the "Blue" FORSCAN forum, it was described on such an engine SPJC 1.4 that there was the same defect.
It is necessary to carefully measure the compression in the state of a cold engine in both modes - "dry" and "wet".
After the "wet" compression test, when the additional oil remains in the chamber, start the engine again on a cold one and check whether there is a defect in the oil-sealed cylinders.

Thank you for your reply and advice.

I've devised a test plan to check the electrics, coils and injection circuits based on your advice and wiring diagram. Looking at the wiring diagram I'm thinking the current demand for the coils and injectors should be around 8 - 10A each circuit. I'm clearly not getting that from the ignition system where I've seen one primary circuit as low as 4.5A, and the other primary circuit was drawing up to 7A.

Questions always remain...

1/ After testing the electics for this intermittent misfire, which is dominently cylinder 3 only when cold for a few seconds. If the misfire does not occur during cold testing because some days the engine is okay and others its not, then such questions now spring to mind...

A/ Why has the engine got fault codes for primary ignition failure if the defect is caused by mechanical issues?

B/ What component in a cylinder can cause intermittent compression problems when the engine is cold some mornings and other mornings the engine starts and runs okay for days on end.

Thank you for reading.

B/ What component in a cylinder can cause intermittent compression problems when the engine is cold some mornings and other mornings the engine starts and runs okay for days on end.

Maybe take a look for coolant in the cylinder in the morning - that would fit your symptoms. - Inc shorting out the plug.

picowight wrote: ↑Sun Oct 01, 2023 10:05 pm

B/ What component in a cylinder can cause intermittent compression problems when the engine is cold some mornings and other mornings the engine starts and runs okay for days on end.

Maybe take a look for coolant in the cylinder in the morning - that would fit your symptoms. - Inc shorting out the plug.

Thanks. I was told by the engineering shop that these cylinder head gaskets don't leak?

I was also told by the same people that the compression rings would cause a misfire? I was also told that a Boredon gauge compression tester was much better than the WPS500x transducer? These blokes are probably in their middle thirties and either taking the micky or genuinely don't have the professional training and understanding of more advanced equipment now available.

I've been around a long time and in my experience I've never seen anything made that was designed not to make money. No matter what or who made it, it will deteriorate and fail at some point. In my day long before Pico was formed as a company I grew up like many using the boredon compression gauge, which was good in its day. I agree the WPS is an advanced piece of equipment and thinking has moved on as technology has changed along the way.

Based on the professional write up five years ago about the manufacturer of the head gasket and the technical design, which came across very convincing, I didn't want to believe that the head gasket was the cause, and to further kick my legs from underneath me, I could not get my head round why the PCM was recording fault codes, specifically P2303 and P2300, which both refer to primary ignition control circuits being low.

Using the current clamps on each primary ignition control circuit, one circuit was always recording a few amps less than the other circuit, which backed up the fault codes above.

I had the ECU tested and they advised nothing was wrong with it, but covered themselves by saying they had another ECU with a two year warranty if I wanted that one! When I got the ECU back a further test with the amps clamps recorded negative current draw as low as minus 7A! I was sure something like a power transistor was lazy in the ECU, but how would I prove it? The people who supposedly tested the ECU advised me that the ECU tested okay recording a result of 1 Ohm?

What did they test it with?

After this I decided to put the boroscope back into cylinder 3 and look again, only this time I decided to pressurise the cooling system. Now this time with some patience I could see the coolant dripping into the cylinder from the head gasket sealing ring area. After cylinder head removal I could see where the burning effect had taken place between the cylinders 2 + 3. I've seen this many times in my lifetime, the burning effect is across the cylinder head between the cylinders, i.e. on top of the cylinder head gasket, and not underneath across the bores 2 + 3. The engineering shop advise that the head gasket leaking is not the head gasket but primarily the cylinder block face? I don't know yet, the design is what we call "Open deck", which means it is possible to look down and around each cylinder bore liner. This design of cylinder block was introduced to people like me way back in the early 1980s at college, but until years and years later we've always worked with the design "Closed deck", which is were you can't see down the outside of the liners because they are a press fit into the block. Much time has moved on and about five years ago when I dismantled this engine even I got confused initially and thought this engine had "wet liners" fitted!

I just to check the cylinder block face now for striaghtness and see if I can experience damage or a dip etc anywhere between the cylinders!

I'll see what tomorrow brings...

I should bring this thread to a conclusion and close it now.

1 / The engine was rebuilt five years ago. I was not convinced that the cylinder head gasket was leaking, because initially I did not see the coolant level reducing during driving cycles of the car, i.e. around 100 miles use.

2/ When the car was delivered with the misfire, after inspection of the spark plugs I knew cylinder 3 was the root cause, the spark plug told me that.

3/ I serviced the engine straight away the car was delivered, and I changed the ignition coils during the service while chaning the plugs and leads.

4/ During investigations I knew from the outset that cylinder 3 was misfiring, and still misfiring after the service. I struggled to identify the cause until I used the scope internally in cylinder 3 to see the coolant dripping in, ever so slightly.

5/After the engine rebuild the engine still had a misfire, but now the misfire was on cylinder 2. Now prior to this Steve Smith examined the scope traces and advised he thought cylinder 2 had a misfire. Steve being much more experienced that I could see that probably on the crank waveform, but I was very much focused on cylinder 3 having seen the condition of the spark plug. The scanner picked up cylinder 2 misfiring when the engine was accelerated, but only after noticing this going to work the following morning as the engine seriously intermittently misfired again.

6/ Now I was seriously wondering where to turn with this problem, the engine had been rebuilt, all ignition components had been changed, no fault codes were being logged and cylinder 2 misfire was detected when accelerated only.

I was in a local transmission centre the following day when I was advised to ring a guy in Warrington. Turns out that he's come across the problem many times and when I advised him of my problem, he said, without hessitation, and without me telling him I'd changed them, take the NGK coils off that you have fitted and put Bosch on and the engine will be right.

I put the Ford OEM coils back on and the engine runs perfect again now.

I thought NGK were OEM quality, but he said no they are now made in Ch*n8