No spark cylinder 3

[mquinn]

1999 Altezza BEAMS

No spark at cylinder 3 

No engine management light on the dash

Swapped coil packs from different cylinders and still no spark, changed all four spark plugs still no spark 

Pin 1 is getting a 12v feed, pin 2 getting 5v feed as should be, pin 4 earth all ok and pin 3 signal wire is reading the same as the rest of the signal wires on the other coil packs. The signal wire was joined previously by someone else near the ecu. No other breaks in the wire, but when you earth the spark plug there is still no spark visible even though all pins are reading as they should. 

Compression tested all cylinders - all are ok. 

all injectors tested including the plugs and all is ok there. 

Any suggestions apart from an ecu fault? 

Thanks

 

[Paul Brooksbank]

Maybe the join in the signal wire is only allowing a small amount of the intended current through? In once repaired an electric fence generator for a farmer after he'd fitted a wire of too thin a gauge to it. 

[mquinn]

The join just seems to have a lot of solder on it, where someone has joined the break in the original factory signal wire. Forgot to mention in the post I tried a jumper wire from the signal pin in the ecu to the signal pin in the coil pac plug and it didn’t make a difference 

[Britprius]

Are you checking the voltages with or without the coil pack connected? It must be done with the coil connected other wise the readings are meaningless. Ideally the signal wire should be checked with an oscilloscope.

John.  

[mquinn]

With the coil pack connected. Yeah I know I just can’t get my hands on an oscilloscope. 
 

[steve2006]

It could well be the ECU, it is known that a faulty coil pack left unattended can damage the semiconductors driving the coils because of back EMF. Problem is finding a known good ECU for that model.

[ColinBarber]

Heard of ECUs being damaged on other makes but not really on Toyotas. Certainly EMF shouldn't be a problem as that would be contained within the ignitor unit within the coil pack. But certainly the ECU could be faulty - whether it was caused by the coil pack or not.

Have you measured the resistance on the wires back to the ECU to make sure you don't have a high resistance on the repair or elsewhere?

The fact that the wire was already tampered with is a worry - has it ever been working since you have owned it?

[mquinn]

Yeah it was running fine when I bought it and then I hadn’t drove it from before Christmas, had it out one day at the start of the month and this happened. 
 

ive measured the resistance for the signal wire pins on the ecu back to the ecu earth and the pin for cylinder 3 was showing a higher resistance than the other 3 pins, so it has to be the ecu. Guy round here repairs them, so hopefully that will do the trick 

[mquinn]

Hi folks quick update,

 

so I got a new second hand ecu that cured the problem for about an hour then she started running on 3 cylinders again turns out the wire into one of the ecu plugs needed changed so fixed that and she ran fine all evening no misfires at all. 
 

Later on tonight she started running really lumpy, got a while strong smell of petrol then a melting rubber smell. Looked under the cover and the coil pack for cylinder 3 is completely melted. Anyone have any ideas or come across a similar problem before? 

[ColinBarber]

Fuel smell in the engine bay or exhaust? If engine bay then it may be that the plug isn't sealing against the head - you have hot gas getting passed, damaged the coil pack which stopped sparking and now the gas getting passed has fuel vapour in it too.

 

[mquinn]

This happened while driving so we could smell petrol inside the car for a few seconds first then the burning rubber smell.

Ive attaches pictures of the coil pack.

[steve2006]

Are you buying new coil packs? The one you show appears to have suffered from HV tracking.

[mquinn]

Well this happened to the coil packs that were already in it when I bought it, after I put in the new ecu to cure the no sparking. 
 

do you reckon it was just a fault in the coil pack itself? There’s no obvious wires touching or shorts when I test the wires 

1 hour ago, steve2006 said:

Are you buying new coil packs? The one you show appears to have suffered from HV tracking.

[steve2006]

Yes, it looks like the high voltage bit has broken down on the insulation due to arcing which wrecked the coil pack.

[ColinBarber]

Possibly the wrong ones or not OEM quality.

[mquinn]

They are the oem Denso 90919 02236 ones but I don’t know how long they have been in the car. I’ll change them and Keep an eye on them.