2g Weak spark?

[Raybert]

Hi guys,

I live in Estonia(Europe)
Car is 2g 98 Talon tsi with CAS!
I can't figure out a problem that i have. I was running on highway about 80-100mph and lost a power.
I had some problems with power for about 2 weeks allready, it was shaking a little bit around 3k rpm, and saw some knock with Evoscan under boost.
But now I was running and lost a power, so I stoped the car struggles when Idling like Subaru.
So I pulled the spark cables on working engine and figured out that 2,3 cylinders doesn't work properly. all 4 have spark and all 4 injectors are firing.
The problem is that if I pull cylinder 2 spark cable out nothing changes and if I pull also 3 I hear slight difference in idle rpms and engine work. But if I pull firstly no 3 spark cable out then also nothing changes and if I pull 2 also then also I hear slight difference in engine work and idle rpms.
So the first notice is if it's a bad Coil for 2 and 3 cylinder? as if i pull both(2 and 3) of them out then only engine work changes but if one of them (2 or 3) nothing changes. It says only one thing for me that the spark is weak because of the coil.
I ohmed and it shows 15,3 both 1,4 and 2,3. Haven't checked the primary...

P.S. Checked the cables, I cleaned and measured voltages on CAS, CPS, switched Spark plugs bpr7es(2 days old only), switched spark cables(NGK 1 month old), Switched Injectors(rc750), measured injector clip voltage to be sure they have a signal - they all have.

Is it a bad coil(2,3) ?
btw, the compression is good and it doesn't show any codes. only if I mess with plug wires it showed me P0300 multiply missfire and P0302 missfire cylinder 2 but It's related to swaping plugs on working engine.

 

[Rsawd95dsm]

Have you checked the PTU? (power transistor unit)

 

[Raybert]

I haven't done it. But will do it in 10 hours.
I'll write here about PTU as soon as i'll check it.
But how PTU affect spark strength? Isn't it more like a transistor which stabilize and separates signals?

 

[luv2rallye]

Yes but the PTU should be bolted to it's bracket and the bracket bolted to the intake manifold so that the metal back of the PTU conducts most of the large ground current through the manifold to get better conductivity [and not just rely on it's small ground wire (pin 3)]. This also helps PTU heat sinking. Also having the coil in it's bracket bolted to the intake manifold helps better return magnetic flux flow for spark.

 

[Raybert]

Yep, it makes sense that it conducts through manifold to chassis ground. Also that Coil is grounded through manifold aswell.
I couldn't check the PTU as I don't have bulb by my hand and don't have analog meter, I only have multimeter.
I will open the bolts and clean the grounds of PTU and Coils, see if that works......hmmm but it's not right, because in this case it should affect the 1,4 cylilnders aswell.

P.S. the spark plugs were dry but they were totaly black. it means that they are geting a lot of fuel but they don't have strength to burn the fuel.
It tells me that resistor pack is in good condition. Also can not be CAS or CPS, because they are working, looks to be in good condition, I have spark and fuel injections on all cylinders. Also they can't fire at wrong time, becuase they get signal from cps and cas in time, but i haven't checked spark time per cylinder with strobe, but I also think it's not a problem according to symptoms, having a spark and black colored sparks.
It leads now only to PTU or Coil pack.
I will check Coil Pack grounding to coil bracket, if there is a problem. If it's a problem I hope that Coil isn't broken now because of that.

 

[luv2rallye]

Yes, check all ignition connections and electrical contact surfaces to be clean and tight. Also battery negative cable to starter mounting bolt (and separate battery negative cable to body) to be clean and tight. There should also be a wire braid from intake manifold to firewall. Can you swap the PTU and/or coil with a known good one? Perhaps one is weak - most likely the 2,3 coil. Also measure coil primaries - should be 0.70-0.86 ohm cold although they tend to increase with temperature (mine goes to 1.4 ohm hot and still runs ok although I wouldn't want any higher). Higher resistance means less current flow in primary which results in less voltage at secondary (to fire spark plugs). A weak PTU can result in less and slower rise/fall times which makes less primary current (and so less spark).
Your primary suspect I'd say however is the 2,3 coil. You might also try reversing 1,4 coil with 2,3 to see effect when pulling spark cables.

 

[Raybert]

Yes, check all ignition connections and electrical contact surfaces to be clean and tight. Also battery negative cable to starter mounting bolt (and separate battery negative cable to body) to be clean and tight. There should also be a wire braid from intake manifold to firewall. Can you swap the PTU and/or coil with a known good one? Perhaps one is weak - most likely the 2,3 coil. Also measure coil primaries - should be 0.70-0.86 ohm cold although they tend to increase with temperature (mine goes to 1.4 ohm hot and still runs ok although I wouldn't want any higher). Higher resistance means less current flow in primary which results in less voltage at secondary (to fire spark plugs). A weak PTU can result in less and slower rise/fall times which makes less primary current (and so less spark).
Your primary suspect I'd say however is the 2,3 coil. You might also try reversing 1,4 coil with 2,3 to see effect when pulling spark cables.

checked the primary both 1,3 ohms cold. secondary 15,3 both.
I can't reverse them at the moment, but will do it in 2 days.
I having a big problem. I'm 2400km from home in Germany, it's about 1500miles. I will recieve PTU, Coilpack and resistor pack on tuesday or wednesday from my other 2g talon and then I can try them.

 

[Raybert]

Finaly found the problem. HG between 2,3 cylinders were blown.
but now is a new problem...I drove 200 miles with broken hg to friend garage and now i've got the result after changing HG...no compression in cylinder 3 and low in cylinder 2... yeeeiiii, full engine rebuilt AGAIN pistonrings and valves and check all the other things.(I did same thing it in October 2013).