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940 orange spark at coil, no spark at plug

J

JPeters

New member
Joined
May 6, 2011
Hi all,

I have an issue here in Holland with my 1998 940 B230FK: there is no spark at the plugs. When I hold the king HT lead to ground, there is a spark, but it is yellow/orange. When I connect the king HT lead to a spark plug and hold it to ground, there is a spark at the plug (but also orange, not blue).
When I connect the king HT lead to the distributor cap, refit the plug to the correct HT lead and hold it to ground, there is no spark at all.

I already found out that one of the connections from the king HT lead is faulty (the tiny spring which connects it firmly to the distributor cap is missing), that may cause the absence of a spark at the plug. I will get a new one tomorrow morning, along with a new power stage, just to be sure. I alreay changed the coil, distributor cap, rotor and rpm sensor. All without effect.

The orange spark directly from the coil worries me a bit. Isn't that a sign that the spark is too weak? And that even with a new king HT lead, there will still be no spark at the plugs?

I've already tested the following:
1) +12V on pins 1 and 15 from the coil, when ignition is on
2) pulse on the red/white lead from the coil, when starting (tested with a probe light)
3) I get 0.3 VAC between the red/white lead and ground when starting (tested with multimeter)
4) Resistance primary and secondary coil is all within specs

Specifically at the power stage:
1) Pin 1 and ground: 12 V with ignition 'on'
2) Pin 4 and ground: 12 V with ignition 'on'
3) Pins 1 and 4: resistance matches primary coil resistance
4) Pin2 and ground: resistance 0 Ohm
5) Pin 5 and ground: 2 VDC (pulse) at ignition 'start'

EZK doesn't have any fault codes (1-1-1).

Any thoughts here? What is going wrong in this car?
 
Some questions:

1. How old is the distributor cap & rotor?
2. How old are the ignition wires?
3. How old is the power stage? (presuming you have BOSCH, not a REGINA system although both have a power stage)

Many times these "weak spark" issues are resolved with a solid stage zero of ignition. If you change the BOSCH power stage, be sure to use the conductive paste so the heat sink works properly..... those transistors get bloody hot!

Good luck.
 
Thanks!
De distributor cap is new. The rotor isn't, I will order a new one tomorrow. I changed it for a used one, without result.
The ignition wires are probably 5 years old. The power stage could be the original one; in the 10 years I'm driving this car, I have never replaced it.

In addition: the injectors are working (I can smell the fuel) and the fuel pump is working.
 
I have a spare Jetronic Bosch 0 280 000 954 (other number is 6 842 448).
Will this ECU work on this car?
 
Make sure the 12v to pin 15 on the coil will brightly light a light bulb. Then you know it's providing enough current. Next I'd put the test light on pin 1 and crank the car and see how brightly it switches. It should flash very quickly on cranking. Bad power stage or engine speed sensor?
Edit: If the rotor is old. Get out your meter and measure the resistance from the center contact to the tip. If I recall correctly it's about 50k ohms. Is there oil inside the distributor cap?
 
Ok, I have replaced the rotor, king HT lead and powerstage but it still won't run.
There's a weak, orange spark directly from the coil but that's it. I have also changed the CPS but that didn't help either.

Any suggestions? What's next? Try another EZK and ECU? I have a 954 for spare (the car has a 984 now).
 
RSR radio suppression relay good?

Doing just a voltage measurement, or just a resistance measurement, is a good start but it doesn't measure the circuit under load. If you have a standard (incandescent) test light, try using it instead since it provides a small load during testing.

With Key On Engine Off (KOEO), start by measuring battery post to battery post and notice how bright the light is. Next, measure battery - (ground) to +12v on the coil -- should be just as bright. Do the same thing for the +12v pin on the power stage. Switch to the battery + post and measure to the ground pin on the power stage. All should be full brightness.
 
Grounds good on the intake manifold? One is for the EZK and the other is for the fuel ECU. They are the two held down with the fuel rail bolts.
 
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