Friday, June 10, 2011

saab 900 coil pack,ignition switch and ecm testing for no spark?

To test Coil pack:

Unplug the ignition coils' 4-pin connector and use a voltmeter to take readings across pins 4 and 1, 4 and 2, and 4 and 3 With the ignition switch in the ON position, the voltmeter should show about 12 V.

If the readings are OK, check the resistance of the primary circuit in the ignition coils by taking a reading across pins 4 and 1, 4 and 2, and 4 and 3. The correct resistance is about 1 ohm.

Now check the secondary windings by measuring the resistance across the High Tension lead outlets for spark plugs 1+4, 2+5 and 3+6. The correct resistance is about 12,000 ohms. If the resistance is not OK, change the ignition coil.

Also check that the ground connection is good, if in doubt, simple add another good ground wire directly from the battery to the ignition coil mounting bracket.


1,2,and3 come from the engine control module and 4 comes from fuse 17.


I do believe that you may be experiencing the effects of a bad ignition switch electrical contact, one of the most common failures on these Saabs. If you're not getting the correct voltage then I think you may need to troubleshoot the power distribution circuits first.


With your voltmeter and the ignition key in the on position, take the negative probe of your voltmeter and attach it to the negative battery post or another good body ground. Use the other probe of the voltmeter and take voltage readings at the top of all the fuses in BOTH fuse panels, the one in the hood, and the one inside the vehicle. At the top of each fuse there is a little bit of the electrical contact that is exposed through the plastic. Probe each and every fuse and measure the voltage on each fuse link. They should all read the same voltage, if not, say a group of them read +5VDC instead of +12VDC then that could indicate a bad ignition switch contact. If all checks out, then move on to checking grounds to the ECM.


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Coil harness unplugged:
pin 4+1 2.3v
4+2 1.4v
4+3 2.8v


pin 4 to ground:
12.6v

Harness plugged in:
4+1 12.6
4+2 12.6
4+3 12.6

measuring primary windings
4+1 0.7 ohm
4+2 0.6 ohm
4+3 0.6 ohm

secondary windings
5+2 11.3 Kohm
3+6 11.0 Kohm
1+4 11.0 Kohm

Grounding bracket on rear of engine, (coil bracket)
ground :
G7P Good
G7L Good
G7s Good

All Fuses should read over 12V

Pins 1, 20, and 21 read 12V+ on the Control Module Connecter ONLY when the 4 pin connector is plugged into the coil (I'm assuming it's back feeding from pin 4 on the 4 pin connector on the coil).
pin 14 ground is good.
pins 27 and 37 power should be 12 volt.

The wiring diagram chart for 1995 to 1997 model:-----

see below:--














This are readings to be tested.
Also there is one method to test coil and plugs.Its old method.
Connect a plug to one of the secondary cables,( or you can do all at one time... lay it on something metallic, or use a ground wire; and with all the plugs out, turn over the engine as if to start..You should see spark, if there is any, particularly at night...If you hear or see nothing, then, either the coil is not receiving current or the coil is shot.


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From the chart check supply voltages:

1. PIN 27 to 14, should be: Battery voltage +12VDC




2. PIN 46 to 14
With the Key ON, Engine OFF, should be: GROUND



With the Key OFF, Engine OFF, should be: Battery voltage +12VDC
*** If there is a problem here, you'll have to investigate the Main Relay and its circuit ***


3. PIN 37 to 14, should be: Battery voltage +12VDC

4. PIN 18 to 14, should be: Battery voltage +12VDC


Grounds:

5. PIN 2 to 14, should be: less than 0.1 volts and check resistance on circuit
6. PIN 14 to (-) BATTERY POST, should be: less than 0.1 volts and check resistance on circuit
7. PIN 24 to 14, should be: less than 0.1 volts and check resistance on circuit

The ECM doesn't get full operating power unless the main relay is working properly, did you check it for proper operation. Just tap the top of it, maybe its sticking.

Fuses 16B, 17, and 28 supply power to the ECM, as well as MAXI fuse #2.

If all still checks out, I'd start to trace each individual wire of importance and check the resistance/continuity on that line: PIN 1, 20, 21 were of concern, check between the ignition connector and the ECM connector, maybe the wiring is shorted somewhere along the line.

After all this is checked, if nothing still works, i'd strongly suspect the ECM is bad.


the main relay location.
Left side of dash, there is a cluster of relays there on a plate that pivot.





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