Ok, so I am troubleshooting not having spark on my 1993 850 (97 engine in it) and when I tested the cam sensor (i have two and tested both), I received the following:

Ground (3) - 0 ohms
Power (1) - approx batt voltage (slightly less) on ignition position
Control (2) - between 0 and .5 volts on cranking


I am worried about the control signal because the manual says "varies between 0-5" volts. Does that mean anywhere in that range is fine? or do I need to hit 5 volts for it to be signalling right?

 

your volt meter probably can't read 5V on a short pulse, you'd need an osccilloscope

 

The control signal should alternate between 0v and 5v; what are you using to measure it (analog or digital meter)? I would think camshaft is turning slowly enough for you to see the response on your meter. Either sensor is bad or you got something pulling the signal down..

 

600 rpm idle is 10 engine revolutions per second, or 5 camshaft turns. most digital meters I've seen take a couple seconds to settle.

 

its a digital multimeter... not good enough to get it? so what can i do?

 

I haven't actually tried this on my car but below is from volvo manual; CMP refers to camshaft sensor. Step 5 refers to the test we're talking about and they specifically refer to a voltmeter; not a scope. I agree, a scope would be nice to have but most folks don't have access to one.

If your meter is reacting too slowly, i suppose you could remove the sensor from the engine and rotate it by hand...

================================================== =======
IGNITION CHECKS
BOSCH EZ129K
1) Disconnect coil wire from distributor cap. Put coil wire
next to ground and operate starter motor. If spark is present, check
distributor rotor and cap. If spark is not present, go to next step.
2) Connect voltmeter between ignition coil connector terminal
No. 15 (Red wire) and ground. Turn ignition on. If battery voltage is
not present, check voltage supply to ignition coil. If battery voltage
is present, turn ignition off and go to next step.
3) Connect voltmeter between ignition coil terminal No. 1
(Blue wire) and ground. Operate starter motor. If about .7-1.3 volts
are present, repeat test using new ignition coil. If about .7-1.3
volts are not present, turn ignition off and go to next step.
4) Disconnect engine speed sensor connector located close to
flywheel. Connect an ohmmeter between sensor terminals. If resistance
is about 200-400 ohms, go to next step and check Camshaft Position
Sensor (CMP) signal. If resistance is not about 200-400 ohms, replace
sensor.
NOTE: Engine speed sensor is also known as Vehicle Speed Sensor
(VSS) or impulse sensor.
5) Remove intake hose. Bend aside rubber sleeve on CMP
connector. Connect voltmeter between connector terminal No. 2 and
ground. See Fig. 4. Operate starter motor. If voltage reading varies
between 0-5 volts, go to step 7). If voltage reading does not vary
between 0-5 volts, go to next step.
6) Connect voltmeter between CMP connector terminal No. 3 and
ground. Turn ignition on. About 10 volts should be present. Turn
ignition off. Connect an ohmmeter between CMP connector terminal No. 1
and ground. Ohmmeter should show about zero ohms. If voltage supply
and ground are okay, repeat test using new CMP. If voltage supply and
ground are not okay, reconnect intake hose and go to step 9).
7) If voltage reading varied between 0-5 volts in step 5),
disconnect power stage connector at ignition coil. Bend back rubber
sleeve on connector. Check ground supply by connecting ohmmeter
between connector terminal No. 1 and ground. See Fig. 5. Ohmmeter
should indicate zero ohms. Check voltage supply by connecting
voltmeter between terminal No. 3 and ground. Turn ignition on. Battery
voltage should be present.
8) Check power stage control signal by connecting voltmeter
between terminal No. 4 and ground. Operate starter motor. Voltmeter
should indicate .7-1.3 volts. If ground, voltage and control signal
are okay, repeat test using new power stage. If ground connection and
voltage are faulty, check wiring. If control signal is not present, go
to next step and check ECU input and output signals.

 

how would you rotate the sensor by hand?

 

any thoughts?

 

my thoughts are, if you saw ~0.5V when you were cranking it, its probably pulsing 0-5-0 (with a fairly narrow duty cycle) faster than your meter can read it, and its working fine, you need to move on to some other source of your problems.

 

ok... any ideas where to look next?

 

those pre-1996 have an OBD don't they, with a button and blinking LED? my 96 855T has OBD-II where you need a code reader. anyways, I'd look for diagnostic codes.

here's a block diagram of the ignition on a 93 850


if you got no spark, see if there's pulses to the ignition module under the coil. if there are, the problem is likely in the ignition module/coil assembly, if not, then its in the EZ ignition module or an input to it, and there should be some sort of diagnostic code. I duno, maybe you need a volvo scantool or something for a 93?

 

Where to look next would depend on where you've looked already. What made you think it was the cam sensor? Have you checked to see if you have spark out of the coil? Have you checked the coil for proper resistance on both primary and secondary?
You could also get a code reader (loaner from auto parts store) and see if the computer might have a stored trouble code to help in pointing to a problem. I know you need spark but do you have injector pulse? Can you smell gas when you're cranking? Are the plugs wet? Some of the sensors when bad stop both the coil and injectors from firing. I have to admit on my 850 I haven't really looked at the function of the cam and crank sensors to know exactly what the result of either going bad is.

 

94 850NA 175K Long story short, bad CRANKshaft sensor...no spark. If it was running fine and quit w/a no spark condition, Id go there next. My 2 c.

 

Where is this sensor? I want to check mine, may be the source of my problems

 

It's on the end of the exhaust camshaft next to the distributor, just below the motor mount that attaches to the firewall.

http://www.matthewsvolvosite.com/for...hp?f=1&t=24925

 

thanks frog