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Trying to diagnose no start on1996 volvo 850:
1. Has 12V from coil to cap
2. No spark at plugs
3. Cam sensor has 12V, 5V, Ground…….all good per software specs
4. Crank sensor good per software specs
5. I suspect cam sensor is bad but software said……….replace to test and if car cranks old cam sensor is bad………thats crazy.
5. Anyone know a reliable test?
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Is the control module applying ground and removing ground to the coil to fire it? Test light hooked to it and to the positive terminal of battery will show you when cranking if it is flashing. If it flashes, then you should have ignition. Check for spark at the coil. A bad rotor or distributor could make you chase your tail needlessly. GM was obnoxiously bad for testing with known good part. Back in the mid 90’s, few shops had digital scopes to check sensor signals. Now most shops do and all shops should, but of those, only half of them know how to use scopes effectively. With one of them you could easily check sensor output. The vantage pro was actually an OE tool for Volvo as well. Also, you may need to look at the signal of the crank sensor as well.
When I remove coil wire from rotor cap it has spark………..tested by holding wire close to ground and I see spark.
[quote=”BubbaGarage” post=176761]When I remove coil wire from rotor cap it has spark………..tested by holding wire close to ground and I see spark.[/quote]
Then you either have a weak coil or a leak to ground inside the distributor or rotor, most likely
With test light hooked to postive on battery and to coil wire…………Light does not flash but neither does my Ford truck.
Not to the coil wire. Ok back to basics, you have a primary and secondary side of an ignition coil. Primary side is the battery voltage and control. Secondary is the side that emits a high voltage spark. On the primary side, you have a positive and negative wire. Positive wire has battery voltage fed to it, negative side connects to ground when it energizes the coil, and disconnects to emit a high voltage spark. You connect a test light between the positive terminal of the battery and the negative wire on the primary side of the ignition coil. Crank the engine and see if it flashes. It should if the ignition module or driver is working properly. Have you attached a noid light to test for injector pulse? If you have injector pulse, then your cam and crank sensors are probably ok. When you crank the engine and check for spark, is it a consistant pulsing spark, or is it only once, and when you stop cranking? How much gap are you putting between the coil wire and the cylinder head when checking spark? Should have no issue with a one inch gap, and probably even more. You may have a weak coil or ignition driver/module/igniter. If you do not have a labscope yet, then you absolutely need to acquire one, as a professional shop you owe it to your customers. For how much used vantage pro’s go for now, anyone can afford one. It even has the test procedures for a lot of stuff built in.
This car was delivered with them knowing I would fix as time allowed (short story version)
1. With test light on postive of batter and blue wire (negative of coil) it flashes like you said it should.
2. Fuel injector has pulse with noid light
3. Spark jump is not very strong in my opinion…..maybe 1/4 inch it jumps goodAbout to remove coil to test primary/secondary resistance
I would say your cmp and ckp sensors are fine. A quick look on identifix explains better on testing, and lots of issues with the coil/module. If you can only get a spark up to 1/4″ of gap, then it may be weak, or the module may be weak. A labscope would let you see the driver pattern on the module. Instead of a clean off and on, you would see a tapering effect. Looked like a lot of people ended up doing the coil and module together. Make sure the rest of the secondary ignition is up to snuff, or you may cook a new coil.
[quote=”BubbaGarage” post=177331]Bad coil was problem but I would still love to know how a test of cam sensor is done.[/quote]
You can check for power and ground at the sensor, and for voltage drops with a conventional dvom, but to verify the signal integrity, and also to check the sync with the crank sensor, you need a scope. Google Vantage Pro, and Vantage Ultra. If you want to truly be able to check the sensors, that is what is needed. Just an interesting note, the Vantage Pro was made in a special version as an OE tool for Volvo. Instead of red, it was a bluish purple color. So that’s even how Volvo tests them. DVOM won’t work because the signal is too fast and the meter will just get you an average voltage reading.
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