No Start - Cam Sensor ?

[TenaciousC]

Hi All,

My suspect fuel pump problem has proven to be something other. Engine cranks, but will not start. It is an intermittent issue, as first occurence, it randonly started fine on a few occasions, and went fine... did not cut out. No fault codes have been recorded on ECU (according to mechanic). AA man proved there was no spark at the plugs.

My suspicion is the cam sensor, as I replaced this four years ago with a second hand part someone kindly sent. However would we expect to see a fault code stored in the ECU? Perhaps because it appears not to have failed whilst running, no code is stored.

Any suggestion welcome?

Cheers

C

[theflyingbrick]

is it obd2? crank sensor normally does throw a code but the symptoms you describe strongly suggest it is faulty....maybe try another if you can,but the problem with intermittent faults is its hard to diagnose quickly!!

[TenaciousC]

yes its a '96 so, it has an OBD2 port. It could be that the mechanic has not read the codes properly. I also read that it's possible to test the sensor fairly easily using a multimeter.

"As you can see, there are three wires for the CMP. A yellow/red one is the ECM output, which should be the 5V reference voltage. The blue/yellow is the signal from the CMP, which should be either 0V or 5V, depending on the position of the camshaft. While I have never tested the CMP (it usually sets a DTC 3-1-4), I would imagine you can first check to see if there is 5V on the reference wire with the key on. Then, turn the engine by hand (remove the right front wheel to access the bolt on the crankshaft pulley) slowly and watch to see if the signal changes from 0V to 5V.

Read more: http://www.justanswer.com/volvo/1iy7w-95-volvo-850-glt-will-not-start-i-ve.html#ixzz3KRiAXL3z
"

not sure why they're saying 5 V as I would expect 12, but the principle seems correct.

C

[theflyingbrick]

I had a '96 obd 2 and I could not find a code reader to read the codes!!! it seems 96 is a limbo year lol I would use the link above and test the cam sensor as described see how it goes

[nobananas]

Check the wiring to the relay under the radiator top panel. The wiring rots internally, gives intermittent starting issues and kills the cam sensor feed, took me a day or two of digging through the wiring when my old T5 stranded me in the Lake District.

[LeeT5]

yes its a '96 so, it has an OBD2 port. It could be that the mechanic has not read the codes properly. I also read that it's possible to test the sensor fairly easily using a multimeter.

"As you can see, there are three wires for the CMP. A yellow/red one is the ECM output, which should be the 5V reference voltage. The blue/yellow is the signal from the CMP, which should be either 0V or 5V, depending on the position of the camshaft. While I have never tested the CMP (it usually sets a DTC 3-1-4), I would imagine you can first check to see if there is 5V on the reference wire with the key on. Then, turn the engine by hand (remove the right front wheel to access the bolt on the crankshaft pulley) slowly and watch to see if the signal changes from 0V to 5V.

Read more: http://www.justanswer.com/volvo/1iy7w-95-volvo-850-glt-will-not-start-i-ve.html#ixzz3KRiAXL3z
"

not sure why they're saying 5 V as I would expect 12, but the principle seems correct.

C

5v is a reference voltage from the ECU and it's what you should see at the Cam sensor. You don't want 12v.

[TenaciousC]

It was the cam sensor. Up and running again ;-) The garage told me that it was diagnosed by an auto electrician with a laptop from inside the car (after cranking the engine), so I assume the ECU threw a error code eventually.

Thanks for your replies.

C