Hi all,

I have a 1995 Volvo 850 with a random crank but no start issue.

Being by myself diagnosing these sort of issues gets frustrating. The first time this happened it would not start back up and I immediately assumed it was a fuel problem. I jumped the fuel pump relay and it still didn't start so I replaced the pump and also the relay just in case. With the new pump installed it still wouldn't start. I verified pressure at the valve on the fuel rail so im guessing spark. Being a VW enthusiast I assumed a bad crank sensor could casue a no spark condition. In reading about testing Volvo crank sensors I came across testing the camshaft position sensor as well so I decided to test both. I first tested resitance values which were all in spec but the last test for the cam sensor required watching the values while cranking. I plugged the connectors back in and set up the multi meter and rigged up a video camera to record the values while I cranked. The car fired up as soon as I turned the key and continued to start as many times as I would try. I drove the car around for several days without issue until one day after driving 2 hours to my grandmother's it wouldn't start again. Out of desperation I unplugged the crank and cam sensor connectors and plugged them back in and by god it started!!

It's now been giving me these crank no start conditions more frequently and I wish it would just become a constant no start problem since every time I try to check something it starts right up. The unplugging and reconnecting of the cam and crank sensors may just have been a fluke but I may just put a new cam sensor in regardless. My question is this...would a cam sensor cause a no start condition? My VW will start with the cam sensor unplugged just not be happy about it. If the cam sensor is on the fritz shouldn't it give me some drivabillity problems like sporadic power loss or stalling? Once the car is running it runs flawlessly until you turn it off then it may start it may not. Is there something else I should be checking for before I was $120 on a cam sensor?

TIA for any ideas

Tom

 

what happens to the battery voltage when you crank? I'd start by cleaning terminals/cables just to make sure you're not seeing a battery or starter issue... just thinking maybe the cranking is dropping voltage below a value that bothers the sensors... Other than that, I'd try cleaning the connectors and checking for continuity. You can snap the connectors together than probe (ie paper clip) to see what happens when fully snapped in.

 

The battery is strong no issues with that as far as I can tell. Ill give it good clean but doesn't look bad at all. Ironically today this issue popped up at the store and wouldn't start until several hours later. Not sure if temperature plays a role or not. When I finally did get it started I noticed the cel was on so the scanner said throttle/pedal sensor. I cleared it just to see if it was a fluke due the extended cranking time today I'll see if it comes back.

 

You might want to read up on testing the throttle position sensor (TPS) to see if maybe it's dropping signal. Not sure it'd be the no start cause though.

Best thing to do is be ready to check to see if you have spark when it won't start. Pull the coil wire off the distributor and have a way to place it close to metal to see or carry a spark plug to slip into the end and lay on metal.

When it won't start letting it sit for a few minutes and then turning the key on try to listen for the fuel pump to prime the system. It should run for a couple seconds.

Trying to narrow it down to spark or fuel would help a lot.

 

I will say that the last time I had problems like this, it was in fact the cam sensor. Don't give up on testing the cam sensor. It's one of the easier things to be sure of.

 

What is missing when it fails to start? Common problems to no spark are coil and cam sensor.