Engine 850: B5252S/2.4/10v: 1994 Volvo 850, 10 valve, non-turbo - fault code 3-1-4

[volvo2]

About a month ago I had the engine light come on and the fault code 3-1-4 (fault with the cam position sensor) pop up. I (eventually) replaced the sensor (genuine Volvo so I am thinking it is probably OK) and all has been well until yesterday, when the engine light, and the same error occurred and I had difficult starting (hot or cold). Actually, starting has been intermittent for a while, ie bursts into life some times and others requires more churning of the engine before starting. In the past has run fine once started.

Could this be a bad connection somewhere? The plug/socket for the sensor looks OK but I’m going to clean it with electrical contact cleaner. I’ll also measure what’s at the socket with the ignition on, which I believe should be about 12v, 5v and ground respectively for each of the three pins. The wires just disappear into the loom. Is there anywhere I could check for a bad connection – maybe a bad earth somewhere that would cause this error code?

[capt jack]

It's not impossible that the new sensor is faulty. If it's only been a month, and it's genuine Volvo (presumably from a dealer) then I'd be tempted to take it back.

Also, when you fitted the new sensor, did you clear the fault code?

I do believe that once logged, a cam position sensor fault code is permanent until it's been actively cleared.

Cheers

Jack

[volvo2]

Thanks for replying Jack.

Yes, I purchased the replacement cam position sensor from the main dealer. I suppose it could be faulty - it just seems unlikely. I'm a little suspicious that it is a poor connection somewhere as for some time I've had intermit starting issues, where it just takes longer to get going on about 50% of start-ups.

Yes, I did clear the fault code after installing. But now it is back. I cleared it again and it seems OK but my worry is that there is a problem that may cause a breakdown.

If I can't sort this out it may be the end of the line as I definitely need reliability (I commute 120 miles each day for work). It will be sad for me to let the car go having owned it for what is now getting on for a quarter of a century.

[Baffler]

Assuming the CPS has the correct values (will post them later) a few other things to consider in relation to prolonged/delayed starts:


1.) Faulty antenna ring around the ignition barrel...

2.) Fuel pump relay starting to fail...on initial starts listen carefully for the fuel pump priming each time you turn the ignition to position II.

3.) Ignition switch (electrical portion) contacts worn.


Given the age of the vehicle I'd replace the above three items for peace of mind.


4.) Weak Fuel Pressure Regulator...which is most prevalent on a hot engine.

5.) Poor spade connection on the solenoid of the starter motor but that would cause nothing to happen when you turn the key.


Also see Paul's thread - 'The Old Random No Start Syndrome'

[volvo2]

Thanks Liam. I have replaced the starter (old one failed) and fuel pump relay (pump primes as you mention). My old 1994 car does not have the antenna on the ignition barrel (thankfully). I think the switch itself is OK but had not thought of that.

Thanks for the link - will take a look.

[volvo2]

I think (hope) I have traced the fault. It looks like the blue earth wire that connects to the battery is broken at the terminal lug that is bolted to the engine. This wire actually has two blue wires (one very large diameter) with the single battery clamp on one end (both wires are attached to the clamp) and two terminal lugs at the other. The larger wire is connected (with its lug) to the engine (the broken one) and the smaller to the body (with its lug) just in front of where the battery is positioned.

Frankly, I am amazed the engine runs at all with this wire broken! It seems (from a continuity test) that the engine is still earthed but I guess not very well.

[Baffler]

Result! Well done!

Frankly, I am amazed the engine runs at all with this wire broken! It seems (from a continuity test) that the engine is still earthed but I guess not very well.

If I remember correctly, on the petrol variant, there's another small earth strap going from the back of the cylinder head to the bulkhead.

[Bigfella666]

I had the same problem a couple of years ago, 314 code changed CPS ( aftermarket admittedly ) made not a jot of difference. Cleaned all the earth contacts made not a jot of difference.

Concluded it must be an electrical fault and did what we should not do - started throwing parts at the problem. However I took the view they needed replacing anyway so hopefully very little to lose.

New bouge leads, diz cap, rotor arm and plugs. Started first time every time since so clearly lost nothing, and of course the Bosch CPS was not thrown away

Posting this just in case your probs re-appear !

[volvo2]

An update – I was unable to source a replacement (used or new) and could not find a generic ready-made battery negative lead long enough - the Volvo lead is well over 80cm long – longer than most it seems).

Luckily the break in the old lead was near the connection onto the engine. So I stripped back the insulation and crimped on a new connector. This is a great tool for the job by the way – Draper BTCT Battery Terminal Crimping Tool (https://www.amazon.co.uk/Draper-BTCT...+cable+crimper).

The starting has dramatically improved. I am still getting churning over on about 10% of start-ups, as I was before things got a whole lot worse. So I still don’t know why that is but at least the major starting problem has now been resolved.