'96 850 T5 (B5234T, M56H): Crank, no start

Cookeh · Post by **Cookeh** » 31 Aug 2020, 06:44

My 850 T5 let me down yesterday, with a crank but no start scenario. Oddly, it does cough every 20s or so of cranking, and tries to run for 0.5-1s.

I have both fuel and air, and my crank speed is normal so starter is good. Haven't checked spark yet, but its the only one left.

I suppose lawnmower syndrome is plausible, but I have no recollection of starting the car since Fri when it completed an 80mi trip - so it seems unlikely.

This morning I broke the multimeter out to test the two main suspects: crank and camshaft sensors. The results for that follow;

Camshaft (at the loom):
Pin 1: 0 ohm
Pin 2: 5v
Pin 3: 12.1v (battery voltage)

Camshaft (backprobed):
Pin 1: 0 ohm
Pin 2: 0.78v
Pin 3: 12.1v (battery voltage)

Crankshaft:
276 ohm

From this it would appear that the crankshaft sensor is within spec (300 +/- 40 ohms), and the big voltage drop within the camshaft sensor certainly points fingers at that being the fault.

The part number listed on the current sensor is Volvo 9146108 and Bosch 0232 101 023. Looking for replacement parts, the search of Volvo 9146108 brings up plenty good used (can't afford new currently!) parts, but they have differing Bosch part numbers (0232 101 030) - does anyone have experience with this and know if they are compatible?

Is there anything else I should check (perhaps coil?) to rule it out?

Cheers,

Post by **abscate** » 31 Aug 2020, 08:34

How fast was it starting before? Crank crank vroom?

You can use ether to check for good spark delivery quickly,

Don’t crank any longer than it normally takes. Hard on both battery and starter

Cookeh · Post by **Cookeh** » 31 Aug 2020, 08:54

Previously it varied from between say 1-3s. Prior to the no-start it was not taking any longer than normal to start.

I don't have an assistant currently to turn the car over whilst I check for spark, but its certainly something I will check conclusively when they are available. I should perhaps invest in a cheap spark tester, which I could then place somewhere visible from the interior.

Cookeh · Post by **Cookeh** » 31 Aug 2020, 10:38

My (un)happy helper returned, so I was able to test spark. I have spark at the coil (the loom for which also tests fine with multimeter), at the distributor, and at the leads for cyl 1 & 2. I did not pull plugs or check more than those cylinders as both plugs and leads have less than 2000 mi on them.

I'm ruling out coil, dizzy cap, rotor, leads and plugs as a result. Which leaves us with the bad voltage reading on the CPM and not a whole lot else. Is it possible for there to be spark with a bad CPM?

Anyone got experience with Volvo 9146108 and varying Bosch part numbers? Or is it known that ones for N/A engines work with turbo variants?

EDIT: Also looking into the antenna ring.

Post by **abscate** » 31 Aug 2020, 13:41

I would back to fuel.

What’s the pressure at the rail in psi?

Cookeh · Post by **Cookeh** » 31 Aug 2020, 14:22

Antenna ring had clean contacts, but I 'wiped' them anyway and replugged it several times.

I also had a look at the MAF, which had some dirty contacts. I cleaned those up with emery paper and contact cleaner.

I tried starting the car again and as before it would start, stumble and fail roughly one in five times. The other four times would be no start. I tried this with MAF plugged in and disconnected, to no avail.

On one occasion, with MAF plugged in, it ran for over a minute before stumbling. It then came back for another ten seconds before stumbling again. This was with me holding it at a fast idle.

Abscate, I'm with you and going back to fuel. I'm suspecting fuel pump relay now - will bridge it tomorrow. I currently have no way of testing pressure at the rail, though if the car runs with it bridged that will point at relay.

Cookeh · Post by **Cookeh** » 01 Sep 2020, 08:37

I bundled my (un)happy helper into the boot today to listen for the pump. It was reported that it was running from Pos II all the way through until it stumbled and died. I then bridged the relay and the car fired and ran as normal for 3 minutes before I shut it off; I am not a fan of leaving cars idling without load. I have ordered a replacement relay and will report back - £13 for a 'guaranteed working' used item from a known good breaker. If that solves the problem I will repair my current relay and use as a spare, using Ozark Lees excellent guide.

Post by **RickHaleParker** » 01 Sep 2020, 09:14

My S40 had the same symptoms when I bought it as a Mechanics special.

Check the timing belt tension. The Tensioner may have broken or come loose. Allowing the belt to jump one or two teeth. Just enough to create no start conditions but not interference.

Cookeh · Post by **Cookeh** » 01 Sep 2020, 10:43

Thank you, I've added that to the check list.

Cookeh · Post by **Cookeh** » 06 Sep 2020, 10:59

I bridged pins 15 and 87 on the relay, and the car started and ran perfectly for ten minutes and throughout the rev range. I ordered the aforementioned £13 relay and swapped it in on arrival. After a thorough 90 minute drive I had zero issues and the car runs well throughout the rev range and varying loads. Timing belt tension was within spec, luckily. That is still 40k away from needing to replaced so that would have been irritating.

I must say I am still slightly confused that the CPM tests badly but seems to work effectively. I'm also slightly confused that the pump relay was an intermittent failure item. Overall I cannot complain as a relay is significantly cheaper than the CPM! I'll be replacing the capacitors in the faulty relay and keeping that as a spare.