Intermittent fault, possibly crank sensor

[Forrest]

1994 940 Auto with 200FT engine. Always starts easily, runs well, but every once in a while and several times in forty miles yesterday the rev counter suddenly drops to 0, the engine loses power but doesn't stall, and the lambda light comes on. After a few seconds everything returns to normal and the lambda light goes out again. The fault has never lasted long enough for me to have to pull over but it can be quite unnerving. I have never had to restart the engine.

I tried to read the fault codes today, but just got 1-1-1 on both positions 2 and 6 on the diagnostic unit.

My next step would be to clean the crank sensor and check the cabling to it, BUT having taken an hour just to achieve a brief glimpse of this sensor and being unable to touch it let alone get a spanner to it I'm stuck. Is this likely to be the cause? How on earth do you get to it?

[NI_Volvo_Nut]

I've read on here the cable wears though and causes a short on the crank sensor, worth a try.

[Forrest]

The situation became critical following a genuine breakdown on Tuesday with a passing policeman having to direct traffic while my sensor cooled down.

Having read quite a bit about replacing the crank position sensor I came to the conclusion that replacement had to be attempted, but that there was a risk of breaking the bracket it fits into. This was an acceptable risk since this is the grottiest of my 940s; so kill or cure it was. In the event, I could see no evidence of the flimsy bracket. The sensor appeared to fit straight into the bell housing. Did Volvo change the design in later models?

Although daunting because of restricted access and visibility the replacement was actually a twenty minute job and probably came close to being a model installation. So I thought I'd share in case it helps anyone else.

Before starting.

Order a genuine replacement from Rufe. P/N 271949 £34.20
Spray some penetrating oil over the corroded bolt

During surgery

Access is nasty. You have to get your hand through a maze of pipes and cables. It helps to be six foot tall with thin arms.



Yes, you've got to get your arm through there to just below the distributor cap. Tips here are to remove the auto transmission dipstick and unclip and tuck out of the way that smaller hose.

The description in the FAQ involves using various extension bars and a 10mm socket. I first tried to get my small 1/4" socket ratchet in there, but there wasn't enough clearance. I think that's when I broke a piece of plastic off the old sensor bracket.

I had found another article, I think on Turbobricks, that recommended using a 10mm ratchet spanner. I had been meaning to buy one of those all week, but never got around to it. What worked really well for me was a standard 10mm spanner but using it the other way up from normal. It seemed to fit over the curved top of the bell housing and gave me enough room to get the bolt loose. As soon as I could turn the bolt by hand I did so, keeping a firm hold on it all the time. The major no-no here is to drop the bolt into the transmission.



The old sensor came out very easily. Others have reported that they can be stiff. Note that the cable is clipped to the heater pipes in two places. My tip here is to remove the first clip from the cable and the second clip from the pipe, counting along from the 3-pin plug on the firewall. The second clip is harder to see and in my case was clipped to a metal pipe near the engine.

The Volvo kit contains two replacement clips of the correct size. Use the replacement clip no. 2 and attach it to the new sensor cable in the correct place and orientation using the old sensor as a guide. This clip will then be in the right place to attach to its pipe when you have installed the new sensor.

Following advice from the articles I had read I smeared a small quantity of high melting point grease on the outside of the new sensor and over the thread of the bolt to aid future removal. I'm not sure if this will ever be of practical use since I suspect the new sensor will outlive the car, but you never know.

Manoeuvring the new sensor into position is definitely a case of needing eyes in your fingers, but it goes into place quite easily. I found that it was best not to put the bolt through the sensor until it was safely resting in its hole in the bell housing. It is quite easy to feel where to position the bolt afterwards and it reduces the risk of dropping it. Fiddlier is getting the bolt into the threaded hole in bell housing but that didn't take too long. Again, make sure it is firmly screwed in by hand until letting go of it. I was able to screw the bolt nearly fully home by hand and then just nipped it in with a small turn of the spanner, this time using the open end from above.



Although I couldn't see any obvious bare wires, the insulation had definitely gone on my old sensor.

I also took the opportunity when ordering from FRF Motors to get some new 3mm vacuum hose and with the help of one of the parts being distributed by Rod25 last month refurbished my PCV tubing which was held together with friction tape in two places. The old girl is running better than ever now.

[940wentworth]

Hi. Sorry for resurrecting an old thread but I have almost the same problem. I have a 1992 940 Auto with 200FT engine. Mine completely cuts out every time though so I have to stop to restart. It doesn't always restart first time it can take several attempts. The problem is very intermittent it can be weeks between it happening although it did it twice today. Like yours inbetween episodes it runs perfectly. Do you think this could be the same problem with the crank sensor? Thanks

[Steve940estate]

I haven't seen that picture before, I guess the ones that don't look that bad could have failed in the same place. I will go and check to see if the plastic clips that hold the lead are fitted properly.

The stalling problem you have having could be the crank sensor. I had starting problems but the car never actually cut out on me. I don't know if this gives any clues about what the fault is but last time mine did it the injector or radio supperession relay as it's called was the problem. My theory is that non starting could be the crank sensor or the injector relay. Stalling seems less likely to be the relay and more something caused by movement or vibration while the car is driving. In this case I would look at the crank sensor first.

There are other possibilities such as loose electrical connections affecting either the ignition or fuel injection system but there seems to be a lot of people suffering with faulty crank sensors. One way to check is to look to see if the rev counter moves when cranking the engine. I haven't see this happen myself but others have suggested it.

[clocks2003]

I had the same problem with my 940 recently - I will see if i can find the thread asking for help as there were quite a few suggestions. It turned out to be the fuel pump relay in the engine bay.
Andrew

This was the first thread, with lots of suggestions which eventually lead me to the answer:
http://www.volvoforums.org.uk/showthread.php?t=209310
This was the second thread, once I had found what the engine fault code was! http://www.volvoforums.org.uk/showthread.php?p=1739452

Hope this helps - but the first thing to do is to get hold of a fault-code reader.

[rogerthechorister]

Would a B230ET have the same sort of Crank Position Sensor? I am still hunting a similar but not identical problem.

[Forrest]

I can report a year on that it definitely was the crank position sesnor in my case. The car is still running very well and the engine hasn't cut out again since.

IMHO, if you can afford to, it's worth having a new/good crank position sensor and fuel relay in your spares stock. I recently needed to use my spare fuel relay in another of my 940s.

In my experience, the biggest clue that a mysterious stalling problem is due to the crank position sensor is strange behaviour of the rev counter. Early symptoms were it "sticking" during motorway driving with some loss of power and then suddenly coming back to life again. As the problem got worse and the car started to cut out occasionally, just before a stall the rev counter would drop to zero. This was very hard to spot, because you had to be looking at the dash at just the right time. My reasoning (possibly flawed) was that a fuel related stall would not cut rpm to zero before the engine died.

If you are really stabbing in the dark at a mysterious stalling problem and just throwing exchange parts at it then the fuel relay behind the ash tray is a bit easier to replace than the crank position sensor. But there are other parts (per the FAQ) that could be the culprit.

[940wentworth]

Thanks for all the help. I think the problem is probably the crank position sensor so I'll look at that first. The rev counter has sometimes been "sticking" during motorway driving with some loss of power and then suddenly coming back to life again. And the rev counter does drop to zero each time just before it stalls.

Thanks guys.

[clocks2003]

I have to say I don't know if the rev counter dropped to zero before the stall in my case, as I tend not to be looking at the rev counter non-stop... However, if the reason the revs show zero is that there is a faulty signal, that will happen the instant the fuel shuts off which will be before you notice the stall.
As I say, the first thing to do (IMO!) is to get hold of (or make up) a code reader so you can see what area the problem is in. There is a good thread on this as well here: http://www.volvoforums.org.uk/showthread.php?t=102112.
I wasted a lot of time messing about with the crank-shaft sensor when this was not the problem...