Cold running issues

[Forrest]

I’ve just ordered a set from Classic Swede. The only source of Bougicord leads I could find at the moment. I could always temporarily borrow one from one of my other 940s but I don’t want to mess with them unnecessarily.

I don’t mind trying new parts that I can easily remove again if this turns out to be something major/terminal such as the HG starting to blow. It was last done at 160k and I’m mindful there is also a coolant loss issue I haven’t solved yet.

That said, this episode has made me even more impressed with the robustness of these cars. At the end of the day I have so far identified and fixed a definitely duff in-tank pump, a turbo air intake with a hole you could see through, and a derelict distributor cap. OK this hasn’t fixed the fault; but the car has previously been running quite well with all these issues!

[Laird Scooby]

"Borrowing" one known good plug lead for #1 pot isn't really unnecessary messing, if it provs the point you can put it back on the other 940 and await your set of Bungeecord leads.

If that isn't the problem then you know you need to continue hunting elsewhere. Don't forget to check/clean/gap the plug while it's out, just to be on the safe side.

[Forrest]

I have managed to do three things today and have made a bit of progress.

Firstly, I replaced the spark plugs with correctly gapped Bosch WR6DC plugs. This part number is specifically quoted in the owner’s manual for the B200FT. As far as I can tell they are identical to the 272464 (made in Germany R6) set that I took out.

The old plugs had quite a lot of carbon (running rich?) but none looked suspiciously clean (HG failure?) or otherwise damaged. Ignore the oil in the picture. I sprayed around them liberally with carb cleaner to remove any dirt before removing them. With new plugs and the old leads the arcing and misfire continued.

Next I changed the leads for the new Bougicord ones - delivered very promptly, thank you very much Classic Swede. This seems to have solved the misfire and arcing, thank you for the suggestion Laird Scooby. I have never had HT leads fail like that and would have taken ages to get there myself. I will confirm the fix with a cold start tomorrow but I am hopeful since the arcing has now stopped.

The problem of the car conking out if going straight from accelerating hard uphill to braking hard remains. I had been suspicious of the non-return valve on the brake servo especially since for many years the car has had a rolling idle when held on the footbrake when cold. Replacing this is not too bad a job. The Bosch part number is 0 204 120 018. I also replaced the hose from the inlet manifold since mine was perished and also seemed to be reacting with the paint on the valve cover. It is 3/8” reinforced vacuum hose. My original Volvo one (p/n 1272328) was even marked 3/8. This one from eBay is less flexible than the original but does the job just fine provided you soak the end in very hot water before trying to attach it to the inlet manifold. It then slides on very easily.

https://www.ebay.co.uk/itm/10mm-3-8-...R/132838845435

Anyway, despite refreshing this, the problem braking on hills remains.

Could this be due to the fuel pressure regulator? I plan to check this by removing the return line and seeing if any fuel comes out of the return port. I will probably attach a hose to a suitable container to be on the safe side. It occurred to me that if the fuel pressure is too high; and it would be high driving hard uphill it might be flooding the engine. However, this fault does seem linked to hitting the brakes as well which suggests it might be vacuum related.

[Laird Scooby]

Originally Posted by Forrest

I have managed to do three things today and have made a bit of progress.

Firstly, I replaced the spark plugs with correctly gapped Bosch WR6DC plugs. This part number is specifically quoted in the owner’s manual for the B200FT. As far as I can tell they are identical to the 272464 (made in Germany R6) set that I took out.

The old plugs had quite a lot of carbon (running rich?) but none looked suspiciously clean (HG failure?) or otherwise damaged. Ignore the oil in the picture. I sprayed around them liberally with carb cleaner to remove any dirt before removing them. With new plugs and the old leads the arcing and misfire continued.

Next I changed the leads for the new Bougicord ones - delivered very promptly, thank you very much Classic Swede. This seems to have solved the misfire and arcing, thank you for the suggestion Laird Scooby. I have never had HT leads fail like that and would have taken ages to get there myself. I will confirm the fix with a cold start tomorrow but I am hopeful since the arcing has now stopped.

The problem of the car conking out if going straight from accelerating hard uphill to braking hard remains. I had been suspicious of the non-return valve on the brake servo especially since for many years the car has had a rolling idle when held on the footbrake when cold. Replacing this is not too bad a job. The Bosch part number is 0 204 120 018. I also replaced the hose from the inlet manifold since mine was perished and also seemed to be reacting with the paint on the valve cover. It is 3/8” reinforced vacuum hose. My original Volvo one (p/n 1272328) was even marked 3/8. This one from eBay is less flexible than the original but does the job just fine provided you soak the end in very hot water before trying to attach it to the inlet manifold. It then slides on very easily.

https://www.ebay.co.uk/itm/10mm-3-8-...R/132838845435

Anyway, despite refreshing this, the problem braking on hills remains.

Could this be due to the fuel pressure regulator? I plan to check this by removing the return line and seeing if any fuel comes out of the return port. I will probably attach a hose to a suitable container to be on the safe side. It occurred to me that if the fuel pressure is too high; and it would be high driving hard uphill it might be flooding the engine. However, this fault does seem linked to hitting the brakes as well which suggests it might be vacuum related.

You should almost always get fuel from the return line of the FPR. Driving hard uphill then slamming the brakes on will shift the fuel in the tank forwards, perhaps causing a fuel starvation problem. How much fuel do you normally have in your tank?

[Forrest]

I normally keep the tank fairly full. I always fill it until full and usually refill every 200 miles or so when I get to about half a tank. It is around half full now.

I replaced the in-tank lift pump around Christmas time because I thought it might be related to these problems. The original in-tank pump had definitely failed. I am fairly confident I reinstalled the fuel sender correctly into the swirl pot affair inside the tank. The tank was exceptionally clean and there was no muck to speak of in the original filter sock. I am not 100% confident I got live and earth the right way around on the new pump but it is only wrong if the new pump had the opposite polarity to both the original and a third-party one I think you posted a diagram of on here a while ago. I have photos before/after so I can easily check the way I wired it without any dismantling!

The cutting out braking predates the misfire which it seems was the cause of lack of power on a cold start. It also predates all of the recent changes I have made so it is probably due to a long-standing fault I have yet to identify.

[Laird Scooby]

Originally Posted by Forrest

I normally keep the tank fairly full. I always fill it until full and usually refill every 200 miles or so when I get to about half a tank. It is around half full now.

I replaced the in-tank lift pump around Christmas time because I thought it might be related to these problems. The original in-tank pump had definitely failed. I am fairly confident I reinstalled the fuel sender correctly into the swirl pot affair inside the tank. The tank was exceptionally clean and there was no muck to speak of in the original filter sock. I am not 100% confident I got live and earth the right way around on the new pump but it is only wrong if the new pump had the opposite polarity to both the original and a third-party one I think you posted a diagram of on here a while ago. I have photos before/after so I can easily check the way I wired it without any dismantling!

The cutting out braking predates the misfire which it seems was the cause of lack of power on a cold start. It also predates all of the recent changes I have made so it is probably due to a long-standing fault I have yet to identify.

Have you got air-con on it as well? There are NRVs/check-valves on that for the vacuum as well and if they leak can cause similar problems. Also about 12-1800rpm there is a fuel cut-off to save fuel so combine that with a vacuum leak and it could potentially give the symptoms you've got.

[Forrest]

The car had been standing outside for 24 hours in near freezing, wet conditions. Started first time with no misfire and I was immediately able to reverse up the drive. So I think conclusive proof that the HT leads were faulty.

The problem with stalling remains though.

On a slightly downhill road, a genuine emergency stop for a deer didn’t cause a stall. Going uphill, straight from the throttle to a full-bore, ABS-activated brake check did. The dash lights all come on towards the end of stopping and it is generally possible to recover it by easing off the brake.

I don’t know whether it’s significant, but because I was stopped on a hill I kept my foot on the brake while I restarted the engine. It always restarts immediately. As it restarted I felt the brake peddle sink some more. Could the servo be leaking? The brakes otherwise feel normal.

I also had the lambda light come on briefly while I slowed down to make a right turn on the level. No codes stored though which seems odd.

[Laird Scooby]

Originally Posted by Forrest

I don’t know whether it’s significant, but because I was stopped on a hill I kept my foot on the brake while I restarted the engine. It always restarts immediately. As it restarted I felt the brake peddle sink some more. Could the servo be leaking? The brakes otherwise feel normal.

I also had the lambda light come on briefly while I slowed down to make a right turn on the level. No codes stored though which seems odd.

Glad to hear the new HT leads solved at least some of your problems, gives us a more even playing field to chase the other fault down now!

If you start the engine, let it idle for a few minutes then switch then hit the brakes and release, hit the brakes again, release - how many times can you hit and release the brakes before you lose servo assistance? Less than about 4 suggests a leak in the servo.

Also once you've exhausted the vacuum doing this, push your foot as hard down on the pedal as you can then start the engine. The response should be instant as soon as the engine fires and should be a steady but quick sink to about halfway at the very most.

If any of this is different to what i'm suggesting it points to a dodgy servo - you can also remove the vacuum hose from the servo and blank it off with a suitable sized bolt and Jubilee clip - be aware you won't have any servo assistance so the brakes will need more pressure to stop the car. Take it for a spin and hit the brakes as hard as you can, if it pulls up without stalling then that will be another pointer to a leaky servo.

[Forrest]

I think the brake servo may have a slight leak. Following the testing regime above it was a bit hard to tell but once the engine was off it seemed to only retain enough puff for one proper press of the pedal, seemed a bit gutless on the second and appeared to have lost servo assistance by the third. The pedal seemed to sink quite a long way when turning the engine back on and there is an audible hissing sound when the pedal is pressed too.

The servo assistance has always seemed less than on my other 940s but they are 1997 models and this is a 1994 with the earlier Bendix B328900 servo.

Today’s operation however was to install a replacement radiator. I managed to trace the coolant loss which I thought initially was the heater control valve to a small crack in the left hand plastic tank under the top bracket. When cold this crack was hardly noticeable but at operating temperature it leaked coolant at a reasonable rate. Fortunately, replacing the radiator is a much easier job than the heater control valve. I used a Nissens replacement. I was very impressed by the quality and fit. The only ways in which it seemed inferior to the genuine Volvo one (itself a replacement fitted in the time I have owned the car) was the apparent absence of metal reinforcement in the outlets and a less convenient drain plug.

[Laird Scooby]

Originally Posted by Forrest

I think the brake servo may have a slight leak. Following the testing regime above it was a bit hard to tell but once the engine was off it seemed to only retain enough puff for one proper press of the pedal, seemed a bit gutless on the second and appeared to have lost servo assistance by the third. The pedal seemed to sink quite a long way when turning the engine back on and there is an audible hissing sound when the pedal is pressed too.

The servo assistance has always seemed less than on my other 940s but they are 1997 models and this is a 1994 with the earlier Bendix B328900 servo.

Today’s operation however was to install a replacement radiator. I managed to trace the coolant loss which I thought initially was the heater control valve to a small crack in the left hand plastic tank under the top bracket. When cold this crack was hardly noticeable but at operating temperature it leaked coolant at a reasonable rate. Fortunately, replacing the radiator is a much easier job than the heater control valve. I used a Nissens replacement. I was very impressed by the quality and fit. The only ways in which it seemed inferior to the genuine Volvo one (itself a replacement fitted in the time I have owned the car) was the apparent absence of metal reinforcement in the outlets and a less convenient drain plug.

That does sound very much like a leaky servo. Had one go exactly the same on my Rover a few years back, quite a game changing it without removing the brake master cylinder completely! Much easier from the look of things on a 7/9xx though.

Good news on finding your leak, hopefully that's one problem solved at least!

Might be worth trying a new NRV/check-valve for the servo before condemning it completely but it does seem to be the culprit.