misfiring 240

My 1987 240 (B230K carb engine) has developed a misfire. It only happens when it has warmed up ie after running for 15 to 20 minutes, and then it starts to miss, especially on overrun and when idling. It is not continuous and the car doesn't stall, it gets worse and even after being parked for a couple of hours the problem continues immediately on re-starting. If left overnight it will take 20 minutes or so before the problem starts again. My local garage man has changed the plugs, points, HT leads and is stumped.
HELP
Leigh

[vjck_uk]

As you say yours is a points setup that's a classic symptom of the distributor condenser giving up as they start breaking down when warmed up.
Do the points need changing a lot? as a duff condenser makes the points spark more and consequently pits them quicker.
You could also have a look under the bonnet when it's nice and dark and see if there are any lightening display going on.
Regards.
Vaughan

[Erling]

Hi,
If the UK version of the B230K has the same setup as on my side of the North Sea, it should have an electronically controlled ignition - a shiny "computer" box behind the glove compartment. It could be worthwhile testing with a different computer from a smooth-running B230K-equipped car.

Erling.
http://home.no.net/ebrox

http://pic7.picturetrail.com/VOL188/...8/23744414.jpg

If, as Erling says, yours is electronic ignition (Bosch EZK)

Then the symptoms you have sound like a heat induced failure of the Hall Effect sensor in the distributor, these are known to give trouble when hot, it is their usual failure mode.

Colin.

1990 740SE B200E/M47, remote C/Locking.

[Erling]

And you can read more about Hall sensors in B230 engines here (testing, replacing etc.): http://www.brickboard.com/FAQ/700-90...ng_Hall_Sensor

Erling.
http:/home.no.net/ebrox

Thanks guys, for the advice. As you say she does have electronic ignition.

Erling - I have looked at the site you suggested (brickboard) but my car doesn't seem to have the same symptons. She never actually stalls (even when the rev counter is flicking rapidly between normal idling speed and near stalling) and always starts without any problem, hot or cold. Today I drove the 20 miles to work without any problem, a couple of "hiccups" (jerks) when I drove slowly into the office car park. This evening the car jerked intermittently when I drove slowly through a built-up area but once I hit the open road and kept a steady 50 to 60 without lifting off she steamed along just fine, only starting the occasional jerk when I slowed down and stopped at lights. Cars!!!

Thanks again
Leigh

[Erling]

Could it be that this is not ignition, but fuel(/air) related? I'm thinking false air. False air can creat a multitude of interesting effects, uneven idle being just one of them. Your B230K has lots of vacuum lines - only the Volvo gods know what they all do. A simple test for false air is spraying "start gas" (I don't know the proper English term for this, sorry) around the intake and the vacuum lines. If the idle picks up, you've got a leak. (I keep a fire extinguisher at hand when doing this, but then I'm a pessimist by heart and conviction.)

Perhaps I'm on the wrong track, but it's an easy test anyway.

Erling.
http://home.no.net/ebrox

[Clifford Pope]

I've had experience with a B230 fitted with the Cisak carburettor and electronic ignition.
There certainly is a maze of vacuum pipes all over the place, in numerous colours. I'd check them all carefully, especially the rubber joiners and T-junctions.
Also check for air leaks in the inlet pipe. The corrugated thing can get splits around the convolutions, and these open/shut as the engine moves. At constant speed it may be fine, but then move and let in air as conditions change.
The crank sensor (does it have one of those?) is crital, and they can break down or malfunction erratically. Look at the state of the wires running to it. Again, engine movement can trigger a blip.

Does it have the awful Pulsair and EGR systems? They are another network of pipes and valves ready to leak or stick.