Hi everyone,

I am new to this site but hope it will be useful.

I have a 1989 volvo 340 1700CC which has done about 170 000 miles and still drives very well with few problems.

I have had an intermittent ignition problem for a couple of months, however. It tends to occur when the weather has been damp and the car has not been driven for a day.
The car will start and drive off o.k. but after 1 or 2 miles I get a weak spark (mis-fire when accelerating at low revs). This will last for anything between 1 and 10 miles before it clears. If I stop the car during this period it may not re-start.
I have replaced the spark plugs, leads and rotor arm. The distributor cap was replaced 4 months ago.
I have cleaned the coil connections and even swapped the RENIX ignition unit with a used spare, but this has not made a difference.

I am considering:

Changing the distributor cap again in case the new one is faulty.
Connecting the earth wire from the RENIX unit directly to the battery earth in case there is an intermittent connection problem in the cars wiring (when testing the earth through the 3 wire plug I have always found it to be good however).
Cleaning /replacing the engine earth strap.
Replacing the angular position sensor.

If you have any other suggestions I would appreciate them.

Regards

Ray

mine used to do this, i changed the plugs, leads, rotor arm, dizzy cap ... they all helped with my constant slight misfire but what made a massive difference to the symptoms you have described was the coil which i replaced.

Mine still gets the problem if you leave the car for more than a couple of days but clears up much quicker now. Using it daily, it never skips a beat

I'd still check everything over and give it all a good clean, thats what i'm doing now i've replaced everything

Hope that helps

Diz cap/rotor/plugs/HT leads should all be changed reguarly anyway. They are service items after all.

As for the coil, measure the resistance using a mutlimeter and see if it falls withing specs still before you shell out on a new one. I seen a new one on the bay the other day for about £15 posted, so that's not bad. When I thought I needed one for my B230 I was looking at £50/60.

As above. A coil should fix weak spark problems.

Check there is no oil in the distributor cap, the oil seal and cam can wear badly causing the problems you describe. If you clean the cap with white spirit or something and the problem goes away for a while (hours/days) then it is probably oil seal issues. Cue is to push the seal in flush with the surface rather than fully home so it sits on a different part if the cam.

Thanks for the ideas.

I shall let you know the results.

Ray