Volvo 240 with a weak spark, won't run! Help please :)

[Bugjam1999]

Hi there,

So this is my first thread here been driving a volvo, in fact one particular volvo 240 my whole driving life. My parents' 1988 'E' plate 240 estate that I and all my younger brothers learnt to drive in is still kept on the road for occasional use. Odometer stopped at 320,000miles, it's probably done about 5,000 more since then. Original engine (head gasket replaced once) still going strong, recon gearbox fitted last year after a new and particularly stiff clutch thrust bearing destroyed the housing in the original. All the electrics still work (windows, seats etc) and it's been phenomenally reliable in the 22 years my parents have owned it.

Not starting now though... could do with a few pointers if anyone has a moment

A little brother went out to start it last week and it didn't... well not properly. it backfires/pops and if you keep your foot on the throttle it'll run at about 2,000rpm + , but sounds like it's running on three below that and will quit.

Diagnosing what's wrong with it is made harder by not being there and asking my dad + brothers who are much nearer to home than I am to do specific things, but so far:

hotwired and checked both pumps run

cleaned all the fuses

fitted new plugs

checked for a spark from each cylinder using a spare spark plug - there's a weak yellow spark of identical size at each one. I think the weak spark is the problem, so i guess the next thing to check is the coil? My dad checked the resistance through the coil and it was within the tolerances noted in the haynes manual.

I know there's a way of checking the coil by having it produce a spark using a spark plug, but i'm struggling to find a decent set of clear instructions online that my dad+brothers - who are not that interested in cars - can follow.

If anyone can point at clear instructions online how to check the coil by making it make a spark, that'd be an excellent help.

Any other suggestions?

Many thanks,

Bugjam.

[DW42]

Not running below about 2000 rpm is a common way for a Bosch ignition coil to fail. I haven't had it happen in a Volvo, but once bought a VW for cheap with the symptoms you describe. Got it home with my girlfriend down in the footwell so that she could put her hand on the accelerator pedal every time I had to change gear.

Coils are not prohibitively expensive -- so you could just try buying a new one and hoping for the best. To test the old one: pull the centre wire off the distributor, and hold it using insulated pliers about a centimetre away from any exposed metal that you can reach. Have someone turn the engine over (you need to not have drained the battery) and check the colour of the spark. It should be blue or white and strong. Yellow or orange are bad. Just as a cautionary note, I set another girlfriend's car on fire doing this -- the engine was very oily, and the oil caught fire. I married this girlfriend.

[john h]

Originally Posted by DW42

Just as a cautionary note, I set another girlfriend's car on fire doing this -- the engine was very oily, and the oil caught fire. I married this girlfriend.

Lucky to get away with that!


I would agree, try a new coil unless you know the one on the car is fairly recent.

By the way, welcome to the forum, and nice story about the car being in the family so long... any photos?

John

[Michael J]

Pop off the distributor cap and check that the terminals are not black/eroded/burned away. If blackened you can scrape the terminals bright again with a screwdriver for temporary improvement. If it's dusty/dirty in there clean the inside with a dry cloth. A new cap is cheap, quick, easy to do. It fixed mine (carb engine, Renix ignition).

[rusty244]

Welcome to the forum, hope your issue is straightforward to resolve. Some great pointers from people so far on things to check.

Good to see another "lifer". My 240 has been in the immediate family from new too, owned firstly by my mum and then bought by me when I was 16 ready to take my test (although having driven it on private land from about 9 years old I was already quite proficient). Similar vintage to yours being a "C" reg. Has served me well and even took it to live in London when I was living/working there for 8 years.

Anyway - apologies for the thread derail and good luck with the fix.

[Bugjam1999]

Thanks guys - I've passed on that test to dad and he'll do it at the weekend and see. I don't recall the coil being replaced anytime recently, I've been servicing the car since 2010 and I've not replaced it in that time. The distributor cap is clean, some wear though- that was replaced about 18 months ago.

There are a few pics of the car, I'll have to dig them out though...oh, just worked out how to upload from my phone.

Will let you know how I get on, thanks again

Bugjam

[Bugjam1999]

Hmmm, lets try that upload again...

[julianps]

Hiya, I have a 1988 B200E and have been down this road myself. The old Haynes advice, to not jump to conclusions, is sage, as is the usual advice to play nice with ignition system voltages; they're dangerous.

My two-pennies-worth on running problems always starts with fuel;

1. Hotwire the pumps, do they both run?
2. Disconnect the fuel pipe after the filter; hotwire the pumps and measure the flow. Volvo says 800cl in 30 seconds though I get 4-450cl in 10 seconds on mine. Reconnect.
3. Disconnect the fuel pipe from the union in front of the wiper; hotwire the pump and look for the same flow-rate on the return. Remove the filler cap and blow down the solid return hose. Can you hear air blowing into the tank (it fuel can't return the carbs will flood or CI pressures go wrong.
4. Reconnect the fuel pump relay. At this point you need a voltmeter, rev-counter or test lamp because you need to test that once the engine is cranking a) there is a trigger voltage from the ignition system; and b) that is converting into running fuel pumps. If you have an electronic ignition module forward of the battery this has an integral cut off switch and this can, and does, fail.
5. Remember that cranking will energise the ignition system so its advisable to have the earth lead (terminal 1) to the coil disconnected when playing like this.
6. Pull the lead off the centre of the distributor and attach a spark plug and using shielded pliers, rubber gloves and rubber boots (kidding) hold the plug to the block and have an assistant crank the engine. A poor spark can be a failing coil or a failing ignition module. Remember too that a lead goes from T1 on the coil to the fuel pump relay and from there to the rev counter. Any leak to earth anywhere along this lead will undermine the integrity of the ignition system.

Other things to think about are if you have the rev-limiter style rotor arm have a solid one for use during diagnosis like this and if you have a Hall Effect distributor rotate the engine clockwise til there's a gap exposing the switch. Disconnect T1 at the coil and turn on the ignition. Now put a 1mm feeler gauge blade into the switch gap and then remove it. This should send 5-8v down terminal 0 at the coil to the ignition module and a pulse to the fuel pump relay. The pumps should run for about 3 seconds.

All of this of course assumes good compression and valve clearances.

Mine's taken me about 4 months, on and off, to solve and the intermittent fault in the ignition module was the root cause of my pain. £30 for an after-market replacement and the Brick Lives!

[Bugjam1999]

that's a pretty comprehensive list of things to work through, thanks

Dad and brothers haven't had a chance to check the coil yet, but if that's inconclusive, i'll get them to work through your list - thanks!

I'll let you know I get on...

Bugjam

[Bugjam1999]

Ok thanks again for help so far.

Dad and brothers tested the coil this evening, using the procedure above, and it produced a yellow spark, suggesting that it is at fault. I think a new coil and a new distributor cap + rotor for good measure and we should be ok... Finger crossed and what not.

Next question- is a 240 coil the same as a 940 coil? An impulse purchase just before Christmas means I've got a B230FK sitting in a friends garage over winter... If a coil purchased now would fit that engine as well, it would make it worth buying a genuine bosch one...