My 240 has lost the spark of life!

Hello all

More starting problems for the gurus out there.

My 240 estate, J reg, B200F now refuses to start.

The problem has been intermittent for a while. After being stranded and calling out the AA I have had the following items changed.

1. New high power battery - fixed problem for a while

Since becoming deceased we have added...

2. New ignition module
3. New crank sensor
4. New distributor cap

The car is now totally dead. The AA man, and now the local garage where the car is currently being stored are totally stumped. Apparently, there is now no spark at all. The engine obviously turns well, but no spark, even with extra power from another vehicle.

Any ideas what the garage, or me, should be looking for?

Any help would be appreciated. I do not want to throw my car away!

Thanks - Clare

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


The system works this way, the ignition control unit ( ECU)
senses flywheel position and rotation from the crank sensor and works out when to fire the coil.
It fires the coil by sending a 5V square wave signal to the ignition amplifier ( power stage in Volvo speak. )
this then switches the coil negative terminal to earth just as old fashioned points systems used to.

With the ignition on you should have 12V at both coil low tension terminals.
Put a test lamp on the negative terminal, and when the engine cranks over the lamp should flash or least vary in brightness.

If this is OK plug a known good HT lead into the coil tower and check for spark.
If you have a good blue spark here the problem lies in the HT leads,
distributor cap or rotor.

If your garage can`t sort this out without fitting parts on a trial and error basis, take the car to someone who knows how to do a proper diagnosis.

Colin.

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

Thanks Colin

We know there is no spark - so this is why everybody is stumped.

Whilst sort of understanding your explanation I am not sure what the implication is when we know we have no spark

Thanks again

Clare

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


Clare,
What I tried to do was to give an explanation of how the system works and suggest a few very basic checks to hopefully guide someone who does not fully understand the system through the diagnostic process to isolate the fault to a particular component of the system.

It is an unfortunate fact of life that most, but not all, mechanics are woefully lacking in electrical knowledge and attempt to make up for this shortcoming by randomly replacing parts in the hope that they will eventually hit upon the one that cures the problem.
Unfortunately these randomly replaced parts which do NOT cure the problem are still charged to the customer.
(Before I get abuse from others for having a go at mechanics I should point out that I`ve been a mechanic/auto electrician for more than 30 years)

The ignition sytstem on these cars isn`t exactly rocket science and anyone with a reasonable amount of knowledge and equipment should be able to sort it out quite easily.

Colin.

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

[Clifford Pope]

Colin is absolutely right. I was terrified when my Torslanda with fuel injection and the full electronic set up started having occasional starting problems. I am used to old fashioned carburetors and points.

But I took it to a one-man car electronics specialist who for a very modest fee (£50) not only gave it a complete once-over, sorted the problem (gave me a spare tested ignition amplifier) but most importantly, a complete guide to how the system worked and how to do basic tests.
Some of the old principles still apply, and any decent garage ought to be able to narrow down the cause or precise point of non-sparking.
As Colin says, there is the low-tension voltage supply to thje coil - test it with a light bulb. There is the quality of the spark at the coil - test it with a spare high-tension lead.
There is the spark at the plugs - test each one with a spare plug on each lead in turn.

The result of each test in turn, progressing along the system, should indicate where the spark stops. Then look at that component, and the wiring to it.