1988 740GLE no spark

Gundulf · Post by **Gundulf** » 24 Apr 2016, 13:19

Hello Guys!

My dear Volvo left me stranded at the Highway the other night.
After much research I find myself stuck at the lack of ideas.
I have no power to the spark plugs.
The thing i have tested:
I have voltage to the ignition coil 12 volts
I have signal coming from the ECU to The power module (7-8 hz)
I have ground coming from the power module to the ignition coil( connecting it to the + of the battery gives me a 25 volts AC reading, which should be okay?
I connected a lap to the + and the - terminals of the ignition coil(disconnected from it) and get a solid on while on power, and get a flickering light when cranking. But if i connect the - terminal to the power coil the signal dies.
I bought a new power coil, and same issue.
at this point, I have no idea. disconnecting the ignition coil everything seems to be working as intended, as soon as i connect it the power module signal dies.
Any thoughts?
Thanks for your time

93Regina · Post by **93Regina** » 25 Apr 2016, 11:44

Gundulf wrote:ECU to The power module (7-8 hz)

See: Volvo TP 31397-13 Ignition

Gundulf · Post by **Gundulf** » 28 Apr 2016, 17:46

Thanks 93Regina! That was something i did not know existed, and should have had

After i posted the question and after a long time scratching my head. I decided oh well lets buy a new ignition module. It arrived today, and i connected it and... no start. I was alone so i could not test the spark and crank the car so i gave up and came to see if i had a reply. And after reading the manual a few times I realized how little i knew about how the ignition worked.
As I understand now, It is to be expected to loose the (-) signal to the coil while the ignition is on, since its a feature of the control unit to avoid overheating and cooking the coil

So I'm sitting here wondering " man i just got a new ignition module" and still no start. And it came to me. Sometimes after a few days without starting my car it seems like the fuel lines dry and unless i step on it while cranking it wont start. So here i go one more time, pull the cable mess up, sneak my foot on to the pedal, crank it up and nothing, and just as i stop cranking, just then a cough of the engine

and now i am excited, I crank it up a little more fuel and success. So in the end it appears my module was fried. I will now need to buy a new distributor rotor, and cap, Since i broke the rotor xD but it needed to be changed since after 113k miles it was well beyond its prime.
Thanks again 93Regina! your help was paramount.