No spark on one bank

Hi all

I have a 1979 Euro 308 GTB, carburettor car with a single distributor. There is no spark at cylinders 1 to 4. I have checked the leads (using the induction trigger on a timing light) and there’s nothing at the lead from the one coil feeding that bank to the distributor.

Amazingly, at idle, it sounds quite smooth on 4 cylinders…

Anything more I should check before ordering a new coil?

Many thanks for any help.

Chris

 

If you are still running points you can check that they are opening. Do both a visual inspection, and check grounding of the neg side of the coil when the points open. If running an electronic switch instead of points, the neg side test should still be valid. It’s more likely to be a basic wiring or triggering (points) issue than a coil issue, but coils do fail.

 

Many thanks for this. I’ll get the distributor cap off and see what I can see.

 

I had exactly the same problem, though only when hot. It turned out to be the ignition amplifier which is a small electronic module mounted on the coil's heatsink. Beware there is a bad batch of these out there. It took 4 attempts to find one that worked. The made in china ones from various brands were all duff, but one sourced from germany worked ok.

 

Thanks for the advice.

 

Could be coil, amplifier, dizzy cap or rotor or bad VR sensor (if electronic), On my car it was a broken wire inside the dizzy.

Best amplifiers

Hella 5DA 006 623-05
Beru ZM005

Tony

 

Unplug the VR sensors from the ignition module, check the resistance of each (should be the same) and then turn the engine over and check that you’re getting a pulse from both sensors. My guess is the VR sensor has bad wires or is dead. You can always plug the 5-8 VR sensor into the 1-4 coil and check for a spark. That could rule out a bad coil or amplifier module.

 

Thanks for all the help everyone. Turns out my car has the SM805A distributor with the VR sensors (as Tony L and Derek W suspected). Not sure if that was standard fitment. I got the distributor cap off and had a look at the distributor, but there wasn't much to see. I removed the distributor to take a better look, and tested the resistance of the sensors - all in line with expectations at close to 700 ohms.

I then went to take a closer look at the coils with the distributor out of the way, and noticed a yellow wire attached to the lower coil, with a further yellow wire coming off it to a spade connector not attached to anything. I checked the wiring diagrams which showed this as needing to be connected to the coils with the other end of it connected to a switch with the 'run position' marked on it - which was a clue to the issue...

With that plugged in, the engine is back on all 8 cylinders. The spark plugs had been changed earlier, and I suspect an arm reaching through to the front bank had pulled that wire off.

Thanks for all the responses for what turned out to be a slightly embarassing fault!. I now need to check the timing - I am pretty sure I got the distributor back on in the same position as it came off, but you never know. I connected the timing light up but am really struggling to see the timing marks on the flywheel. I will try a paint pen to highlight the markings, but let me know if there is a better way.