Thread: Electrical gremlins

Whats your earth for the meter?

something in the dash or did you go back to battery/chassis?

Thanks for reply Dave, the test is between battery positive to coil negative ign off should read 0 volts but reads 14.5v. ign on should still read 0v but I have .15v but doesn't tell me what it could be if the figures are not right. Cheers,Wayne

Originally Posted by whlump

Thanks for reply Dave, the test is between battery positive to coil negative ign off should read 0 volts but reads 14.5v. ign on should still read 0v but I have .15v but doesn't tell me what it could be if the figures are not right. Cheers,Wayne

Whatever you've measured sounds pretty much right, not sure what you're trying to achieve here? Turn the ignition key on and there's power to the ignition coil. The ignition coil negative will be at exactly the same voltage as the ignition coil positive unless the engine is actually running. Then there will be a fast varying voltage at the coil negative that your meter won't pick up as its too slow. 0.15V voltage drop to the coil with the ignition switched on is trivial.

14.4v on the meter without the engine running?


before you go any further check what voltage is on the battery post to post. I think the first thing you need to sort is that the battery in your meter is going flat or the meter is out of cal.

its been a very very long time since I had to do low compresion engine stuff. can you point me at which rave, section part and page you're using so I start out with the same fault finding page as you do?

You should only get 14+v with engine running , i get 14.4 but then settles back to around 13.2 with engine off and around 12.9 after 15 mins or so.

Sent from my GT-I9300 using AULRO mobile app

Thanks for replies, I should have said it's a 95 V8 auto dual fuel to start with, Dave the pages I am on Rave cd discovery, workshop manual, discovery 2nd edition, 86 electrical, fault diagnosis, lucas constant energy ign system V8i. the car doesn't start turns over no worries fuel pump starts test 1 no spark, test 2 ok, test 3 funny numbers but doesn't say what to look for, I have read about the spider unit so maybe it is that that I need to look at anyway thanks again, cheers. Wayne

ok, couple of secondary tests....

confirm the voltage at the coil from bat neg to coil positive with both the ignition on and off. it should come up as whatever your meter reads across the battery when the ignition is on.

now with the ignition off disconnect the connections on the -ve terminal and the HT terminal on the coil.

check for voltage with the ignition on from battery negative to the positive terminal of the coil, then the negative side of the coil you should see the battery voltage (or near enough to) in both places, if you dont you now need to check the coil for continuity.

assuming that passes. (I never worked out why Landrover didnt start with the simplest check first)

do test 5 and check the pickup in the dizzy and redo the checks on the amp.

I suspect that if you have 14v from battery + to the negative side of the coil with the ignition off that the amps output is shorted and the amp needs to be replaced.

the fault finding follows the same basic principle as for doing points. the step you've tripped over is the same as for finding shorted points. When the points (in this case your amps output) are open you should see 0v when they are closed 14v. But because the amp needs to be powered up (it gets its power from the +ve side of the coil as per the pictographic for getting v1-4 voltages for test 2) to make the electronics goto closed to allow the coil to charge the initial checks have the voltages reversed to what you would be looking for on a points setup.