To the ignition experts again:

Back in the US and back to the No-Start 1995 Discovery 1.

Still trying (its been six months now) to get the 1995 Discovery to start. Still no spark. (Remember the history? Already 2 new ignition amplifier units and a new coil, and not more than a week or two with each before she failed to spark again).

Can someone please explain the following from the RAVE Manual on testing for spark:

Page 86 ELECTRICAL

TEST 2:
L.T. Voltage
Switch ignition ’On’ - engine stationary.

(a) Connect voltmeter to points in circuit indicated by V1 to V4 and make a note of voltage readings.

V1. Battery+ to battery-. I get 12.6 volts

V2. Battery– to Coil+. Reading is 0 volts

V3. Battery– to Coil-. Reading is 0 volts

V4. Amplifier screw to earth. Reading is 0 volts


(b) Compare voltages obtained with specified values listed below:

Expected readings

V1. More than 12 volts. (Of course)

V2. 1 volt maximum below volts at V1. (Why would there be a 12 volt reading from the earthed (negative) terminal of the battery? Then I could do the test by connecting the Coil positive to any earth?

V3. 1 volt maximum below volts at V1. (Same question as above).

V4. 0 volt - 0.1 volt. (This test is also connected to earth, so why only 1 volt max in this case?).

NOW LOOK AT TEST 3:

TEST 3:
Amplifier Switching
Connect voltmeter between battery positive (+ve) terminal and H.T. coil negative (-ve) terminal.

Voltmeter should register 0 volts. (I get 12.3 volts)

Switch ignition ON. Voltmeter should still read 0 volts (I get 12.3 volts)


My questions:

1. Can the experts please explain to me how the 12v DC electricity works here? The test requirements do not make sense to mem but vehicle electricity and electronics are not my forté.

2. If the test requirements are correct why do I get these opposite readings?

Thank you for just the short facts please. I rather expect another amplifier failure as they seem to have about a 14 day life - but before I order another amplifier and coil I have to get to the bottom of the above.

By the way, the pick-up coil and its connection to the remotely mounted amplifier tests OK. (But can one trust the RAVE manual for accuracy of the mentioned resistance?).

Thanks for your time and expertise.

 

Hi Montero Man I'll try to answer questions based on my 12vdc experience and info you provided, I dont have the rave to check and this is all based on what I would do:

V2 I think is verifying positive power to coil. If you dont get voltage between positive on coil and neg on battery with ignition on then your problem is whatever powers coil? I think if it asked for coil + to battery - in that order it would be less confusing but its the same thing. The manual is probable assuming your wiring is good and you are testing the equipement. Yes you could test to any metal since the battery ground goes to body & chassis at two points. .

V3 If the amp controls the power through ground then you are bypassing that when you connect to battery to make sure voltage is at that point.

V4 seems to be looking for a drain/leech in excess, possible corrosion identifier? Its not 1v it is .1v showing you do not have power leech I believe

For test 3:

If the voltage between power + and coil - should be zero when truck is off then perhaps the amp controls the coil through the ground and it being open identifies amp as issue. I would find that ground for amp and check for corrosion and replace maybe you are burning through amps because the ground is poor? Your circuit is being completed when it should not according to your info. I think you are getting a ground when you should not off the coil.

I think it is safe to say the amp is probably bad but its not the main issue. Your issue is that faulty power is burning up your equipment and sensitive stuff like this can burn up quick with poor or irregular voltage. I think you have a wiring issue (most hopefully the ground) the circuit is not supposed to be complete without the truck running. Is there any sort of relay that controls this system? If so check it as well as they can remain stuck too.

Some dc electronics are controlled through the ground (like the a/c blower) but in that case the voltage controls the speed of the fan. This is all speculation based on your info I hope it helps!

Your readings are not opposite they are just showing a complete circuit where it states there should not be one....yet(?)

Also what remotely mounted amp do you mean? Do you have a test unit?

 

Many thanks, I appreciate your kind assistance.

On these vehicles the ignition amplifier unit used to be mounted right on the distributor. On this and maybe later models it was moved to a remote position next to the radiator on the left side, close to the ignition coil.

You are probably correct about a grounding issue somewhere in the system because it is ridiculous, even with Lucas equipment, to burn out an amplifier unit and ignition coil every week or so.

I have in fact cleaned every single grounding strap between the engine and body.

There are quite a number of wires coming from the cockpit area to the engine which have no further connections - this is just the way it was when I took posseseion of the vehicle and was assured by the local seller that she was a very good runner (Well she was for a week, I must say)...

Maybe a first step would be to remove all those superfluous wires. I believe the ignition lock is quite a challenge to open up and remove and disconnect/reconnect the necessary, and my knowledge of wiring is at that level where the task seems rather daunting.

Another question: What is the risk for me to bypass the ignition key and hotwire from Battery Positive (or as you have explained negative) to the coil Low Tension Positive? I want to see if there will be a spark from the coil HT lead to the engine block when the engine is cranked.

Thanks again for your time and knowledge.

 

well if all the grounds are good then maybe a pinched + or those cut wires may be contacting?

I would be very careful about bypassing key as you may activate the alarm ecu killing the truck. I dont know if you have a functioning alarm system but if you do you do not want the alarm ecu thinking you are stealing it and you will have a new outdoor sitting area.

 

I completed and posted the 4 tests you requested on my thread regarding my fuel pump issue on my 94 Disco I. They are posted on that thread. Thes tests were slightly different from the tests you requested on this post.

 

...that the polarity between the battey and the LT terminals on the ignition coil is reversed from what it should be.

1. I should get battery voltage between the battery negative and both coil LT terminals, but my system reads zero volts.

2. I should get zero volts between battery positive and both coil LT terminals but mine reads battery voltage.

This quite likely is the reason why this vehicle kills an ignition amplifier every week or so.

I am not sure where to start looking for the cause of this but shall remove the few loose wires that do not go anywhere, and then examine what comes out of the ignition key barrel.

Any suggestions, Scouts? Or any auto-electrical expert?