BX breakdown

ellevie · Post by **ellevie** » Sat May 26, 2007 11:31 am

Those are much better pics Mark.

The connection between the sensor and the amp seems to be a bit of a mystery.

Two possibilities suggest themselves.

One:
As suggested by the circuit diagram above, the sensor and amp may be directly connected. Have you actually taken the amp off to see if there is a connection underneath. If there is, then you can measure the resistance of the sensor and also clean the contacts with a few drops of WD40 and plugging it in and out a few times. Can you take a pic if this is the case.

Two:
It might not be a 3-way connector to the amplifier as I have assumed, but instead it's a 5-way or more to include the extra wires for the sensor. In this case, I would expect there to be a sensor plug, about the size of a thumb-nail, on the opposite side of the distributor.

Good weather today for multimetering.

mnde · Post by **mnde** » Tue May 29, 2007 10:48 pm

I decided to remove the ignition module and here is what I found underneath:

The hidden magnetic sensor terminal!

And I've been busy with the multimeter.

Resistance (Ohms)
=======
* Coil multiplug:
Term 1 (nearest head) = 22.9
Term 2 = 23.2
Term 3 = 22.6
Term 4 = 22.6
* Ign module 3 way plug
Top terminal = 23.3
Middle terminal = 0.08
Bottom terminal = 22.7
* Sensor = 318
* Coil HT Lead. Set at 0-200K Ohms range, reading was 5.0

Voltage (ignition on)
=====
* Coil = 12.03 volts at each terminal on the multiplug

* Ign module
Top terminal = 12.03V
Middle terminal = 0V
Bottom terminal = 12.03V

I didn't get time to test the other HT leads.

So what's all this mean, and what else can I test? I found a wire seemingly from the module going to the earth bolt on the ns inner wing - I unscrewed this and saturated the whole area with WD40.

Ellevie, you say you got a primary reading of 0.8 Ohms and secondary 7000 Ohms. How do you do this? (i.e where to touch the multimeter probes)

Cheers,

Mark.

ellevie · Post by **ellevie** » Wed May 30, 2007 10:02 am

Great Mark, that's the sensor mystery solved. It looks like the little black thing is an adaptor between the amp and sensor. Don't forget to also give this the WD40 push on & off cleaning treatment; also check it for continuity on the lowest resistance range. This little adaptor plays the same role as 3 connectors and 2 cables in my 19TRS. It also looks like the circuit diagram above is a fairly accurate description of the circuit.

We're certainly beginning to tick the check boxes off now. 5000 Ohms on the secondary and 318 Ohms for the sensor are broadly similar to my 19TRS. You've also got 12V present on the coil.

I measured the resistance of the primary by,
1) selecting the lowest resistance range of 200 Ohms
2) the 2 probes shorted together measured 0.6 Ohms.
3) connecting the probes across the primary spade connectors measured 1.4 Ohms
4) the difference 1.4 less 0.6 gives the primary resistance of 0.8 Ohms.

If the diagram is correct, in your cases contacts 1&2 are connected together at one end of the primary and 3&4 form the other end. As you can see at 0.8 Ohms the primary is practically a short circuit.

The secondary is connected to the primary at pins 1&2 so I simply measured between the HT output and the primary or LT spade connector to get the secondary reading.

To check for continuity of the cables it is best to disconnect them at both ends and measure as I have done for the primary above. For short cables like this you are really checking the cables act as a short circuit between the probes, reading the same values as with the probes shorted together. However you need 4 hands or an assistant to connect the probes to both ends of the cable at once. The easiest way to verify sound connectivity between the amp and coil is to disconnect the 3-way connector at the amp whilst leaving the 4-way connector still connected to the coil, and measure the resistance between contacts 3N-1 and 3N-3 because these are effectively shorted together by the primary of the coil so they should be acting like one long wire, thanks to the coil. If you were to measure say something like 7 Ohms here rather than a short circuit, then you would know that there was a problem here. See if wiggling the cable cause the short to suddenly go "high".

Also with the 3-way connector still disconnected verify that the middle contact 3N-2 gives good continuity to ground/chassis.

If all the connectivity checks out "ok" and it still doesn't produce a spark then it will be time to check out the individual components by substituting from or to your other car starting with the amplifier and then the coil and so on.

You're nearly there !

mnde · Post by **mnde** » Fri Jun 01, 2007 3:51 pm

Thanks for the info and encouragement Ellevie

I'm going to have another look at this hopefully tomorrow, but if I don't get anywhere I'll be at the stage where I think I need assistance on this one from someone who really knows what they're doing. I will even offer transport both ways in my trusty GSA Estate as an incentive.

I'll be moving house within the next two months, so I really need to get the car up and running again soon but don't have all that many free evenings/weekends to devote to it. I may have to sell it too, if the new place doesn't have enough parking spaces for 4 cars...

Cheers,

Mark.

mnde · Post by **mnde** » Thu Jun 07, 2007 12:24 am

Right I've been busy with the multimeter again! Some readings might be irrelevant (sorry) but I've written them down anyway.

Multimeter @ 200 Ohm setting
===================
Probes shorted together = 0.05
Reading btw 3N-1 and 3N-3 (measured with 3-way connector removed from amp) = 1.0
Reading btw amp 3-way negative (3N-2?) and chassis earth bolt = 0.06

Multimeter @ 20k Ohm setting
===================
Reading btw coil HT terminal and 4way connector = 4.81

Now, I found some surprising differences in readings between the two amps I have. Amp 1 is the one from the dizzy that Ken gave me. Amp 2 is the original one and gave some entirely different results (highlighted in bold). Readings obviously taken with the amp removed from the distributor.

Amplifier 1 (Amplifier 2 results in brackets & italics)
======
@ 200k Ohm setting
Reading btw 2 sensor pins on rear: 41.9 (42.0)
Reading btw upper amp pin and upper sensor pin = 47.2 (45.5)
Btw upper amp and lower sensor pins = 5.9 (4.1)
neg amp and upper sensor pins = 44.9 (45.4)
neg amp and lower sensor pins = 3.6 (4.0)
lower amp and upper sensor pins = 47.6 (45.8 )
lower amp and lower sensor pins = 6.3 (4.4)

@ 20k Ohm setting
Reading btw upper and lower amp pins = 5.05 (272 @ 2000 Ohm setting)
Upper -> Neg = 2.33 (148 @ 2000 Ohm setting)
Neg -> Lower = 2.72 (414 @ 2000 Ohm setting)

@ 2000 Ohm setting
Reading between 2 sensor pins on dizzy = 324 (326)

Also, with Amp 1 now back in place on the dizzy, I took readings between the amp pins and the 3way connector terminals:

@20k Ohm setting
Upper pin to upper connector terminal = 2.39
Lower pin to lower connector terminal = 2.77

@ 200 Ohm setting
Neg to neg = 0.5

NB, I haven't yet tried swapping back to the original dizzy mated to Amp 1. But I've tried both amps on Ken's dizzy with no joy.

God this must be boring to read, but I hope it makes sense to somebody! Is there a clue in these readings??

Cheers,

Mark.

ellevie · Post by **ellevie** » Thu Jun 07, 2007 4:12 am

Good work Mark, you have been busy !

Reading btw 3N-1 and 3N-3 (measured with 3-way connector removed from amp) = 1.0

This is good, 1 Ohm is about what you would expect from a good connection. You have verified that the primary appears as a short circuit and in doing so you have also verified that the two wires in the cable are good conductors.

Reading btw amp 3-way negative (3N-2?) and chassis earth bolt = 0.06

This is also good, you have verified that the amp has a good "earth".

You have also previously verified that the 12V supply is present.

It only remains to convince yourself as best you can that the little adaptor that connects the sensor to the module is doing its job. This adaptor is small but it is very important, poor connectivity here could easily kill the spark.
When you plug the adaptor on to the sensor and on to the module in turn, does it feel loose or nice and tight ?
Can you use the adaptor as an extension to measure 42 Ohms between the two sensor pins on the module ?
Can you use the adaptor as an extension to measure 324 Ohms on the sensor itself ?
Significantly higher readings would indicate poor contact between the adaptor and the sensor or between the adaptor and the amp.
It may be trivial but you should also measure directly across the adaptor to confirm that each path behaves virtually as a short circuit.
You should get the same reading you would get with the probes shorted on the lowest resistance range.

As for the discrepancy between the readings for the two modules, it might be accounted for by the modules being made by different manufacturers, but it's best to be suspicious. Are they from different makers ?

It seems unlikely that both amplifier modules are duff but if this turns out to be the case, they are available for £11.93 from VEO
http://www.vehicle-electrics-online.com ... ry_id,520/

It is possible to test for a failed coil in situ, but you will need a spark tester costing just a few quid and also some test leads with crocodile clips. I suggest you buy these as they are indispensable for diagnosing these problems. Look for "spark tester" and "crocodile leads" on eBay

I will advise how to do this test in due course, but a little care is needed as the coil can be damaged if 12V is applied directly across the primary for an excessive time.

mnde · Post by **mnde** » Thu Jun 07, 2007 10:07 am

Hi David,

Thanks for this and your reply to my PM

As for the discrepancy between the readings for the two modules, it might be accounted for by the modules being made by different manufacturers, but it's best to be suspicious. Are they from different makers ?

No I checked, they are exactly the same Bosch model, same model number.

When you plug the adaptor on to the sensor and on to the module in turn, does it feel loose or nice and tight ?

I think the connection is tight both sides, and it's all WD-40'd up. BTW I got the same readings for the sensor (324 Ohms) across the sensor pins on the dizzy *and* across the terminals on the adaptor when fitted in place. So that seems to rule out the sensor side of the connection.

Can you use the adaptor as an extension to measure 42 Ohms between the two sensor pins on the module ?
Can you use the adaptor as an extension to measure 324 Ohms on the sensor itself ?

I think I know what you mean but just to check, where exactly do I put the probes for this test?

I recognise the spark tester - that's what the AA man used to verify there was no spark. He first placed it on top of the spark plug furthest from the distributor and held the HT lead to it while I turned the engine over on the starter, then he unplugged the HT lead from the coil and did the same test there. Which still points to the amp/sensor end of things...

Cheers,

Mark.

ellevie · Post by **ellevie** » Thu Jun 07, 2007 8:46 pm

No I checked, they are exactly the same Bosch model, same model number.

This does look like one of them might be duff, although the discrepancy could still be caused by them being significantly different revisions from Bosch.

I think the connection is tight both sides, and it's all WD-40'd up. BTW I got the same readings for the sensor (324 Ohms) across the sensor pins on the dizzy *and* across the terminals on the adaptor when fitted in place. So that seems to rule out the sensor side of the connection.

I agree. Now you just need to rule out the amp side of the connection by removing the amp and plugging the adaptor into it and measuring for 42 Ohms through the adaptor.

I think I know what you mean but just to check, where exactly do I put the probes for this test?

As described above, basically the adaptor has 4 connections any of which could be making poor or no contact. Using it as an extension to measures both ways first 324 Ohms and then 42 Ohms will test these 4 connections.

I recognise the spark tester - that's what the AA man used to verify there was no spark. He first placed it on top of the spark plug furthest from the distributor and held the HT lead to it while I turned the engine over on the starter, then he unplugged the HT lead from the coil and did the same test there. Which still points to the amp/sensor end of things...

When it works it makes a very bright orange flash easily visible in daylight. When you get the tester and test leads I mentioned in the PM, I'll tell you how to use them to test the coil with the amplifier disconnected.

David

mnde · Post by **mnde** » Mon Jun 25, 2007 5:35 pm

OK, I've verified that there is 41.9 @ 200k Ohm reading with the adapter plugged into the rear of the amplifier (and 324 Ohms with the adapter plugged into the sensor). So that rules out the adapter.

I'm going to go and nab the coil and amplifier off the other Meteor tonight, so I'll let you know if my BX is resuscitated!!

Out of interest - what sort of voltage should I read across the sensor pins on the distributor with the engine turning over on the starter? I wanted to verify the magnetically induced pulses are working!

Cheers,

Mark.

ellevie · Post by **ellevie** » Mon Jun 25, 2007 7:40 pm

Good Mark, it looks like the wiring etc is sound, so it should be fairly straight forward to fix by substitution. If the other car is nearby, then it might be quickest to try the amplifier first to save you the trouble of removing the coil if it turns out to be the amp.

The voltage waveform from the sensor is a double pulse, where the second pulse is of the opposite polarity to the first one. I believe it is supposed to be about 3 volts but you would need something more sophisticated than a multimeter to observe it correctly. It would look kind of like the letter "S" on its side.

Good luck !

David

mnde · Post by **mnde** » Tue Jun 26, 2007 11:52 am

Thanks David!

Last night I removed the coil, amplifier and the associated wiring loom from the other Meteor (7 miles away), so tonight, weather permitting (

), I will start substituting parts: first the amplifier, then the coil and then if necessary the wiring. At the moment my money's on the coil...

The garaged Meteor has the SEV Marchal distributor and amp. I'm hoping this amp will be compatible with the Bosch distributor... it certainly looks very similar!

Cheers,

Mark.

adamskibx · Post by **adamskibx** » Tue Jun 26, 2007 1:18 pm

Wow. I might print this thread off to help me diagnose the GT later! Good work ellivie. Good luck with your car Mark.

ianselva · Post by **ianselva** » Tue Jun 26, 2007 4:23 pm

That was exactly the trouble I had with my BX16, . Just come out of the Gothard tunnel into France towing my racer at 2.00 in the morning when it just died.
It took me some time to get it going again. I thought it must be the ignition module but all I could do was pull off each terminal in turn , clean it and put it back. Then I tried again and it fired. It never gave any more trouble and was still going strong the following year when I sold it. So it must have been poor contact on one of the connections.