Petrol BX ignition timing.

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adamskibx
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Petrol BX ignition timing.

Post by adamskibx » Sat Mar 25, 2006 1:45 am

Im rather curious. Petrol BX's have electronic ignition. Does this mean that the distributor still contains points? I have managed to get the "new" engine into the GT and is all up and running etc, but I have had to use the GT's original distributor even though the TRS one had the same plastic wire connecting block (mounted to distributor body, not on a wire like the GT one). When I originally put the TRS engine in, I decided to keep the original distributor for that engine as timing had been set to 7 deg BTDC for unleaded fuel-absolutely no sparks at plugs, so I assume the electronic ignition in the GT works differently. This means that I have simply plonked the GT's distributor on with no idea what the timing is. It runs but will obviously need fine adjustment.

Two things im unsure about are:

What on earth does the "Top Dead Centre sensor" on the flywheel do, and what on the flywheel allows it to sense when top dead centre passes? I assume that its the recessed bit about 4mm long and deep, and, if it is what is the Top Dead Centre "marker" on the flywheel if its not that?

Although timing the ignition with a stobe light is usually an easy job, I have no idea what is what on the flywheel on these engines. When I had a Dyane, I just did all this statically, and all the marks were obvious.

Adam

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Post by DavidRutherford » Sat Mar 25, 2006 6:49 am

My method for timing a "distributor" petrol engine when no timing marks are visible:

Disconnect and plug the vacuum advance line from the Carb.

Drive the car up the road in 2nd gear with your foot flat to the floor. Does the engine pink?

No: advance the timing by a bit, and try again.

Yes: Retard the timing by approx 2-3 degrees, Make sure this has removed all Pinking, and lock the distributor there. Reconnect the vac line, and you're done.

This means you have as much advance as is safe, and hence you have the best fuel consumption possible, without the risk of damaging the enigne.
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Re: Petrol BX ignition timing.

Post by (CZ)enda » Sat Mar 25, 2006 10:28 am

My understanding is this:
TDC sensor is electromagnetic sensor on the flywheel casing, bolt-size thing in the casing side closer to the bulkhead. Anytime the notch on the flywheel passes by, the sensor sends a signal to ECU (it may also be that it is the other way around and that ECU detects lack of TDC sensor signal instead). This signal is then processed in ECU to provide for exact ignition timing.
TDC sensor is only present on petrol engines with electronic injection and on diesels, while on diesels it is used as rpm sensor providing data for tachometer.

Quote:
Petrol BX's have electronic ignition. Does this mean that the distributor still contains points?

My understanding of "Electronic ignition" is that the distributor is that of breakerless type, i.e. without cam/contact assembly. The signal is processed in ignition module (which, on my 16TRS, is flat blue thingie with BOSH-something written on it, located on aluminium plate below ignition coil). The rest of the system consists of traditional distributor cap (with points :wink:) and cables.

I think there should be timing marks located on the engine/gearbox flange visible from above in the flywheel window, possibly on brass-colored plate. If memory serves right, they show 0° and 10° :?:

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Post by adamskibx » Sat Mar 25, 2006 5:56 pm

OK thanks for the tips guys. I like your method of timing the distributor David, but ive got two questions; how obvious is "pinking" and what are the main symptoms? Also, if you get the "not pinking" position just right with the vacume advance hose off, what happens when the vacume advance is connected up again? Would it not advance the ignition to a point where it pinks again?

(cz)enda: Thanks for explaining all that. Your dead right about the timing marks being on a brass plate ranging from 0-10 deg, and I need to match the mark on the flywheel against 7 degrees rather than the standard 10 apparently, for unleaded fuels etc. One thing im still confused about is, if the distributor still has points, what is the the job of the TDC sensor becasue surely you set the timing with the distributor (with points inside it).

One other way I was thinking I could time the ignition is this:

The original distributor had markings on it and the engine, and was set to 7 deg BTDC according to the log book of the donor car (unleaded fuel setting). If I were to place this distributor back on the engine in this position, then connect up a multimeter to measure resistance to the connections, then turn the engine over by hand until the points either break or make, and note the engine position by marking the flywheel etc. Then I could remove the distributor, place the other one on, and rotate it so that the same result can be obtained with this distributor. Does that sound barmy or could it work lol? I suppose this might help explain which of the odd marks on the flywheel is the propper marking at least. The other thing I really dont get is; why wont the original distributor work? The only thing I can think is that the connecting block of both distributors is identicall, and has three pins, but there are only two wires; maybe Citroen deliberately used a different two of the three pins for the later type distributors?

Thanks a lot, Adam

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Post by adamskibx » Sat Mar 25, 2006 6:16 pm

Ahh; I have just re-read your method David and think I have understood it a bit better now. I take it when you have found the point of pinking, the retarding by 2-3 degrees takes it back as much as the vacume advance could ever bring it forwards when under load and revs etc.

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Post by ellevie » Sat Mar 25, 2006 8:49 pm

I have an 1988 BX19 TRS which has no TDC sensor and no points. Instead of points in the distributor there is a small magnetic sensor which produces a weak signal which is amplified by the transistor module and then used to switch the coil. Timing is adjusted with a stroboscope pointing at the flywheel TDC and instead of rotating points you loosen the distributor retaining nuts and rotate the distributor body to adjust the TDC notch to the required position.

I had an ignition problem quite a few years ago, where a poor or completely absent spark was traced to the three pin connector which plugs into the magnetic sensor on the distributor housing. This connector forms one end of a short lead about 8 or 9 inches long which has a bigger 3 pin connector at the other end which is strapped to the bulkhead. You should be able to remove this lead and check for good continuity with a resistance meter. In my case it was one of the two signal lines which was faulty but the earth line is important too as I think this is the earth path for the transistor module.

It might be worth substituting the known good short lead for the suspect one if it fits, to see what happens. In my case I ran a bypass wire and it has worked fine for years.

Hope this helps.
David

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Post by adamskibx » Sun Mar 26, 2006 4:03 am

Thanks for the reply ellevie. Its odd that your BX19TRS had no top dead centre sensor, as the G reg (1988) 19TRS car I took the engine from has one, and the original 1985 GT engine had one too. From my years of Dyane/2cv ownership, I know that you could upgrade this engine to electronic ignition which used the original points, but took away the full coil low tension current from the points, and just amplified it instead, but if you fitted a Visa 652cc engine, it would have a magnetic sensor on the flywheel instead. Unless I can find out how I can time the ignition back to its original setting, I think I will try and use David's method as this sounds quite practical. Its actually amazing that I got the thing started; not only did I randomly screw on the old GT distributor, I had to make do with the knackered old GT ignition leads for now, dating form 1985. Not only are they old and crusty, but they had got wet where I had to leave the car with no bonnet on overnight while I had to rush off somewhere at 6 pm on the day of fitting the engine. The later type 1905cc engines head seems to have much narrower spark plug recesses than the early engines, so the leads from the GT distributor had to have the rubber water proofing surround cut down in order to fit (the TRS distributor had male type connectors, the GT's has female). Ellevie, your explaination about small magnetic impulses instead of points would explain the fact that the TRS distributor wouldnt work with the GT's ignition electronics; perhaps the GT has a different amplitude of magnetic impulse, or is of the on/off points type instead.

Time to go down and have a good investigation I reckon! Ill need my thinking cap on thats for sure.

Thanks for all the posts.

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Post by adamskibx » Mon Mar 27, 2006 12:57 am

Right. She's all bolted together and ready to drive off now, but today it only fired on 3 cylinders!! Arhhh! Sounds quite dramatic but I can tell its due to the misfire from the exhaust gas implulses coming form the exhaust. Well at least I can drive it away now so it wont be trapped by houses; I suppose its just a case of cleaning the igniton system up now, then setting the timing. I found out the reason why the TRS distributor would'nt work; the ignition module is on the distributor body and the GT one is on the bulkhead like yours was ellevie. This means that when I connected up the TRS distributor to the GT, there were 2 ignition modules in series, so it was bound not to work. I found a notch in the flywheel too, which is additonal to the TDC sensor notch, so this is bound to be the timing mark, even though at the point this meets up with the 0 mark on the scale, the TDC sensor is not near the TDC recess in the flywheel?

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Post by DavidRutherford » Mon Mar 27, 2006 12:30 pm

Adamski.

With my method of timing the engine, the "pinking" can be very obvious, as it sounds like there is a big bracket loose on the engine which is clattering about all over the place. When it's a bit less, it sounds like there's a midget in the engine bay with an array of hammers, banging on the rocker cover!

The retarding of 2-3 degrees is to ensure that you avoid pinking completely, as it can be very damaging to an engine.

This is all done with the vac advance removed to reduce the amount of ignition timing scatter, and effectively puts the timing at the point it would be when you are at "full throttle".

The vacuum advance can actually advance the ignition by 20-25 degrees, but this only occurs at partial throttle. when you "boot it" the vacuum in the carburettor drops to almost nothing, and hence the ignition is retarded back to the point it was set at (but, there is of course still the mechanical advance.. the two weights in the bottom of the distributor)

What the vacuum advance does is to advance the timing when the engine is working at a low volumetric efficiency (part throttle). This is possible, as the compression pressure is reduced a lot by the reduced volumetric efficiency, and you can run with a lot more advance, mainly for fuel efficiency.
Basically : Smaller throttle opening = less overall compression = can run with more ignition advance.
So the system is: smaller throttle opening = more vaccum in carburettor = more ignition advance

Some engines don't even have the vacuum advance (my old Fiat X1/9 being the most obvious I can think of). You can run your BX with the Vac advance pipe disconnected and plugged, and it will still run just fine, but will have slightly worse fuel consumption.

What you are doing, is setting the engine to run best at its best volumetric efficiency (throttle wide open) and allowing the design of the distributor to "get it right" for all other situations. Handily, the engine runs at it's best just before it would "pink", so by making it pink, and then retarding by a couple of degrees, you're getting the best you can. You're also not just doing "dynamic" timing, at idle, but dynamic timing right across the rev range.
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Post by adamskibx » Thu Mar 30, 2006 1:14 am

Ahh I see. Well I have to say I have learnt a heck of a lot about cars from doing this engine change! Thanks for all the technical help and tips to all who have replied to my posts!