.: Replacing the Ignition Impulse Sender

[Greg323i]

This is an old thread but I'll comment anyway.

After losing all kinds of tiny parts, like that locating dowel, I now do all my disassembling in cheap kitty litter trays that I pick up from the $2 shop, or somewhere. They hold everything and they're easily stackable when I'm done with them.

[fullswing]

Thanks for the kind words, but again, credit to Attila (BoostedE21) and Graham (GDAus) for showing me the way.

[duhannig]

You wrote " but no AC pulses from the distributor."
How did you check? With a multimeter (ac voltage or hertz frequency)?

[Layne]

You wrote " but no AC pulses from the distributor."
How did you check? With a multimeter (ac voltage or hertz frequency)?

You can check it with a voltmeter. It's about 4v so you'll use the lowest AC setting.

[jrcook320]

wow, I don't think I ever saw this. Great write-up. WaTF (Will add To FAQ). lol

oh wait... looked back and I already did. I forgot.

[fullswing]

LOL - need some sleep?

[waferman]

Fun step back in time. Wow, I was more of a smart-ass back then! I'm melowing with age. And beer. And while I've purchased the impulse unit, it sits in my parts drawer, never to be installed. I bought it just to make something new again, but it ain't broke (nor is my spare!) so I figure it will sit for some time

[benjaminfrankln]

Does anyone happen to know the resistance of the distributor pickup? My car cuts power and i think its culprit. Thanks

[epmedia]

Does anyone happen to know the resistance of the distributor pickup? My car cuts power and i think its culprit. Thanks

I have no idea, but that's a very good question (I'm a points person).

Worst case, you can buy a spare (ie: ~10-15 bucks at rockauto) while they're still available, then measure it's resistance. I highly recommend getting a spare because impulse sender issues are on the rise due to their age.

You also want to replace the 3 pieces of fuel hose on the suction side of the external fuel pump if they are the original cloth braided hoses.

[benjaminfrankln]

Thanks for the heads up. I appreciate it.




I checked ac voltage while driving and it seems to be a bit low. 2.5v while at idle.



And I ohm checked it. 1,172,000 ohms seems a bit high

[GDAus]

Thanks for the heads up. I appreciate it.
I checked ac voltage while driving and it seems to be a bit low. 2.5v while at idle.



And I ohm checked it. 1,172,000 ohms seems a bit high

Ummm ... that's 1.172 kΩ ... it's a decimal point on your meter, not a comma!

And the resistance I've found in BMW fault finding literature is O.99~1.21 kΩ ... and that is measured at the plug end of the wiring going to the ICU to include the wiring resistance and any contact resistance. So your 1.172 kΩ I would regard as acceptable. I've replaced mine with one from Rockauto that was made in Italy and it reads 1.161 kΩ and it works fine.

As to the voltage .... the minimum voltage is 0.3 volts at cranking speed and can rise to over 90 volts at high RPM .... the detection system in the ICU doesn't care what voltage it is (as long as it is over the minimum), it actually senses the point where the A.C. voltage goes to zero as it alternates from positive to negative. The other point is the AC waveform generated by the pulse generator isn't a sine wave .... so the the reading on the multimeter is not really accurate, but as long as it increases as your RPM's rise, you shouldn't have a problem. Multimeters are designed for mains frequency AC ie 50~60 Hz. You really need an oscilloscope to properly see what is going on.

It is important that the connections are the right way round from the distributor to the ICU as the zero crossing detector in the ICU triggers on a negative going pulse. ... SEE the attachment.

I'll dig out some more stuff when I get home. I must admit I was going to do a more comprehensive write up of the stuff I sent to Jimbo earlier in this thread ... but life does tend to get in the way of having fun with BMW's sometimes

Cheers

[benjaminfrankln]

Awesome! Thanks for the great info! One last question: what should the air gap be on the trigger wheel from the pickup?

[GDAus]

Awesome! Thanks for the great info! One last question: what should the air gap be on the trigger wheel from the pickup?

0.35 ~ 0.70 mm (0.014 ~ 0.028 inches) it's best if you use a non-magnetic feeler gauge to set these.

Cheers

[benjaminfrankln]

bumping this so i find it later

[Yogibuur]

Does anyone know if the impulse sending wheel has to mount a certain way? with rotor pointing at one of the points on the wheel?

[GDAus]

Does anyone know if the impulse sending wheel has to mount a certain way? with rotor pointing at one of the points on the wheel?

If you go back to the first post in this thread .. Jimbo show lots of pics of how everything comes apart.

Technically, there is only one way it will fit, there is a round keyway in the distributor shaft and the hub of the impulse sending wheel and a very small round metal dowel locates the impulse sending wheel to the shaft.

However there can be a problem with this. The impulse sending wheel is made from 2 parts .. the magnetic rotor part (the teeth part) and the hub. The rotor part can move relative to the hub if it catches on something! I've found this out the hard way

With the distributor cap off and the dust cover isn't in place, the upper catch for the cap can flop down and catch the impulse sending wheel as the engine is being rotated to set TDC or other alignment reasons. If this happens the impulse sending wheel slips a bit relative to the hub and your timing ends up quite a bit off. In the 9 years I've had my E21, I've managed to do this twice. First time it took me a while to figure out what had happened!

If this has happened all you need to do is twist the impulse sending wheel back into the right relationship to it's hub ... its pretty stiff but it is doable if you are careful! All the teeth are the same .. so it doesn't matter which one you use to align with the distributor rotor notch.

I've added some captions to one of Jimbo's original pics to show the alignment of the wheel to hub. It's not super critical but it should be close .... there should be enough adjustment for the distributor position relative to the engine to get the timing right.

Cheers

[Yogibuur]

If you go back to the first post in this thread .. Jimbo show lots of pics of how everything comes apart.

Technically, there is only one way it will fit, there is a round keyway in the distributor shaft and the hub of the impulse sending wheel and a very small round metal dowel locates the impulse sending wheel to the shaft.

However there can be a problem with this. The impulse sending wheel is made from 2 parts .. the magnetic rotor part (the teeth part) and the hub. The rotor part can move relative to the hub if it catches on something! I've found this out the hard way

With the distributor cap off and the dust cover isn't in place, the upper catch for the cap can flop down and catch the impulse sending wheel as the engine is being rotated to set TDC or other alignment reasons. If this happens the impulse sending wheel slips a bit relative to the hub and your timing ends up quite a bit off. In the 9 years I've had my E21, I've managed to do this twice. First time it took me a while to figure out what had happened!

If this has happened all you need to do is twist the impulse sending wheel back into the right relationship to it's hub ... its pretty stiff but it is doable if you are careful! All the teeth are the same .. so it doesn't matter which one you use to align with the distributor rotor notch.

I've added some captions to one of Jimbo's original pics to show the alignment of the wheel to hub. It's not super critical but it should be close .... there should be enough adjustment for the distributor position relative to the engine to get the timing right.

Cheers

wow!! thank you so much, i seriously thought i was going crazy because i couldn't dial in my timing. That's exactly what happened in my situation, the upper catch for the cap flopped down and as i was turning the engine it cause the impulse sending wheel to slip. I ordered a new distributor from cardone and noticed that it was defective, the rotor wasn't mounting up to the ipulse sending wheel/teeth. The tech confirmed that the distributor was indeed defective, the replacement should be coming in today. Hopefully i can get my car running again!

[GDAus]

wow!! thank you so much, i seriously thought i was going crazy because i couldn't dial in my timing. That's exactly what happened in my situation, the upper catch for the cap flopped down and as i was turning the engine it cause the impulse sending wheel to slip. I ordered a new distributor from cardone and noticed that it was defective, the rotor wasn't mounting up to the ipulse sending wheel/teeth. The tech confirmed that the distributor was indeed defective, the replacement should be coming in today. Hopefully i can get my car running again!

Glad to help ..

But just saying ... you should should be able to re-align the existing teeth section on the impulse sending wheel without having to replace the complete distributor.

I re-aligned mine just by grabbing the distrubutor shaft with a pair of pliers (using a bit of aluminiium from a drink can to protect the top of the shaft where the rotor goes) and twisted the teeth part back where they should be.

Cheers