Oscilloscope waveforms of fuel pump, hall sensor, injector, spar

[davlance01]

Anyone know the wiring pinout on that TDC sensor that isn't documented hanging off the alternator?

I think its time I tap into that. I'm assuming its a 3 wire hall effect just don't know which is + and - pins.
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[davlance01]

just probed the pins until I got a signal from that weird diagnostic port.

Assuming TDC.

Yellow- hall signal from distributor
purple- TDC sensor on flywheel.

All seems good to me.

Guess its time to start looking at the other sensors, temp II, air flow etc etc etc
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[DigiMatrix]

Hey, I was just playing with the simulator some more and I am wondering if you have an issue with your ECT signal getting back to the ECU.

From VW document SSP 103: if the signal (ECT) is interrupted whilst the engine is operating, the Digifant control unit switches back to the basic firing point and no adjustment of the firing point occurs. If interruption occurs before starting up, the Digifant control unit switches over to the assigned map value for the warm engine (>60 deg C)


If ECT is disconnected before start the scope trace looks like this:

ECT sensor connected and working at start

a timing difference of 27.4 deg BTDC

edit: added 2nd scope trace to make comparison easier

[davlance01]

Thats interesting.

What is ECT? Is that the hall effect or ?
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[davlance01]

signal at pin 1 with TDC signal.

So this is what is coming to the ECU from pin 7 of the ignition control module.

I took the case off of the ECU to get to the pins so I can read the values with the engine running.

It looks like the signal is making the trip anyway.
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[davlance01]

purple- TDC
cyan- ignition signal (number 1 cylinder)
yellow- hall

more testing is in order here.
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Life is short and the road is long so if you want to see it all you have to drive fast!

[DigiMatrix]

[Merian]

how about spark plug wire waveforms?
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[davlance01]

[davlance01]

[DigiMatrix]

Thought I would add this info because it pertains to this discussion. I'm not sure if the 78 deg BTDC is with or without the base timing, but the irregardless, the hall window opening is 72 degrees (78 - 6)

Maybe you can set your timing with the TDC sensor waveform and the waveform from the Hall sensor.

[davlance01]

DigiMatrix that is really helpful. (although I am running digijet, I'm not sure if there is a difference or not)

It does look like in the picture they have the rotor cap pointing at number 1 piston based on that little notch I see in the picture.

I guess measure the angle against the hall sender?

Word to the wise though....
If you purchase a secondary pickup from hantek and you buy good wires that are well insulated the hantek has a really hard time picking up the signal.

I wrapped the spark plug wire with bare copper wire then clamped onto that and I'm getting a better signal. I do not know enough about electronics to know if that bare copper wire is helping or hurting me.
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Life is short and the road is long so if you want to see it all you have to drive fast!

[davlance01]

[davlance01]

Ok, here is what I ended up doing to get a good spark wave.

1) I hooked up my crappy little ht25 to the coil wire.
2) Then I wrapped the number 1 spark wire with 1 wrap of copper wire and set the probe at 10x.
3) Set my trigger at the spark plug wire then pulled the good signal from the coil.

Worked like a charm.

My waveform on the other hand is showing low spark voltage and a possible fuel issue! I have seen that spark voltage jump up to 10k then down then up, it really seems to bounce around a lot.

Next I'm going to check that #1 injector and post that waveform so you all can look at it.
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[Abscate]

There is a lot of stuff you can so wrong trying to measure this, like having capacitance in your probe , an unreliable probe.

From PHYS 369 almost a half century ago

“ an oscilloscope with an unreliable trigger has nothing to say”
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.ssS!

[davlance01]

[hans j]

For decoding ignition waveforms, start with watching some Jim Morton videos:

Link


Here are the known goods that I found in my personal library

Injector voltage/current and the distributor signal.

This was a new fuel pump, but many of them require time to break in. If I were to capture this on a car with a fuel pump concern, I'd be suspicious of this pump pattern. Broken in pumps need to be smooth oscillations with no drop outs.

snap throttle of maf and fuel pump.

Digijet idle control stabilizer. It appears all it does is slightly amplify the signal going out to the ECM. The reason I have this capture is because I had a bad one, and it was getting the signal from the distributor, but it was only intermittently sending it to the ECM.

And I had this one as a pdf, but didn't save the .psd unfortunately.
Blue: Ignition coil voltage
Red: Spark kV
Green: Ignition trigger
Yellow: Coil current
The jump in the red trace is an acquisition issue and it doesn't actually jump up like that. The coil is current limiting type, that's why it reaches the peak and tries to hold it. I need to redo this one since I've since learned a few things, including how to arrange "pretty" waveforms.

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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[Abscate]

That’s a small 200 mV ( y scale) ripple on the fuel pump voltage, but any DC motor will have a couple of ripple frequencies from the spinning armature . You ca actually see a couple of different freesia that plot. Did the scope have an FFT button? That would make them jump out

The loop coupling onto theHV lead could be changing a lot with small vibrations of the lead. Try making several wraps of wire to make those changes small relative to the sampled area.

Are you coupling in at 1 Meg impedance?
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.ssS!

[davlance01]

hans_j: If you were standing in front of me I'd give you a hug!

Thanks for that information, it is a very helpful post (although I am a little jealous of your pico scope)

This is my old original fuel pump. I got a new pump but I swapped it out because I suspected the new amazon pump might have been bad.

Mine is pulling a little less amps than yours. I watched a video that said I should suspect a pump with less than 3 amps. Mine appears right on the line of that.
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Life is short and the road is long so if you want to see it all you have to drive fast!

[davlance01]