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good crank, no start condition, no dtc

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19 Oct 2021 04:03 #52117 by Kudu.123
good crank, no start condition, no dtc was created by Kudu.123
Hi All, i have a merc W168 A190 with non start/splatter condition, first it logged dtc on throttle body and replacement of same resolved this error, and started couple of time perfect. it stalled and no start now evident in scoping cam, crank, ignition voltage feed and injector pulse no 1 cylinder, in cylinder compression test and fuel pressure all seems good. i do not have comparative waveform to verify. the spark plugs are wet with fuel seems no spark or at wrong time but should still then burn off?. looking at wave form the voltage to coil cyl no 1 fires with injection pulse at beginning of intake stroke and not as expected just before TDC? my question is should fuel injection and spark be at same time and not just before tdc? it seems to be out by 180degree but to perfect for chain to jump by this much. your advise is highly appreciated. 
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19 Oct 2021 08:05 - 19 Oct 2021 08:09 #52119 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc
What makes you think the coil fires at the wrong time? How did you define TDC compression in your waveform¿?

Looking at your waveform I see one pulse of the green trace happen at the same with one pulse of the yellow/golden trace. I "suppose" green is igmition and yellow injection. Looking closer you will find that there are two pulses of the yellow trace for one of the green trace, in other words the yellow trace pulses each crankshaft revolution whereas the green pulse takes place only once every complete engine cycle/720 degrees.

If my assumption about green being ignition and yellow being injection happens to be true then this would reflect a pretty common pcm strategy where at start up the system does not operate in a sequential injection order until cylinders are identified. Depending on model it may even not feature sequential injection.

It may be beneficial if you did a relative compression test with an ignition sync signal on a second channel, on a much shorter time base, just to verify ignition timing to TDC compression.

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Last edit: 19 Oct 2021 08:09 by juergen.scholl.

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19 Oct 2021 08:19 #52121 by Kudu.123
Replied by Kudu.123 on topic good crank, no start condition, no dtc
hi sir, sorry seems compression test did not load but i have now loaded again, the in cylinder compression test shows the green pulse being injector and yellow being cyl no 1 voltage being fired at intake opening event. injection understand but form my understanding ignition coil event to take place just before tdc? 

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File Name: incylcompt...4.psdata
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19 Oct 2021 09:47 #52125 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc
I can´t download your psd file.... 8-( Can you upload it somewhere else or just show a picture with an appropriate timebase? Otherwise it´s hard to get useful information from your data given.

If yellow shows the ignition then there seem to take place two ignition events during one complete engine cycle, the second one occuring in the area around 420 degrees?

The red trace is the trigger signal for the coil?

Please share the YMM information.

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19 Oct 2021 11:25 #52128 by Kudu.123
Replied by Kudu.123 on topic good crank, no start condition, no dtc
many thanks for help s far, will it perhaps be better if i rescope with cam, crank, compression in cyl 1 and coil voltage cyl 1?
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19 Oct 2021 11:29 - 19 Oct 2021 11:31 #52130 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc

many thanks for help s far, will it perhaps be better if i rescope with cam, crank, compression in cyl 1 and coil voltage cyl 1?

Yes, this would be really helpful.

If I click on the ps file it only opens as text document in another window. I can not dowload it.

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Last edit: 19 Oct 2021 11:31 by juergen.scholl.

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23 Oct 2021 05:40 - 23 Oct 2021 06:14 #52210 by Kudu.123
Replied by Kudu.123 on topic good crank, no start condition, no dtc
hi , sorry for delay but here are different scope with crank, cam, ignition no 1, and in cylinder pressure on cyl no 1,

while doing test a spark pugs are grounded fitted to coil pack and visual inspection appears they are very weak and sometimes not firing at a? same anomaly with olso and new coil pack unit.
 
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23 Oct 2021 10:05 #52217 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc
Once again, I can not download your pico file, it onlyopens as text when I click on it. Please check this, though I don't think the problem is on my side, but who knows.....

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23 Oct 2021 17:02 #52229 by Matt T
Replied by Matt T on topic good crank, no start condition, no dtc
Juergen,

The psdata files are working for me with firefox and pico6. Maybe try opening the thread in a private window, or a different browser, so you're not logged in. That'll let you use right click.
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23 Oct 2021 19:56 #52230 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc
Matt,

Firefox allowed to download and it opened in Pico7, only. Tthank you.

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23 Oct 2021 20:38 - 23 Oct 2021 20:49 #52232 by juergen.scholl
Replied by juergen.scholl on topic good crank, no start condition, no dtc
Kud,

the ignition timing looks good to me. Being a waste spark system, as you mentioned coil pack, you´ll see one spark event within every crank revolution. The coil is fired approx. 5 degrees before TDC and the dwell time is almost 4 ms. Primary voltage stays over 10.5 V during cranking. All these values are within reasonable ranges.

How did you measure primary voltage on the control side of the coil? The self inducton spike only shows close to 20 volts and then it seems to be clipped off. What were your scope settings and probes/attenuator? Could you redo the primary voltage reading within a range that shows peak induction voltage, please? If you could add primary current that would allow even deeper insight...

You said you only saw what seems to be a weak spark....within the scope capture I can not dinguish one single spark event, the (low?) stored coil energy is just drained off to battery voltage level again, no back swing either.

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Last edit: 23 Oct 2021 20:49 by juergen.scholl.

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23 Oct 2021 22:26 #52236 by Tyler
Replied by Tyler on topic good crank, no start condition, no dtc
We're bouncing this waveform around in the Zoom meetup. :cheer: I see that you did a fuel pressure test, so I figure you would have noticed, but is it possible there's diesel in the tank? :huh: That may account for the lack of spark (washed plug), and still not starting.

Will diesel wash out piston rings the same way that gas will?

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