Erratic dwell times

[domestos75]

Hi all,

Currently having an issue where the dwell time for the coils becomes erratic. It usually happens when I back off the throttle and it also coincides with the tacho needle fluttering a little bit and also the battery voltage shows the same spikes at the same time. I've taken a pic of the issue and you can see what's happening quite clearly. Just wondering if anyone has had this issue before and what could be causing it. Could it be the regulator in the alternator starting to die out or is it a wiring issue? I am running NGK U5014 coils and the 2 grounds are wired as such:

- one set of grounds runs to a tab on the distributor housing that's bolted to the block.

- the other set of grounds runs into the cabin and bolted to the chassis ground which is also where the ecu is grounded to.

My car is a '92 Nissan Pulsar GTiR.

I've received some helpful replies and help from the Link Ecu Facebook community which I will attempt tomorrow to see if it fixes the issue but I've mainly posted this so I can attach the log for people to view in the hopes that it helps a bit more.

Cheers!

long drive.llg

[Adamw]

Yeah you have a lot of trigger errors in there.  Even sometimes on overrun when ignition energy is low so it is probably not ignition noise related.  Can you do a few trigger scopes at around 2300/2400/2500RPM as most of your trigger errors happen around that RPM. 

 

  

[domestos75]

Hi Adam,

Attached are the trigger scopes at 2300,2400,2500 rpm. I hope they are what you're after. I've added another quick log too.

Trigger Scope Log 2022-08-17 2300rpm.llg Trigger Scope Log 2022-08-17 2400rpm.llg Trigger Scope Log 2022-08-17 2500rpm.llg voltage and dwell drop.llg

[Adamw]

Whats your trigger 1 edge and trigger 2 edge set to?

[domestos75]

Trigger 1

-Pullup - ON

-Trig edge - Rising

-Multi tooth posn - Cam

-tooth count - 24

Trigger 2

-Pullup - ON

-Trigger edge- Rising

-sync mode - Cam pulse 1x

[Adamw]

Ok, if they were both set to falling there would have been a clear edge clashing issue, but the rising edges are well away from each other so we can rule that one out.  

Is this something that has only started recently whereas it was previously ok, or is it a fresh install?  Are the coils a recent addition?

There is one spot in one of the triggerscopes that is potentially a capture of the issue happening.  It looks like the CAS disc has suddenly bounced backwards as the waveform initially started to rise earlier, then suddenly drops all the way back to zero before rising again a millisecond later following the same shape as the other adjacent "teeth".  Since this rises above the 1.5V arming threshold and drops back below the 1.0V low threshold, this little zigzag would be considered an extra tooth.  Is there anything loose in the CAS or drive system?  It gives me the impression it is more mechanical than electrical since voltage doesnt drop below or spike above the normal waveform voltage.  The normally do have some backlash but I assume there must usually be enough drag to keep the backlash in check.  Whats the trigger 1 filtering level set to?  I dont think filtering will help but it might be worth a try.

[domestos75]

This install I've had for almost 2 years but I've never checked the dwell as I just assumed it would be fine since everything fired up once we got the timing right. I was running a Motec M4 with an ignition expander so I could do the coil swap but because it's a dinosaur of an ecu, it had no capability that modern ECUs have today. Fast forward to this problem, what prompted me to check and log the dwell was because I decided to check my voltage values as sometimes my idle would go funny and then go normal once I'd blip the throttle. On start up my voltage would drop to 9.5-10V and whilst logging I would noticed a stable voltage of 11-12 sometimes. Since my dwell table is dependant on voltage, I didn't want to be running high dwell times which would lead to my coils burning out.

I have checked the AEM 24-1 trigger disc and it seems perfectly clean and there is very little play when I try to turn the disc. I tried attaching a short video of me checking the trigger disc but the size of the file was too big but I did attach it to the Link Facebook page that that you commented on the other day. One thing I did notice that MIGHT potentially be an issue is my wiring for the sensor grounds and shield grounds. So the sensor ground for the distributor/CAS is connected to the sensor grounds for the MAP and TPS sensors and this goes to pin #24 on the 'A' plug of the Thunder ecu. The shield grounds for the distributor/CAS wiring and TPS are connected together and these go to the shield ground pin #7 on the 'A' plug. Would the way I have wired the sensor and shield grounds cause the issue that we're seeing?

The trigger 1 filtering is currently set to low. I'll try the medium filtering level tomorrow night after I finish work and see how it goes.

[domestos75]

*UPDATE

Started the car from cold and was watching the log as it was warming up. I blipped the throttle to try and induce the dwell to spike but I was only seeing small spikes of around .1ms. As the engine warmed up, the spikes got bigger- around .5-1.0ms. Changed the trigger 1 filtering to "2" and there was only small spikes of around .1ms. Changed the filtering to "3" and same result happened. Below are the logs for each of the filtering settings and I also did another trigger scope at filtering set to "2". Hopefully somebody can explain what has been happening all this time.

Cheers!

 

dwell log trigger 1 filter set to 2.llg dwell log trigger 1 filter set to 3.llg Trigger Scope Log trigger 1 filter set to 2.llg