RPM spikes mostly at low rpm (<650)

[BigBlockMopar]

In the last two days since I've installed the MS3x in my daily, I'm noticing an occassional RPM spike, during idle/low rpm (mostly below 650rpm).

Yesterday I encountered a spike when doing a tooth log while idling, but it didn't show up on the log (The tooth-log got overwritten however during a next capture).

Tried looking for clues in the datalog but couldn't find any, which led me to believe the tach-input simply got an extra signal.
Also tried altering dwell settings but this didn't seem to help. Started out from 3.0ms. Engine only started missing at 1.6-1.8ms dwell so I settled with 2.5ms.

Background info:
Sparkcables have a steelcore wiring and I recall the sparkplugs themselves are non-resistor type.
The car has been running flawlessly before with its stock ignition, a HEI 7-pin module and MSD e-coil. It could run steady as a rock at 500rpm in Drive without any hickups (LPG/Propane fuel).

Since the MS3x install, I'm using a different HEI 7-pin module, only now in Bypass-mode with the MS3x controlling timing, dwell and such.


I'm wondering if noise-filtering could cure this?



Tune
https://bigblockmopar.nl/msextra/201702 ... rt.msq.zip

Datalog
https://bigblockmopar.nl/msextra/2017-0 ... .19.36.msl

(Looking for the large spike at 581 seconds into the log. This happened when idling at a stoplight.
Engine stumbled butI managed to keep it running by upping the rpms with the throttle.

There's another at 476 seconds and a tiny one at 492 sec.
Also at 533 and 535 sec, only these do seem to happen at higher rpms.

[slow_hemi6]

I only use common Bosch sports inductive core leads and BPR5ES or BPR6ES plugs.

[BigBlockMopar]

During today's commute I noticed there were some spikes in higher rpm ranges as well. I guess it's just more noticable at lower rpms.

I will try turning on some noise filtering to see if this helps.
I think a 0.2 - 0.4ms filter after a valid tach signal should work in my case.

I'm not quite ready to replace spark plugs and cables just yet as they've never caused ant hickups or interference before with the stock ignition.

[racingmini_mtl]

Using resistor plugs is essential and it's useless to try and solve this issue before you replace them.

Jean

[slow_hemi6]

During today's commute I noticed there were some spikes in higher rpm ranges as well. I guess it's just more noticable at lower rpms.

I will try turning on some noise filtering to see if this helps.
I think a 0.2 - 0.4ms filter after a valid tach signal should work in my case.

I'm not quite ready to replace spark plugs and cables just yet as they've never caused ant hickups or interference before with the stock ignition.

You never had a efi controller before. Stock ignition is too basic to care about spikes or noise. EFI computers are susceptible to spikes and noise and that is why all efi cars use the plugs and leads they do, along with twisting and screening of sensor cables and careful grounding schemes.

[AbatelliCristian]

Question:

Why there isn't lostsync if there are noise?

[slow_hemi6]

Because it is not a wheel decoder type ignition system.

[BigBlockMopar]

I figured the ECU electronics could be more susceptible to electrical noise and such. But I also would have expected way more noise/rpm spikes with 8 cables/plugs producing electrical noise.

During the weekend I'll disconnect the 3 wires from MS to the HEI-7 so the engine will run on fixed timing with the HEI-module alone. Would be a nice check to see if the HEI-module experiences the same possible noise issues.
I can also move the HEI-module inside the car near the MS3 under the dash as a simple test.

Will do some more logging.
If this all fails to supress the noise spikes I think I still have an old set of plugs and wires somewhere to try out.

[BigBlockMopar]

Not quite sure what has changed but it lately occured to me the rpm spikes seem to have vanished.
I didn't change the spark plugs or cables yet.

Noise filtering is still On, but I recall this didn't fix the issue earlier.

Only thing I have changed is I hooked up the Coolant wire to the engine and more recently added a MAT sesnsor, which resides inside the airfilter housing as of yet.