6 pin Bosch CDI - either no RPM or max RPM signal

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wiggle_puppy
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6 pin Bosch CDI - either no RPM or max RPM signal

Post by wiggle_puppy »

I have a Porsche 911SC that used to run on Megasquirt 2. I purchased the MS2 unit pre-built in a kit from DIYAutotune. My car has a 6 pin Bosch CDI box with a wire that feeds a signal to the factory tachometer. I tapped into this wire for my tachometer input and fed it into pin 24 on the Megasquirt unit. I drove the car for a few weekends and started getting the tune more to my liking (I loved it by the way) then my MS unit stopped reading RPMs. I sent it in to DIY Autotune and they replaced the daughterboard under warranty (I guess it died).

When I got the ECU back I had cleaned up the wiring with weatherpack connectors and reworked the injector batch schema. My car starts now but my RPM reads 9000-10000 RPMs in TunerStudio and the car needs a lot of throttle to run I guess since it wants to dump fuel commensurate with the revs it believes it sees (even though the car is really running at 1000-2000 RPMs). There is also no reading to my MAP sensor but I feel like that will be easily sorted once I figure out this RPM thing. The only wiring schema change was to rewire the injectors to fire in different batches (with the firing order rather than by cylinder bank).

My signal wiring has remained unchanged - the white wire from shielded pair (pin 24) taps into the black/purple wire from the CDI box (tachometer signal) and neither the black wire (pin 1) nor shield from this shielded pair are connected to anything. I have fiddled with R52 and R56 (currently they are fully CCW) thinking this might make a difference, but it did not. The jumpers on the both boards are untouched and in the "factory" configuration.

I have tried to use both rising and falling edge for my RPM signal but it doesn't seem to change anything - in fact I'm now no longer able to read any RPM signals in TS again. I have attached the MSQ that I initially used to start my car (the base tune) but can also attach the last known "good" tune that I was using before the failure. Both of these tunes exhibit the same behavior.
Attachments
start1.msq
Base tune
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wiggle_puppy
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Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by wiggle_puppy »

Hi all,

Please let me know if I'm omitting useful information - I'm a bit new to this so I'm not being intentionally vague. I'll be working on the car all day today so maybe I'll figure it out on my own, but who knows. Also, this is a fuel-only install at the moment.

Thanks!
rickb794
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Location: Portland OR

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by rickb794 »

Did you recalibrate all your sensors after installing the new processor?
That info is not saved in the MSQ.

I can't help with triggering off a 3rd party box. Have you tried substituting a CDI box or checked spark and spark control?
Does your tach read correctly?

Doing fuel only off the tach signal means you will have to go through all of this again if/when you include ignition control.
In my eyes it is less head banging to go ahead with ignition control now rather than later, so you don't have to repeat setup.
Is there some reason you need to keep the OEM CDI box?
Is there a way to trigger the OEM CDI box with a Megasquirt?
Assuming your CDI is triggering off a distributor is there a later model locked distributor available? (to trigger the MS directly)
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
Matt Cramer
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Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by Matt Cramer »

Can you get a tooth log of the RPM signal?

Are you able to get an oscilloscope on that tach signal?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
wiggle_puppy
MS/Extra Newbie
Posts: 10
Joined: Tue Oct 10, 2017 4:27 pm

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by wiggle_puppy »

rickb794 wrote:Did you recalibrate all your sensors after installing the new processor?
That info is not saved in the MSQ.
Doing fuel only off the tach signal means you will have to go through all of this again if/when you include ignition control.
In my eyes it is less head banging to go ahead with ignition control now rather than later, so you don't have to repeat setup.
Is there some reason you need to keep the OEM CDI box?
Is there a way to trigger the OEM CDI box with a Megasquirt?
Hi Rick,

I did not recalibrate my sensors which I imagine is the source of my MAP signal error. My RPM signal isn't really coming from a sensor though so I don't think that's it.
I completely agree with you on the "double work" part. I'm doing fuel only for two reasons:
1. Budget.
2. Easier tuning for someone who is a complete idiot at this stuff - once I get the fueling down I plan to move to crank triggered ignition with 12 COPs with internal ignitors. The biggest issue right now is that a crank wheel setup is ~$400 from what I've seen for my car.

With that in mind I'm keeping the OEM CDI box only for another 6-8 months until I can plan out and purchase all of my ignition stuff.
Also, unfortunately there is no way that I've found to trigger the OEM CDI box. Al Kosmal (who is a literal god at this compared to me) has not, to my knowledge, found a way to do it yet.

@Matt,

Thank you for the suggestions, I'll give it a look and I'll get that log up ASAP and see if I can conscript my EE buddy with a scope to get out here and help me with it :)
rickb794
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Joined: Sun Dec 21, 2008 10:28 am
Location: Portland OR

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by rickb794 »

If your motor is dual plugged you would only need 6 double-ended coils.
To fire them sequentially you will need an MS3.
The best an MS2 will do is wasted spark on a 6 cylinder. (it is limited to 4 spark outputs)
That would actually be fine up to a medium boost application.
High boost you would likely need a coil on each plug for maximum spark energy. (along with water/alcohol injection to keep it from eating itself up)
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
wiggle_puppy
MS/Extra Newbie
Posts: 10
Joined: Tue Oct 10, 2017 4:27 pm

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by wiggle_puppy »

Hi Rick,

I know there are a few people running around with dual EDIS-6 modules triggered from an MS2...ultimately I think that's the way I'll go. Maybe I'm wrong and that's not possible at all. Either way I appreciate your input and you've given me the push I need to scrap my ignition and dive in headfirst...I'm going EDIS.

All, I really appreciate the input and I think we should close this thread. I can't get a tooth log because I can't get a signal at all (not even on the factory tach). I believe the coax wire from my distributor to my CDI module is completely shot. There is no longer any insulation on about 4-5" of the wire and the connector just crumbled when I removed it from the distributor. Since my options for "fixing" that are buying a new $77 wire and splicing it into the "good" section of my old wire or buying a new $140 wire (longer from a 928) and wiring it entirely back to the CDI, I've decided to skip fuel only and head to EDIS. I guess I'm feeling the burn of the "Porsche tax" for this d*** car.

It looks like I can get a trigger wheel, pulley, sensor, and sensor mount for ~$250 and then find a junkyard EDIS-6 module to test and that's where I'm going with this now rather than hoping that my nearly 40 year old CDI unit and coil will continue to function happily.
rickb794
Super MS/Extra'er
Posts: 6155
Joined: Sun Dec 21, 2008 10:28 am
Location: Portland OR

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by rickb794 »

There are native solutions rather than using an EDIS module.
EDIS support is a legacy thing that goes back to the v2.2 main board that has no ignition output.
Using an EDIS module also limits the feature set available with MS.

An EDIS trigger and coil pack work well these parts connected directly to your MS will provide a 4 times more accurate crank position signal and provide full functionality.
3 of the 4 tower EDIS coils will fire a dual plugged 6 cyl in wasted spark mode. Or 6 GM DIS coils.
There are also other 4 cylinder wasted spark coils like a Neon coil and also Smart coils that don't need high current drivers.

https://www.ebay.com/itm/HUCO-Ignition- ... 2670338939
Or similar

https://www.ebay.com/itm/Ignition-Coil- ... 2931237419
3 of these will do

https://www.ebay.com/itm/Ignition-Coil- ... 2339878117
2 of these

http://shoptalkforums.com/viewtopic.php?t=143878

Using the double ended coils on a dual plug motor is not the way they were intended to be used but work fine with a conservative plug gap.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
wiggle_puppy
MS/Extra Newbie
Posts: 10
Joined: Tue Oct 10, 2017 4:27 pm

Re: 6 pin Bosch CDI - either no RPM or max RPM signal

Post by wiggle_puppy »

Awesome info, that's great feedback. I just ordered my trigger wheel and pulley. I'm going to pull some EDIS stuff from the junkyard for now to see if I can get the car started before the snow flies. Even if I limit myself a little bit by directly triggering the EDIS off a 36-1 wheel, I can migrate to the wheel decoder and manual triggering later and I imagine that whatever I do will still be better than my ancient distributor setup. Over the winter I'll re-evaluate my options as I plan to drop the motor anyways.
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