Tach Signal & Ignition Control

Ask questions about DIY board assembly issues, fault finding and testing. (Covers all Megasquirt versions and board.)

Moderators: jsmcortina, muythaibxr

Re: Tach Signal & Ignition Control

Postby Six_Shooter » Fri Dec 29, 2017 6:37 pm

I just looked up the diagrams on the SL1 pertaining to teh engine, most directly the ignition system.

The Saturn uses a very different ignition system than the "GMDIS" that's discussed in the manuals. The GMDIS that's discussed is the 60 degree V6 ignition system most spefically, though there's a 4 cyl variant that's very similar IIRC. In this case however the crank signal is fed to the ICM and then has the same signals between it and the ECM as the dizzy based HEI ignition system, though the EST output is 60* advanced from what a dizzy based system would use. This is why "basic trigger" can be used with that DIS system, and the wastespark part of it is handled by the dual tower coils, not the ECM.

The Saturn DIS feeds the crank trigger directly to the ECU, and then triggers the coils by some other method. I don't have clear descriptions of the wires, but it's possible that these are signals that trigger each coil directly. There are two wires that are just labled as "Ign module" in my diagrams, that could correlate to triggers for each coil. There's also a "cyl 4" wire that I'm note sure what that does, other than maybe there's some engine positional sensing happening and this is a signal for that, sorta like a cam trigger.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Yes, it's MS'd
Tha Daily: 2000 GMC Yukon, not so fun
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Six_Shooter
Master MS/Extra'er
 
Posts: 416
Joined: Mon Oct 17, 2011 7:28 pm
Location: South Western Ontario

Re: Tach Signal & Ignition Control

Postby billr » Fri Dec 29, 2017 8:34 pm

I think you are mistaken there, at least in regard to the "gen1" (OBD1) S-series Saturns. The CKP sensor does not feed directly to the PCM, that signal goes to the ICM and is "decoded" by the ICM. What kind of pattern is sent on to the PCM, I don't know. That's why I hope the OP can post more detailed info. The "cyl 4" signal is a CMP signal that is generated within the ICM from current/voltage in the 1-4 coil circuitry. My understanding is that the CKP pattern is a standard GM "7X", with the wheel built-in to the crank just to the rear of the center main bearing. Oh, and the earliest S-series ('91-92?) have a different clocking of the wheel than all later years; different by about 10 deg, I think.
billr
Super MS/Extra'er
 
Posts: 5016
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: Tach Signal & Ignition Control

Postby Six_Shooter » Fri Dec 29, 2017 8:55 pm

Definitely not, unless Mitchel is wrong, which is where I looked up this information. I used the info in the OP's first post for year and model...
Attachments
CKPSensorSaturnSSeries.PNG
CKPSensorSaturnSSeries.PNG (111.55 KiB) Viewed 53 times
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Yes, it's MS'd
Tha Daily: 2000 GMC Yukon, not so fun
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Six_Shooter
Master MS/Extra'er
 
Posts: 416
Joined: Mon Oct 17, 2011 7:28 pm
Location: South Western Ontario

Re: Tach Signal & Ignition Control

Postby prof315 » Sat Dec 30, 2017 4:48 am

The Saturn DIS you're looking at ( where the 7X goes directly to ECM and the Ignition module produces the cam signal) is the late model Ecotec engine system, not the old 1.9 Saturn engines. ALL 1.9s use an ICM to condition the 7X as well as fire the coils. The signal that the ICM sends out to the ECM is a basic trigger type square wave.
Linfert Performance: Come run up front
92 Corrado 2.0L ABA and Borg Warner EFR 6258 on MS3Pro.
94 Ranger 2.3 Twin Plug on MS2
Support the developers!
prof315
Super MS/Extra'er
 
Posts: 2487
Joined: Sun Jan 18, 2009 3:13 am
Location: Melbourne, FL

Re: Tach Signal & Ignition Control

Postby billr » Sat Dec 30, 2017 9:04 am

Yep, if that schematic screen-shot posted is what Mitchell's has for the 1.9l S-series Saturn, it is simply way wrong.
billr
Super MS/Extra'er
 
Posts: 5016
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Previous

Return to Board assembly and testing

Who is online

Users browsing this forum: No registered users and 1 guest