Megasquirt Support Forum (MSEXTRA)

MS3 v3.57 built by DIY, 2002 Saturn SL1

Previous Condition:
The vehicle is running and driveable with the only issue being my inability to control IGN timing. The ICM is able to provide a constant 10*ADV because of the 5v Reference from the grey TPS wire. The IGN/Tach settings were GM7x for this configuration

Goal:
To understand why I could not control IGN advance
[Probably due to EST command not coming from the MS and overriding the bypass map]

Current Condition:
I looked at pages 77 and 122 of the MS3v3.57 manual for the correct settings to use for the GMDIS system that I have. I only soldered in the 1kOhm resistor for R57 to adapt it for those settings and adjusted the Tunerstudio settings [GM7x -> Basic Trigger].

However that results with this unsatisfactory characteristic:
https://youtu.be/Y9pkZCM2eZg

No matter how I adjusted the pots, Basic trigger just output some weird RPM signals. I could simply switch over to GM7x and RPM reads normally, but that doesnt help me to my goal...

wtf mate?

Also I dont understand why wasted spark ign is not allowed with basic trigger if its supposed to be for GMDIS systems...

Why are you trying to use "basic trigger"? That Saturn has GM7X, and that is not the same as basic trigger.

I would be tempted to "gut" the stock ICM and install two BIP373s, retain just enough of the ICM to mount and connect to the coils.

Have you looked at the "mods" forum on <saturnfans.com>? I think people there have 'squirted the S-series Saturn successfully.

So if I gut the ICM, how will the MS3 setup need to be modified to drive the coils directly?

billr wrote:Why are you trying to use "basic trigger"? That Saturn has GM7X, and that is not the same as basic trigger.

I would be tempted to "gut" the stock ICM and install two BIP373s, retain just enough of the ICM to mount and connect to the coils.

Have you looked at the "mods" forum on <saturnfans.com>? I think people there have 'squirted the S-series Saturn successfully.

That's EXACTLY how I do it.

alexofnazareth wrote:So if I gut the ICM, how will the MS3 setup need to be modified to drive the coils directly?

You'll need to install 2 BIP373s

alexofnazareth wrote:Also I dont understand why wasted spark ign is not allowed with basic trigger if its supposed to be for GMDIS systems...

I think the mods to MS are trivial, just add two jumpers on the mainboard, and maybe remove one if Q16 has already been enabled. Since you have a V3.57 the two "logic-level" spark outputs can be brought out cleanly through the spare DB15 connector.

The Saturn ICM mod is more of an unknown, and how tough that is will depend on how it is assembled and your set of skills/tools. No doubt, the circuitry in there is "potted", and removing that potting can range from easy to quite difficult. Some potting is soft and can be removed easily. Some is hard, but softens easy with the tip of a soldering iron (use and old tip, it will probably get contaminated enough to no longer be ideal for soldering...) Then, there is hard potting that has to be cut out with a tool, like Dremel or end-mill. You only need to save the ICM case, to mount the coils, and I would try hard to save the connector, so you don't have to re-invent that. Saving those should be doable even if it is hard potting and has to be cut out. If, however, the potting can be removed "elegantly", then try to save enough of the PCB to retain the spade connections (tabs) that carry current to the coils; as well as power, ground, and two signal traces from the connector. If you are really lucky, you may find that the OEM coil drivers are TO220-like devices with pin-out similar to the BIP373, so that the BIPs can replace them with very little re-wiring inside the ECM.

The one downside to putting the BIPs in the ICM is the heat in that area, on the block near the exhaust manifold. The OEM ICMs last for a very long time (forever?), so I am hopeful the BIPs will be OK.

Anybody in my area have and old Saturn ICM I can have? I would love to research this further, for future reference.

Lets just say we pull the coils off of the ICM entirely.

The ICM can sit there producing the clean tach signal I've been getting.
How do you drive the coils directly with the MS3?.

It seems there are only 2 spade connectors for each coil on the ICM so I'd rather make additional spade connectors to plug in there instead of messing with cutting the ICM open.

If you don't want to tear into the ICM, then add just one BIP373 inside the MS, there is already one in there (Q16). I prefer to keep the large coil primary currents (and noise from the coils) out of the MS box, but many people do use internal BIPs successfully.

This is how you modify a GM DIS ICM :https://www.diyautotune.com/support/tec ... er/gm-dis/ And yes it's my article.

The Saturn ICM doesn't look exactly like that, but in pictures it does seem to have that "easy-to-remove" tin cover. If the potting inside is the soft coating, then an easy job to mod it, whether the BIPs go in there, the MS, or a separate box. Just be careful of how you do the internal jumpers, since the Saturn connectors aren't quite the same as shown in the article.

Yeah the Saturn ICM is different, but you could probe the connector pins and internals to see what's what.

So even if the BIPs go into the ICM instead of the megasquirt, I'll need to add an additional spark output onto the DB15 connector since we only have spark B on the DB37, correct?
Also, how would you mount/install BIPs inside of the ICM? I'm only finding info for installing it into the MS box.

Yes, you would have to use the DB15 to bring out at least one of the spark outputs, but there is really nothing else to add except two jumpers to connect the DB pins to the existing LED spark outputs. Personally, I would bring both spark outputs through the DB15, it seems simpler/neater to keep them together, but one could come out through the DB37 pin 36 reserved for the built-in "single-coil" BIP373.

To mount the BIPs in the ICM, I would cut away the PCB enough to screw them to the heatsink behind the PCB.

Leave the BIPs on the mainboard. Yeah, yeah, yeah Bill; noise. I get it. I have run as many as 6 BIP373s mounted to a V3.0 or V3.57 mainboard and didn't suffer noise issues. And no the Saturn ICM isn't quite the same as the one in the link but I just modified one last month. It works fine. As far as installing BIPs inside the gutted ICM goes.... It would take a LOT of effort to get all of the potting material out. Not worth the trouble IMO.

Just ordered the extra BIP. Time to read up how to wire the outputs to the DB15 connector. Speaking of which, I need to go dig around for that connector as well...

After some discussion with some of the other Saturn guys, I'm going to move forward with the following configuration:

1. I'm just going to use the OBDI ICM to generate clean tach signal [Remove coils and 5v ref]
2. For Ignition, I'm going to install an OBDII ICM and coils. They will only require 5v input from the MS logic circuits to fire the ICM/Coils.

***edit***
In another past thread, I was looking into connecting SPR3 and SPR4 to PAD1 for ignition output.
Should I connect both SPR3 & SPR4 to PAD1 to drive both coils for wasted spark?

A bit off-topic but, do you have schematics or a good circuit description of the OBD1 ICM? I have three older S-series (all stock) and am always wondering just how I could test the ignition circuitry, especially the ICM, if I ever run into ignition problems. I'm looking for enough info to look at signals in/out of the ICM and diagnose whether a problem is in the ICM or PCM or wiring between them.

Sure thing. I'll try to post everything into this thread so that it can be a catch-all for people looking to go this route. I'll work on doing that later on tonight.

*bump*

I would still like any info you have on the Saturn ICM, either/both Gen 1 and later.