I'm lost as to why people say you have to use an OBDI ICM to run our DIS. I have been reading through both the HEI module and DIS write-ups, and never once do they mention needing the OBDI module. Also, the HEI module is used to completely replace the DIS right, and not supposed to be used in conjunction with the DIS, right? In the DIS write up they make reference to the HEI module, but they don't say that you use it.

I guess I'm just lost as to why I can't just wire directly from my Megasqurit-II ECM to the 98-02 2.2L ICM I have to control the spark on my hybrid quad.


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"Youth in Asia"...I don't see anything wrong with that.

Nevermind, I am looking at the wiring diagrams, and there is absolutely no reason it shouldn't work. I didn't get a chance to wire the car yesterday (May 14) due to being asked to work last minute. Hopefully I will have a chance to do it today. Thanks anyways guys.


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"Youth in Asia"...I don't see anything wrong with that.

Well I read more writeups and found the mistake. Our newer DIS systems uses ionization detection and I also don't believe have a bypass either... Well, time to hit up the scrap yard.


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"Youth in Asia"...I don't see anything wrong with that.

The ionization detection isn't the major problem.

The very simple answer to your question is because there are two ignition signals the OBD2 ICMs need to see coming from the ECU. The Megasquirt systems can only produce one ignition signal.




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^we have a winner!!! - you need an older Q4 ignition module...then you will have no more problems.

Mr. Pute wrote:The ionization detection isn't the major problem.

The very simple answer to your question is because there are two ignition signals the OBD2 ICMs need to see coming from the ECU. The Megasquirt systems can only produce one ignition signal.

That and the fact that the signal from the crank angle passes through the ECU before it goes to the ignition module.

I already have everything wired and installed except for the "bypass" and "throttle signal." I don't have a clue what the heck the bypass is, and I'm lost as to how I'm suppose to get a rpm signal to my tach if it gets translated by the dash's microprocessor (or is that just for 00'-05' cavaliers and sunfires?).

Joshua Dearman wrote:^we have a winner!!! - you need an older Q4 ignition module...then you will have no more problems.

I had picked up a module/coils from an 89' corsica on Tuesday so that I can run external coils. Thanks anyways Joshua.



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"Youth in Asia"...I don't see anything wrong with that.

The bypass line is the switch which enables ECM generated timing signals to trigger the ignition coils rather than processed crank position signals. When first cranking the ignition module uses the crank position signals to trigger the coils directly. After engine rpm reaches a specific level the ecm applies 5V to the reference line and takes control of ignition timing. Dwell calculations are also provided in some code but the DIS module seems to handle dwell control internally.

From a functional point of view the original DIS system is a "drop in" replacement for the distributor. Neither system relied on signals from a cam position sensor or ecm to synchronize spark to the correct cylinder. Later generations of DIS moved the ignition coil control directly into the pcm and the coils could not fire without the pcm, even during cranking. MSII does not include the necessary hardware to drive multiple ignition coils.

For the tach signal you may be able to use the REF line from the DIS module providing that the tach impedance is high enough to prevent the REF signal from being pulled too low. The better choice is to use the TACH output which is pin A of the larger connector on the DIS module.

Ionization detection modules should work just fine to generate a cam position signal for older vehicles with no cam sensor, but there's still the issue with the coils needing to be triggered directly by the pcm.

-->Slow

Thanks slowolej. I was reading through the HEI module writeup again and had my suspicions that the part where they say to setup a relay where it is "hot in run/not in crank" was what they were referring to for the bypass, and your explanation has affirmed this. Regarding the tach though, I know I need to use pin "A," but I am confused as to how I would go about wiring it to my stock tach when my Haynes manual says that the display cluster uses a microprocessor to analyse the data for each of the gauges. Would I need an aftermarket tach or what? Because I REEAALLLYYY don't like the tacky look of a huge tach mounted to the dash. I would rather use the stock gauge if possible.


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"Youth in Asia"...I don't see anything wrong with that.

For some reason I thought you had an aftermarket tach. Stock tach cannot be connected directly to the ignition module. You're going to need to connect the OE PCM to an ignition input anyway. If the PCM doesn't think the engine's running it won't be trying to shift the transmission.

-->Slow

hmm....

Does that mean I would need to splice the ignition signal wire?
...or....
Wire up the entire stock ignition in tandam with the older ICM, but remote mount the original ICM, so that all it does is fire without actually affecting anything?


I'm thinking the second, would be the most logical, as I may run into the same problem as the TPS with splicing the wiring, except then how would it know the speed of the crankshaft? I'm quickly coming to the realization that Megasquirt isn't too entirely friendly to autos that are electronically controlled...lol.


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"Youth in Asia"...I don't see anything wrong with that.

Yeah, I think this will be a fight. You'll probably need to send the crank sensor signal to the original pcm and to the older ICM. You may need to connect resistors across the injector terminals for the original pcm so it thinks there are injectors connected. You may need to connect the original ICM or resistors to the original PCM so it doesn't think there's anything wrong. You should use a separate temp sensor fro MS and the PCM since the OE PCM uses a special circuit which switches from high resistance to lower, internally, as the engine warms up. And you'll need to find a way to make that TPS work, although you might be able to feed a fixed voltage of about 3-4V to the PCM so it always thinks you're at 75 - 100% throttle.

I know the 2.2 engines use a different crank sensor in 97 than the older engines. Hopefully yours isn't the same way. Then again, if it is you might be able to use the tach output from the older ICM as the crank / rpm input to the pcm. It's worth a look...

I think this may be the first MS + E type auto trans install I've seen here.

-->Slow