What kind of crank/cam signals is the 7730 looking for?

[paramax55]

As you have probably guessed, I am putting a 1976 305 into a Jaguar with a 7730. I know I need to fabricate (or buy) some sort of crank trigger and cam trigger. The Motronic on the BMW wants a 60/2 signal on the crank and uses the distributor to take care of everything else. I know the 7730 can run a calpac, so it needs some sort of cam signal, right? What kind of signal is it looking for on the crank?

[Six_Shooter]

The '7730 (and similar ECMs) are looking for a "Ref hi" signal, which is not like a typical cam crank signal. Though I would say it's closer to a "crank signal", simply because of the number of pulses per revolution it is looking for.

This signal is extremly easy to get, when using a dizzy, you simply use a 7 pin ICM (Ignition Control Module), that gives you all the ignition connections between the ICM and ECM that are needed. This will provide the RPNM reference to the ECM, the EST to control actual timing, the 5V bypass so that ECM crontrolled timing can be used or bypassed and a ground reference.

There is not a seperate cam and crank signals needed, just this connection from the ICM.

[paramax55]

OK, so I can just use a HEI dizzy and an ICM (7 pin) and I am ready to go? this seems ridiculously simple. Why didn't you do that for your Z? It looks like your pickup is much more elaborate than a simple "dummy" cap for a dizzy that is no longer used.

Also, which manual will have the best wiring diagram for the 7730? Maybe a Chilton's from a 90 iroc? The Chilton's has the best wiring diagram that I've seen for the BMW.

[Six_Shooter]

I did run the ignition in that "rediculously simple" way for the first 3 or 4 months I had it running, since I was still using a dizzy at the time for spark distribution. I have since changed to DIS which requires the still quite simple crank trigger that I am using. Think of my crank trigger as the reluctor that is inside a dizzy. The crank trigger is connected to the DIS ICM and the DIS ICM uses the 7 pulses from the crank trigger to determine RPM and engine position (the 7th notch is 10* off one of the 6 notches for a #1 home signal), and also send and recieve the proper signals to and from the ECM.

[paramax55]

Well, it was probably no big deal to get the reluctor made with your granddad being a machinist and all. However, I made a gear once. It worked, but the spacing was less than exact. It was a quick lesson in the subject of "tolerances." A reluctor wheel is something I would like to have correct within less than 1 degree. I couldn't do it with the equipment that I have. If it is possible, I might just use the reluctor inside the dizzy, a DIS module, and - if I get really bored - make a fake dizzy cap that looks "cool."

[Six_Shooter]

Well, it was probably no big deal to get the reluctor made with your granddad being a machinist and all. However, I made a gear once. It worked, but the spacing was less than exact. It was a quick lesson in the subject of "tolerances." A reluctor wheel is something I would like to have correct within less than 1 degree. I couldn't do it with the equipment that I have. If it is possible, I might just use the reluctor inside the dizzy, a DIS module, and - if I get really bored - make a fake dizzy cap that looks "cool."

Easier to make an external reluctor wheel, than to try and get a dizzy to trigger the DIS module, mostly due to the 7th 'odd spaced' home signal notch.

Also people have found that with small reluctor wheels, the signal can be reduced at higher RPM and cause either missed spark events or improper timing. A larger reluctor wheel allows for more time between each notch, creating a stringer signal.

[paramax55]

Hmmm... I need to go to the junkyard and look for a stock 305 and see how GM did it. Maybe I can "frankenstein" some stock 1990 stuff onto my 1976 block...

[Six_Shooter]

Oh yeah, your working with a V8, which changes things a bit, or at least the way I was thinking....

MUCH easier to use a dizzy in that case, partly because the electronically controlled dizzies are easy to find, mostly because you have to use either an LT5 coil pack and related parts, or a Northstar coil pack and related parts. LT5 is hard to find and expensive, Northstar is easy to find, but requires more parts and a very specific trigger wheel. Do-able, just involved.

[paramax55]

OK, so we're back to a HEI dizzy and a 7 wire ICM?

[Six_Shooter]

OK, so we're back to a HEI dizzy and a 7 wire ICM?

Yeah, that's definatly the easiest way to get it done, at least for now.

I apoligize for forgetting that you are working with an 8 cylinder, I've also been helping a guy with a 4 cyl, and it's easy to get the two of you mixed up.

The LT5 DIS is the easiest electrically to retrofit, since it uses a single crank position sensor and a simple trigger wheel, but are hard to find and expensive, believe me I've looked I have a couple V8 projects, that I want to put DIS on.

The more available but also more difficult option for DIS is the Northstar DIS system. It requires two Crank position sensors, and possible a cam position, but people disagree with the cam position sensor being needed, and it has been swapped using only the two Crank position sensors. But the trigger wheel is quite involved and uses seemingly randomly spaced notches, but they are in fact very specifically spaced so that the DIS module through the input of the two crank position sensors to determine where the engine is in rotation.

Information on both systems and using with other ECMs than they were intended to be used with can be found on Thirdgen.org, in the DIY PROM section, along with downloads for the trigger wheels and mechanical set-up information.

You will be able to find a Dizzy to drop into your 305 easily at the wreckers or through swap meets, since they were used on many vehicles from the mid '80s to mid/late '90s, in both large and small cap configurations. You can also convert older dizzys for use with the ECM controlled ICMs, if you absolutly can't find a later model dizzy.

It would also be easiest to use teh dizzy due to changes needed in the bin to run the DIS. Using a dizzy will allow you "proof" the system, and get it tuned in very well, then if you feel the dizzy is holding you back, then switch to DIS and make the needed changes to the bin, which might require getting into editing directly in HEX.

[paramax55]

Thanks for the info. I have been perusing the Thirdgen website. It seems to be the place to get information. My already slow project has been pushed back a little. I toasted a rod bearing in my DD at the autoX Saturday. Been busy getting that rebuilt and back on the road.