You said you always eliminated teh HEI when using an msd and FAST. Well mine is the newer (87+ i think) with the divorced coil. It has the 8 pin HEI module that has the two connectors on the back. I know there's a two pin connector coming off of msd box's to go right into the magnetic pickup inside my distributor. That's teh only way I could bypass the HEI right? But then how does the FAST get an rpm input? Now it's getting it through the 4 pin connector coming from the back fo the HEI module. I guess i don't understand. Is there any way you can clear it up for me? I'm going to buy a new HEI module this weekend and try it unless i can totally bypass it and be fine. I appreciate all the help!
Craig, one last question about the HEI/MSD, plz
- Thread starter Spooled
- Start date
Craig Smith
That was easy!
- Joined
- May 25, 2001
I'm a little confused now myself. I definitely think the problem exists between the HEI and the MSD, but not being there and seeing what is connected to what, my head just can't take the pain of trying to figure it out. 
I am trying to envision a way in which a FAST computer for HEI, an HEI module, and an MSD box can live in harmony. The FAST box takes a square wave signal generated by the HEI module, and returns a slightly different square wave signal to the module. This signal being sent back by the FAST unit is what is firing the coil, in a strictly HEI system. I believe on the later model HEI setups, this is pin D on the 4-pin connector, which should be referenced as "EST" in any documentation you have. Is THIS the wire you are sending to the MSD? Forgive me if you already told me this - I can't concentrate because I'm too geeked about getting my motor running on alcohol a little bit ago!!! The dyno gave me a little grief, but I really think I'm gonna see an increase of close to 100 ft lbs of torque and probably almost that much horsepower.
Sorry to change the subject... so where does the output (EST) wire from the FAST go to right now?
I am trying to envision a way in which a FAST computer for HEI, an HEI module, and an MSD box can live in harmony. The FAST box takes a square wave signal generated by the HEI module, and returns a slightly different square wave signal to the module. This signal being sent back by the FAST unit is what is firing the coil, in a strictly HEI system. I believe on the later model HEI setups, this is pin D on the 4-pin connector, which should be referenced as "EST" in any documentation you have. Is THIS the wire you are sending to the MSD? Forgive me if you already told me this - I can't concentrate because I'm too geeked about getting my motor running on alcohol a little bit ago!!! The dyno gave me a little grief, but I really think I'm gonna see an increase of close to 100 ft lbs of torque and probably almost that much horsepower.
Sorry to change the subject... so where does the output (EST) wire from the FAST go to right now?
Ya, this is kina confusing. Sounds like your doing great on your motor! Feels good, don't it Anyway, in that last post I had, I tried to explain how it was all wired up. Here it is again but in a briefer sense. The HEI module has two electrical connectors on that back of it that stick out teh back of the distributor. The one on the passengers side is a 4 pin connector. The one on the drivers side is a 2 pin connector. The 4 pin is plugged directly into the 4 pin connector that came as part of the FAST wiring harnass. I believe it was labeled "Ignition". All four of those wires stay "internal" in the FAST wiring harnass. What triggers the MSD and in-turn the coil is one of the pins from that 2-pin (drivers side) connector from the HEI module. Like i said, i've had it running before wired up like this but it's always been hard to start. I've been at college all week and now am back home so i can fiddle with it more this weekend. I guess i'll just spend the money and get a new HEI module and see if that works. I'll probably look for a signal at the pickup to make sure the HEI module is in fact getting a signal from that. As long as it is, i think the HEI module is the cause. I posted a picture of an identical distributor on my previous post about this if your not sure what it looks like. The way I see it is that the HEI sends a signal to the FAST for an RPM input through the 4 pin connector and it sends a signal to the msd/coil via the 2 pin connector. Since i'm getting an rpm signal when cranking when looking at the dashboard, i GUESS only one side of the HEI is bad...isn't that the weirdest thing you've ever heard. That's my only thought at this moment. And like i said in the first post, i touched the white msd wire (the trigger wire) to ground and it produces a nice spark so i know the msd box and coil are ok. It's just not getting a signal from the distributor. It won't spark while cranking but when i let off the key it'll spark once. That's all I can tell you. THANKS SO MUCH! This is EXACTLY the reason I decided to go with the FAST system and not the Gen 7 or soemthing else. The support is great on this site! THANKS AGAIN!!!!!!!!!
Anyway, in that last post I had, I tried to explain how it was all wired up. Here it is again but in a briefer sense. The HEI module has two electrical connectors on that back of it that stick out teh back of the distributor. The one on the passengers side is a 4 pin connector. The one on the drivers side is a 2 pin connector. The 4 pin is plugged directly into the 4 pin connector that came as part of the FAST wiring harnass. I believe it was labeled "Ignition". All four of those wires stay "internal" in the FAST wiring harnass. What triggers the MSD and in-turn the coil is one of the pins from that 2-pin (drivers side) connector from the HEI module. Like i said, i've had it running before wired up like this but it's always been hard to start. I've been at college all week and now am back home so i can fiddle with it more this weekend. I guess i'll just spend the money and get a new HEI module and see if that works. I'll probably look for a signal at the pickup to make sure the HEI module is in fact getting a signal from that. As long as it is, i think the HEI module is the cause. I posted a picture of an identical distributor on my previous post about this if your not sure what it looks like. The way I see it is that the HEI sends a signal to the FAST for an RPM input through the 4 pin connector and it sends a signal to the msd/coil via the 2 pin connector. Since i'm getting an rpm signal when cranking when looking at the dashboard, i GUESS only one side of the HEI is bad...isn't that the weirdest thing you've ever heard. That's my only thought at this moment. And like i said in the first post, i touched the white msd wire (the trigger wire) to ground and it produces a nice spark so i know the msd box and coil are ok. It's just not getting a signal from the distributor. It won't spark while cranking but when i let off the key it'll spark once. That's all I can tell you. THANKS SO MUCH! This is EXACTLY the reason I decided to go with the FAST system and not the Gen 7 or soemthing else. The support is great on this site! THANKS AGAIN!!!!!!!!!
S
SingleTurboIroc
Guest
ok i think i can help or at least clear some things up for craig
with an 87+ small cap distributor there are two connectors on the back of the distributor....
one connector goes from the distributor to one side of the coil
the other connector goes back the computer i belive (haven't traced it yet since the wiring harness isn't out of my camaro just yet)
but the way this connector works is, is that when the motor is cranking it senses this and sends a signal back to the computer to ground out the injectors to send fuel into the chamber
CASE IN POINT
one time at the track with my old blower, we couldn't get the damn car to start for ****....nothing. had spark, just no fuel and the injectors weren't "clicking"
so i tested the injectors with a noid light and nothing (started to worry i had a short somewhere)
then i tested the injector pigtail with a power light tester and it was getting power so that left two things
bad computer or faulty ignition control module (the little thing underneath the rotor on the distributor)
so i changed the module with a $25 replacement from a local parts store and WALA! car started
so maybe your hard starting is attributed to a weak module or possibly, a dirty fuel filter
just trying to help
with an 87+ small cap distributor there are two connectors on the back of the distributor....
one connector goes from the distributor to one side of the coil
the other connector goes back the computer i belive (haven't traced it yet since the wiring harness isn't out of my camaro just yet)
but the way this connector works is, is that when the motor is cranking it senses this and sends a signal back to the computer to ground out the injectors to send fuel into the chamber
CASE IN POINT
one time at the track with my old blower, we couldn't get the damn car to start for ****....nothing. had spark, just no fuel and the injectors weren't "clicking"
so i tested the injectors with a noid light and nothing (started to worry i had a short somewhere)
then i tested the injector pigtail with a power light tester and it was getting power so that left two things
bad computer or faulty ignition control module (the little thing underneath the rotor on the distributor)
so i changed the module with a $25 replacement from a local parts store and WALA! car started
so maybe your hard starting is attributed to a weak module or possibly, a dirty fuel filter
just trying to help
Craig Smith
That was easy!
- Joined
- May 25, 2001
Good point. If the computer isn't seeing an RPM signal from the module, it won't fire the injectors but you will still see spark. The bypass circuit in the HEI module generates its own spark while the bypass line is activated, which is during cranking. However, the fact that there is an RPM signal seen by the FAST unit here further adds to the confusion.
Even though I'm joking, this is why I tell people I hate cars AND I hate computers and I must be working in the wrong place! We'll get her figured out.
Even though I'm joking, this is why I tell people I hate cars AND I hate computers and I must be working in the wrong place! We'll get her figured out.
