turbofiat124
New member
- Joined
- Nov 27, 2010
Hey, it's me again. The guy with the turbocharged Fiats. I discovered something the other day you turbo guys might be interested in. Since the advance/retard module used on early Volvos and Saabs seems to be no longer available.
It's a cheap way to retard the ignition timing (10 degrees cam timing/5 degrees crank timing) using a 5 pin HEI ignition module and it works with Bosch distributors.
Here's some pics of one of my cars. It's a 1987 Yugo with a 1500cc Fiat engine, T25 turbo, blown through a Weber 32 DFTA carb.
http://s222.photobucket.com/albums/...turbofiat/Yugo/
Here's a CC of my post to the Fiat forum:
I spent this weekend wiring in a 5 pin GM HEI control module on my Yugo that is supposed to retard the timing 10 degrees when the small pin adjacent to the pickup connectors is grounded. Turns out that's 10 degrees in cam timing, not crankshaft timing so when measured with my timing light, it's 5 degrees. But still seems to do the job.
This module was used on 1980 and 1981 Pontiac and Oldsmobile V8s. It is variation of the 4 pin GM HEI modules used on Spiders and Bravas with the Marelli electronic ignition systems but with a retard function to offset detonation under wide open throttle and help the engine start easier on high compression engines. It was wired through a vacuum switch on GM cars but in my application I ran mine through a Hobbs pressure switch which activates at 1 PSI.
It will also work on Bosch distributors but for whatever reason the polarities have to be reversed in order for it to work. Or someone just posted the wrong information I read on the internet and I ran with it.
On Spiders and 131s it's a drop in replacement. No mods needed to the wiring but requires shaving off a small tab on the finned coil unit otherwise the connector won't clear it because the pins are angled differently.
Now here is the suprise. I pulled the dual diaphram advance module I had been using (the infamous Golf mk1/Rabbit) and discovered it was not advancing or retarding the timing at all! The diaphram will hold vacuum but the arm just won't retract which makes me think the spring inside got twisted or something. So no wonder the car ran like crap.
I put the factory (advance only) module back on and connected it to manifold vacuum (not ported vacuum) that way it appears I'm running 20 degrees BTDC at idle.
The car idles so smooth and no detonation under boost. It has been in the 60s here lately so it's too early to tell how well the car is going to run in freezing weather but so far I've tried lugging the engine in top gear at 1000 rpms and no bucking or backfiring.
Eventually I'm going to try this on my Spider. If it works I'll remove my Jacobs Boostmaster I have been running to simply things.
If you want to know how to wire this up to a Bosch distributor read below.
Here's some photos:
http://tinyurl.com/89r37us
GM 5 pin module (e.g. 1980 Olds Toronado V8)
C--> Negative side of coil
B -> Positive side of coil
R --> Ground through pressure switch (Normally open)
H --> Green wire to trigger in distributor
L -- > Brown wire to trigger in distributor
(Color on trigger wires may vary, if engine won't start try reversing the polarities)
There is a ground wire that goes into the harness going to the magnetic trigger. But this wire connects to nothing at the other end. Must be a shielding wire. Ground this wire to the heat sink mount. Note in photo.
If the 7 pin BOSCH connector has a tach wire going to PIN 1 on module, just connect this to the negative side of the coil so tachometer works.
Reply if you have any questions.
It's a cheap way to retard the ignition timing (10 degrees cam timing/5 degrees crank timing) using a 5 pin HEI ignition module and it works with Bosch distributors.
Here's some pics of one of my cars. It's a 1987 Yugo with a 1500cc Fiat engine, T25 turbo, blown through a Weber 32 DFTA carb.
http://s222.photobucket.com/albums/...turbofiat/Yugo/
Here's a CC of my post to the Fiat forum:
I spent this weekend wiring in a 5 pin GM HEI control module on my Yugo that is supposed to retard the timing 10 degrees when the small pin adjacent to the pickup connectors is grounded. Turns out that's 10 degrees in cam timing, not crankshaft timing so when measured with my timing light, it's 5 degrees. But still seems to do the job.
This module was used on 1980 and 1981 Pontiac and Oldsmobile V8s. It is variation of the 4 pin GM HEI modules used on Spiders and Bravas with the Marelli electronic ignition systems but with a retard function to offset detonation under wide open throttle and help the engine start easier on high compression engines. It was wired through a vacuum switch on GM cars but in my application I ran mine through a Hobbs pressure switch which activates at 1 PSI.
It will also work on Bosch distributors but for whatever reason the polarities have to be reversed in order for it to work. Or someone just posted the wrong information I read on the internet and I ran with it.
On Spiders and 131s it's a drop in replacement. No mods needed to the wiring but requires shaving off a small tab on the finned coil unit otherwise the connector won't clear it because the pins are angled differently.
Now here is the suprise. I pulled the dual diaphram advance module I had been using (the infamous Golf mk1/Rabbit) and discovered it was not advancing or retarding the timing at all! The diaphram will hold vacuum but the arm just won't retract which makes me think the spring inside got twisted or something. So no wonder the car ran like crap.
I put the factory (advance only) module back on and connected it to manifold vacuum (not ported vacuum) that way it appears I'm running 20 degrees BTDC at idle.
The car idles so smooth and no detonation under boost. It has been in the 60s here lately so it's too early to tell how well the car is going to run in freezing weather but so far I've tried lugging the engine in top gear at 1000 rpms and no bucking or backfiring.
Eventually I'm going to try this on my Spider. If it works I'll remove my Jacobs Boostmaster I have been running to simply things.
If you want to know how to wire this up to a Bosch distributor read below.
Here's some photos:
http://tinyurl.com/89r37us
GM 5 pin module (e.g. 1980 Olds Toronado V8)
C--> Negative side of coil
B -> Positive side of coil
R --> Ground through pressure switch (Normally open)
H --> Green wire to trigger in distributor
L -- > Brown wire to trigger in distributor
(Color on trigger wires may vary, if engine won't start try reversing the polarities)
There is a ground wire that goes into the harness going to the magnetic trigger. But this wire connects to nothing at the other end. Must be a shielding wire. Ground this wire to the heat sink mount. Note in photo.
If the 7 pin BOSCH connector has a tach wire going to PIN 1 on module, just connect this to the negative side of the coil so tachometer works.
Reply if you have any questions.
