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Old 12-07-2011, 01:35 PM   #1
turbofiat124
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Default Cheap retard trick

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.
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Old 12-07-2011, 04:29 PM   #2
15A
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Very interesting. The link to your car pics doesn't work. I'd like to see a turbo'd Fiat.



Btw....I saw "cheap retard tricks" and thought it had something to do with politics and/or the lemmings who still watch it.
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Old 12-07-2011, 06:55 PM   #3
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Very interesting. The link to your car pics doesn't work. I'd like to see a turbo'd Fiat.



Btw....I saw "cheap retard tricks" and thought it had something to do with politics and/or the lemmings who still watch it.
Try this link then you can see my entire photo album.

http://s222.photobucket.com/albums/dd148/turbofiat/
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Old 12-07-2011, 08:30 PM   #4
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Based on the title, I was fully expecting a TB trolling thread...Instead, I was greeted with useful info and a holiday gift! God's own collection of obscure tiny cars!

Thanks
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Old 12-07-2011, 08:37 PM   #5
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Really nice collection of fine and more scarce autos there. Brought back alot of memories.

I had a friend of mine back in the early 90's trade a really nice '80 Spyder to a guy in Galena Ohio for a slightly newer (IIRC it was an 81) Lancia Zagato. The Zagato only had 40k on it and was already on its 3rd clutch. The PO claimed they were known for that....I wasn't sure if he was talking about the car or its owners.
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Old 12-07-2011, 08:59 PM   #6
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Will the GM 5pin module work with a Bosch lh2.2 head mounted dizzy from a 700series???
Thanks
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Old 12-07-2011, 09:40 PM   #7
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Originally Posted by turbofiat124 View Post

It's a cheap way to retard the ignition timing (10 degrees cam timing/5 degrees crank timing)

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.
Thats the wrong way around, 5 deg at the cam is 10 at the crank. Unless you are talking about some wierd motor. Does the amount of retard change with rpms?
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Old 12-08-2011, 09:53 AM   #8
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Does the amount of retard change with rpms?
With boost.
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Old 12-08-2011, 03:39 PM   #9
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I understand its a hobbs switch activated by boost to trigger the retard function, but I was asking if its always 5 deg retard, i.e. on or off type operation, or whether you get more than 5 deg retard at higher rpms. I'm guessing hes only tested it with a timing light at idle?
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Old 12-08-2011, 03:59 PM   #10
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I see what your saying but I think he is using a gm module to retard 5deg more on top of what his dizzy is doing now, but I'm not sure...
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Old 12-08-2011, 08:28 PM   #11
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Will the GM 5pin module work with a Bosch lh2.2 head mounted dizzy from a 700series???
Thanks
This module *should* work on any "dumb" distributor. Meaning any distributor that uses a magnetic trigger, centrifical advance and a vacuum advance.

I've seen the earlier "4 pin" modules used on all sorts of ignition systems which use a magnetic trigger. Where people have gutted Ford Duraspark and Chyrsler ignition boxes that have went bad.

If the distributor uses a HALL sensor or the advance is controlled by a computer or has a knock sensor then I'd so no it probably wouldn't work.
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Old 12-08-2011, 08:45 PM   #12
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Thats the wrong way around, 5 deg at the cam is 10 at the crank. Unless you are talking about some wierd motor. Does the amount of retard change with rpms?
Your right, that has always confused me when regarding ignition timing.

The guy that said this module gives 10 degrees retard did not specify what "type" of retard. When I tested the module by grounding it, my timing light only showed a 5 degree retard and I was like "WTF?". But it still seems to work.

This module just retards the timing 5 degrees instantly when the tiny pin is grounded. It's not progressive like a vacuum advance.

However yesterday it was pouring down rain and 20 degrees cooler and I noticed this bucking condition returned as I open up the throttle. ARRGGHH!!!

However when this happens, it's when my boost gauge is below 10" HG. Anything above that such as 20" HG, the car runs smooth. Before when the vacuum advance was not working the condition cropped up as low as 20" HG.

I orginally thought it was in the jetting but believe it's related to the ignition timing because if I advance the static timing 5 degrees, the problem goes away but the engine pings under boost. I seem to think below 10" HG, the throttle is open more so the vacuum advance is providing less advance.

However I may have a defective Hobbs pressure switch that may be grounding the module just enough to where it's retarding the timing. I had to pick out the best one out of three I had laying about. I ordered some new switches from Omnicontrols.com made by Drywer.

My ohmsmeter shows a slight bit of resistance between the contacts when the engine is not running so it makes me wonder.

My ohmsmeter was showing this switch was stuck when I first tested it so I opened it up and thought I had fixed it. Maybe not.

I've got yet another trick up my sleeve. I'm going to use a check valve going to the vacuum advance to "lock" the advance in at it's maximum (10 degrees) when I close the throttle and the engine vacuum falls to 30" HG, so the advance does not vary with engine load.

Then an A/C solenoid valve activated by the same pressure switch will bleed pressure off around the check valve and release the vacuum when the switch detects pressure.

I don't know if this makes sense or not.

So stay tuned and I'll post some pics..
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Old 12-08-2011, 08:48 PM   #13
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Originally Posted by swiggy View Post
I understand its a hobbs switch activated by boost to trigger the retard function, but I was asking if its always 5 deg retard, i.e. on or off type operation, or whether you get more than 5 deg retard at higher rpms. I'm guessing hes only tested it with a timing light at idle?
Yes it's either on or off. Not progressive like a vacuum advance would function.
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Old 12-08-2011, 09:15 PM   #14
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MSD makes a module that allows you to retard timing between 1 and 3 degrees per psi of boost. Food for thought...
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Old 12-08-2011, 10:03 PM   #15
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MSD makes a module that allows you to retard timing between 1 and 3 degrees per psi of boost. Food for thought...
Yeah and the whole setup will run you $500 to $700. Allot of money if you need a minimum amount of retard to do the job.

The HEI module is $36 and the pressure switch is $18.
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Old 12-11-2011, 04:59 AM   #16
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This is brilliant! I may end up using this for my VW. Thanks for posting this
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Old 12-13-2011, 01:56 AM   #17
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I've been driving my Yugo a lot after making some ignition adjustments. Mainly because it's been very cold here in Tennessee and since this bucking issue tends to crop up below 60F this is good tuning weather. Like I said in the middle of summer, this car runs like a champ.

Seems this bucking issue crops up at it's the worse when it's raining at almost any temperature. I thought it was because the air was more humid and it was causing my plug wires to cross arc but otherwise the car idles fine, runs fine under cruise and accelerates fine under boost.

This bucking can occur while trying to accelerate off cruise in top gear (4th), sometimes in 3rd but not often.
under these following conditions:

1) RPMS are less than 3000
2) Temperature is <60F
3) Humidity is high (rain). In this case if the temperature is above 60F, the bucking can occur.
4) Boost guage shows engine vacuum is between 10" HG and atmospheric pressure. Probably the point where the vacuum advance is not doing anything.

When this bucking occurs, my air/fuel meter goes from rich to full lean (no bars). I was told on another Fiat forum this was a missfire but couldn't this also indicate that fuel is not being drawn up through the jets properly because maybe the turbo is spooling up causing a vacuum interuption? If that makes sense.

Now here's the kicker. Advance the static timing from 10 BTDC to 15 BTDC and the condition goes away completely but the engine pings under boost so I can't have that.

When the problem does not occur:

1) RPMS is above 3000 (any gear)
2) Temperature is above 60F
3) I go from cruise to WOT
4) Static timing is bumped from 10 degrees to 15 degrees

So in other words if I am tooling along at 40 mph in 4th gear and want to accelerate, if the engine starts to buck simply downshift into 3rd gear and bump the RPMs to at least 3000. Now if I am doing 55 mph and I am in 4th gear, I'm turning more 3K rpms anyway so the problem doesn't occur.

It seems that the condition is related to RPMs and timing advance.

On the other hand, the high humidity might be messing with the fuel mixture which could mean I am running too lean a primary main jet.

Another weird thing is I drove this car home from work the other morning and it was 23F. BBRRR!!! But the engine seemed to run better than at 45F and piss pouring rain.

I just don't get it. Why is rain playing a major factor here? Looks to me if I had some issue with leaking plug wires, the engine would missfire all the time. Plus my Magnecore plug wires I am using are only 6 years old. In comparison the Magnecors on my Fiat Spider are 13 years old.
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Old 12-13-2011, 01:56 AM   #18
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OOPS, hit the post button twice.
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