Diagnosis

[james singleton]

Recently I pulled an electronic ignition system (dizzy & module) from an 82' Fairmont @ the "junkyard". I believe the module is "not" the stock module because it is from Napa, but is the same size as the stock modules that I have seen pictures of in the "Sticky" and elsewhere; approximately 4" x 4" or so. Here is my question: In other posts with pictures I see modules that are about the size of a match box (2 - 3" long or so), very small in relation to the other module, and would like to know what is the difference between these two different size modules. People mention the need for a "heat sink" for the smaller modules, so which module is better, or is there an advantage with one over the other?? Are they both Duraspark modules but from different years??? Is the smaller module an aftermarket module??? Thanks for clearing up my confusion! Jim

 

[Bort62]

The smaller module is a GM module.

 

[grocery getter]

it looks like you fed that red wire around the grommet. if you did,the firewall will easily cut through the insulation.

 

[frogmn666]

I'll fix that grommet issue getter.

Bort, the 6.* volts was before I bi-passed the resistor. With it running, I get 13.40 volts.

Ref, if it didn't return at idle, it would run easier. I even tightened the light spring so it would return to zero advance.

If I start it, then push the dizzy as far as I can, I can get it to idle down to about 1000, but that is with 42° advance, but then it kicks back and won't start. I did notice that as I decrease the idle, the timing retards. I'm getting advance at a very low rpm, but it still should idle down with 10° initial advance. When it dies, it quits like I pulled a fuse. When I can keep it running, I get about 2" of vacuum and only goes to 5" when I rev it to about 2-3K. I'm using the 1100 and the vacuum is not connected, but plugged.

What am I missing here? With my turbo VW engines, I would set the initial at 10° and total to 24° and it would idle fine.

Is it possible that as I idle down, the timing gets closer to zero? I'm thinking I need a heavier spring so it doesn't advance till higher rpm.

 

[Bort62]

Okay, hold on a second.

You are only gettign 2" of vacuum at idle? Where are you measuring it.

Are you idling on the main or on the idle circuit in the carb? (does the idle mixture screw have any effect)

Wait, crap - I just remembered something. You may have the pickup leads from the distributor to the module backwards. Timing moving all around and overall weird running is the result.

 

[james singleton]

Thanks Bort62. So the smaller module is a GM! I assume that this smaller module only works on a GM set-up; and not the Ford set-up??? Correct?? Are there many differences between the Ford Duraspark set-up and the GM set-up??? Or I should say are there any advantages, or disadvantages, of one over the other?? Does one work better than the other? Is there a cost a factor? Etc., Etc.,.....?? Thanks again, Jim

 

[Bort62]

Thanks Bort62. So the smaller module is a GM! I assume that this smaller module only works on a GM set-up; and not the Ford set-up??? Correct?? Are there many differences between the Ford Duraspark set-up and the GM set-up??? Or I should say are there any advantages, or disadvantages, of one over the other?? Does one work better than the other? Is there a cost a factor? Etc., Etc.,.....?? Thanks again, Jim

The ignition module doesn't know what brand of car it is in. It sees a rising signal on the input and closes a relay (well, probably a transistor) on the output to spark the coil.

GM, Chrysler, Ford - they all work the same basically.

The GM one just happens to be cheap, small, and reliable.

It was also used on just about every GM car from 1974-1982, and as a result is pretty easy to come by.

 

[frogmn666]

Okay, hold on a second.

You are only gettign 2" of vacuum at idle? Where are you measuring it.

Are you idling on the main or on the idle circuit in the carb? (does the idle mixture screw have any effect)

Wait, crap - I just remembered something. You may have the pickup leads from the distributor to the module backwards. Timing moving all around and overall weird running is the result.

If I try to adjust the idle mixture, the engine dies if I adjust too far and the rpm drops, so I am on the idle circuit. It was tuned perfect with the old dizzy and the mixture should not change with a new dizzy.

Read the text at this post:
http://fordsix.com/forum/viewtopic.php?t=18841

I am measuring it at the hard line from the carb that went to the original dizzy, but if I understand it, from the above link, it should be seeing manifold vacuum. I see 3" and when I hook it to the dizzy nothing changes. If I suck on the hose to the dizzy, the rpm does go up some, but if I turn the idle down, it still dies around 1050 @ 10°.

I just rebuilt this carb and maybe the spark valve is no good. Still, I think it should still idle at 10° unless these engines and electronics won't allow it. How much vacuum should I get at idle to the dizzy?

I just tried reversing the orange violet and it does make a difference. Sounded like some munchkins were in the head pounding on the pistons with a 20# sledge hammer. Someone else reported hard starting with the leads being incorrrect from the rebuilder. When I did get it running, it still died when the rpm dropped.

The timing is not jumping all around. It advances as rpm increases.

I just checked vacuum at the 1100. 3". At the PCV valve 19.5. I then hooked my MityVac to the dizzy and pulled 20". Hot damn, I can get the idle down to what sounded like the correct rpm. Didn't have the tach hooked up. But, how would I check timing with the vacuum off as it should be. Something else is causing this.

So, my guess it the Spark Control Valve is bad. I blew out all the passages in the carb, but maybe one path didn't flow when it should have. Will see if I still have the old one.

I have heard of people leaving the vacuum line off with no problems. Seems like mine needs the vacuum.

 

[frogmn666]

Found the old SCV and it is worse. Can only get vacuum if I rev it.

With the SCV removed, I get 10" at the SCV hole. Plugging it has no effect on dizzy vaccuum. Doesn't sound right does it?



At the heat line to the auto choke, I get 16" and plugging it has no effect on vacuum at other points.

I still get 3" at the 1100 and the line at the dizzy.

I forgot to mention, I replaced the light spring with a heavier one and now do not get any low rpm advance and can see it doesn't advance till 2200 rpm. Still won't idle down like it should.

Plugs are still at .035", but that shouldn't matter. It's almost like when the rpm gets low, the spark stops. I could put my oscillicope on the dizzy output, but I wouldn't have anything to compare it to. I may do that tomorrow to see if the waveform decreases with lower rpm.

Here is a thought. If the SCV sees 19" from the manifold and the dizzy port is blocked off, it will draw the air from the venturi port thus showing lower than 19".

 

[frogmn666]

Here is the waveform I took last night. Probably wouldn't have shown up in daylight.

The volts did not change as rpm dropped. As expected, it did change in wave length. The top one is the "G" lead and the bottom is the "W" lead.
This is getting frustrating and I may put the stock dizzy back to see if it runs better and take vacuum readings.

 

[Bort62]

Isn't an O-scope a wonderful tool. People wonder how I can diagnose ignition problems so rapidly when they bring the car over

That waveform looks correct.

You mentioned using a SCV valve, but you have a duraspark distributor. The two are not compatible.

You need to feed your duraspark's vacuum avance (IMO) full manifold vacuum. Some will suggest ported vacuum, but the difference basically is whether or not you want advance at idle or not. IMO, more advance at idle lowers fuel consumption and idle temperature as well as generally makes the car idle more smoothly. Regardless of that difference in opinion, the SCV vacuum is undoubtedly wrong.

However - that is not your only problem. You should be able to idle down to ~ 500 rpm w/o any vacuum advance at all.

So, if I understand you situation correctly, you have a duraspark distributor installed w/ a GM module - and if you try to adjust idle below ~1200 rpm it conks out on you.

You have confirmed you are running on the idle circuit as the idle mixture screw will kill the engine if turned in too far.

You are pulling 19.5" of manifold vacuum at idle (good!)

Your voltage at the coil and module is < 12v while idling.

Your initial advance is ~10*.

If all of the above things are true, then you have something subtle going on. Have you verified that your balancer's outer ring has not slipped, giving you a false initial advance reading ?

 

[BIGREDRASA]

Have you checked/changed your PCV valve? It can act like a major vacuum leak if it's bad.

 

[Bort62]

Have you checked/changed your PCV valve? It can act like a major vacuum leak if it's bad.

+1

Sorry, I made the assumption that you had confirmed no vacuum leaks.

 

[frogmn666]

New PCV valve. +13.40 volts at idle. Timing set to just below where it kicks back when cranking. Idled fine without vacuum on stock dizzy.

Ian, we are on the same page. There is no reason it shouldn't idle unless the pulse goes away < 1050 rpm. If it is not the dizzy, then it must be the HEI module or the coil. I have a couple more 12 volt coils. Maybe I should try that first. When it died with the scope hooked up, there was no drastic change in the waveform.

 

[Bort62]

It could be a bad module.

Scope the output side of the module (neg side of coil) relative to gnd.

 

[Bort62]

Timing set to just before it kicks back while cranking suggests to me however that it is way too advanced.

Since ignition advance and idle speed are somewhat coupled, it is sometimes possible to get yourself into a corner where both are totally screwed up.

It might be worth finding TDC and sanity checking yourself. it is possible that you are running just way too much initial advance. This can make the engine behave very strange

 

[BIGREDRASA]

+1

 

[frogmn666]

Had to throw a blanket over myself and the scope to get a half-way decent pic.

With a voltmeter, I get ~4.5 volts at a high idle that goes up to ~9 volts at higher rpm, which makes sense since it is pulsing to ground.

Sorry for the crappy pics. Not easy even with an overcast. Wonder what the neighbors thought of a guy with an army blanket over his head, bent over, taking pictures.

With the stock dizzy, I could run close to kick back with no problems. I've always set all my motors to just below kick back.

[/url]

 

[grocery getter]

this is getting long we need a recap
have you proven you have spark when it dies? one trick is to use the timing light when you lower the rpm, if it dies and the light still blinks look to the fuel side.

one thing to keep in mind is... the rotor has to be pointing to the dist cap peg to transfer the spark. you mentioned it's in an awkward position
and it needs extreme advance to idle. it might be too far away from distributor peg when you idle it down and it retards.

EDIT---> I was typing while you posted last. Where are you getting 4.5 volts at idle?

 

[Bort62]

That looks right on the Scope, the question is - what happens when it dies. Does the module keep triggering as long as the distributor is turning ?

Do you have a function generator?