Monday, November 27, 2017
Thursday, November 16, 2017
We Have Ignition
Last week I drove with my daughter to a cruise-in at the local Rock & Brews. Since the car had been sitting for several weeks while I shipped off my master cylinder, I had to fill the carb bowls using a pipette in order to start the engine. She fired right up and off we went. As soon as we got out on the main road, however, I noticed the engine started miss-firing slightly. If I held in the clutch the engine would try to idle then slowly die. But if I stomped on the loud pedal the car accelerated okay so I figured it was getting plenty of fuel. I figured it was probably spark related.
I have a manual choke which I have set up to mainly bump up the idle when the engine's cold and doesn't really choke off the carb. So I bumped up the idle a little bit so it wouldn't stall and continued on to the show since it was so close. When I got there I let the engine cool off a bit and then poked around a bit checking the obvious things like plug wires and the distributor cap. Nothing seemed out of whack.
Driving home things started to get worse. I had to raise the idle up to around 1200 rpm to keep it from stalling at lights. Engine vibration was increased and the exhaust note sounded different making it feel like she was only running on 7 cylinders.
My current ignition setup consists of an MSD 6AL control box coupled with a MSD Blaster 2 coil feeding a stock rebuilt distributor. I've been wanting to get rid of the stock points and go with something electronic for a while now--no time like the present.
I tore down the stock distributor to see what's what and found that my mechanical advance was set up to provide 30 degrees of timing. You can see it's using the 15L slot which gives 15 degrees off the camshaft, or 30 degree at the crankshaft. This is a problem since I've got the initial timing set at 12 degrees before TDC, meaning I have 42 degrees of total advance. It should be more like 36 total. Now, I could pull the distributor and rotate the shaft to use the 10L slot, but then I'd only get 20 degrees of mechanical advance, or 32 total. Not enough. This setup if fine for a stock engine that only needs 6 degrees initial timing, but my cam requires more. In order to use the 10L slot I would really need 16 degrees of initial timing, which might be too much.
Interesting side-note: I've been studying engine timing a lot lately so here's some of what I can remember. Engines require the spark to fire before TDC because it takes time for the fuel/air mixture in the cylinder to burn and you want it burned completely by the time the piston has reached the end of the power stroke. At idle, the cylinder pressure is low--there's not as much air in the cylinder because it's being choked off by the throttle. This thinner mixture burns slower, because there's less fuel and air than at higher rpm, which requires an initial timing advance. For a Ford 289 the initial timing is 6 degrees before TDC. However, a radical camshaft like mine will reduce cylinder pressure at idle even more, which requires more initial timing.
As the engine spins faster you need to fire the spark even sooner than TDC, thus a mechanical advance is used. Centrifugal weights are used to advance the timing on top of the initial setting. You can see them attached to the springs in the picture above. At idle the weights are retracted all the way and don't start to move until just above idle speed. As engine speed increases they swing out advancing the timing until reaching their maximum advance at around 3000 rpm.
As the engine spins faster you need to fire the spark even sooner than TDC, thus a mechanical advance is used. Centrifugal weights are used to advance the timing on top of the initial setting. You can see them attached to the springs in the picture above. At idle the weights are retracted all the way and don't start to move until just above idle speed. As engine speed increases they swing out advancing the timing until reaching their maximum advance at around 3000 rpm.
There's a third factor in controlling engine timing and that's vacuum advance. At low throttle openings cylinder pressure is still low which requires more timing advance than the mechanical advance can provide. So a vacuum diaphragm advances the timing in high vacuum situations, as much as 40 additional degrees in some applications. Traditionally this vacuum canister was connected to manifold vacuum so as to provide this additional advance whenever high vacuum was present, even at idle. Eventually, however, engineers discovered they could reduce emissions at idle by using a ported vacuum source, which blocked any vacuum advance at idle.
I hooked my Mighty Vac up to my vacuum diaphragm and saw that it didn't start to move until 7" of vacuum and reached its maximum travel at 16. Since I'm only getting around 8-9" at idle this vacuum advance wasn't really doing much for me. I had it hooked to the ported vacuum source on my Holley, so as soon as I cracked the throttle it just barely provide any advance at all.
After a lot of researching I decided I wanted to switch to using manifold vacuum for my source. But this brought up a problem. If I simply moved the vacuum hose to the manifold source I would start seeing vacuum advance at idle. Since my diaphragm is just starting to move at 8" I would also see an additional few degrees of timing advance. This in turn would raise my idle speed slightly which in turn would increase my vacuum, which would then add more vacuum advance, and so on. This no doubt would make my idle very unstable. Not good.
To fix this you need a vacuum advance that is fully advanced at a value lower than your idle vacuum. So I need a diaphragm that reaches its max travel at 7" or less. Chevy made one back in the '60s for this exact situation, but apparently not Ford Motorcraft. Shelby totally bypassed this conundrum by using a dual point distributor without any vacuum advance. Great for performance but not so much for economy.
At this point I was ready to replace the points distributor with an electronic one. If I went with an HEI version I could eliminate the MSD box as well. My MSD's been mounted in the cabin on the passenger kick panel and it buzzes very loudly. If I can hear it over the exhaust then it's making too much noise. I could move it under the hood but the loud buzzing makes me feel like it's not working like it should be.
I decided to order a PerTronix D130700 Flame-Thrower billet distributor which comes with their Ignitor II module. Unfortunately it only comes with a non-adjustable vacuum canister, even though Pertronix makes an adjustable one. So I also ordered a Crane Cams 99601-1 Adjustable Vacuum Advance Kit that would hopefully work with my big cam.
In order to install the adjustable vacuum canister you need to remove the distributor shaft. I drove out the pins for the collar and the drive gear.
With the shaft removed you can remove the plates that cover the mounting screws for the canister.
Here's the new adjustable canister in place with the limiter cam in place. You can see that it interferes with the bushing so I'll have to leave it off. It's designed for a '60s Chevy distributor which is designed a little different, oh well. I can still adjust the vacuum level at which the canister operates but I can't limit the amount of advance.
Here's a shot of the distributor put back together and ready to go in the car. Installing it was straightforward but I had the hardest time getting the engine to fire. With a points distributor you can static time the engine by turning the crank to where you want the initial timing to be and then rotate the distributor until the points open. With an electronic distributor this won't work so all you can do is point the rotor at terminal #1 and guess on the rotation of the distributor.
No matter where I turned the distributor the engine wouldn't fire. So I began my troubleshooting looking for spark. I attached a spare spark plug to the coil and set it next to a ground. When I cranked the engine, no spark. I thought maybe the distributor could be defective to I looked for a way to test it. Pertronix says there isn't a way to test the Ignitor II but they provided a check list of what to check. The most important thing is that you should have 12 volts at the coil + terminal.
The factory uses a resistor wire to provide around 6 volts to the coil to help the points live longer. This wire was bypassed when the MSD 6AL was installed so I knew I had 12 volts but I checked anyway. That's when I found something peculiar. With the distributor connected to the coil I was only reading 2.6 volts. But if I disconnected the positive wire going to the distributor I then read a full 12 volts at the coil. WTH? I felt like the Ignitor II module was to blame. I could jump a ground to the negative coil terminal to induce the coil to spark only if the Ignitor II was disconnected.
After contacting Pertronix they agreed to send me a replacement module. In the meantime I figured I would order a chrome PerTronix 45001 Flame-Thrower II coil to replace my 10 year old MSD Blaster 2. With the new module installed I rechecked my voltage readings and was shocked to still see only 2.6 volts at the coil with the Ignitor II connected. Unbelievable!
At this point I was totally lost. First, I thought maybe I was getting a bad ground from the distributor through the engine block so I ran a jumper wire to what I assumed was ground on my starter solenoid. Stupid me, there is no ground there so when I tried to start the engine I ended up sending a full 12 volts straight to the body of the distributor. There was a loud pop and the wire I was holding got instantly hot and tried to weld itself to the vacuum canister before my knee-jerk reaction pulled the wire off. Close one.
I then tried running a jumper to an actual ground but that made no difference to my voltage reading. So I made a quick trip to the local parts store and picked up a relay. I was hoping that for some reason my coil wire from the ignition couldn't supply enough current for the Ignitor II and was dropping the voltage. And it worked! After wiring up the relay I was getting a full 12 volts at the coil even with the Ignitor II connected.
Now when I tested for spark it worked. It only took me a few tries with the distributor turned to different positions before the engine finally fired. Hallelujah!
After finding junk in the fuel line and carb and then replacing the carb I could finally do some fine tuning. I used a pair of springs from the vacuum advance kit to give me full mechanical advance by 3000 rpm. I set the initial timing at 12 degrees and with the new distributor's 24 degrees of mechanical advance I got the full 36 degrees at 3000 rpm. I then plugged in the vacuum advance hose to the manifold vacuum port on the carb. Right away the idle rpm increased from the extra timing so I dropped the idle speed back down to 850 and checked the timing. At idle the timing was about 38 degrees before TDC. Obviously the engine likes the increased timing since the idle speed increased. When I disconnected the vacuum advance the idle speed dropped to the point of almost stalling so it's helping.
At this point I was ready to replace the points distributor with an electronic one. If I went with an HEI version I could eliminate the MSD box as well. My MSD's been mounted in the cabin on the passenger kick panel and it buzzes very loudly. If I can hear it over the exhaust then it's making too much noise. I could move it under the hood but the loud buzzing makes me feel like it's not working like it should be.
I decided to order a PerTronix D130700 Flame-Thrower billet distributor which comes with their Ignitor II module. Unfortunately it only comes with a non-adjustable vacuum canister, even though Pertronix makes an adjustable one. So I also ordered a Crane Cams 99601-1 Adjustable Vacuum Advance Kit that would hopefully work with my big cam.
In order to install the adjustable vacuum canister you need to remove the distributor shaft. I drove out the pins for the collar and the drive gear.
With the shaft removed you can remove the plates that cover the mounting screws for the canister.
Here's the new adjustable canister in place with the limiter cam in place. You can see that it interferes with the bushing so I'll have to leave it off. It's designed for a '60s Chevy distributor which is designed a little different, oh well. I can still adjust the vacuum level at which the canister operates but I can't limit the amount of advance.
Here's a shot of the distributor put back together and ready to go in the car. Installing it was straightforward but I had the hardest time getting the engine to fire. With a points distributor you can static time the engine by turning the crank to where you want the initial timing to be and then rotate the distributor until the points open. With an electronic distributor this won't work so all you can do is point the rotor at terminal #1 and guess on the rotation of the distributor.
No matter where I turned the distributor the engine wouldn't fire. So I began my troubleshooting looking for spark. I attached a spare spark plug to the coil and set it next to a ground. When I cranked the engine, no spark. I thought maybe the distributor could be defective to I looked for a way to test it. Pertronix says there isn't a way to test the Ignitor II but they provided a check list of what to check. The most important thing is that you should have 12 volts at the coil + terminal.
The factory uses a resistor wire to provide around 6 volts to the coil to help the points live longer. This wire was bypassed when the MSD 6AL was installed so I knew I had 12 volts but I checked anyway. That's when I found something peculiar. With the distributor connected to the coil I was only reading 2.6 volts. But if I disconnected the positive wire going to the distributor I then read a full 12 volts at the coil. WTH? I felt like the Ignitor II module was to blame. I could jump a ground to the negative coil terminal to induce the coil to spark only if the Ignitor II was disconnected.
After contacting Pertronix they agreed to send me a replacement module. In the meantime I figured I would order a chrome PerTronix 45001 Flame-Thrower II coil to replace my 10 year old MSD Blaster 2. With the new module installed I rechecked my voltage readings and was shocked to still see only 2.6 volts at the coil with the Ignitor II connected. Unbelievable!
At this point I was totally lost. First, I thought maybe I was getting a bad ground from the distributor through the engine block so I ran a jumper wire to what I assumed was ground on my starter solenoid. Stupid me, there is no ground there so when I tried to start the engine I ended up sending a full 12 volts straight to the body of the distributor. There was a loud pop and the wire I was holding got instantly hot and tried to weld itself to the vacuum canister before my knee-jerk reaction pulled the wire off. Close one.
I then tried running a jumper to an actual ground but that made no difference to my voltage reading. So I made a quick trip to the local parts store and picked up a relay. I was hoping that for some reason my coil wire from the ignition couldn't supply enough current for the Ignitor II and was dropping the voltage. And it worked! After wiring up the relay I was getting a full 12 volts at the coil even with the Ignitor II connected.
Now when I tested for spark it worked. It only took me a few tries with the distributor turned to different positions before the engine finally fired. Hallelujah!
After finding junk in the fuel line and carb and then replacing the carb I could finally do some fine tuning. I used a pair of springs from the vacuum advance kit to give me full mechanical advance by 3000 rpm. I set the initial timing at 12 degrees and with the new distributor's 24 degrees of mechanical advance I got the full 36 degrees at 3000 rpm. I then plugged in the vacuum advance hose to the manifold vacuum port on the carb. Right away the idle rpm increased from the extra timing so I dropped the idle speed back down to 850 and checked the timing. At idle the timing was about 38 degrees before TDC. Obviously the engine likes the increased timing since the idle speed increased. When I disconnected the vacuum advance the idle speed dropped to the point of almost stalling so it's helping.
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