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  #11  
Old 06-11-2011, 12:00 PM
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Rzeppa Rzeppa is offline
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I think the next thing I am going to do is visually inspect as much of the wiring to the solenoid as I can. I will also re-study the section of the manual where it describes the condition(s) under which the power is removed from that solenoid other than turning the switch off - I seem to remember something about deceleration. If that turns up nothing, then I will remove both jet access ports from the front of the bowl and try compressed air in one, coming out the other and vica versa to clear out any potential debris. Then if that doesn't work, I may try hardwiring the solenoid to switched power instead of letting the computer control it.
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  #12  
Old 06-11-2011, 04:38 PM
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There is a vacuum activated switch called the vacuum switch that should be mounted on the driver side fender close to the headlight. I had several of these measure bad. It might cause the "computer" to shut off the idle solenoid at a bad time. Yes, try wiring the idle solenoid to be on with the ignition to see if the stall goes away.
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  #13  
Old 06-11-2011, 05:43 PM
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In addition to all the good advice already given, don't rule out the EGR. Disconnecting the vacuum line won't have an effect if it is stuck open, which is common. Do a quick test of pulling vacuum on it (by mouth works fine) and see if the diaphragm is moving freely. If it's stuck open you would have exhaust gas dumping into the intake at idle when warm, which would cause a stall. Just something quick to try before you start opening up your carb.
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  #14  
Old 06-13-2011, 10:00 AM
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Quote:
Originally Posted by MDH33 View Post
In addition to all the good advice already given, don't rule out the EGR. Disconnecting the vacuum line won't have an effect if it is stuck open, which is common. Do a quick test of pulling vacuum on it (by mouth works fine) and see if the diaphragm is moving freely. If it's stuck open you would have exhaust gas dumping into the intake at idle when warm, which would cause a stall. Just something quick to try before you start opening up your carb.
I thought I had written this, but always going for the easy stuff first, I disabled the EGR system by disconnecting the hose between the vacuum modulator and the EGR valve and capped it off. It made no difference, so there is one potential cause eliminated.
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Old 06-15-2011, 09:22 AM
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I was having the same issue and went through a bunch of emission stuff, But for some reason i think i nailed it with a vacuum leak on the manifold (make sure all of the bolts are tight) I also adjusted the valves at the same time and re-timed it. It still does not run quite like i think it should, so my next step will rebuild the carb but i dont have the idle issue anymore.
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  #16  
Old 06-15-2011, 10:14 PM
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As a reminder, this is an intermittent issue and only manifests when rolling. She will sit there in the driveway and idle all day with no issues. It's really hard to stick your head under the hood and fiddle with stuff while rolling.

So, I did some more diagnostics but have not yet found the root cause or the fix.

Since I have already eliminated the EGR as the culprit, I focused on the idle fuel cut solenoid and the HAC systems this evening. I have already tested the solenoid by turning the key on and then disconnecting and reconnecting the connector at the carb and listening for the clicks. It clicks.

This evening, with the engine running, I tried disconnecting and reconnecting the solenoid. There was very little change in RPMs at all. With the engine running, I re-verified system voltage is present at the connector. From Bruce's suggestion, I tested the vacuum switch. It is not working. It is closed whether vacuum is present or not. It is supposed to open if there is more than about 14" of vacuum. I didn't measure the vacuum, but my NIST-traceable calibrated fingertip said that the hose had plenty of vacuum. It is unclear whether this non-functioning component has anything to do with intermittent stalling at idle, especially since she idles just fine whether the solenoid is plugged in or not.

Next I poked around the HAC system. This is where it gets interesting. I disconnected the vacuum advance on the outer diaphragm of the distributor and immediately noted a marked increase in idle speed. I thought it might be due to the HAC no longer advancing the distributor - hey I can fix that! But when I plugged the end of the hose with my finger, the idle speed went back down again. WTF??? All that should be doing is allowing a small vacuum leak into the manifold and possibly closing the HAC valve. Supposedly the HAC valve is supposed to open at our elevation (above 3930 feet). It lets a small amount if air into the primary, secondary and idle circuits when open, to make for a slightly leaner mixture, and via the secondary diaphragm on the distributor advances the timing by 7.

Thinking I had maybe found the issue, I adjusted the idle back to stock and then drove around the block and promptly stalled at every opportunity. So that wasn't it. After scratching my head for the allotted time and staring under the hood for a while, studying the manual and all that, I cranked the idle speed back up, closed the hood and vowed to post up my observations in the hope of getting pointed in a better direction.
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  #17  
Old 06-16-2011, 08:15 AM
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I'd be surprised if you're pulling more than 14 in. Hg vacuum ever at this altitude.
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  #18  
Old 06-16-2011, 08:51 AM
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Quote:
Originally Posted by Rzeppa View Post
...I have already tested the solenoid by turning the key on and then disconnecting and reconnecting the connector at the carb and listening for the clicks. It clicks.
Good news to hear the switch activates when power is applied.

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Originally Posted by Rzeppa View Post
This evening, with the engine running, I tried disconnecting and reconnecting the solenoid. There was very little change in RPMs at all.
This is odd. Your results indicate primary circuit is feeding fuel at idle. What RPM was the engine idling at when you did this check? When tuning a carb I want start out at the lowest RPM (500 or less) the engine will run at; to insure it is running off the idle circuit. I would have expected that when power is cut to the solenoid, there would be a very noticeable change.

Quote:
Originally Posted by Rzeppa View Post
This evening, with the engine running, I tried disconnecting and reconnecting the solenoid. There was very little change in RPMs at all. With the engine running, I re-verified system voltage is present at the connector. From Bruce's suggestion, I tested the vacuum switch. It is not working. It is closed whether vacuum is present or not. It is supposed to open if there is more than about 14" of vacuum. I didn't measure the vacuum, but my NIST-traceable calibrated fingertip said that the hose had plenty of vacuum. It is unclear whether this non-functioning component has anything to do with intermittent stalling at idle, especially since she idles just fine whether the solenoid is plugged in or not.
If I'm tracking with everything (that is a big IF), this would indicate that when the solenoid is connected to the broken vacuum switch - there is no power to the solenoid. In effect the carb is running w/o the idle circuit and it is consistent with the intermittent issue you are having. At lower RPM feeding fuel from the primary it will idle just fine, but in the varying conditions of driving the vacuum varies enough that sometimes it is not strong enough to keep pulling fuel through the primary circuit - resulting in stalling, whereas as the higher RPM vacuum is sufficient to keep the flow of fuel going.

Easy enough to validate, jump the idle cutoff solenoid to power, drop your RPM back down and go for a test drive, i.e. bypass the vacuum switch. Of course when you turn off the ignition you will have some dieseling because the cutoff is jumped to power.
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  #19  
Old 06-16-2011, 03:07 PM
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Quote:
Originally Posted by RicardoJM View Post
This is odd. Your results indicate primary circuit is feeding fuel at idle.
Not necessarily - my results are that (1) power is present at the connector and (2) the solenoid clicks audibly. That doesn't necessarily mean fuel is being fed through the slow circuit. However, among the things I tried a while ago was adjusting the idle mixture screw. It is currently set at 3 turns out. I thought that perhaps things were a little too lean but opening more makes no real difference, whereas closing it up does reduce idle speed.

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What RPM was the engine idling at when you did this check?
Around 900. I don't think she will run much below that.

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Originally Posted by RicardoJM View Post
When tuning a carb I want start out at the lowest RPM (500 or less) the engine will run at; to insure it is running off the idle circuit. I would have expected that when power is cut to the solenoid, there would be a very noticeable change.
See above, and yes so would I!

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Originally Posted by RicardoJM View Post
If I'm tracking with everything (that is a big IF), this would indicate that when the solenoid is connected to the broken vacuum switch - there is no power to the solenoid.
There is power to the solenoid. I measured it with a DMM with the engine running and not running.

Quote:
Originally Posted by RicardoJM View Post
In effect the carb is running w/o the idle circuit and it is consistent with the intermittent issue you are having. At lower RPM feeding fuel from the primary it will idle just fine, but in the varying conditions of driving the vacuum varies enough that sometimes it is not strong enough to keep pulling fuel through the primary circuit - resulting in stalling, whereas as the higher RPM vacuum is sufficient to keep the flow of fuel going.
It sure seems like the slow circuit isn't getting fuel at times, but as I wrote, plugging and unplugging the solenoid while the engine is running does not seem to make much difference in idle RPM.

Quote:
Originally Posted by RicardoJM View Post
Easy enough to validate, jump the idle cutoff solenoid to power, drop your RPM back down and go for a test drive, i.e. bypass the vacuum switch.
60s are not like 40s. The idle solenoid get + power through the ignition just like a 40, but unlike a 40, it gets its ground through the computer. The vacuum switch is not directly connected to the solenoid, it is simply an input to the computer. There are several inputs that make the computer decide whether the idle solenoid should be open or closed. Vacuum or no vacuum is one of them, RPM is another. I am at work and don't have the manual in front of me but it isn't about dieseling - it is about preventing the cat from overheating under certain circumstances.

But the business with the HAC is a real head-scratcher for me. What the heck is up with those observations?
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  #20  
Old 06-17-2011, 04:54 PM
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In my continuing saga of trying determine the root cause of the intermittent stalling at idle, I turned my attention to the Hot Idle Compensation (HIC) system. What it is supposed to do is lean out the mixture as the engine gets hotter. It does this with the temperature-sensitive HIC valve and Hot Air Inlet (HAI) diaphragm.

Below is the table which shows how it is supposed to operate:
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