Setting the Fast Idle Log Out | Topics | Search
Moderators | Register | Edit Profile

Australian RR Forums » Silver Shadow Series » Setting the Fast Idle « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 380
Registered: 6-2009
Posted on Tuesday, 21 May, 2013 - 10:36 am:   Edit PostDelete PostView Post/Check IP

First, the pertinent pages from Chapter U of the Workshop Manual for U.S./Canadian delivery cars with EGR for the 1979 . . .

Figure U20 - Mixture Weakening Device:
Figure U20 - Weakener Device & its connections

Figure U23 - Fast Idle Mechanism:
Figure U23 - Fast Idle Mechanism

First, a question about the fast idle cam. In the unaltered figure this is shown as being a perfectly even arc shape with the stop finger protruding at the far end. The actual item on my car is slightly different. At the end of the cam away from the finger there is a very slight projection of the arc that looks like a miniature "diving board" sticking off the end of the main body of the cam. The arc shape between that projection and the red dot is slightly flatter than shown, and there is a clear transition at the red dot that looks a bit like a large obtuse angle that's rounded off at its vertex. It's quite clear that this is not a modification, but that it's always been that way.

In Step 4, they describe the fast-idle adjusting screw as resting on the tip of the fast-idle cam. Am I correct in presuming this means on that tiny projection, that I've drawn in with a green line? If not, would it be just past the "transition bump"? They also mention, "At this point an extra load will be felt due to the action of the extended fast-idle plunger ceasing." I really don't feel any distinct change in load when pushing the control rod lever through its travel. There's a slight resistance during the whole process, no matter how far along the cam's arc I get by pushing on it.

In Step 3 they use the term, "pressure tapping cap." Is the presumption I made about that being the weakener device signal cap correct?

There were lots of interesting developments today but I won't go into all of them until I've got these questions answered as well as clearing up what's what with the weakener and anti-dieseling solenoids.

Brian
Top of pagePrevious messageNext messageBottom of page Link to this message

Jeff Young
Prolific User
Username: jeyjey

Post Number: 151
Registered: 10-2010
Posted on Tuesday, 21 May, 2013 - 07:54 pm:   Edit PostDelete PostView Post/Check IP

Hi Brian,

Yes, the "pressure tapping cap" is the signal cap.

My fast idle cam also has the "diving board". The rest of the cam should be increasing radius (so the farther away from the diving board you go the higher idle you get). The red dot probably marks the maximum radius, after which it's constant radius to the stop.

When you give it some throttle you lift the fast-idle-stop off the cam, and the cam is free to rotate based on the linkage coming down from the choke. This sets the fast idle speed.

As the engine warms up, the cam is friction-held by the fast-idle-stop, and so the idle speed doesn't change. If you goose the throttle a bit, the fast-idle-stop lifts, allowing the cam to rotate again. Assuming the engine is part-warmed up at that point, the cam will rotate toward the diving board, where the radius is less, lowering the fast-idle-stop (and therefore the fast idle speed) a bit.

Once the engine is fully warmed and you goose the throttle, the fast idle cam will fully rotate, the fast-idle-stop will miss the end of the diving board, and the idle speed will then be controlled by the idle-stop on the front of the carbs.

Cheers,
Jeff.
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 383
Registered: 6-2009
Posted on Wednesday, 22 May, 2013 - 12:47 am:   Edit PostDelete PostView Post/Check IP

Now that I have the answer to the anti-dieseling and weakener solenoid questions. I'll continue the saga of the ongoing work here.

Yesterday was, to me anyway, a very good day in the garage. Some initial observations:

- when the engine is started from cold, and before I did any alterations at all (including the throttle butterfly synchronization), that's when you get the most pungent exhaust fumes and these are "thin but quite visible white." They're not blue, like oil is burning, nor do they smell like oil in the exhaust (which I'm all too familiar with from a Mitsubishi engine with bad rings).

- the above reported fumes get less white and less pungent as engine speed is increased, even when the engine is cool-ish, and continue to decrease significantly as the engine warms up

Now, on to the fast idle set procedure and things I found, in all cases the vacuum line has been removed from the weakener solenoid tee and that tee blanked and the signal cap is off of the weakener device:

--------------------------------------
When I position the fast idle screw on the very tip of the fast idle cam, "the diving board"

- the fast idle is not fast at all. Somewhere in the area of 325 RPM or so.

- if I remove the blanking plug it speeds up quite a bit

- if I put the vacuum back into the tee it may slow down just the tiniest bit and/or stall, given how slow it is at this setting

- if I put the signaling cap back on (or even cover the opening orifice with my fingertip) the car instantly stalls. I believe this is regardless of whether the solenoid tee is blanked or not (but I left my notes at the garage). It definitely is the case if the setup is as prescribed by the workshop manual.

---------------------------------------------

When I position the fast idle screw just past the red dot "crest" on the cam

- the fast idle is quite fast. Somewhere in the area of 1200 RPM or so.

- if I remove the blanking plug it speeds up quite a bit

- if I put the vacuum back into the tee it may slow down just the tiniest bit, but it doesn't stall given how fast it's going

- if I put the signaling cap back on (or even cover the opening orifice with my fingertip) the car instantly goes back to its very, very rough idle and then quickly stalls afterward. I believe this is regardless of whether the solenoid tee is blanked or not (but I left my notes at the garage). It definitely is the case if the setup is as prescribed by the workshop manual.

------------------------------------------------

In both cases, when the signal cap is off and the vacuum tee is blanked the idle is much, much smoother than it has ever been otherwise. In the first instance it's somewhat rough, but has no issue continuing even at that slow speed unless I turn off the key. In the second instance it is silky smooth - not a burp or bobble at all; I'd never heard the car run this way before.

I am presuming that:

1. I need to set the fast idle to within spec using the "diving board" as the correct position of the fast idle screw.

2. Something's off with either the weakener device and/or the vacuum connections to same. I'm hoping the above descriptions might help someone to guide me in this regard.

3. That the idle setting with the idle stop screw will need to be set correctly once whatever may be up with #2 is resolved.

Brian

P.S. to Jeff - all of the things you describe with regard to the fast idle cam do occur as the engine warms up
Top of pagePrevious messageNext messageBottom of page Link to this message

Jeff Young
Prolific User
Username: jeyjey

Post Number: 152
Registered: 10-2010
Posted on Wednesday, 22 May, 2013 - 02:55 am:   Edit PostDelete PostView Post/Check IP

Hi Brian,

Sounds like your weakener air filter (or air filter hose) is blocked. The design of the weakener is to deliver part vacuum to the float chambers by "watering down" the full manifold vacuum with air from the weakener air filter. If the filter is blocked then the weakener will deliver pretty much full vacuum, and act just like the anti-diesel circuit.

Removing the sensor cap (or the blanking from the T-piece) allows more air in, watering down the vacuum.

Disconnect the air intake hose from the weakener ("G" in the diagram) and see what happens.

Cheers,
Jeff.
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 384
Registered: 6-2009
Posted on Wednesday, 22 May, 2013 - 03:17 am:   Edit PostDelete PostView Post/Check IP

Jeff,

Thanks again. I'm heading out to the garage shortly and will try this after setting the fast idle to within spec (since that's already done with the signal cap off).

All of the above happens with a warm engine (other than the early exhaust description stuff) since a warm engine is a requirement for setting the fast idle.

Do you know the weakener air filter "cleanable"? It's easy to check the line for blockage and clear that out if it's the problem or to replace it. I've got scads of high-temp silicone lines of varying diameters for vacuum line replacement on hand. If it's not able to be cleaned, is there a readily available replacement or is this one of those Crewe-Original-Only parts?

Brian
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 386
Registered: 6-2009
Posted on Wednesday, 22 May, 2013 - 10:32 am:   Edit PostDelete PostView Post/Check IP

Well, if I could dance I would be dancing today!! I haven't had more success and more satisfaction in the garage for more than a year!! Thanks to all who've been helping me along and shaping my thinking.

I'm not quite sure which of the things I did before leaving the garage yesterday was the pivotal one, but I have my own theory which I'll get to later.

At the end of the day yesterday I decided that I also needed to take a look at the anti-dieseling and weakener solenoids and their electrical connections. I also did the same for the small "black box" (that I think I was told is a diode, marked with yellow arrow) that's right next to the weakener solenoid connections. All of them were horribly oxidized so that meant immediate cleanup for all. I clean the male-to-male slide that's used to connect the two female connectors between the solenoids and the car with steel wool, back to a high gloss. The connections on the solenoid itself and the car are a bit trickier. I have used "the correct deoxidizer," Caig DeOxIt, in the past and have found the result OK. However, for myself, what I find works much, much better is dipping the female slide connectors (still with their loose plastic sheaths) into either Lime-Away or CLR, waiting a few seconds for it to clean and deoxidize the brass and copper, then follow with two dips to rinse thoroughly and allow everything to dry. That's what I did this time, and you can see the result through the sheaths in this photo:

Anti-Dieseling and Weakener Solenoids

For those who may be be horrified by this cleaning technique all I can say is that I've been using it now for years after finding it when I was "in a pinch" and it's never caused one issue. Of course, all these connections got a generous coating of NoOxId A-Special electrically conductive grease when put back together. It was also time to give the both solenoids a good shot of WD40 and power cycle them multiple times and let them sit overnight. Both seem to be working perfectly.

In replacing the solenoids, initially unbeknownst to me, I managed to knock off the weakener vacuum line to the B-bank carb (hidden very near the red arrow). I could hear it as soon as I started the car and figured when I put it back on it would go back to stall condition - but it didn't!!

Suddenly, before even going through any additional tuning the car started and was running with everything hooked up as it was supposed to be as it never had before, though still not perfectly.

I then set about setting the fast idle per the workshop manual instructions, which went without a hitch. After that was done the regular idle was still a bit slow, so that got bumped up a bit using the idle stop screw/idle speed screw so that it was almost precisely 650 RPM.

Compare the first 15 to 20 seconds of a cold start on May 8th (and a warm start wasn't much better) to the sound of a warm start after today's work. The cold start was with choke and fast idle fully engaged. Even considering the exhaust leak and the fact that the recorder is sitting practically in the engine compartment, the difference is like night and day.

Today's temperature was about 85F/30C so the weakener solenoid was never energized and remained open throughout the process (confirmed by a test light).

My current theory is that the "flip side" of Jeff's weakener solenoid air feed having been partially or fully blocked. Since everything was working so much better, before doing any tweaks today and the weakener solenoid was definitely not energized and remained open, I think it was the anti-dieseling solenoid that was the culprit. My gut is telling me that the anti-dieseling solenoid never closed completely when energized and was allowing additional vacuum that shouldn't have been applied at all to be continuously applied when the car tried to run. It wasn't stuck fully open, or the car should never have started or would have run only for seconds, but I suspect it was stuck partially open. I guess I'll never know.

Now at least I'm at a point where I can safely drive the car on to its transport, get the exhaust attended to, put new tires on, then start making some drives to "burn the carbon out."

This supposes, of course, that I have the same result when I try to start the car in a couple of days when the temperature is set to drop about 10 to 15F. Wish me luck. I'd really like to believe that I've finally made several major steps forward without just as many back.

Brian

Add Your Message Here
Post:
Bold text Italics Underline Create a hyperlink Insert a clipart image

Username: Posting Information:
This is a public posting area. Enter your username and password if you have an account. Otherwise, enter your full name as your username and leave the password blank. Your e-mail address is optional.
Please quote Chassis Numbers for all vehicles mentioned.
Password:
E-mail:
Options: Enable HTML code in message
Automatically activate URLs in message
Action: