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Everything reassembled; both vacuum and mechanical advance mechanisms operational. But, the high idle remains. Car drives great down the road.
Naturally I was hoping to find a problem with the vacuum advance pull rod. Specifically, a pull rod length situation where simply attaching the rod to the advance plate caused a slight 'pull'.....which would advance the timing and increase the idle speed. But, that was not the case.
(As an aside I am compelled to mention the customer service from the outfit I bought the vacuum advance from:
I had sent an email asking for thoughts on a possible pull rod issue. I received not one but two return phone calls. As it happened I was unable to take either call but the fellow left voice mails offering advice and pledging any assistance possible. He seemed genuinely interested in helping. As we all know, that kind of service cannot always be found nowadays. It deserves some recognition.)
Base plate scuffing
On reassembly I was naturally attentive to anything that would account for this issue. I made a bit of a discovery on this.
The pickup coil base plate is held in place with two small screws but is located into position in the distributor housing by three tangs. These tangs are an interference fit into the housing. Very interference as it turns out. It is possible to install the pickup coil without the base plate being fully and squarely seated. This naturally throws the geometry off and can cause the reluctor wheel to drag against the base plate. The hold-down screws are tiny; nobody would ever dream of tightening them so hard so as to push the base plate fully home and, if they did, the threads would probably pull of of the aluminum distributor housing.
To solve this I carefully bent the tangs downward just a mere fraction of a fraction of an inch. This allowed the base plate to be reliably seated fully home, and perfectly flat, into the distributor housing using a bit of thumb pressure.
With this new insight I am convinced that the base plate was not fully seated when I replaced the pickup coil a few years ago.
I'll add that the new pickup coil is safely in the "OK" resistance range, showing 3.5K ohms rather the the previous 2.2K ohms. This makes me feel better.
Throttle position sensor
My new red-style TPS arrived today. This is the replacement for the defective one that caused the crazy oscillating idle mentioned a couple weeks ago or so. I'm presently running on the Mustang TPS. I'll install the new red TPS install it next week and let everyone know how it goes.
I'll mention that the supplier, Engle Imports, was ultra prompt and polite in the matter of the defective part. No argument, no quibbling. Good service.
As for the high idle, well, there's nothing to do but keep digging
The teeth on the reluctor wheel are becoming eroded. I forgot to take a picture but just imagine the tips of each tooth looking a bit jagged and crumbly.
I'm not sure how this effects operation. I'll be looking for a new one.
Doug,
Similar irregular idle, 6 weeks into T/S'ing found "scuffing" on my pickup coil, set gap with brass feeler gauge etc. no help... turned out to be worn upper bearing...
Rgds
David
I forget to check into bearing wear/play.
I dunno how many miles this engine has. I'm guessing 100k at minimum; probably much more.
Makes & models: Distributor Doctor can recondition all models of Lucas distributors from the 1940s up to the late 1970s.
We specialize in the following manufacturers, but also undertake work on a wide range of others. If you don't see yours listed, please contact us - we can almost certainly help you!
Rgds
David
Last edited by David84XJ6; Apr 10, 2021 at 03:58 PM.
Reminds me of a similar event, way back in the day. Circa 1856 a work mate acquired a 1940 Buick/ A big sedan with the big straight 8. A total loss that was repaired. Not quite perfect, but passable. Ran great, but a rough idle. Diagnosis, wobbly distributor plate. it rode in a groove, but was not stable in that groove... part to fix NLA!!!!
My new red-style TPS arrived today. This is the replacement for the defective one that caused the crazy oscillating idle mentioned a couple weeks ago or so. I'm presently running on the Mustang TPS. I'll install the new red TPS install it next week and let everyone know how it goes.
I'll mention that the supplier, Engle Imports, was ultra prompt and polite in the matter of the defective part. No argument, no quibbling. Good service.
As for the high idle, well, there's nothing to do but keep digging
This is turning out to be quite an adventure. Gotta love a weird mystery. Or cry over it.
Installed the replacement red TPS today. No change in idle speed. Nor did I expect a change. But..... the crazy oscillating RPM came back exactly as with the previous red TPS. This condition simply does not occur with the Mustang TPS.
Either the replacement TPS is faulty in the exact same manner as the previous one ......or there is something else afoot.
More digging to follow. The Mustang TPS is back in the car and I'll continue efforts to solve the high idle. When that's solved I'll return to the TPS weirdness.
Had a thought, and it may be silly, but if I say nothing, that would be sillier.
I dont know the fuel enrichment system your market has.
We have the micro on the capstan, and the vac (Blue.White) valve.
One I chased, ages ago, for odd stuff, and found that Vac switch was leaking vac, not enough to register as a normal vac leak by the system, and the contacts inside were always closed, and the ECU was in Open Loop operation, and among other things about 300RPM too high due to the 10% fuel richness.
Only found out due to human error leaving that switch disconnected, and the engine was fine. Noticed the wires, plugged them in, bugga instantly.
More digging to follow. The Mustang TPS is back in the car and I'll continue efforts to solve the high idle. When that's solved I'll return to the TPS weirdness.
High idle solved ! Idles perfectly at 600 RPM in "D"
Y'all are gonna have a laugh when I reveal what was wrong.
I'll try to be brief here.
Having gone thru some many exercises, checks, and repairs my head was spinning a bit. I decided to go right back to square one on this high idle issue. Start afresh as though none of all this 'stuff' had ever happened. Now somewhere along the line in all this process I had checked the throttle linkages for and binding and checked and reset the throttle gap. I can't remember exactly when amidst all that I've done, but I know I did so. Still, going back to square one meant doing it again.
I dutifully checked the gap......and was shocked. My .002" blade fell right thru the gap. So did the .003". So did the .004" In fact, I found both blades set at exactly .005". You couldn't possibly ask for a more perfectly set .005" clearance.
Except, of course, it's supposed to be at .002"
One very plausible explanation is that I messed up and selected the .005" blade. But in fumbling about with my feel gauge I think I discovered what actually happened.
Had a thought, and it may be silly, but if I say nothing, that would be sillier.
I dont know the fuel enrichment system your market has.
We have the micro on the capstan, and the vac (Blue.White) valve.
One I chased, ages ago, for odd stuff, and found that Vac switch was leaking vac, not enough to register as a normal vac leak by the system, and the contacts inside were always closed, and the ECU was in Open Loop operation, and among other things about 300RPM too high due to the 10% fuel richness.
Grant, I know this phenomenon. I've experienced it. I just don't understand why it occurs.
Suppose your engine is running at idle with the (supposedly) correct fuel mixture. Now, richen the mixture without adding any additional air. Seems to me the engine should reject the extra mixture and slow down. Not speed up.
It makes me think the engine is running lean and it likes the sweetness...and thus increases RPM
You held the feeler gauge in the opposite hand and the inverted number on the .005 blade registered in your mind as .002. Or you're a recreational dyslexic like me.
Doug
My thoughts on the higher RPM are that the HE runs very lean anyway, and at idle particularly so; adding a bit more fuel will give you a bigger bang, as the richened mixture will burn that bit better. Probably because at the lean state not all the oxygen is being used and also because flame propagation would be far easier, at the expense of higher unburnt hydrocarbons. It would not be until the mixture was really over-richened that it would stumble.
When I read up about the May head, the idea of it is to concentrate the fuel around the spark plug, thus allowing it to get set alight by the spark because the mixture in that zone is rich enough to be ignited; once going, the flame will light up the super lean mixture filling the rest of the combustion chamber. Without that May head fuel concentration effect, the actual overall average leanness in the combustion chamber would be too weak a mixture for the spark to reliably light up.
Last edited by Greg in France; Apr 14, 2021 at 01:03 AM.
Thanks everybody for following along and helping. It blossomed into much more than I anticipated but, in the end, the car is better for it and I learned a couple things. To recap-
-Inoperative vacuum advance replaced ...which was the original mission. My fuel economy should improve. Discovered a good parts supplier.
-Ignition module replaced. Despite suspicious timing the failure was not related to other work. The oft-mentioned advice to use only AC Delco modules seems to have merit. Also learned the present day Delco modules don't have the interesting (and perhaps important) grounding tab
-Replaced pick-up coil. New part safely within spec as supposed to just barely within spec. Learned that is possible to install the module with the base plate not fully seated which will cause scuffing of the reluctor wheel.
-Repaired inoperative centrifugal advance which, a bit to my shock, I never knew was seized. Learned that the oiling passageway can become clogged...something that would never have crossed my mind
The engine is running great so I'm gonna drive and enjoy the car for awhile. My old Ford truck is a gem but it ain't a Jag! After a bit I'll revisit the unresolved TPS issue.
