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#3383562 - 05/28/14 09:42 PM Pinging goes away after vacuum adv disc - why?
sasilverbullet Offline


Registered: 08/22/04
Posts: 843
Loc: San Antonio, Tx
This one's stumping me - on my newly overhauled 460 in my 70 Lincoln MK III, it pings on acceleration. If I disconnect the vacuum advance it doesn't ping.

Why?

??? ??? ???
_________________________
70 Lincoln Mk III - Delo 15W-40
14 Honda Civic EX-L - Honda Synthetic 0W-20 for now
04 Nissan Titan - Amsoil 5W-30 XL

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#3383570 - 05/28/14 09:54 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
spackard Offline


Registered: 03/24/11
Posts: 676
Loc: CA
Because you're retarding the spark.
Don't you have some delay thingy, maybe hooked onto the air cleaner, that won't give your distributor full vacuum for about 10 seconds?

(Used to own a '73 Marquis with a 429, it had one of the above and I looked it up in a parts manual to see what it did.)
If you don't have a vacuum advance delay then you'll get a lot of pinging every time you accelerate.

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#3383571 - 05/28/14 09:56 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
tom slick Offline


Registered: 05/26/03
Posts: 8511
Loc: Central Coast, Calif.
Is the advance hooked to the correct port on the carb?
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#3383575 - 05/28/14 10:07 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
crazyoildude Offline


Registered: 07/23/08
Posts: 5156
Loc: new jersey
Is your timing set to the correct specs? Are u using the correct Gas?

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#3383577 - 05/28/14 10:10 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
SuperEd73 Offline


Registered: 08/14/07
Posts: 207
Loc: Glen Cove, NY
When you disconnect the vacuum advance you're only using the mechanical advance weights in the distributor that are based on engine rpms. Couple things you'll need to check: 1) Make sure your base timing is correct. Not sure if you rebuilt your engine back to stock or if it was beefed up in some way. But if your base timing is too high, that could be a problem. 2) You'll need to check the timing advance curve of your distributor and make sure it is correct for your engine. I ran into a problem with that when I purchased a rebuilt distributor for my '68 Dodge. It was rebuilt with the wrong weights and/or springs and it was advancing way too quickly which lead to lots of pinging when the vacuum advance was connected. 3) Check and recheck any rubber lines/fittings for any vacuum leaks. 4) I'm not familiar enough with 1970 emissions standards so I'm not sure if they already started using an EGR valve. If it has it, check for proper operation.

And as tom slick said, check that the vacuum advance line is using the correct port on the carb.

Ed B.
_________________________
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#3383578 - 05/28/14 10:10 PM Re: Pinging goes away after vacuum adv disc - why? [Re: tom slick]
The_Eric Offline


Registered: 03/31/10
Posts: 3144
Loc: Iowa
Originally Posted By: tom slick
Is the advance hooked to the correct port on the carb?


First thing to check. You do not want full manifold vacuum, but ported vacuum. Failing that, I've have to monkey with cherry picking different part number cans to change the point and amount at which they advance OR use an aftermarket adjustable vacuum advance.

It would also be helpful to know your initial and total advance and also what RPM you're all in by.
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#3383580 - 05/28/14 10:13 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
440Magnum Offline


Registered: 02/01/09
Posts: 6095
Loc: Texas
Now you're talkin' my era ;-)

Simple checks:

- vacuum line connected to correct port on the carb (ported or manifold, whichever the car calls for- most cars use ported vacuum)

- make sure timing is set correctly, including being sure that the TDC mark on the crank pulley is really at TDC (sometimes old harmonic balancers rotate on their rubber ring and it throws the timing marks way off).

- Make sure you have the right distributor for the car, with the right vacuum advance servo. Also, some servos are adustable with a small allen wrench stuck down the vacuum nipple (sounds crazy, but its true!) If that adjustment lets the servo apply too much advance for low vacuum, then you'll defnitiely get pinging because it should back off the advance when the manifold pressure rises (vacuum decreases as the throttle opens). I start out with the servo set so that it takes lots of vaccum to engage it (spring is tightest- on Mopar distributors that means turning the allen wrench all the way COUNTER-clockwise). Then I twiddle with it until I notice a little pinging, then back off- takes me a few days of driving to get it right.


Give those a check, and let us know.



Edited by 440Magnum (05/28/14 10:14 PM)
_________________________
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'08 Ram 1500 4.7/545RFE
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'99 Cherokee 4.0, '11 Grand Cherokee 3.6

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#3383596 - 05/28/14 10:28 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
Kruse Offline


Registered: 10/05/05
Posts: 3016
Loc: Kansas
You might also ask your dyno shop about this.
They ran straight premium gas and it ran fine, no pinging. Remember?

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#3383620 - 05/28/14 11:11 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
1 FMF Offline


Registered: 08/12/02
Posts: 1479
Loc: CT
my guess would be you have the distributor vacuum advance connected to ported vacuum on the carb, that is generally wrong.
for basic operation you do want manifold vacuum, because under load you have lower manifold vacuum which reduces distributor vacuum advance. under light load [cruise] conditions you have high manifold vacuum and that causes the distributor vacuum advance to advance ignition timing which is what you want under that condition. under light load cruise if your carb is set up properly it will be on the lean side (for fuel economy reasons) and a lean mixture burns slower and requires more ignition advance. rich mixtures burn quicker and require less ignition advance. you can find many articles online about distributor vacuum advance, the 'ported' vacuum port on the carb was for emissions equipment and various other frankenstein systems of that era. you really need to understand the carb and what ports are what on it, but generally 'ported' vacuum refers to tapping off the vacuum in the carb throat which is mostly opposite of manifold vacuum, as more air flows through the carb ported vacuum signal gets stronger and is not directly related to engine load but more so to throttle position and engine rpm. as the engine picks up rpm and especially if it's under load where you have the power valve or fuel enrichment circuit supplying more fuel you certainly don't want to further advance ignition timing over the distributor mechanical advance.


Edited by 1 FMF (05/28/14 11:15 PM)

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#3383625 - 05/28/14 11:15 PM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
tom slick Offline


Registered: 05/26/03
Posts: 8511
Loc: Central Coast, Calif.
In general, the vacuum advance should not be operating during idle or acceleration, only during even light loading such as driving on the highway. With the vacuum advance disconnected the timing should smoothly go from base timing to about 28* BTDC as the rpm rise. With the vacuum advance connected the timing should continue up to 45* to 50*.

These are numbers I'm pulling out of memory and the actual numbers for your engine may be slightly difference. I haven't owned a vehicle with a vacuum advance for 10 years.
_________________________
You get what you pay for...
So keep in mind how much you paid for this advice.

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#3383695 - 05/29/14 05:11 AM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
NHGUY Offline


Registered: 10/09/11
Posts: 3241
Loc: USA
Shouldn't that have a dual diaphragm vacuum valve that the vacuum connects to.A device that bolts to the intake that has inputs from both forms of vacuum (ported and full time) and one vacuum form overrides the other.Maybe its shot or hooked up backwards.

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#3383713 - 05/29/14 06:44 AM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
Trav Offline


Registered: 11/20/06
Posts: 9088
Loc: MA, Mittelfranken.de
As others have said in this thread. It sounds like its hooked to full manifold vacuum.
Put a vacuum gauge on the line you should have zero or almost then it should rise gradually with RPM. If you have full vacuum there you are getting max advance at low RPM causing the pinging.
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#3383791 - 05/29/14 09:03 AM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
sasilverbullet Offline


Registered: 08/22/04
Posts: 843
Loc: San Antonio, Tx
Thanks for all the replies - I'll try and sum up all the answers:

1. Dyno shop ran premium gas only
2. Dyno shop did NOT have anything connected to the vacuum advance
3. Dyno shop said there was no pinging
4. Dyno shop has the timing set to 36 degrees max
5. As per the factory manual - vacuum to the distributor is supplied from the "full time" port on the carb. One line goes from the carb to a three tee distribution mounted on the top of the thermostat housing. Another line comes straight from manifold vacuum. The last line goes off the tee to the distributor.
6. That is a rebuilt dist with Pertronix II installed. I was running that distributor before the engine overhaul - and had a bad pinging problem then also.
7. Engine is not stock, it's now dyno'd at 569HP and 630Ftlbs torque.


I will try a couple of things base on ya'lls suggestions:
1. Use my trusty vacuum gauge to see what actually on the dist line.
2. Depending on the results, probably run a line direct from the "timed" port on the carb to the dist and see how that fairs.
3. Depending on how that all works, might try adjusting the vacuum advance if it's adjustable.
4. If all else fails, ditch the vacuum advance entirely.
_________________________
70 Lincoln Mk III - Delo 15W-40
14 Honda Civic EX-L - Honda Synthetic 0W-20 for now
04 Nissan Titan - Amsoil 5W-30 XL

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#3383832 - 05/29/14 10:04 AM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
440Magnum Offline


Registered: 02/01/09
Posts: 6095
Loc: Texas
Based on your last post, it sounds like the dyno shop tuned the advance using the "total advance at XXXX RPM" method. That method really (in my experience) works great if you don't ever use vacuum advance, but results in way too much advance when you hook up the vacuum advance. I'm not saying its impossible, but those are the results I've consistently gotten. When I'm planning to use the vac. advance at all, I do the old school "set the base timing at idle with vacuum disconnected, and let total advance fall where it may. If I then go back and look at how much total advance results from that method (comparing apples to apples by leaving the vacuum disconnected during the total advance test), I have always found it to be significantly less than when I set the total advance directly.

It may be that switching to ported vacuum solves the problem, too. Hooking direct to manifold vacuum causes the engine to idle with all the vacuum advance dialed in, so when you first hit the throttle, it takes a fraction of a second for the vacuum advance to retard, and you can get a burst of pinging off the line or during sudden throttle application. And then the engine kinda falls on its face when the advance comes off :-/ That's why I've never liked setting an engine up with manifold vacuum to the advance can, and why so few manufacturers ever did so (Ford in the emissions years being one of them). Ported vacuum was almost universal pre-emissions, and in fact *most* cars remained set up from the factory with ported vacuum advance (and even using orifice valves and thermal valves to delay it even further) right through the emissions years.

I live in the Mopar world- your mileage may vary.
_________________________
'66 Dodge Polara & '69 Dodge Coronet R/T both 440/727
'08 Ram 1500 4.7/545RFE
'12 Challenger SRT8 392/6-speed
'99 Cherokee 4.0, '11 Grand Cherokee 3.6

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#3383833 - 05/29/14 10:05 AM Re: Pinging goes away after vacuum adv disc - why? [Re: sasilverbullet]
punisher Offline


Registered: 09/11/04
Posts: 1897
Loc: snowblind in TX
I did not know they started all of that thermostatically controlled VSV action back then. Those valves controlled ignition timing depending upon engine temp- more advance when cold, then after engine warmed up timing went to "normal" or timed vacuum from carb.

You might double check the vac diagram and see if one vac to that VSV on the thermostat housing isn't supposed to be timed. Warm the VSV delivers timed vac, cold it delivers full time vac.

Just a thought.

Nice ride by the way. Very familiar with San Antonio as I got all of my FoMoCo certs from their training facility down on South Presa St.

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