News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

When i shut down my engine...

Started by Soren Johnson, September 13, 2008, 03:27:17 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Soren Johnson

...it just don't stop right away.
I don't know what you call it in english, but the engine, when I turn the key off, sort of self ignite and takes a couple of cranks before it dies.
Any one have any idea why?
It's a DeVille -72 with a 472.
Starts fine and runs great, but when i shut i off...
Soren Johnson, Sweden

Guidematic


It's called dieseling.

A few things can cause this, an idle speed too fast, a lean mixture, a hot engine or a combination of any of the above. Most common is a combination of a lean mixture and an idle too high.

Check for any vacuum leaks and set the mixture screws correctly. Idle should be about 600 RPM in drive. Check your manual for the correct specs.

An idle that is set too high can also be a function of an overly lean mixture. The idle may have to be set high for it to idle at all.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

RobW

Yeah what Mike said. Another solution is a higher octane gas. Try premium it'll probably fix it.
Rob Wirsing

Otto Skorzeny

Be sure to check the entire ignition system. Plugs, wires, cap, rotor, etc. Weak points in any of these areas can cause a weak spark and contribute to the run-on problem. Check the timing as well. Ignition that's too advanced will also cause run-on or dieseling.  I've found that this problem is usually a result of a combination of some or all of these things. Don't forget to consider the fuel as a source for problems, as well. Ethanol is often overlooked as a culprit in fuel related problems in old vehicles.
fward

Ask not what your country can do for you, but what you can do for YOURSELF

HUGE VENDOR LIST CLICK HERE

David #19063

Quote from: RobW on September 13, 2008, 05:07:45 PM
Yeah what Mike said. Another solution is a higher octane gas. Try premium it'll probably fix it.

Like Rob said, premium gas will solve it.

But you should also check your timimg as well.
David #19063
1996 DeVille Concours

J

yes i had the same problem with my eldorado  and thought of all the major things that could be wrong and it was simple i used premium 100% gasoline and fixed  a cracked vacuum hose problem has been solved and  thank you everyone that helped me!
Cadillac got me!!!

TJ Hopland

Until you solve the problem the way to keep it from happening is to shut it off while still in gear.  The load of the transmission tends to be enough to kill it.   Dont forget to put it in park before you get out.

Like others said, make sure the normal tune up stuff is done.  A nice long drive may also help if you tend to do a lot of short ones.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Guidematic

 Timing should not be an issue. When you shut off the engine, you shut off the spark so that removes this from the equation. Higher octane gas may eliminate it, but it only masks the problem. These cars were designed to run on regular unleaded gasolines. However, the volatilty of gasolines, as previously mentioned, may contribute some to the problem.

You may try a top end cleaner like GM Cleens or Sea Foam. That helps eliminate carbon deposits from the combustion chambers which masy contribute to the problem. You should be able to run the car on unleaded gasolines then.

I have also heard that when MBNA was added to gasolines as an octane booster, they were notorious for causing deposits and gumming. This was easpecially predominant on cars that were not driven regularly, like our hobby Cadillacs. There may be some leftover deposts there contributing to this problem.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

TJ Hopland

I think the reason timing is brought up is that retarded timing (something simple like failed vacuum modulator)  could be causing higher operating temps and that coupled with the other factors like deposits could do it.  Running lean also tend to bring up temps.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Otto Skorzeny

Hi Mike, sorry I have to disagree with you about the timing. If the timing is overadvanced, it can cause knocking while running and dieseling after shut off.  

After switching the ignition off, the unburned fuel is not being ignited by a spark but rather by hot spots in the combustion chamber.
fward

Ask not what your country can do for you, but what you can do for YOURSELF

HUGE VENDOR LIST CLICK HERE

RobW

#10
I keep reading that these cars were "designed to run on regular gas". I understand the compression was lowered on these engines but my 73 owner's manual clearly states the fuel requirement is a " good quality low lead or unleaded of fuel of at least 91 octane. The closest thing to this is 93 octane from all the major brands except for Getty/Lukoil whose premium is 92 octane. Mid-range gas is 89 octane and regular is 87 octane. My 73 coupe set to factory specs pings like crazy under load and runs on/diesels on anything less than premium.
Besides, at 27.5 gals to fill the tank and there being just a $0.10 difference between grades, we're talking $2.75 savings using mid-grade or a whopping $5.50 between premium and regular. :o
Rob Wirsing

35-709

#11
This will probably forever be an argument, compounded by the fact that, except for us older folks, no one remembers that the way octane numbers were determined changed sometime in the mid to late 70's.   
Back in the 70's and prior, gasolines were rated on the RON or Research Octane method as opposed to the Motor Octane method (MON), two different ways of measuring the octane ratings in fuels which will give different octane numbers for the exact same fuel.  Sometime in the mid to late 70's it was decided that gasoline octane ratings in the U.S. and Canada would be based on RON + MON divided by 2.
               
This in effect lowered the octane ratings of the same fuel that we were purchasing at the pump before the new rating system went into effect.  91 octane regular gas became 87 octane overnight!  A 1973 Owners Manual calling for 91 octane would be the same as 87 octane based on the RON + MON divided by 2 that was later adopted.  European and other countrys have NOT adopted this                                                         
system, which is why you often see or hear someone from Europe talking about buying 100 octane fuel which is the same as our Hi-Test gasoline, it is just rated by a different method.  You can read more about this at .....
http://en.wikipedia.org/wiki/Octane_rating

Cadillacs from 1971 on, until they started building hi-test gasoline engines again, were ALL designed and rated to burn regular 91 octane (or 87 octane under the new rating method) gas, period.  My 1971 Sedan DeVille (recently sold) ran fine on regular gas under all load conditions and driving conditions without ping or diesel-ing.  In my opinion, anyone's Cadillac of 1971 and on vintage (before the "modern engines" came out) that will not run properly on regular gas is either getting inferior gas (not up to the rating stated on the pump), or the car has a problem with it's state of tune, it's ignition advance, or other problem.
:)
                                             
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Mike Beda

A Caddy engine in very good condition will run fine on regular.  BUT my experience is that older engines, Caddy or otherwise, build up carbon in their combustion chambers, creating hot spots which cause pinging and dieseling.  By all means check the timing, mixture, and make sure the car isn't running too hot.  But beyond that, well 10 cents a gallon for higher octane gas is pretty cheap compared to an engine rebuild (which is the only way to really get rid of carbon deposits).  My '76 (with 180,000 miles on the original engine) definitely prefers 89 octane over 87.

"Cadillac Kid" Greg Surfas 15364

Soren,
On your '72 there is (supposed to be) an "idle stop solenoid" (ISS) that is intended to speed up  the idle by pressing the carburetor throttle arm located on the drivers side of the carb.  That is where the solenoid is and it is mounted on a bracket and is threaded with a lock nut for idle speed adjustment.  This solenoid is energized anytime the ignition is turned on and de energized when it is turned off.  It is common for this device to cause idle speed issues.   The solenoid may be improperly adjusted, or may be "frozen" in one position, causing someone to miss adjust it in order to keep the engine running.
The main purpose is to fully close the throttle blades when you turn the ignition switch off, so the engine WILL stop.  They will all "run on" if the ISS malfunctions or is locked in the "running" position.
You can easily check the ISS.  With the engine off, and someone holding the carburetor back to about 1/4 throttle, turn the key to run (not start) and see if the ISS moves.  There is not enough power to move the throttle from the closed position, but the system assumes the old method of holding the pedal down when you start the car.
To adjust the idle speed with a working ISS, with the car warm, loosen the locknut on the ISS and turn it in or out until the proper speed is reached. Check your manual and you will find the recommended idle speed and how you test it.  Don't forget to tighten the lock nut and I have a feeling your  "run on" problem will disappear.
Let us know
Greg
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Guidematic


Yes, the 1972 Cadillac carburetor came equipped with an anti-dieseling solenoid. It required proper adjustment in order to function properly. Often they cease to function and do not allow the throttle plates to close when the engine is shut off, or they do not open the plates to the correct idle. Thus the idle is either set by the idle stop screw on the carb or with the screw on the solenoid which will not move. This is part of the proper idle setting procedure.

Also, it is correct that older engines build some carbon deposits within the combustion chambers causing run on or pre-ignition. This can usually be cleaned out with a good top end cleaner.

Late ignition timing tends to make the engines run hotter, so that to me that would help predispose run on rather than advanced ignition.

Starting in 1971 all GM engines were designed to run on regular low or no lead gasolines. To do this, compression ratios were lowered across the board, and hardened valve seats were installed. For GM engines, there were no exceptions. This was also the year that they published both net and gross horsepower ratings, and starting in 1972 all power ratings were in net. That is the prime reason why power figures were so much lower than that of previous years.

I had heard there was a change in rating the octanes in gasolines, but was not sure how, or when it was done. Thanks Geoff for clearing that up for me. That is why my '70 runs fine on 94 octane when the manual requires 97.
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

Mike Beda

A Caddy engine in very good condition will run fine on regular.  BUT my experience is that older engines, Caddy or otherwise, build up carbon in their combustion chambers, creating hot spots which cause pinging and dieseling.  By all means check the timing, mixture, and make sure the car isn't running too hot.  But beyond that, well 10 cents a gallon for higher octane gas is pretty cheap compared to an engine rebuild (which is the only way to really get rid of carbon deposits).  My '76 (with 180,000 miles on the original engine) definitely prefers 89 octane over 87.

-mB

Guidematic


I give my '70 a fairly regular dose of Cleens. It makes for a lot of neighbour annoying smoke, so you have to do it in a secluded area. But it does work.

The 250,000 mile '75 CDV I had for years preferred at least the first level of premium, usually 89, but a fter a good dose of this top end cleaner, it ran fine on regular. There are other top end decarbonisers on the market. Follw the istructions, and generally they work fine.

An old timer's method is to pour some water down the carb whit the engine running. It also seems to work OK.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

David #19063

All I know from experience is that my '71 Buick GS350 and my '71 Buick Electra Custom 455 would ping and diesel with regular or unleaded but ran fine with premium.

And both were supposed to be "low compression" engines.
David #19063
1996 DeVille Concours

Mike Josephic CLC #3877

#18
I have to agree with Mike Jones reply a few posts back.

I've owned a '73 Eldo for many years (35) and if the anti-dieseling solenoid is
not operating or not adjusted correctly, the engine will "diesel" or run on
after the ignition is shut off.  The solenoid was designed to prevent that.
High test gas is a good idea (despite claims that the engines would run on regular)
but that, I believe is not the total solution in this case.

In fact, the start up instructions tell you to first set he key to "on", pump the
gas petal, then start it.  That sets the solenoid and helps the car idle at the
correct RPM.  When you shut the ignition off, the solenoid retracts and shuts
the throttle /carb down and "no dieseling" should occur.

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region