1969 Coupe DeVille 472 engine runs rough until it warms up

[Mihai Tarţa]

That's the one I have. It's pdf, but unfortunately non-searchable.
It was one of the first things I bought for this car.

[cadillacmike68]

Well, you have the correct manual then.

But you confused the hell out of us with these two earlier posts:

"P.s: the manual is a pdf version called "Detroit Iron"
That's all I know about it , but it's been very accurate so far"

and this:

"The year of the manual is 1968"

And just for the record, your car's carburetor originally had TWO vacuum breaks on the passenger side and the A/C idle speed up (if you have climate control) is on the driver side where the accelerator linkage connects to the carburetor. And it did originally have a dashpot in that same driver side area. These are probably all still there.

If your secondary vacuum break is defective or removed, you must be sure to plug that vacuum line, otherwise everything goes to pot.

These cars ran on vacuum. Gasoline was converted to vacuum in a secret area, and any vacuum leak played havoc with the car's operation. 

[Mihai Tarţa]

) sorry for the confusion, but I wasn't sure what you mean by "year of the manual" as I didn't think you'd assume that I' m trying to repair a '69 car based on a '68 manual.

["Cadillac Kid" Greg Surfas 15364]

Mihai,
Sounds like the plugs (or at least one of them) was the culprit.  Like I suggested earlier, with an engine that burns (not leaks) oil, you have the distinct possibility of fouled spark plugs.  If the car just gets occasional and not highway use this condition will reoccur more frequently.  Next time it happens I would suggest you ask your mechanic (if you don't change the plugs yourself) to number the plugs as he pulls them out (by the cylinder they came from) and give them to you.  If there is only one (and it sounds just like mine where there was one) you can change that plug (again the NEXT time) instead of the whole set.
Thanks for tolerating all the "static" and seeing the project through. 
Greg

[Mihai Tarţa]

The mechanic gave me the old plugs, but unfortunately I don't know which is which. I'll take a look at them, maybe take some pics and I'll get back to you.
The car doesn't leak oil, but I'm very curious how much oil it consumes, since the initial consumption of 1quart per 600 miles was determined when the car used to also leak oil due to a bad oil pan gasket. That is fixed now and I'm positive that the car no longer leaks oil.
The car doesn't see highways as we (Romania) have a total of about 300 miles, most of them in the south-east (I'm in the north-west) ). I'm mostly driving around town.

Thanks for all the suggestions !

[cadillacmike68]

So you are tooling around with chaushesku's old car eh?? 

[Mihai Tarţa]

) As far as I know he had a Mercedes-Benz 600 Pullman, which was sold in the early 90's at a ridiculously low price... but good one! )

["Cadillac Kid" Greg Surfas 15364]

Mihai,
These cars were intended to be "road burners" and see a lot of highway usage.  If they set for extended periods or don't get driven at highway speeds often they tend to get "cranky".  30 minutes at 60 MPH every few weeks will do wonders for you car's temperament.  I would just see how long it takes before the rough running returns if it does.  Plug changes, especially if you isolate any particular easily fouling ones are easy on your car.
Greg Surfas

[cadillacmike68]

Mihai,
These cars were intended to be "road burners" and see a lot of highway usage.  If they set for extended periods or don't get driven at highway speeds often they tend to get "cranky".  30 minutes at 60 MPH every few weeks will do wonders for you car's temperament.  I would just see how long it takes before the rough running returns if it does.  Plug changes, especially if you isolate any particular easily fouling ones are easy on your car.
Greg Surfas   

Except for # 7!

[TJ Hopland]

Except for # 7!

That is why you need an Eldorado.  Engine sits higher and forward (and off center) so all 8 are easy to get to. 

[Mihai Tarţa]

Here are some pictures of the plugs. Unfortunately I don't know which is which.

[Mihai Tarţa]

And the other four:

[TJ Hopland]

How many miles on those plugs?    How often do you drive the car and for what sort of distances? 

[Mihai Tarţa]

1500-2000 miles. I usually drive it on short distances every 2-3 days from March until October. Over the winter I store it in the garage and I start it once a month and let it run until it warms up.

I installed an electronic ignition conversion kit bought from rockauto.com (Standard motor products)

[dadscad]

I'd say  you are not getting the engine up to full operating temperature. Plugs have to get to operating temperature to burn clean, Those plugs look fouled from cool running. If you can't get the car out for a 50 mile non stop highway speed drive on occasion, I'd suggest putting the next step hotter plug in the engine. A hotter plug will get closer to operating temperature at lower speed short trip durations. They may be too hot for a sustained trip at highway speed, but would help in your described style of driving. Another alternative would be to resign yourself to put new plugs in it every spring.

HTH,
David

[curly]

Plugs look carbon fouled (rich mixture) except for the first one in the second group pictured, it looks like oil fouling. Its hard to tell from the pictures, but the gap looks too small on some plugs.  With the Electronic ignition conversion, did you open up the plug gap? I'd suggest at least .045 to see how it does.

Besides the short trips, other causes of carbon fouling like that are wrong/stuck/missing T-stat, late ignition timing, choke not fully opening, carb adjustment.  I'm sure others can add to the list.

T Lewis

[Mihai Tarţa]

Thanks for the replies. I'll look into all those things to make sure everything is OK.

[Steve W]

Not to hi-jack the thread, but its time for me to check out my spark plugs too.

I had the points replaced with Pertronix, but they didn't change the plugs. In fact, the plugs are the same ones that were in my car when I bought it 4 years ago! Since the original spark plugs are no longer made for this car, what do you guys recommend...brand and # and why...and what gap with the Pertronix?

And anyone have any tips or tricks for getting at that #7 plug on the 472 in the 68 Coupe deVille?

[cadillacmike68]

Not to hi-jack the thread, but its time for me to check out my spark plugs too.

I had the points replaced with Pertronix, but they didn't change the plugs. In fact, the plugs are the same ones that were in my car when I bought it 4 years ago! Since the original spark plugs are no longer made for this car, what do you guys recommend...brand and # and why...and what gap with the Pertronix?

And anyone have any tips or tricks for getting at that #7 plug on the 472 in the 68 Coupe deVille?

A competent parts store can get you the proper AC plugs for the engine.

I use a dual hinge swivel to get # 7 out.

On 1994-96 Fleetwoods the # 8 (same position, down by the suction throttling valve assembly) you have to remove the passenger side front wheel to get that plug out! 

[TJ Hopland]

I agree with the others that trips are a little short.  IF that is what they looked like with long trips I would say you are either going to have to live with it or rebuild it but with short trips you just may need to get it out for a nice long run.   I think I would throw a new set of plugs in it, an oil and filter change, and then take it out for a couple nice long cruises maybe 100+ miles if possible.  Ideally not a lot of stop and go stuff.   See what it runs like after that.  Have a look at the plugs then too and see what they look like.  Be sure to note which ones came from where. 

I have had a lot of older engines that just did not quite seem to run right but as soon as I got enough stuff fixed on them to make them safe / reliable enough for a mini road trip I got them out and after the trip things seemed a lot happier. 

Many years ago I had the spark plug thing all figured out but of course I did not write it down so I seem to have forgot it all now.  I think you can still get the correct plug they just changed the numbering system around a little.  I think it had to do with the fancier plugs that you can't field gap. The new number system includes the gap and they just applied the same system to the 'old' copper plugs too.  I'm pretty sure the points vintage 472-500 use the R44 XLS.  I don't think they changed the plug when they dropped the compression for 71.   When they changed the head slightly in 74 they went to the R45 but I suspect that is just one temp range different otherwise the same plug.  When they went to the HEI around that same time there is now an extra number at the end so a plug R45XLS is likely the standard 0.35 gap.  An R45XLS6 is the same plug but factory gaped to 0.60.

0.045 should be safe for any sort of electronic ignition system.  More starts to get a little more complicated.