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1958 Cadillac vacuum leak and clog

Started by Matt I #21633, August 27, 2006, 11:34:49 PM

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Matt I #21633

When my 1958 Cadillac gets to operating temperature, it starts to sputter and run rough.  Thinking it was a misfire, I replaced the wires and inspected all the plugs - the plugs were burning clean and with the new wires on there was no change.  I then looked for a vacuum leak and found it in the tube that goes from the Carter AFB carburetor to the vacuum advance on the distributor.  The front port from the carburetor had no vacuum.  I temporarily spliced into the port coming from the intake manifold that goes to the windshield wipers to feed the vacuum advance.  I re-timed the car and reset the idle mixture per the shop manual.  It runs better but still misses every now and then.

Do I have a misfire or a lean burn on account of a vacuum problem?  Also, is there an explanation to cleaning out the vacuum port on the Carter AFBs or will the whole carb need to be rebuilt?  I blew on the hose going to the port and I hear it coming from the butterflies, so it is not clogged.  

She used to purr like a kitten - please help and thank you in advance!

George #3739

Have you tested the vacuum advance to make sure its not leaking?

Matt I #21633

Hi George,

Yes, I checked the vacuum advance and even installed a brand new one.  No change.  

Thanks for your suggestion,
Matt

Matt I #21633

I am still trying to diagnose a vacuum leak on my 1958 Cadillac SDV.  Even after disconnecting all the vacuum hoses, it is running rough at idle.  Cruising down the highway and/or when the engine is first fired up, it runs perfectly!  Only when the car gets to operating temperature does it start to run rough.  Any thoughts on what could be going wrong to make the car run rough after it warms up to operating temperature?  The idle mixture and timing were all set to factory specs.  Please help!  Thank you much in advance.  Matt

Geoff Newcombe #4719

Might be a valve sticking.  Sounds like another tough one that everyone will be waiting to hear the solution too, but I never really got the vacuum leak part to begin with, especially after the trouble shooting you described and what you have done so far as noted in your first and second posts.  If the leak is that bad it should affect the running of the engine hot or cold.  Time to move on from the vacuum leak in my opinion.

Matt I #21633

Hi Geoff,

     Thanks for replying - yes, I am hoping I can get this fixed and have some other CLC members learn from it as well.  I have gotten lots of great suggestions, but nothing cured it yet.

     A sticky valve sounds likely, as I am hearing a "miss"-like sound from the exhaust.  But, I had the engine rebuilt 2 years ago from a highly qualified machine shop and less than 2,000 miles has been put on it since.  Also, I hear the miss sound from both sides of the exhaust indicating that if it were a sticky valve, I would actually have at least two of them.

     I explained to Porter (a fellow CLC member) the car used to shoot water on the windshield from the washer jets after the engine was shut off.  Also, the power brakes would be very powerful when the engine was first started, but then became very difficult to stop the car when it warmed up.  Those problems have not been apparent recently, since I changed the check valve on the brakes.  But maybe they are related to the engine problem?

     I am still trying to understand the physics of what is happening.  Is the engine running well when cold because of the increased fuel mixture from the choke?  Or, is the heat causing expansion between two surfaces that is somehow causing a vacuum leak?  

     While the engine was hot, I was only getting 12" Hg on the vacuum gage.  I am going to see what I get at first start-up to compare the readings.

     Again, thank you for your suggestion and any other information you can offer!

Matt

Porter

Matt,

Now you are on the right track, Geoffs comment will show up with the vacuum gauge.

http://www.secondchancegarage.com/public/186.cfm TARGET=_blank>http://www.secondchancegarage.com/public/186.cfm

http://autorepair.about.com/cs/troubleshooting/a/aa112401a.htm TARGET=_blank>http://autorepair.about.com/cs/troubleshooting/a/aa112401a.htm

http://www.findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956 TARGET=_blank>http://www.findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956

Heres some homework for you to read up on, LOL

12" HG is way to low, is that a steady reading ? My 66 429 pulls a steady 21 or so.

Well get to the bottom of this.

Porter

Geoff Newcombe #4719

Porters right, 12" is way too low.    
If youre hearing the miss sound from both exhausts it could just mean you have a crossover pipe (do you?), so you would indeed hear it on both sides eventhough it is only one cylinder causing the problem.  2000 miles on an overhaul means nothing other than, "oh, thats too bad, bummer!" Its a piece of machinery, and s**t happens.  Might be an idea to drive it by the engine overhauler and let them check it out ..... seems the least they could do after only 2000 miles.  Did they offer any kind of warranty with the rebuild?   Im going to hang with my valve theory for the time being.
Porter will keep you straight.  

Porter

Matt,

Dont assume anything, if need be well bring in a ringer, John Washburn, he has seen it all.

Assuming you have strong compression well go down the checklist and find the culprit.

They can even drive the pros crazy sometimes.

Porter

JIM CLC # 15000

09-09-06
Matt, Sounds like the valves were set a little too tight. Have the rebuilder re set or you readjust the valves. If they are set too tight they will open-up a little when the engine becomes warmed-up to normal operating temputerture.
HTH
Good Luck,JIM

JIM CLC # 15000

09-0-06
MATT, My previous post was a WAG, But, I still think the valves are too tight, but that is Just A Shot In The Dark (JASITD)
HTH
Good Luck,JIM
P.S. If readjusting the valves does not fix the problem, Try running a propane cylinder around the intake manifold(not burning) If the engine speeds-up, it has a vacuum leak and is pulling-in propane.(Repair & enjoy).

Mike #19861


 An old trick to finad a vacuum leak is to use the acelylene from a torch set around the engine. Wherever you find the leak, it will suck in the acetelyne and the engine will speed up and run smoothly. You can accomlish much the same with a propane torch. Just turn on the gas and pass the torch around any possible point of leak.

 12" is far too low, but if the idle is very low it could also give a low reading. This is a pretty significant leak and should be easy to find. Dont discount the carb either. There may be some restricted porting or a very low float level.

 Personally, I doubt the valves to be too tight. If the engine ran fine before, the valves should be fine. The dont normally tighten up on their own.

 Mike

Mike Simmons (938)

Matt: No brilliant solution here, but I do know that utilizing manifold vacuum for a distributor is a no-no, since carb vacuum and manifold vacuum vary inversely- when using manifold vacuum, you are getting max vacuum, and max distrib advance, with throttle plates closed. If you tested the carb vacuum at idle,you shouldnt get any, nor any distrib advance. Hook your vac meter to the carb spark port and see if you get any as you open the throttle blades.

Mike #19861

 Manifold vacuum is commonly used on the vacuum advance.

 Mike

Porter

We need proper feedback from Matt to diagnose this problem accordingly, this is where the club performs best.

The best posts in the past are when people have engine problems that need to be solved, the expertise solves the problem and we all learn.

Nothing gets taken for granted and we start with the basic diagnosis. Often times the engine is presumed to be sound and a component is the problem, not always the case.

My SBC ( small block chevy (s) ) always had adjustable hydraulic lifters, my 66 429 doesnt. Does a 58 Cadillac have adjustable hydraulic lifters ?

Looking forward to solving this problem, and learning more about engine diagnosis.

Porter





JIM CLC # 15000

09-11-06
Porter, I would have to assume that the 58 has adjustable lifters, since my La Salle had/has them. But if memory serves me correctly, the La Salle has a 47 Cadillac engine in it and before that it has an ARMY tank engine from the early 1940s
I say his valves MAY be too tight.Some people thank they are smarter then the engine builders and dont always go by the book.
HTH
Good Luck,JIM

Chris Short CLC 18184

Hello,
    On one of my cars Im having this same problem..  The symptoms are the same..  Thats all I can think that it would be..  Ive replaced everything..  Either the intake gasket or a really bad case of burnt valves..  What ya guys think??
    Also a few years ago I had a engine rebuilt by what I thaught was a good engine shop here.  I had the engine rebuilt everything was fine but after about 6 months the engine started to miss and run poor no matter what I did.  Did a compression check on it and found air leaking past the valves..  I took the heads off the engine to find that when the machinist did the valves he didnt nurl (not sure how to spell that) the valve guides properly so the valves didnt line up properly with theyre seats..  Causing them to burn.  I think the machinst ground the valves first and then nurled the guides.  Never again will I ever have this done..  Always use new valves and guides..


Chris Short

Chris Bryant #19358

Hi Matt,

Years ago, I went through a similar situation and did all the things you did with a 327 SBC in my case. It turned out to be a worn lobe or two on the camshaft. One was worn almost entirely off!

A couple of suggestions:

1. When you have the rough running condition, remove the air cleaner and put both hands over the air intake on the carburetor. If the thing sucks like mad and the engine stalls, then vacuum leak in carb or elsewhere is not the problem. If it keeps running, then yes, you have a massive vacuum leak probably brought on by the expansion of parts as they warm up.

2. If the previous test tells you nothing, then try removing and replacing plug wires one at a time with the engine running until you have isolated the cylinder where a problem might be found. Remove the corresponding rocker cover and with suitable protection from oily messes, try to measure the rise and fall of the rocker arms for that cylinder. Compare with adjacent cylinders. This is how I isolated my problem.


Good luck,

Chris Bryant

Matt I #21633

First, off I would like to extend my most sincere gratitiude and appreciation to all of you who offered suggestions and input from the problem.  Porter promised wed get to the bottom of this and I think we are well underway.

As it turned out, I found a major vacuum leak - the chole heat tube (that sucks hot air from the exhaust manifold to the thermostat) was loose and nearly fell off.  Once I put it on properly and tightened it, manifold vacuum went up to 18".

The needle was fluttering rapidly at 18", so I advanced the timing slightly and that brought it up to about 19.5", still with a flutter.  At the exhaust, it sounds much better and the engine is running much smooter.  It has a VERY low idle, so I had to increase it from stalling.  But, the "misfire" sound is almost entirely gone - I just hear a hollow sound from both pipes very 15 seconds or so.

Based on some literature Porter send me, the flutter can be caused by improper spark gap or bad points.  I have an order in now for a new set of Blue Streak points and condenser.  Any other thoughts on what can cause a rapid flutter in the vacuum gage?  Could this be my problem?

Thank you all again!

Matt

Porter

Matt,

If you slowly covered the carb (reduced the air intake) while running and the idle smoothed out that would have verified a large vacuum leak, glad you found that, your major problem.

Try the new points and do your tuning, as Geoff suggested if you have a minor fluctuation that would most likely be a valve, maybe not, nothing you cant live with if the idle is smooth and you are pulling 19.5 HG on the vacuum gauge, nice strong reading.

I would remove and inspect at least one spark plug, if you pull all of them you might find one that looks a little subpar, that could indicate a minor problem with that cylinder or maybe just a bogus plug. Depending on how you drive your car the plugs can foul easily with these old cars, local non highway driving, get it out on the highway and kick it in the *ss once in awhile, good for the engine. If you really want to know what you have do a compression test and see what you get, that will isolate a weak cylinder with a minor subpar problem, if the problem persists or you just want to know, we can all live with an idle that is not stone cold smooth, I had a 65 327 and you couldnt even tell it was running, a rare bird, most engines dont idle that smooth.

Still have to get my 66 429 running right, the car sits and just gets moved around, instant spark plug fouler.

Porter