429 engine problem ..

[Fizz]

Hi!

First, i apologize for my, perhaps, bad english ...
You dont learn to much "mechanics" english at schools over here
in sweden, so there are alot of technical terms i dont now ...
If you dont understand something, please let me now, and i´ll
try to explain it better .. =)

Now to the problem ...

My Cadillac 429 has a really anoying problem, it doesnt run very well...

the car can one time go forever on idle, but the next time the engine gets to much fuel, it starts to "stumble" and just run on 6-7 cylinders ... if the car doesnt die, it keep goin´like that for a while,
but suddenly, just like flipping a coin, it goes perfect again ....
then it goes good for a time (could be seconds or minutes),
but it always falls back to the same bad behavior again ...
only runs on 6-7 cylinders and so on ....

it always run nice on higher rpm´s thou ...

i´ve had this problem for about a year, it comes and goes ...

These items has been changed since the problem started;
* Carburator (bought a factory remanufactured Carter AFB)
* The vacum timing advance unit on the distributor (brand new)
* Distributor cap, condensor, contact points, rotor cap, ignition wire´s and spark plug´s (brand new)

I have cleaned the ventilator valve which controlles the fumes
from the crankcase. It says in the shop manual that if the valve
is faulty it can affect the air-fuel ratio ....
I cannot get a new one, because the guy i buy all my Cad. parts
from is currently visiting the USA ... =)

I have try´d to adjust the idle mixture screws, but that did´nt
make any difference ..

I have´nt touched the idle air screw, could that cause such a
problem?

I also have a very leaky exhaust system .... goin to fix that soon ..

I´m really hopin´ that you guy´s can help me, or i´ll go crazy ...

Thanks for all possible tips or answers!

[lxndr]

Check for vaccuum leaks. Use a can of carb cleaner or starting fluid and spray it at the base of the carburetor and intake manifold while the engine is running. If you have a leak the idle will even out for a moment as the fluid seals it. Check your hoses for cracks.

Also, make sure that your alternator and voltage regulator are supplying the propper voltage and check that your battery is in good condition.

You may also want to check your fuel pump to see if it is supplying enough pressure.

Does your car blow smoke?

[Fizz]

no, it does´nt smoke at all, besides when you cold start it ..

tha battery is brand new, 92 A ....

i have done some searching for vacum leaks, but i´ll
do some more .. =)

thanks for the tip!

[bodybyfisher]

Check the vacuum line that goes to the vaccum modulator on the transmission, if bad, it will leak air and sometimes fluid in to the intake, and cause your problem.

[Fizz]

thanks for the tip! ...
i haven thought of that at all ..

i´ve changed the PCV-valve, and after that the car seems to run fine.
i have´nt had any problems since ...

i will replace the vaccum modulator, just to make sure!

[bodybyfisher]

You can check it by sucking on the hose, if ya dont mind sucking on a hose that is hehe

[bodybyfisher]

also... if you are running the original carb, that old 4 jet... the throttle bores wear out, and leak alot of vacuum there. sometimes it will leak more than other times because of the position of the throttle... sometimes one side of the bore where the shaft goes through will wear, and sometimes the shaft will settle on that side or the other, making it inconsistantly change your idle

[bodybyfisher]

ah I see you are using a carter, sorry

[Fizz]

yeah, a carter AFB ...

the car is in the garage for the winter now ...

wont probably drive it at all for the nex 4-5 months ... =(

[bodybyfisher]

Cool. Well at least you are taking care of it!

[azimuth2000]

I had a problem like that once and it turned out to be the pickup coil in my distributor. Not sure if your distributor has one or not but it is a ring with wires. It had a loose wire on mine and it would cut out now and then. i changed carbs and everything until a mechanic found it and replaced it. The car ran perfect after that.

Good luck!!