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Check the bottom of the dist cap for vents... there are supposed to be 2 vents... if they are there make sure they are clean. if there is a screen poke it out. if there are no vents drill 2. if it cant breath it will corrode it is also my belief that the aluminum contacts are not the best... get copper.

· Registered
4,270 Posts
drill the vents bigger? hmmmm man I feel your frustration... I had a hell of a time getting my truck started 2 winters ago and after a week of thinking it was a fuel delivery problem I finally figured out that it was the distributer... i got a new distributer and in the instructions it had mentioned the vents... except I didnt have any.

if you have the vents and they are clear then something else is causing the corrosion to happen. it is a chemical reaction but out of my expertise...

· Registered
4,270 Posts
well this is really bugging me so I have dove into google and have come up with some ideas... This is a gm design flaw. for me drilling the holes solved my problem but for others like yourself your changing the distributor every 6 months... which dosent sit well with me. earlier in this thread I had said I bought a billet dist. but the transaction got cancelled. I have yet to get one but still havent had any problems and Im not much for changing things that arnt broken.

Im guna post up a few things to try here, from

There is a TSB about this-- the vent holes in the base of the cap, or is it the distributor base? The holes or screens get clogged with your basic filth. Dang filth. Hate the stuff. Anyway, take some toothpicks or a toothbrush (not your own) to the vent holes and screens. If you're a real buckeroo, consider drilling a few more vent holes through the base of the cap. Going on 100 years and GM still can't make a good distributor. Don't try flushing the screens out with brake cleaner, the residual fumes will blow up the cap.

Also if your car has the cold AC pipe running over the distributor, condensation drips off that and makes things worse. Slip a piece of pipe insulating foam over the cold pipe and tie it down with baling wire, or with actual hi temp capable tie wraps for a more professional look.

Plagued with Problems by Design

The presence of a white or tan residue on the inner walls of
the cap and rotor, and the terminals will be encrusted
(see illustration 1).

The contaminants are conductive and
can promote a misfire condition, resulting in misfire
codes being stored in the diagnostic memory.
Inspect the base of the distributor and the distributor
shaft for the presence of rust. While the distributor
housing is made of plastic, you are looking for an
accumulation of debris from other internal metal components.
Components that are affected by corrosion
should be replaced. The accumulation of debris in the
distributor housing can restrict the ventilation screens.
Most technicians are not aware that this style distributor
is fitted with vent screens, as the distributors on these
applications seldom have to be pulled for service, with
the exception of replacing the intake manifold gaskets.
The vents are positioned at the base of the distributor and
are almost impossible to see with the distributor mounted
in the engine (see illustration 2). In fact, the screens are
easily missed while viewing the distributor on a work
bench. The two vent screens are approximately the
diameter of a pencil eraser and they are easily plugged
when debris is present. The frequency in which they plug
increases with vehicle mileage. Naturally, as the engine
wears, the blow-by gases increase, thus an increase in
the gases collected in the distributor housing. A malfuncccasionally
you will encounter a system or component
that develops a history of pattern failures
that can elude your best efforts. Problems or premature
failures can result from a manufacturing defect with a
component, a problem due to the design of the system,
or a secondary system malfunction may lead to a premature
component failure. When the industry encounters
the same failures or circumstances, then most likely you
are dealing with a design issue. It is unlikely that multiple
manufacturers of the same part would make the same
manufacturing mistakes. Identifying and acknowledging
these issues early on are imperative in making an
accurate diagnosis in a timely manner, and in maintaining
good customer relations.
GM trucks and SUVs equipped with the Vortec engine
are good examples of an ignition system that has developed
some common failures that would be considered
a normal characteristic. Distributor cap and rotor contamination,
resulting in a misfire condition and stored
misfire codes, has become a common occurrence. The
codes may be cylinder-specific or random misfire codes.
It is not uncommon to remove the distributor cap on one
of these engines and observe heavy deposits of a white
or tan powdery residue. The distributor caps used on
these applications are susceptible to more than just
contamination problems. Read on for a thorough description
of some of the problems and possible solutions.
The aforementioned ignition system has encountered
excessive levels of distributor cap corrosion, resulting in
internal arcing and misfiring. Many technicians are of
the opinion that the type of metal used in the construction
of the terminals is the reason for the heavy concentrations
of deposits and misfire conditions. This is not the
case. GM has acknowledged what we have suspected all
along, that the corrosion condition and the heavy deposit
formation is the result of inadequate ventilation in
the distributor housing. The gases collect in the distributor
cap and housing, and in the presence of heat and high
voltage, form corrosive deposits, resulting in internal
arcing and misfire conditions. When these conditions
are present, the cap and rotor will usually reflect the
tion in the PCV system can produce the same results. The
vent screens should be washed with a solvent, such as
brake clean, and any contamination expelled with air
pressure. Wear safety glasses to prevent an eye injury.
These conditions have prompted GM to release two
revised distributors that incorporate larger air-flow screens
for improved ventilation. GM recognizes 2001–2003
trucks and SUVs equipped
with 4.3L, 5.0L or 5.7L
engines as being the recipients
of the revised distributors.
Our research
shows that both distributors
(V-6 P/N 93441559
and V-8 P/N 93441558)
can retrofit applications
back to 1996. The list
prices of the distributors
from GM are $303.78 for
the V-6 and $447.75 for
the V-8. Considering the
cost of the replacement
distributor, many opt for a
clean-up of the existing
Convinced that moisture is collecting inside the cap and
promoting misfire conditions, some technicians seal the
distributor cap with silicone. Sealing the cap is not the
solution and may actually worsen the condition, especially
in cases where plugged vent screens are present,
preventing the escape of the gases. The moisture condition
may be influenced by the A/C system. On many
applications, the A/C accumulator line is routed directly
over the distributor cap (see illustration 3). The condensation
from the line drips directly onto the distributor
cap and housing. If you identify this condition, installing
a foam sleeve over the accumulator line can minimize
the moisture problem. Water dripping on a hot distributor
cap can promote electrical tracking and arcing.
The low profile design of the distributor caps for these
applications is necessary, as the engine compartment
space for the distributor is limited. On most distributor
caps, the terminals are spaced a minimum of an inch
apart. With this style cap, some of the terminals come
within 1/8 inch of an adjacent terminal. The close
proximity of the terminals makes manufacturing of the
part a challenge. Any air or gas pockets in the plastic
molding process can eventually result in high voltage
arcing. The potential for arcing/flashover is great, while
leaving little evidence the condition has occurred. The
problems are further aggravated when high secondary
circuit resistance conditions are present. Current takes
the path of least resistance and often will arc to an
adjacent terminal, creating a misfire condition. For
example: Installing a new cap on a set of bad spark plug
wires can lead to a premature failure of the cap.
In summary: The design of this distributor makes for an
above-normal failure rate of caps and rotors. When
diagnosing a performance problem on this ignition
system, the cap and rotor should always be a first
suspect, regardless of how long it has been on the
engine. The high voltage terminals are molded into the
plastic housing in close proximity, which is a manufacturing
challenge. The manufacturer must consider terminal
position and molding issues such as air and gas
pockets in the plastic. The distributor has a history of
inadequate ventilation, which prompts an accumulation
of conductive deposits. When this occurs, the result
is misfiring, an illuminated SES lamp and stored trouble
codes. The cap is positioned directly beneath the A/C
accumulator line, which can drip water onto the distributor
Due to the design of the system, the distributor cap and
rotor are destined for failure.

· Registered
4,270 Posts
another from

OK, I'm going to guess this is yet another one of those regional things, low humidity here where most of my miles are put on, lessens to near negates the effect------partially anyway.

The PCV system needs to be kept up, and check you distributor shaft for wear--------if mine was any tighter it would try to seize. I cannot get any slack at all out of it.

If yours has this issue and everything else is right, I would take it down as far as I did, make sure the distributor is tight, and drill out those vents to 1/4"------then put something like brass wool in there so breathing isn't inhibited but critters can't get in.

Way back when, when the first HP ignitions with high voltage coils were introduced this was an issue, but distributor shafts commonly had some clearance as well. On pure race cars, we drilled several holes around the outside of the cap but away from the contacts-----glued flattened brass wool strips over the holes. And, companies like Mallory made snap in breathers, you drilled a certain sized hole in the cap and these things snapped in. Looked like a little sight glass.

I dont know anything about this site but this makes sense to me...

Something which might help you diagnose the issue better is to do an old school trick on your just replaced distributor cap. This would be to generously spray the inside of the cap and the rotor with WD-40. Many people use this as a lubricant to help with stuck nuts and such. The WD in the name actually means Water Displacement. By spraying this inside, it will keep water out of the cap and off of the parts. WD-40 is also non-conductive, so will help to eliminate carbon tracking, which can cause the engine to miss on one or more cylinders.

· Registered
4,270 Posts
hey no problem! I honestly dont have anything more to add other than I hope you get er figured out! I searched google with "why does a 97 gm distributor corrode" not what iv searched in the past... the info I got came from the instructions with the new dist cap n rotor...

@kennythewelder so do you recommend the billit distributor? seems like you had a bunch of trouble with it...

· Registered
4,270 Posts
man thats a mess in there eh! look at all that dirt n grim and a rusty screw! swap that rusty screw out or remove it and clean it.... clean that dist. right up spray it all with wd40 n see what happens.... are there vents in the bottom of that housing?
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