Ozone and your Distributor

Tue Feb 15, 2005 8:00 pm

This story sounds extremely far fitched but is true. I have a 2002 Chevy 3500 Express van I've owned since new. About 6mos after I bought it I started having intermittent problems with it missing under load. One time it wouldn't even start at all even though I had great spark and fuel. Over the next 2 1/2yrs I had it in the dealership 4 times and everytime all they did was put a new cap and rotor on it and everything was fine for just a couple of months then back in I go. I decided to try and investigate this problem on my own so I sent one of the caps to Wells Mfg Corp. with a letter stating my issue. They launched an investigation that lasted 6mos and this is what they found. The cap I sent them they said was perfectly fine. How could this be I asked ( as I had personally witnised that cap causing one of my no starts and with the new cap it started right up). In fact none of the previously replaced caps were indeed bad. The problem was Ozone. Yes I said Ozone! Whenever an electrical arc jumps in ambient air it creates ozone. Now this happens quite frequently under a distributor cap and if there isn't a vent in the cap or body the area under the cap will become saturated enough to cause I kinds of funky things to happen from missing at idle, under load or just plain no start. My distributor was missing the vent under the rotor. Simply lifting the cap up and reinstalling it would been the same as a new cap. Now you say I know people who have sealed their caps down and didn't have any trouble like this. Todays ignition systems are triggered by crank sensors and therefore fire every cylinder on every stroke. In the ozone laden enviroment under the cap the spark chose to go to the cylinders that were on the exhaust stroke not compression, that is why I appeared to have good spark, just not in the right place at the correct time. I know now that ignition caps are vented more so for Ozone than for moisture. If you think I've lost it check out wellmfgcorp.com and look under Wells Counter Point Volume 8 Issue 4 Fall 2004. The editor's notes section has a picture Of my cap and rotor explaining this condition. Everday is a new learning experience! :lol:

Tue Feb 15, 2005 9:43 pm

If i read you right there is a defect in the distributer in that a vent is missing. Do i understand it correctly? If so is yours the only one? Are there thousands?


Tue Feb 15, 2005 10:26 pm

If i read you right there is a defect in the distributer in that a vent is missing. Do i understand it correctly? If so is yours the only one? Are there thousands?

I think there are probably thousands. GM has since issued a service bulletin and I now have that bulletin installed. I did some internet searches and found others with the squawk. I'll bet this is a rampant problem. The distributor body is plastic and I'm therorizing the vendor had a quality control issue with not puncting out the vent during manufacture. By the way Wells is an OEM vendor for many automotive parts many of them Delco. However they told me sometimes Delco OEM parts are sold in their boxes as well. The bottom of the rotor has a built in fan for the purpose of purging clean air from under the cap. Basically I always thought caps were vented for moisture reasons, now I know its really to purge out the Ozone. Wells told me in the 70's there was a problem with distributor caps blowing off on some model cars. It was the same issue-lack of venting.

Tue Feb 15, 2005 10:44 pm

Wow that is some detective job. Thanks for sharing it with us.
Wait a minute another part just sank in to my thick Square Head. There is an extra spark on the exhaust stroke? I could be out of time 180 degress and still be in time?????????????????


Tue Feb 15, 2005 11:12 pm

Years ago I had a '77 Jeep with the AMC 6 cylinder engine. Every so often the distributor cap would hop off when you were trying to start it. The spring clips had lost their shape and springiness. I new a guy with an AMC car and the same engine. It happened to him too.

I don't think it was a pressure thing as it seemed to happen when starting the engine. I think it was just clips that had gone bad.

Tue Feb 15, 2005 11:25 pm

Bill, My Van was the last year for any engine with a distributor. It won't be to many years before they will be all but a memory on automotive type vehicles. Distributless is almost 20yrs old on some models already. My van has the 350 that is completely gone from the fleet as of "02". I'm not sure if you were kidding about the timing. Of course you know there is no such thing as timing anymore. Eventhough I have a distributor that is all it does- distribute spark. When to throw that spark is completely computerized. The crank sensor merely tells the ESC what position the crank is in. Then based upon inputs from the eletronic control module it determines when to trigger the coil. Timing constantly varies at all times based on driveabilty factors. Cool isinit :lol:

Tue Feb 15, 2005 11:31 pm

Actually Jim I believe it was AMC that Wells mentioned. Seems funny the springs were only week during start. My fatherinlaw knew someone who owned a car that the cap would blow off just driving down the road. They would stop and put it back on and it would last a little while longer. They never did find out what the problem was. Wells told me it very likely was the same problem. The older a car gets the more likely crud might plug an existing vent.

Tue Feb 15, 2005 11:37 pm

Every so often the distributor cap would hop off when you were trying to start it.

Jim, back in 77 cars had points. While cranking the resistor was bypassed to help give a hotter spark. It's possible that the increased energy coupled with the formentioned problem was your deal. Stiffer cap springs just overcame the problem.

Tue Feb 15, 2005 11:42 pm

The power-unit I recently bought has all original parts on it and the cap has 3-holes in the bottom side. Even the plug wire boots have I-H on one side and a W on opposite side. I was wondering if the W stood for WICO as in mag.

Wed Feb 16, 2005 12:05 am

The springs were always weak. They didn't hold anything except for a little while each time I bent them. It had a magnetic pickup, no points. With the clips not holding anything, the cap rattling along wouldn't have held any pressure.

I always thought the roughness of a cold engine just starting was more likely to pitch the cap off than the relatively smooth engine after it warmed up. It seems even more unlikely that pressure to pop it off would be greatest when it was starting.

I suppose it could have actually jumped off when the engine was shut off. Never did find it off when opening the hood before starting it.

Sun Feb 20, 2005 11:27 am

This is the document without the pictures. It’s really ashame when someone pays so much money for a vehicle and gets no satisfaction when returning to the Dealer so many times.

In my opinion today’s automobiles are very complicated and Dealer Technicians are not given the proper time for diagnosis and repair the complaint correctly. The only thing most Dealers want to do is sell the vehicle and forget about (what they say) the necessary evil of the shop behind the Dealership.

The factory gives the Technician the education (the shop has to give the time), the factory Tech assistance , factory software and service manuals (paid by the service department)
to satisfy the customer on their concern(s). The problem is the factory will not give the proper time for diagnosis and repair; therefore the Dealer (owner) gets upset when the Technician takes longer than factory allowed time. In the shop I work at you have to be 100% productive. We are a Union shop and the Union agrees with this.

This is why I think “Independent” auto repair shops have a better reputation than the factory dealerships.

When someone tells me about a good experience of repairs on their vehicle I say “you better stay with that shop”.

Years ago I had a '77 Jeep with the AMC 6 cylinder engine. Every so often the distributor cap would hop off when you were trying to start it. The spring clips had lost their shape and springiness. I new a guy with an AMC car and the same engine. It happened to him too.

I don't think it was a pressure thing as it seemed to happen when starting the engine. I think it was just clips that had gone bad.

Jim, if I remember the issue on this was, fuel vapors were penetrating through the vacuum advance diaphragm.(when the engine was shut off) After engine was started fuel vapors would explode inside the distributor and causing the cap to project.

Jack Fowler

Document ID# 1589507
2002 Chevrolet Express

Poor Engine Performance-Misfire, Rough Idle, Stalls, Engine Cranks but Does Not Run, SES/Check Engine Light On, DTC P0300 Set (Inspect Distributor Ignition(DI) System Components, Replace as Necessary) #03-06-04-041A - (Jan 28, 2005)
Poor Engine Performance - Misfire, Rough Idle, Stalls, Engine Cranks but Does Not Run, Service Engine Soon/Check Engine Light Illuminated, DTC P0300 Set (Inspect Distributor Ignition (DI) System Components and Replace As Necessary)
2001-2003 Chevrolet Astro, Blazer, Express, S-10
2001-2003 GMC Jimmy, Safari, Savana, Sonoma
2001 Oldsmobile Bravada
with 4.3L, 5.0L or 5.7L Gas Engine (VINs W, X, M, R -- RPOs L35, LU3, L30, L31)
This bulletin is being revised to delete a model and add information to subject and inspection of distributor vent screens. Please discard Corporate Bulletin Number 03-06-04-041 (Section 06 - Engine/Propulsion System).

Some customers may comment on poor engine performance and the Service Engine Soon/Check Engine light being illuminated. Upon investigation, the technician may find DTC P0300 set.

This condition may be due to high levels of internal corrosion in the distributor, causing misfire, rough idle, stall and Engine Cranks But Does Not Run. This corrosion is attributed to a lack of airflow internal to the cap caused by the vent screens being clogged with debris.

Remove the vent screens and inspect the internal components of the Distributor Ignition System using the procedure listed below. If the distributor base has to be replaced, the vent screens will also have to be removed on the new distributor. If there is evidence of this internal corrosion, replace the affected component. Refer to the appropriate procedure in the Engine Controls sub-section of the applicable Service Manual.
Important: All of these inspections can be done on-vehicle.
1. 1. Inspect the distributor cap. You may notice a white residue on the cap walls. For higher mileage occurrences, the interior of the cap may have changed to medium brown in color
2. 2. Inspect the distributor rotor. You may notice the presence of black streaks on the plastic surface. More typical evidence would be visible green spots on the copper surface of the rotor segment.
3. 3. Inspect the distributor base. You may notice high levels of surface rust on the distributor shaft or surface contamination on the sensor hold down screws.

4. 4. Inspect the distributor vent screens (1). If the vent screens are present, remove them by using a plastic-handled, long blade awl or pick (2). Insert into the airflow vent screens and pop them out. Refer to the figure for removal procedure. If the vent screens have been removed from the base of the distributor, then check the airflow inlets for being clogged with debris.

Parts Information
Part Number Description
10452458 Cap, Distributor V6
10452457 Rotor, DistributorV6 and V8
93441559 Distributor V6
10452459 Cap, DistributorV8
93441558 Distributor V8
Parts are currently available from GMSPO.

Warranty Information
For vehicles repaired under warranty, use:
Labor Operation Description Labor Time
J4360 Cap, Distributor - Replace Use published labor operation time
J4380 Rotor, Distributor - Replace Use published labor operation time
J4530 Distributor Assembly - Replace Use published labor operation time
Add To remove Distributor vent screens 0.1 hr

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
Last edited by JackF on Sun Feb 20, 2005 6:54 pm, edited 2 times in total.

Sun Feb 20, 2005 1:54 pm

Jack, thanks for your reply, I'm not sure I ever had the vent as I've only got 21,000 now and this started at 14,000. The engine is spotless clean still. No build up of grime yet. I didn't get the Paul harvey on all this until after my last visit to the dealership when they installed the bulletin. A couple of weeks later the Wells report showed via UPS delivery with my old cap in a box stating the real problem. I never got a chance to insp. my old distributor so I'm just guessing the vent may never have been there. I had the problem real bad to the point I wasn't sure if I could take the van very far or not. My first trip to the dealership resulted in a no fault found even after I told them to inspect under the cap. Later I discovered they hadn't even bothered to look they as the road test is all the did. I would have been fired at my job if someone brought me a plane and with a similar complaint and I failed to follow through.