More on Random Misfire

I'm new here, but not new to the misfire problem that many here experience. For me this has been a problem for 3-4 years and I'm very frustrated with the service from dealerships and independent garages. I have done a lot of surfing on the net on this subject as I'm sure many of have too. I joined this forum because I felt with the members here we would have the best chance of resolving this issue. I'd like to give some background and some thoughts and open it up to more discussion. If I can't resolve this in the next few months I will drive it off a cliff LOL.

What I've done so far:

replaced 2 coils - one at GM dealership, one at independent garage
replaced 2 caps - one stock, one an Accel with brass posts
replaced rotor with Accel unit
replaced wires with Bosch premium wire.
Pulled distributor and inspected, gear OK (110k kilometers, 65k miles)My thoughts and observations:

problem is more prevalent when cold and damp, near freezing or during a wet snow fall.
occurs only when lightly loaded - my thought on this is that in this condition the computer adds a bunch of timing which increases the distance from the rotor terminal to the post therefore leaking spark either to another post or around the coil or other ground path. It is not a problem with the coil, it's just that the spark is trying to find the path of least resistance.
step on the throttle when a miss is present and miss goes away.
looking at the cap, the posts have the typical arcing marks but they are always on the advanced side of the post - this tells me that the phase relationship of the cap to rotor is off. If I could turn the rotor mounting plate to put the rotor in a better phase relationship to the cap, I think I will see an improvement. I might try this with another distributor.
Pulling the cap off and wiping it clean inside with break clean then spraying some Wynns ignition spray stops the miss right away and works for about a month. If it weren't for the damn doghouse, I could probably live with it. (I think I removed it in my sleep once :iceslolan ). This is an indicator of spark scatter in the cap which wouldn't happen if the rotor was closer to the post.I've read about needing to set the "cam retard" which phases the crank position sensor to the cam sensor in the distributor. Anyone know more about this. I would of thought the dealership mechanics would check this.

Sorry for the long post, but I looking forward to your thoughts and comments.

Ron

Welcome Aboard!

This is not an uncommon problem with both the V-6 and V-8s using the CMP in the distributor. You are so close to the solution it almost bit you in the... err.. Ankles!

Getting the CMP "in phase" with the CKP is not difficult, since the CMP is "ON" for about 180º of distributor rotation. The real trick is getting the distributor cap and rotor in phase after the base CMP position is set. You have already seen evidence of the rotor leading the cap termminal position by your analysis of the wear. Advance the cap relative to the rotor about 15º (just like you would set the timing on an old-style distributor) and see if the problem is resolved.

The two things which contribute to the problem are aftermarket distributor parts and moisture.

Regardless of how hard they might try, it seems that the aftermarket just can't seem to get the epoxy or bussing right to prevent problems. These forums are full of anecdotal evidence of that.

The fact that moisture is present seems to aggrevate the condition. Having the distributor and rotor out of position requires the coil to produce a higher voltage to bridge the wider gap, and the arc inside teh distributor is longer, ionizing more air before it can discharge to the plug terminal. Both conditions mean that more ozone is produced inside the distributor, and that faster breakdown of both the metals and insulation in the cap can occur. With a hot engine, the moisture which may have intruded into the cap is usually driven out (baked), but a cold engine can have plenty of latent moisture to shunt the spark energy away from the intended plug. The fact that applying a water displacer solves it only reinforces that.

Unfortunately, it sounds like your cap may already be damaged. I'd suggest a new factory cap AND rotor, and adjusting the distributor base position as described.

How do I adjust the distributor base since the hold down clamp is fixed due to it being square and the base being square. I was thinking of elongating the bolt hole and getting the 10 degrees I figured I'd need but thought I'd screw up the cam sensor timing. Can You elborate on what I should do?

It looks as though the rotor mounting plate is just pressed on the distributor shaft. Has anyone tried to turn it 10-15 degrees and tack it?

Too bad about the Accel cap and rotor, cost me over $100 and is only 5 months old. Heard it was recommended from a couple of other sites. When I inspected it last month there was corona everywhere and judging by your post, I don't need to tell you that corona (ionizing the air causing ozone and a white powdery residue FYI for others) is an insulation killer. Gotta wait till it gets above freezing to change it though.

Hi,

I am not a mechanic but I try, so take anything I am going to say at its value.

Everything the last guy (sorry did not look at the name) says seems true and I cannot disagree with any of it but I cannot figure out how to adjust that position myself and I just looked at mine (since I am in there working on the fuel system - see post, help if you can).

Could it be that the factory anticipated this misalignment possibility and chose not to make an adjustment possible becuase it would not be a concern without the moisture, making the moisture the problem.

After looking at alot of these posts trying to findvan answer to my problem, I have seen alot of people mention drain holes at the base of the distributer that plug up and cause excess moisture (theres something about a design change and screens - look up one of those posts for better info). I would try looking at those drains before I started hacking mounting tabs or cutting and tacking a distributer gear.

Love this forum, and hope it leads you in the right direction (basically becuase iit sounds easier than the proposed laternative.

Thanks,

Chris

After looking at alot of these posts trying to findvan answer to my problem, I have seen alot of people mention drain holes at the base of the distributer that plug up and cause excess moisture (theres something about a design change and screens - look up one of those posts for better info). I would try looking at those drains before I started hacking mounting tabs or cutting and tacking a distributer gear.


I check the vent holes everytime I'm in there, their always clear. My 95 Safari had an adjustable distributor which I adjusted so I think that when it gets warmer, I'll get another hold down clamp and modify it.

Ron

....After looking at alot of these posts trying to findvan answer to my problem, I have seen alot of people mention drain holes at the base of the distributer that plug up and cause excess moisture (theres something about a design change and screens - look up one of those posts for better info). I would try looking at those drains before I started hacking mounting tabs or cutting and tacking a distributer gear....

You hit the nail right on the head! When the engine has achieved operating temperature and then shut off, condensation forms inside the engine. It will form on the highest points due to the warm temperatures rising, such as the underside of the intake manifold and inside the distributor cap. The holes in the distributor base are there to help ventilate and let the warm moist air & vapors out of the distributor cap, (a chimney of sorts). Some manufacturers design distributor caps with vents in the top to help with the ventilation process. It is very important to keep those vent holes clear to reduce the formation of condensation which leads to voltage arcing in the cap when the engine is restarted.

Before you go through all of the other great help provided here, do yourself a favor and get an actual AC/Delco Rotor. Before you put it in, compare the electrode length on the aftermarket rotor to the AC/Delco one. I found the the very expensive aftermarket rotor I had installed was about 1/8" to 3/16" shorter than the AC/Delco. I put a new ac/delco rotor and cap on and haven't looked back, no more misfires. I attribute the misfires I had to the increased gap between the rotor and cap causing scattered spark. Good luck.

Again, if you are certain that the static position of the rotor is incorrect when the #1 cylinder is at TDC, someone has moved it. Vortec V-8s have a provision to move/rotate the distributor. V-6s may have to have the distributor removed and reinstalled to achieve correct phase. Since you previously reported that either you or your mechanic "Pulled distributor and inspected, gear OK (110k kilometers, 65k miles)" you may need to revisit the phase issue. V-6 distributor caps do not lend themselves well to moving plug wire positions to correct this, so it has to be done by distributor installation. You'll very probably have to reposition the oil pump drive when you do this or will end up retarding the position yet another tooth upon installation.

Your analysis is still likely correct. The firing is leading the distributor position by too many degrees, and you're seeing the evidence of this at the cap terminals. Advance under no-load operation can be almost 50º BTDC via the PCM programming, which is 25º of distributor rotation. Ignition timing is almost NEVER retarded past TDC by the programming, and never by more than a few degrees. One tooth of misalignment of the distributor shaft accounts for 25.71º of rotation on the standard 14T distributor gear used in SBC engines (sound familiar?).

My apologies if I wasn't clear on this in the first response.

I'd suggest a new factory cap AND rotor...

Follow the advice of the others who've posted and inspect any vents. Follow prior advice and install a factory cap and rotor. Then install the distributor in the correct positon.

Thanks for all the replies. I will first install a new AC Delco cap and rotor and go from there. When I inspected the distributor gear, I re-installed it it the exact same location, not a tooth retarded. Some here say you probably need to replace the cap and rotor each year. Is that typically the case?

Ron

Not with me. My 2000 is still running on the original cap, wires, and plugs, but it just turned 90,000 so it won't be long before the ignition system gets some service. The plugs looked good at 70,000.