Wet weather misfires

[sdg3205]

I'm replacing the wires with Grady's AC Delco. A new rotor, cap and plugs from DMCNW. They're all 7 years old now and given this is a new issue for me I can only guess that it is due to parts wearing out.

[Rich]

I'm replacing the wires with Grady's AC Delco. A new rotor, cap and plugs from DMCNW. They're all 7 years old now and given this is a new issue for me I can only guess that it is due to parts wearing out.

Those would be typical parts to replace without more information. Might skip the rotor since it's inside the cap. You did not mention the coil but if you are running with the plastic cover in place over the coil it may not be getting very wet in the rain.

If you want to try something before swapping parts here's quick assessment method: take a look at the entire secondary ignition (from the coil all the way to the plugs) in the dark with the engine misfiring. You may see telltale sparks (exterior of dist cap, coil, coil/plug wires/boots). It will not show internal oversparks, only ones on the outside. Will not show any plug problems, either.

An extension idea from that method. In case the car isn't misfiring fill a hand-spray bottle with plain water. Use that to "rain" on selected parts of the system with engine running in an effort to isolate the problem area.

Both of these only work with the car stationary, of course.

[dmcnc]

I also had pretty bad misfiring kicking in over the past week or so after the big storm that swept through the Southeast. I found and corrected two issues:
1. Cylinder # 6 was full of water. Dried it up, but I still had some light misfiring, which led me to
2. Spark Plug wires arcs all over. I had no idea how bad it was until I did the water mist test on the wires at night with all lights turned off. I had about 6 points where you could see sparks jumping from the wires to the nearest ground, i.e....stainless fuel lines, auxiliary air pipe, and intake corners facing the interior. I insulated the wires with electrical tape and reduced or eliminated most of them. These wires are only a year old, but I'm going to change them out soon.

The car runs very smooth now.

[David T]

Those would be typical parts to replace without more information. [I]Might skip the rotor since it's inside the cap[/I]. You did not mention the coil but if you are running with the plastic cover in place over the coil it may not be getting very wet in the rain.

If you want to try something before swapping parts here's quick assessment method: take a look at the entire secondary ignition (from the coil all the way to the plugs) in the dark with the engine misfiring. You may see telltale sparks (exterior of dist cap, coil, coil/plug wires/boots). It will not show internal oversparks, only ones on the outside. Will not show any plug problems, either.

An extension idea from that method. In case the car isn't misfiring fill a hand-spray bottle with plain water. Use that to "rain" on selected parts of the system with engine running in an effort to isolate the problem area.

Both of these only work with the car stationary, of course.

Good practice is to replace the rotor and cap together since they wear to each other. The other reason to replace the rotor is I have seen rotors that have arced to the distributor shaft leaving a carbon trail on the rotor. Difficult to diagnose and verify but it happens. Coils can also arc but it seems to be rare for the Bosch coils to fail that way. Bad wires and caps seem to be the main causes for arcing in the Delorean. Make sure you gap the plugs properly or that can lead to premature failure of the wires. If the gap is too big it might be easier for the wires to arc than for the spark to jump the gap on the spark plug. Also handle those new wires tenderly. The core is carbon and it doesn't take much to damage it. Tightly bending them or stretching them is all it takes.

[ssdelorean]

Damn! so with the crack it was fine when dry, but misfired when wet?

Exactly what happened to me a couple years back. My cap's crack was so small it could barely be seen without flexing the cap to see it open up.

Rare for a cap to crack but if mishandled or not fit to the dist properly it can happen.

Figures that it is a rare thing and happened to me. But if I recall correctly, I think I was over the recommended replacement millage by about 15k miles or so. That may have a factor in it's fatigue. :-)

[AugustneverEnds]

Put the intake on and got everything back together today, first time starting and driving with Bougicord spark plug wires. Started right up, no misfiring or other odd ignition behavior. Felt good on a short test drive, so far so good is the initial verdict. Interested how the AC Delco's compare to the previous Bosch's.