No apparent spark after cap and rotor replaced (Solved)

I have no apparent spark after swapping cap and rotor. I also have no apparent spark after putting the old parts back in place. This confuses the heck out of me. I’m not a total gearhead but I’ve done my own basic tuneups (plugs, wires, cap and rotor) for decades as well as oil changes and such. I can easily handle most basic things such as alternators, starters and so forth. I will often take my vehicle to a mechanic for things such as brakes which are critical to safety. That’s my background; a basic skill set with a reasonable foundation in theory and such.

The vehicle: 1989 Dodge D100 with the 318. This last week my truck started running rather rough until it warmed up so I figured well heck, plugs are in order anyhow so why not just throw some in there? I replaced the plugs, getting the gap to .035 on each. That made it idle slightly better but it still ran rough when cold. I decided to replace the cap and rotor myself with my 14 year old as a learning experience (WAY back against the firewall so I often pay a guy to do it for sheer hassle prevention). It’s one of those locations where you can’t just transfer one cable at a time and you have to darn near climb inside the compartment.

Now, I know the firing order (1-8-4-3-6-5-7-2) but to teach him “proper” procedure we documented the position of each cable on the cap and I had him draw a little diagram. I verified it and all seemed just fine. We discovered, however, that the rotor sold to us was a different size and, go figure, the auto part store was closed. (That’s what I get for procrastinating!) Not thinking about it, I left the cap and air filter housing off overnight but the hood was closed.

This morning, we swapped the rotor and got to it. Everything went reasonably well, we got it together and tested starting it. It’ll crank just fine and if you leave it cranking it sort of tries to go just a little. If you leave the key on after cranking it sort of shudders as though it’s trying to run but it isn’t really running (I only allowed it to do that once but it seems to be consistent). I’ve verified the firing order and such just to be sure; it’s in order. I’ve reseated every connection on both ends of each cable. I can’t see anything else that may have come loose while working on it and we were pretty careful anyhow. I can smell gas after trying to fire it up so I’m pretty sure I’m getting fuel (I had a new pump just a couple of years ago and it hasn’t been acting up at all that I can tell.)

I’m at a loss. The only thing I can think of is leaving the cap and air cleaner assembly off overnight may have been a bad idea; I didn’t really think about it because the hood was closed. Though it did rain last night, there was no water inside the engine compartment and I checked the distributor to be sure; no signs of water that I can see.

Can anyone think of something I missed? I’m hoping I’m just missing something trivial here. Sorry for the long-ish post but details can matter.


Pull the rotor and check for continuity from the tip to the post. Also look for any cracks under the post. I have seen them where a hareline crack existed, but i had one once that I could not even find a crack, but it still shorted the spark to the shaft of the distributor. Very annoying.

Now the above is based on assuming that you did check for any spark and got none. If you haven’t yet, stick an old plug into one of the sparkplug wires and lay it on the engine. Crank the engine and check for spark. If you do get spark, then you probably got the number one plug wire in the wrong position in the distributor cap, and of course all the others are also off a hole, following the number one.

When you do this on a 318, or a small block chevy, the best way is to mark each plug wire by wrapping a piece of scotch tape around it and marking the cylinder number on it. Then remove the cap and wires together. Then on the ground, transfer the wires to the new cap. Then put it back on. In most cases, you can even keep the wires in their looms so rerouting them is easy. Then remove the scotch tape.

Ah, so I could have it off a hole! Shoot, I though I got it in line but that’s very possible. I haven’t actually TESTED spark yet (kid had to go back to his mom’s and a client call got in the way).

Crap, is there any way to figure out which location on the cap the number 1 wire should go in? I’ve never had an issue like this and aside from swapping them never got that deep into distributors. I suppose I’m basically a guy with just a little too much ambition and not quite enough knowledge here. Hehe.

Oops; I forgot to say I will test for continuity on the rotor but since it does the same thing with both and the old one seemed to work well enough before I would presume that’s not it. I know, anything’s possible! I’m a full time computer geek consulting on issues and repairing stuff. It’s always something simple you ignore that comes back to bite you. “Is it plugged in? Durrrrrrrrr!” LOL

I’ll test continuity and check back in.

Pull the #1 spark plug. Have an assistant bump the key while you hold your hand near the spark plug hole. When you feel air rush out of the spark plug hole, you know you are near the top of the compression stroke, which is when spark is to occur. Check the orientation of the rotor. The tower it is pointing at will be #1, so install your wires from there if they are incorrectly installed. Rotor rotation is clockwise on this engine.

For what it’s worth, the last 318 I had used this firing order in relation to the clips holding the cap onto the distributor: 1,8,clip, 4,3,6,5,clip,7,2. This may or may not be helpful, just putting it out there.

SOME caps have a line on them at the number one post. It depends on whether the cap you got was specific for your engine or if it is a generic cap.

You can crank the engine just a bump at a time until you get the timing mark very close to TDC. Then pop off the cap and see where the rotor is pointing to. It should be pointing to either #1 or #6 depending on weather #1 is TDC on the compression stroke or the exhaust stroke.

Lets say for example that it is pointed in the vicinity of the post for #3. since #3 is next to #6 in the firing order, than #1 is TDC on the exhaust stroke. Now you could bump the starter to get the engine around to #1 TDC on compression, or just mark the post opposite of the one the rotor is pointing at. Whiteout is very good for marking purposes.

One more thing, watch the direction the rotor goes when you crank the engine, that will be the direction the firing order goes in. You might have 1 & 6 right but the others on the wrong side of the cap.

Ok, continuity is fine on the new rotor. I’ll see what I can manage on the positioning. I’ll have to mark the stupid cap in the future for #1 before pulling it. I didn’t think to have the rugrat (well, not so much a rat these days but …) note the clip positions on his diagram and now I can’t remember for sure where #1 was. I’m second-guessing myself, ya know?

The way you lay it out sounds correct. I know 1 is right by a clip but can’t be sure if it’s set 1,8,clip or 1,clip,8 at the moment. Back out to the truck and if it’s something simple like this it’ll just be a good “well, son, don’t be an idiot like your old dad!” lesson.

If you don’t have white out, use a blue or red magic marker or sharpie to mark the body of the distributor. If the timing mark is very close to TDC, preferably right on but that is hard to hit on the nose, then mark the body where the rotor is pointing, if close to where you had #1 originally or make the body where the butt of the rotor is pointing if not.

You can use mark method to insure you are on the compression stroke, but you still want to turn the engine as close to TDC as possible. If the marks are close to the scale, you might be better off moving that last couple of degrees by tugging on the belts. i have rotated a few engines that way, and if the #1 plug is out, there wont be any compression (not much anyway) to overcome.

Do you need instructions on finding the timing marks?

laughs That was it; I had #1 off one spot clockwise. Swapped in the new parts and it fires up instantly like always. Slight aside: I love how well this truck starts. Even after I was out of town for over a month once, it fired up instantly and ran without any trouble. You have to let go of the key in about a quarter second or you could start grinding the starter motor since the engine is fired up NOW. Anyhow,

Yeah, timing is kind of black magic to me right now. I’m sure it’s very simple; I have just never needed the information before. I probably won’t mess with the timing just yet either way, though. You have to be darned near a contortionist to get to the distributor cap and after basically swapping it 3 or 4 times today, my back is not happy with me. I have to be careful of overdoing it; I had a major accident some years ago and won’t ever be at 100% again.

That said, anyhow, I truly appreciate your help, guys. I knew it had to be something ridiculously simple.

Edited to reflect input for both Mark and Keith. My bad on not noticing I had to helpers at first. Sorry, Mark!

Ok, new comment here for simplicity’s sake. After starting the truck and letting it run a little bit, it runs MUCH smoother. It’s still got a slight … hesitation every so often though. The RPMs seem to drop then it revs itself and evens out. While doing the cap about a bajillion times I did find a couple of wires with a strange wear pattern or almost notch in them. It looks for all the world as though they rested on something hot like a small pipe or a corner with a radius to it like the edge of the valve covers except that there’s no melting at all. It’s more like someone cut out a nice, neat little notch.

The strangest part of this is these spots are VERY close to the cap where there’s no way possible they could have rested on anything at all. I can’t figure out how this could have happened. I’ll try and take a picture once I replace them and post it.

Anyhow, bottom line is the truck’s running somewhat better and looks to need new wires after all. Go figure; they’re in fantastic shape otherwise. Ah well, I can’t complain. This thing gives me almost no trouble ever. If it weren’t so ugly, I’d keep it forever. As it is, it’s my daily driver since my Honda got totaled a while back but it starts every time I ask it to.

Now to catch up on some other stuff, I suppose.

That could be the Idle Air Control (IAC) motor sticking just a tad. As long as it doesn’t die on you, I’d suggest ignoring it. Cost/benefit doesn’t justify the repair.

Heh, never heard of it. I’ll look it up though.

Question for you, if you don’t mind. I noticed a crack in the hose that goes to the (I may have the term wrong) PCV valve from the air cleaner assembly. It’s the little valve doohickey in the valve cover on the passenger side. The hose connects it to the bottom of the air cleaner assembly. The crack isn’t terribly bad but it definitely doesn’t seal around the PCV valve quite right. It’s possible it happened when I started doing all this; the hose is kind of hard now. The crack’s underneath, though, where it wouldn’t be seen until this is all taken apart.

Is that something that’d cause issues like I’m seeing or is it just a minor thing? I’ll fix it either way; how much can a little 6 inch hose possibly cost, right? (Well, assuming it’s not for a Mercedes or something!) I’m just unsure what, exactly, that’d make the engine do, if anything.

Keith, I looked up the IAC. The symptoms described when one sticks are almost exactly what my truck’s doing. It sounds as though you can clean and lube (?) them a bit without replacing them. I’d probably eventually replace it anyhow since it is quite hard to drive the truck until it warms up; it just won’t go until it does and then it’s fine. I hate being the guy at the light that looks like he can’t figure out how to make his truck move. The other issue is when it revs to catch up, it wants to GO and if I’m not really holding the brake, it’d move on me. I’ve been putting it in neutral for safety but it’s annoying as heck anyhow.

Maybe thing’ll be better enough now, though, to just live with it. I’ll see. Thanks again for your input today.