This past week my car has developed what I think is a miss. It occurs during acceleration and cruising rpms. Its like it misses a beat or two. Its worse when cold and almost goes away completely once the car has been running a good while. Its does seem to be getting slightly worse, though, as this week has ended. Could this have anything to do w/ my stuck mech. advance? It didn't start doing this until at least a week after I discovered the stuck advance. I'm going to take out the multimeter and check the coil and wires. Can someone post what ohms, and other electrical #s, I should be seeing for a stock coil, wires (Accel 8mm Superstock), etc. It is the original coil, so I'm wondering if this can be a sign of it going bad? Pretty sure its not bad gas. Can a really dirty air filter cause a miss? I'll also check the fuel line as the car did this once before, but to a much lesser extent after I replaced the fuel pump and I had a very slow drip at the flare to carb inlet fitting (just needed to tighten up the nut a tad).
Okay, I just checked the resistance of the coil. I checked it with the wire leads still connected, key off. I did have to take some sand paper to clean up the studs a bit. The lowest reading I got was 2.4 ohms. That seems a bit high, yes? Unless I need to clean the contact surface more. What do people think of this reading? Could it cause an erradic miss?
First guess: if it misses on the same cylinder (s), it's not the coil. Second guess: If it misses more cold than warm, it could be a vacuum leak. If you have known problems, FIX THEM FIRST. (Mechanical advance) You won't hurt anything by fixing the advance, and "Maybe" the problems are related.
I dyank the dist. cap and check the contacts and the rotor. Could be as simple as one of the contacts having excess carbon buildup. Also.....CLEAN UP THOSE COIL TERMINALS. You cant diagnose a problem with little things that need fixin' in the way
Check the easiest stuff first man! Put an ohm-meter on those spark plug wires! Anymore than a 1,000 ohms per foot and you might have trouble especially with higher compression. I had a set of wires that was fine for 8.5 to 1, but no good at 10 to 1. An even faster way to isolate a missing cylinder (due to electrical) is to rotate your timing light around the plug wires. See if you have erratic flashing :Brow: .
Well.... So, I take the leads off the coil and clean up the studs as best I can. Lowest reading I got this time was 1.8 ohms. Took off the cap and wiped out the inside, cleaned up the inside contacts and the rotor contact real quick. Meanwhile, something I didn't mention before was that I had noticed a little coolant puddled up by the thermostat housing. Well, as I'm cleaning the coil up, my arm leans on the upper rad house, and I hear hissing. So I tighten the clamp and no more hiss. I also took some gumout to the carb. Well, no miss driving to work and no miss driving home tonight. So, I'm wondering about the rad house. Could it have been erratically spitting out coolant, and if the coolant hit the coil, could that have caused the erradic miss? I don't I'll ever know for sure, as I did too many things at once. All I know is that I think I cured it, so I'm happy . P.S. What is the life span on points anyway? Those were like the first thing I changed when I bought the car, and that was 25K-30K miles ago.
Im voting it was the cap and rotor , since I suggested it :Brow: :grin: points and condenser are cheap, not hard to do, and can greatly affect how the engine runs. .....and since you'll have the cap and rotor off anywho......do them to :TU: :spank: :TU:
Yo Zach, When you get the coin, get a davessmallbodyheis conversion dist. Points are good for many thousands of miles, but I'd much rather not have to deal with them. Glad you got it sussed.
Its back Well, it seems to have returned, coming home from work today. So, I pop the hood and check a few things. Tranny fluid was a pint low. I'm wondering if the miss is actually the tranny slipping/hunting? So I added some fluid. I also checked the coil resistance again, this time w/ it at temp. Coil wire off, wire leads off, studs not shiny, the lowest reading I got was between 1.8 - 2.0 ohms, which is higher than the 1.2 - 1.4 ohms the Chassis book calls for (not sure if light oxidation on the studs would increase the resistance this much??). So, I'll take it out again tomorrow and see how it runs w/ the added tranny fluid. I think I have my old points, too, which I might quickly swap in and see if it makes a difference. I'll probably change the fuel filter, too, (not that old, though), as that is a cheap to do. Otherwise, what do you all think?
Check your plugs for fouling. Is it a miss that is constant? - like is it in a particular cylinder or spot in the RPM?
Miss Just an off the wall idea. Since you said it was low on tranny fluid,check the tranny vacuum modulator. It may have a diaphram leaking and pulling tranny fluid into your intake. Ed :beer
Miss Had the modulator diaphram split on a 70GS an did not smoke at all but did cause it to run rough. It pulled about a quart out of the tranny in one weekend's driving. Ed
There was some light white smoke out the tails, but I attributed that to the fact that its cold out now. Looking at my chassic book, it looks like the vac. modulator can be removed by undoing one bolt. Is this correct?
Checked most of the plugs. They all were gray to white in color on the porcelein, and top tang. Bottom electode dary grey to black. Checked timing once more, still sitting at about 14, whether at idle or 3000 rpms. I'm going out now, going to buy new fuel filter, air filter, and points. Even its not the points, I think they should be changed anyway at 30,000 miles. Just going to get cheap set (not the uniset, don't worry).
Did you say that the timing is the same at idle that it is at 3000 rpm? At 3000 you should have pretty much full vacuum and mechanical advance and it should be much higher than 14. It should be at least 34 degrees up to 38. Have you just found your problem?
LaMarr is right Zach. With a timing light you should be able to watch your timing mark move from where it is initially (+8 or so) to right off the chart. If it doesn't move at all your advance weights are stuck. If it moves then stops just off the marks on the timing cover (at about 14 like you said) then the advance isn't going far enough. From an ititial spot of about +8 or +10 the mark should disappear. The best way to time these things is while facing the balancer, measure 1.76" clockwise from the original timing mark around the circumference of the balancer. Make a mark with paint and put a dot above it and below it so you can tell it from your factory mark. This new mark represents 30*. Shine your timing light on the balancer and you'll see your new mark well below the timing tab on the timing cover. When you rev your engine and watch the new mark, it'll climb up toward your timing tabs on the timing cover as the ignition advances. If you rev your engine to get all the advance "in", and the new mark climbs up and stops at 0 on the timing pad and wants to go no farther despite more revving, you have 30* advance. If it stops at +2, you have 32* advance. If it stops at +4, you have 34* advance, and so on.
Geezz, some of you guys must be getting old, because your memory is failing fast :grin: :grin: . I know the advance is stuck, I mentioned that a couple of weeks ago. The thing is, there was no miss then, even w/ the stuck advance. It only started this week. I went out and bought new points/condensor, fuel filter, and a cheap coil. Cost be barely $25 for all of it. Tomorrow, I'm going to change the fuel filter and test drive, then points and test drive, then coil and test drive. If no change, well, I don't know. Maybe the less than 1 yr old fuel pump is going bad? Hopefully not. I'll fill ya all in tomorrow.
