inconsistant missfire?? Help!

[beandip]

You have not indicated what ignition is on the engine , this would help. If you think that it might be fuel related and are running only a working mechanical pump , be positive that there is not a pin hole leak or crack in a fuel line. The pump can be pulling air and can cause what you are describing. What all have you done already? Gary

[Mr Camouflage]

I'm not sure what you're talking about here in regards to your distributor cap?

Two caps on your distributor? What does that mean? Do you have a picture or something that will help to explain what you're on about?!

He means capacitors. cap is geek speak for capacitor in the electronics world.

Well at least thats what I think he means.

Edited August 10, 2008 by Mr Camouflage

[ozconnection]

He means capacitors. cap is geek speak for capacitor in the electronics world.

Well at least thats what I think he means.

Thanks for the interpretation. Can you clarify this point AggieZ so that your info can be correctly understood and made useful for liltuber.

[JimmyZ]

He meant the rotor. He was trying to describe the cap and rotor. OR Perhaps he was trying to describe the condenser. The other "cap" he was mentioning (inside) might have been a hint at an internal resistor type rotor. The early Z doesn't have such a rotor. No noise suppresion. Sometimes a rotor with an internal resistor can go bad.

Sometimes there are dimensional differences in cap and rotors if you mix and match different aftermarket brands w/ factory.

I think we should wait for some feedback from the original poster. (If it ever comes) He might have fixed it and doesn't care to share. Love it when they do that.

Cya,

Jim

Edited August 10, 2008 by JimmyZ

[liltuber]

Sorry guys, long weekend from work to a funeral. I did have a chance to put on the filter and notice no change.

So i did a couple things and i can update you on some others. I went out and tightened all the connections on the resistor but that didnt change anything. The distributor cap and wires are fine. All the elctronics are new except for the resistor. I put my ohm meter on it, and read a resistance so i didnt think it to be necessary. New condensor, coil, points, cap, rotor. plugs are pretty new but are a little fuel fowled. The ignition switch is the original but i wiggled my little heart out on the wires and saw no significant change.

I also wiggled the distributor shaft and it was very snug.

It is more of a missing fire than a misfire.

I am going to try putting a different coil on it right now, but I doubt that will do much. If it works I'll let you know.

Jimmyz, can you explain to me how to use the test light on the plugs and wires?

Keep shooting me options guys, one of them has to hit.

[liltuber]

ok, midnight update.

Factory coil... no help.

I did start playing with the point gap though and some things changed.

I got it to one point were it almost seemed as though the rpms were jumping up instead of down but the car didnt sound right so i adjusted again. This time the car seemed to run like it should! for a while. At first it was only bouncing around 50 to 100 rpms, but after about a minute it dropped and i had to hit the gas to recover it.

So i'm thinking its in the points system somewhere. Any thoughts?

[JimmyZ]

Jimmyz, can you explain to me how to use the test light on the plugs and wires?

Keep shooting me options guys, one of them has to hit.

Here's a cheap timing light. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3343

Otherwise $25-$50 ought to get one from Autozone etc..

The following is for a "normal" timing light that has an inductive pickup and a 12V connection. You can spot a missing/fouled plug by simply running the engine and connecting the inductive pickup to each wire. (All 6 and then the coil wire) This is using the timing light as a diagnostic tool rather than a tool for setting timing. Make sure the pickup is firmly closed or you may get an intermittent flash. You can check all the wires without turning off the car. Be careful when working near the fan and belt(s)!

What you are looking for is a miss or "hiccup" in the strobe. This will indicate that there wasn't current passing for one reason or another. The inductive pickup senses a peak of the magnetic flux which comes from the collapse of the field in your coil. (each time a plug is fired)

If the car is "missing" but the wire(s) still show good spark with the T-Light then it's a fuel issue.

Normally you connect the timing light to the #1 wire and shoot the crank pulley while turning the distributor to adjust timing.

It sounds like you may need to check the condition of your points faces. A regap sounds good too. In a pinch you can use a piece of cereal box cardboard to set the gap. A dwell meter and replacement of both points and condenser at the same time is the way to get long life out of a set of points.

Proper tensioning and fastening of the points is important too. It's easy for points to slip a little if the hardware is on wrong.

Here's an ignition page I started but haven't finished yet. It's more for troubleshooting points systems that don't run but there are pictures. Look at the spark picture and compare. http://warbuddies.homestead.com/240Zignition.html

Edited August 12, 2008 by JimmyZ

[liltuber]

Thanks jimmyz. I have access to a tl but the quick lesson was great.

Earlier this morning I solved the problem. It was the point faces. I took a little sandpaper to it and it ran great. Had a great drive to the gas staion. The points are only a month or two old though. So it makes me think, why did they foul so soon?

I noticed something that i'm not sure what it is. Maybe you guys can help name it w/o a picture. I looks like a condensor on the outside of the distributor on the block side. The wire it runs to connects to the points plate on the inside of the distributor. Is it a condensor? If its bad could it cause the points to go bad?

[JimmyZ]

You're welcome and Yep...

That's the condenser. As they get older they change. (At least that's what I'm told) An old condenser can cause the points to arc/pit faster. Best to replace both points and condenser at the same time.

More than likely what happened was that the points slipped a bit and the gap was too close causing them to arc and pit faster. It's a bit anal but a dwell meter is a good tool to check your points with. A coil with the ballast resistor wired backwards will have the full 12V going to it while the car is running. Check that the voltage to the coil is around 6V when the car is running. It's easy to switch the leads which are both black.

Make sure that the car is at the manufacturer's specified rpm when checking the dwell angle. (600 rpm in Haynes manual) For the meantime it wouldn't hurt to check your gap every now and then. Here's a cheap dwellmeter from sears...

http://www.sears.com/shc/s/p_10153_12605_00902165000P?vName=Automotive&cName=Tools&Equipment&sName=Automotive%20Testing%20Equipment&psid=FROOGLE01&sid=IDx20070921x00003a

Glad it's running better.

Jim

Edited August 13, 2008 by JimmyZ

[liltuber]

Ya i cant believe I've never seen that condensor before. I will be replacing that condensor and the points today.

Thanks for all your help.

Adam