Thoughts on my idling problem?

[will e]

My engine specs are in my sig. They include a mallory unilite (small cap).

My issue: Car runs fine unless I drive it for a bit and then the idle gets progressivly worse. It always runs a little rough when I start it since I have no choke and am running rhodes lifters.

Once it warms up (5 to 10 minutes of driving) it idles just fine.

Add another 10 or more minutes and the idle starts to flutter and gets progressivly worse. To the point it almost won't idle in gear. I get some diesel kind of smell out of it when it is doing this.

A little history:

A couple of weeks ago it all of the sudden ran really rough at an intersection. I barely made it across. I parked it for a bit, fired it back up and it ran fine. I thought I was low on gas so I filled it up but it only took like 10 gallons.

The next day I went to drive it to work. It started and ran fine but about 3 miles from home it started running rough again at an intersection. Then it was almost undrivable. Lots of missing even at speed. Accelleration was strained and I had to baby it up to speed. I had it towed home and while checking things out I took off the distributor cap and the broken center contact fell out in pieces. I replaced the cap and the car ran like normal.

I parked it at a location I was a little concerned about so I disconnected the 3 prog connector between the coil and distributor. (I do this a lot)

Plugged it back in and drove it home no problems.

Next day I take the car to work. While pulling out of the neighborhood it died. The connector came apart. I reattached it and it started and I drove on. Then, again making left turn and getting on it a little, it died again. Once again the connector had come apart. I realized I had ran it over the fuel rail instead of under. I ran it under again and drove away, no problems. Got all the way to work and it was fine. Running over the fuel line there isn't much slack in the wire, I think the engine would torque just enough to pull it back apart.

I drove it a few more times to work and such. Probably 120 miles total with no problems.

Then the problem started just a couple of days ago. Temp is fine. I checked all of the wires. I even went ahead an replaced the cap with another new one while the problem was happening and it didn't fix it.

Plenty of gas, bowls are not over flowing. I am going to do drive it some more and see what happens.

 

[jb73Mach]

Your ignition is vastly different from mine (was a 71 with a dual point from a K motor on a 302) and the dry AZ weather might eliminate this possibility, but I had consistent problems with condensation inside the distributor cap. Started fine and then the condensation formed and boom (or rather sputter sputter). It can't hurt to pull the cap and see when you have a problem.

 

[will e]

Thanks for the thought. The cap is dry.

I remembered I had an old comp 9000 in the attic so I went to grab the unilite module from it. I don't think what I describe is a normal failure mode for the module but what the heck right? Anyways, I went to remove the one in the car and one of the two bolts that secure it was loose. It seems unlikely this is the problem but I went ahead and tightened it down and drove it around. Idle seemed to be okay. No issues under load at all but I didn't drive it very far. I will drive it a longer distance tomorrow or on Monday I will take it to work and see what happens.

I just can't see it being fuel related. And the weather hasn't changed drastically, I have made no other modifications to the car.

 

[TommyK]

I don't think what I describe is a normal failure mode for the module...

It is for an ignition coil though. Can you beg, borrow or steal one to try?

Also examine the loom for damaged wires carefully.

 

[will e]

I don't think what I describe is a normal failure mode for the module...

It is for an ignition coil though. Can you beg, borrow or steal one to try?

Also examine the loom for damaged wires carefully.

Interesting. I will clean and double check all of the connections. I have had the mallory coil for over 20 years. I might be able to come up with a spare coil.

I hate these kinds of problems where it doesn't just break but runs funny part of the time...

 

[Jeff73Mach1]

I don't think what I describe is a normal failure mode for the module...

It is for an ignition coil though. Can you beg, borrow or steal one to try?

Also examine the loom for damaged wires carefully.

I was getting ready to suggest a coil failure.

 

[Mikes73]

Sounds for sure like your spark is getting weak after running for a bit from a coil that is getting tired. I have my own testing techniques lol but look for good blue spark at the plug with the engine running, I just disconnect the #1 sparkplug wire from the plug and use another good sparkplug I have that I then connect to the wire and lay it on the shock tower brace. Start the car and observe the color of the spark {it will be only running on 7 cylinders so it will idle crappy} if spark is white or faint that is no bueno. A good blue spark that jumps the plug gap with good snap is what you want.

 

[will e]

If the coil was getting weak why would performance above idle not drop off as well?

 

[Jeff73Mach1]

As the coil heats up, it gets weaker. Perhaps at higher RPM the alternator is kicking out more voltage and boosting power a bit. Typically a bad coil will start and run when cold (initially) and as it heats up it will get worse until it stops operating.

 

[Totalled]

I will also likely be hot enough to burn you when the engine is fully warmed up. Only other thing I can think of is if you have a sticking float, or the float's are set when cold, and then the fuel level gets too high when warm from expansion.

 

[MeZapU]

How hot is your intake manifold getting? Did you use a valley pan or plug the EGR crossover?

 

[will e]

I checked the floats and they are good. I blocked the crossover. When it happened last time I touched the coil and it wasn't hot at all.

It didn't do it yesterday. I drove it far enough twice that it 'should' have done it but it didn't. The only changes made were tightening one of the two hold down screws on the unilite module (and checking the other) and I had removed the pins from the electrical connector. Since I didn't think this would work I simply pushed each of the three into its corresponding slot on the female end. Wrapped some electrical tape around it. We will see how she does today. At least I have an excuse to drive it around and the weather here in Phoenix is really really nice.