Strange problems

I'll try to congregate all of my posts from Moparts in one thread to a single post here:

The Demon's engine suddenly died on me on Wednesday. I started it up that morning without any issue, just like every previous day since I started the engine for the first time. By the way, its a 5.9L Magnum with a full-roller outfit, a HV Melling oil pump, a Carter fuel pump, and a Holley 4160 carburetor.

So anyway, I started it up that morning to go to work, drove a couple blocks to the highway, and got on. I get on the highway doing about 60MPH at maybe 2500RPM (normal), and then get off at the next exit (it's easier and faster to take the highway than surface streets). I had done this routine multiple times before with the same combination, but without issue.

I get off at the next exit and stop at the stop sign there. I turn left, and drive to the next stoplight. I am idling at the light, first in line, at 850RPM (also normal), when suddenly my RPM dips to 650. Then 500. Then 400. Then it gasps and dies, but it sounded like it was trying to breathe. It did not sound like it was out of gas (plus the gauge said I had half-a-tank).

I instinctively drop it into neutral and try to start it. The starter cranked like a champ, but the car wouldn't start. I was able to safely push it to a side street where I took a look at it better. The car was fine in regards to volts, oil pressure, fuel level, and water temperature. I cranked and cranked on the starter for about 10 seconds. Nothing. I kept cranking on it, and finally it started to have what I call a 'distant' sound, acting like it wanted to start it. I tried a little more, and it started up again. Revving above 1000RPM or so, it ran like a champ. Let it idle, and it would go through its death scene - 650 to 500 to 400R to zero RPM - almost instantly.

So I got it towed back home :angry7: where I left it, and took the Mini to work. I got back that afternoon with a bunch of tests in mind:

Checked voltage to the resistor: 12v
Checked voltage to the negative side of the coil: 9v
Checked spark to the distributor from the coil: sparking
Checked spark to the spark plugs from the distributor: sparking
Checked fuel to the carb by pressing throttle lever: getting fuel

A couple things I noticed:
1. carbon-fouled plugs that smelled like gas. The gas smell could have been due to my excessive pumping in the morning, but I thought my mixture was really lean - the idle mixture screws were only about 1-turn out.
2. dirty (but flowing) fuel filter.

I replaced the plugs, and we were able to get it to start, albeit a little rough still. I put a vacuum gauge on the manifold vacuum port and leaned out the motor until we had it stumble a bit, then leaned it back 1/2 turn to where it had the highest vacuum (15Hg). The car idled great. We thought we were done, but about 20-25 seconds into its idle, it starts it death scene again!

We considered the idle circuit in the carb may be bad, so that night I took apart the entire Holley and cleaned each passage out with carb cleaner and compressed air. Put it back together and left it overnight (as it was too late to start the car again). I also checked the power valve by sucking on the big end, and the diaphragm checked out.

Came back home yesterday after work with some more tests to try. Placed the carb back on, made the idle mixture/speed adjustments, and placed the spark test light between the plug and the distributor (it still feeds the plug, just shows the spark is getting to it). I was told it could be a bad ECU box. Fired it up, and it idled rough for a second or two, then died again the same way as before. But from what I could tell, the plug was getting good spark up until when it died. I know a test light isn't really the end-all, but I'm thinking it pretty much rules out the ECU or coil? Am I wrong to think that? Other than that, the carb is dribbling fuel out of either the fuel line tube that connects the bowls where it meets the bowl at the o-ring, or from the accelerator pump. Neither of which should be an issue at idle, but it is dribbling. Oh, and for some reason now fuel comes out of the boosters for almost twenty seconds after the car's been shut off. It only did it once, but I'm not keen to try it again.

Today I have a couple more tests to try before anything. I didn't think base timing had been affected, but I am going to throw a timing light on it to check. Also, my friend has an Edelbrock 650 that we're going to throw on and check. If it runs, albeit good or bad, we'll know it was the carb preventing it from running for a long time. If it does the same thing, we can look elsewhere.

Does anyone have any experience with a problem like this, or any other advice they can offer? I know the catch-all way to test a motor is to make sure it's getting air, fuel, spark. I know it's getting spark (but don't know when), I know it's getting fuel (but I don't know whether my fuel levels are accurate), and I know it's getting air (it runs for a little bit). I just don't know what's going on :sad7:
Author: admin