Sudden Rough idle and Stalling Issues

[Gweiner]

Stumped by this recent issue and could use some help troubleshooting the issue. The Bronco was running great. All of a sudden, the truck started sputtering, almost misfiring and idling really low. It was bucking under acceleration and idle was erratic. Crawled a mile home and began trouble shooting but now stumped. Thought it could be a fuel delivery issue. Cleaned out fuel lines and fuel filters. Seemed OK. Checked top of carb and it seemed clean. Next checked spark wires and they all were intact. Everything is new on the ignition EXCEPT the original distributor. Recent points, cap, rotor, capacitor change, new wires, new coil, etc. Recently timed as well. 74 EB, stock 302 2bl Carb.

How do I know if I have a bad distributor? What else should I be checking?

Appreciate any advice.

 

[ECEB]

Exhaust leak? I had a worn out gasket break once and had similar symptoms.

 

[Gweiner]

Thanks. Brand new exhaust from manifolds back. I dont suspect a leak. No offroading so cant imagine anythimg lossened up on the exhaust.

The misfiring and backfiring (it happened once) suggests a timing or soark issue to me. Wondering if the old distibutor gear is worn or something else maybe. I failed to mention that I recently upgraded to a 1 wire 130A alternator but have been running it for several weeks without issue.

 

[DaveLev]

Sounds like fuel delivery to me as well. You cleaned the filter, so I presume you mean the one going from the pump to the carb (or on the intake side of the carb if factory carb). Did you rebuild the innards of the carb? You cleaned out the fuel line - compressed air and see stuff shoot out? You removed lines from fuel pump and put pressure tester on that, too? Didn't put fuel lines on backwards? What about the sender - did you pull that out of the tank? Mine was gone when I pulled it out. What about the aux fuel switch - did you try to bypass that with a piece of 3/8 fuel line going straight to main/rear tank? Does this only happen when under load/on demand, or when at idle in the driveway, too? What about seafoam into the tank? Is tank original? Hope these questions help start a good discussion. I've restored more than a few vehicles, and really it can be anything from replacing the gas cap or fuel tank or lines or pump or filters or carb jetting to anything in between. Verify that fuel delivery is not the problem, then look at ignition. You may, however, want to take a voltmeter (fluke is my choice) and measure voltage at the battery, and the alternator, and at the fuse panel. It would be odd, but possible if the voltage to the coil was bad, or the coil itself went bad. Many of my vehicles still run stock 12v coil...including the one on my 68 Bronco.

 

[67RT]

Blow out idle circuit with carb cleaner (pull idle mix screws and blow thru there) and then clean your electrical connections from distributor back thru to firewall. Pull apart, clean, and dielectric grease.
Mine had same issue and I am not sure what cured it but did both of these and it worked..

 

[Gweiner]

Wow, lots of great tips here. I will get to work on these today. Thanks guys. If it were not for this site, I would not have this Bronco.

 

[CopperRanger]

Also check for a vacuum leak, I had a big vacuum plug on the back of intake manifold pop off and was acting similar.

 

[valveamp]

Just wanted to mention my experience recently. I experienced symptoms something like yours. One difference was that it ran ok when I was on the freeway. But, if I came to a stop, it wouldn't idle and would die. After that, it was hard to stop. When it did get it started, I, sometimes, had gas pouring out of the vent holes in the top of the carb cover (Autolite 4100). It's a long story, but, in the end, it turned out that I had some type of contamination in my gas tank. It looked like black paint flakes that were being "ground up" and getting through the fuel. Still not sure where the flakes came from. The tank looked pretty clean inside. Maybe someone sprayed the inside at some point, I don't know. I replaced the tank, cleaned the carb, new filters and all is good now. I'd say check your carb. Good luck.

 

[Gweiner]

Thanks. I did see a few little black plastic looking flakes when cleaning out the fuel lines. My main tank is about 5 years old and plastic. Guess I need to drop that amd clean it out but hoping i dont need a new one since its not that old.

 

[ryan97]

Sounds like fuel system- filter, pump, lines or carb

 

[Justafordguy]

If you find no fuel/carb issues, Change the condenser in the distributor, sure sounds like the problem to me.

 

[SteveL]

X2 on the vacuum leak. Power brakes? Could be the booster going.

 

[jw0747]

If you find no fuel/carb issues, Change the condenser in the distributor, sure sounds like the problem to me.

x2. I would also change the points and be sure to set gap and dwell correctly or replace points and condenser with electronic component like Pertronix.

 

[Gweiner]

In the process of removing the rear main tank and removed the filler neck. Its got a decent amount of surface rust but no holes or leaks. Is there a way to clean this or should I buy a new one? Also, the bottom of the carb had some of the fine black particulates. Found more of it on the intake manifold. Is this coming from the tank or the lines? Or both?

 

[jckkys]

About 15 yrs. ago I had the main tank pick up filter get plugged up with what appeared to be rust. The truck is a '77 so the tanks are plastic, ruling out rust originating in the tank. I cleaned it out with simply water and haven't had the same problem since. Friends who worked as mechanics for many years told me, this happens when people fill up at a gas station that just got a fuel delivery, and the sediment in their tank is churned up and pumped into the customer's vehicle. If I see a tanker truck at a gas station, I move on to another one. Removing and cleaning a gas tank is a real PITA. If you have decent quality filters, nothing big enough to hurt the carburetor should get through. My Bronco is ONLY 40 yrs. old, but I can't think of any problem originating in the tank or lines. The stock filters last at least 10 yrs. The fine dirt in the carburetor may be small enough to get through the filters or come off the gaskets in the carburetor. All this being said, the problem could be something as simple as loose screws securing the points. In fact I would have looked at the internal functions of the distributor first.

 

[El Kabong]

X2 on the vacuum leak. Power brakes? Could be the booster going.

x3. A sudden change like that can be vacuum related. How is it while driving? A big vacuum leak will make it run terrible at idle, but sometimes will scream at WOT. It burns valves, so not a good performance trick.

 

[Gweiner]

Cant even get to idle smoothly. Stalls out. Tried everything. Could be a bad rebuilt carb bc everything else looks good on the fuel and ignition side of the equation.

 

[Deano]

Vacume line somewhere sounds like

 

[Gweiner]

All new vaccum lines. Will need to see if there is a vaccum leak elsewhere but not sure how to find it if I cant get the thing to even idle. Is there a way to pressure test for vaccum leaks with the motor off?

Sorry for the dumb questions. I am clearly not a mechanic and cant even pretend to be one.

 

[blubuckaroo]

Have you pulled the distributor cap off? Maybe moisture, a broken rotor tab, or loose point screw.
Also check to make sure all the plug wires are snapped into the cap real well. I've seen new wire boots fit too tight and actually unplug the wires from the cap by themselves.