Pesky problem

[grouch]

I've got a pesky problem that has me stumped. I've got a 1984 W-150 Dodge pickup. 318 automatic. It doesn't want to idle. It will run fine down the road but idles poorly when cold and stalls when warmed up. My trouble trees keep telling me I have an ignition failure. Work done so far include swapping the engine controller with a known good one, rebuilt carburetor (the old one cracked), new fuel filter, cap and rotor, plugs (cap rotor and plugs were routine mantenance), vacuum reading is 16 inches, timing is spot on, air filter is clean, base of carburetor and intake have been checked for vacuum leaks and all vacuum lines are properly sealed. Either with new hoses or plugged off. The coil is several years old and is an aftermarket performance unit. I plan to remove the pcv hose and plug it off lest it be sucking too much vacuum although I think that will show up on the vacuum gauge.

Any ideas of what else it might be? I don't like throwing parts at a problem but may have to start.

[DonTom]

"rebuilt carburetor "

"It doesn't want to idle."

Does it sound okay at higher RPM's, or does it seem to be missing? What do the bottom of the plugs look like? All rich? Some different than others?

But I am going to take a guess that you replaced your bad carburetor with another bad carburetor. Rebuilt carbs that don't idle seem like the norm these days, IMO.

But, if not, can you tell if all 8 cylinders are firing? You didn't mention anything about replacing the ignition wires. At least check them with an ohmmeter.

-Don-

[grouch]

"rebuilt carburetor "

"It doesn't want to idle."

Does it sound okay at higher RPM's, or does it seem to be missing? What do the bottom of the plugs look like? All rich? Some different than others?

But I am going to take a guess that you replaced your bad carburetor with another bad carburetor. Rebuilt carbs that don't idle seem like the norm these days, IMO.

But, if not, can you tell if all 8 cylinders are firing? You didn't mention anything about replacing the ignition wires. At least check them with an ohmmeter.

-Don-

The plugs are text book clean. Just enough discoloring to show some useage. The wires are also fairly new. I've been leaning to the carburetor and I think I got a 1 year warranty on it. There is a slight miss at slow speeds but it will hammer down the road just fine. All sorts of power that the old carburetor didn't have. I'm trying to find a good coil to swap in but those aren't something I save when I part a car out. Before I pull the carburetor though, I may enrich the mixture screws quite a bit and see what that does. I don't drive this truck much but swapped my other pickup off for some work on the house. When I drove it today, I had to shut the heater off and open the vents. My scraper and heavy gloves are still in it. The installation instructions said I shouldn't have to adjust any screws so I never bothered the mixture screws.

[DonTom]

"The installation instructions said I shouldn't have to adjust any screws so I never bothered the mixture screws."

I wouldn't bet on it.

-Don-

[Eric]

I've got a pesky problem that has me stumped. I've got a 1984 W-150 Dodge pickup. 318 automatic. It doesn't want to idle. It will run fine down the road but idles poorly when cold and stalls when warmed up. My trouble trees keep telling me I have an ignition failure. Work done so far include swapping the engine controller with a known good one, rebuilt carburetor (the old one cracked), new fuel filter, cap and rotor, plugs (cap rotor and plugs were routine mantenance), vacuum reading is 16 inches, timing is spot on, air filter is clean, base of carburetor and intake have been checked for vacuum leaks and all vacuum lines are properly sealed. Either with new hoses or plugged off. The coil is several years old and is an aftermarket performance unit. I plan to remove the pcv hose and plug it off lest it be sucking too much vacuum although I think that will show up on the vacuum gauge.

Any ideas of what else it might be? I don't like throwing parts at a problem but may have to start.

Which carb are you using?

I agree with Don that most of today's "off the shelf" rebuilds are complete junk. The only ones worth using are new (not "rebuilt") Holleys or Carter AFB/Q-Jets made/old through Edelbrock and so on.... you may have simply replaced one bad carb with another bad carb....

[grouch]

I think I may have found the problem on my pickup. It doesn't get driven much so I haven't fooled with it for a while. I don't like something that doesn't work right though. I decided to pull the carburetor and see if the idle ports got gummed up from sitting even though the new carburetor wasn't that old. When I pelled the unit off, I turned it over to drain the float bowl. (Over some weeds of course.) There wasn't any fuel in the carburetor. My Jeep had the fuel pump fail from this wonderful gasoline we get now. I'll bet I've got as pinhole in the pump diaphram. I've been on 12 hour shifts all week so I'll be replacing the pump this weekend. The Jeep only had about 50 miles on the pump when it failed completely. (It sits a lot and the fuel went sour.)

[Eric]

I think I may have found the problem on my pickup. It doesn't get driven much so I haven't fooled with it for a while. I don't like something that doesn't work right though. I decided to pull the carburetor and see if the idle ports got gummed up from sitting even though the new carburetor wasn't that old. When I pelled the unit off, I turned it over to drain the float bowl. (Over some weeds of course.) There wasn't any fuel in the carburetor. My Jeep had the fuel pump fail from this wonderful gasoline we get now. I'll bet I've got as pinhole in the pump diaphram. I've been on 12 hour shifts all week so I'll be replacing the pump this weekend. The Jeep only had about 50 miles on the pump when it failed completely. (It sits a lot and the fuel went sour.)

I've been hearing a lot about problems with older/carbureted vehicles being fed gas with high alcohol content, I can eat right through rubber, etc. not designed for "modern" gas.... so far, the Q-Jet on my Pontiac has been ok, though...

[DonTom]

"There wasn't any fuel in the carburetor."

I assumed you did the obvious basic checks and checked the fuel pressure first!

Always remember the basics during troubleshooting anything. IOW, if you have fuel, compression and spark, it will most likely run.

But if all at the correct times and fuel pressure, then it MUST run.

The troubleshooting of the basics has not changed over the years. IOW, this stays true even with the newest gasoline cars. Even computers and all that will not change the basic troubleshooting.

-Don-

[grouch]

"There wasn't any fuel in the carburetor."

I assumed you did the obvious basic checks and checked the fuel pressure first!

Always remember the basics during troubleshooting anything. IOW, if you have fuel, compression and spark, it will most likely run.

But if all at the correct times and fuel pressure, then it MUST run.

The troubleshooting of the basics has not changed over the years. IOW, this stays true even with the newest gasoline cars. Even computers and all that will not change the basic troubleshooting.

-Don-

The truck is idling now, but not right. I've sprayed for vacuum leaks, cleaned the carburetor, replaced the fuel pump (the old one had a crack in the actuation lever) and done everything else I normally would do. When I get time, I'll bypass the ballast resistor as those puppies can cause problems and look okay. I'm also going to pull the coil and check it. Coils rarely fail but this is an aftermarket unit. It helped power and mileage when I put it on. Coils rarely fail though. I think I've replaced two as a repair in my entire life.

[DonTom]

"I'll bypass the ballast resistor as those puppies can cause problems and look okay."

I had those fail too. However, I have only seen them completely open and kill the engine and then no restart. Those are cheap enough to replace, and are a common failure item. I wouldn't bypass it which will increase the current to everything in the primary ignition system. A least not for more than a few seconds. However, I've done it myself in a 1974 Dodge for a quick test and sure enough that was the problem (stuck on the freeway, even drove it home with the jumper (two miles). I am not sure how safe it is to do on later vehicles. I wouldn't worry about the coil as much as the ECM and other more expensive stuff.

-Don-

[grouch]

"I'll bypass the ballast resistor as those puppies can cause problems and look okay."

I had those fail too. However, I have only seen them completely open and kill the engine and then no restart. Those are cheap enough to replace, and are a common failure item. I wouldn't bypass it which will increase the current to everything in the primary ignition system. A least not for more than a few seconds. However, I've done it myself in a 1974 Dodge for a quick test and sure enough that was the problem (stuck on the freeway, even drove it home with the jumper (two miles). I am not sure how safe it is to do on later vehicles. I wouldn't worry about the coil as much as the ECM and other more expensive stuff.

-Don-

I used to fool with mostly Mopars and have seen just about every type of failure the ballast resistor can have. I remember one time the car would run but poorly. It wouldn't speed up but would cut out. The resistor had almost, but not quite, corroded through and was partially melted. I suspect the carb. is the problem but I want to make certain it isn't anything else before I spring for a rebuilt, $200 unit. I don't like to spend more money than I need to but I will spend money if needed. I just want to make sure I only spend it on stuff that needs replacing.

[DonTom]

"I remember one time the car would run but poorly. It wouldn't speed up but would cut out. The resistor had almost, but not quite, corroded through and was partially melted. I suspect the carb. is the problem but I want to make certain it isn't anything else before I spring for a rebuilt, $200 unit. I don't like to spend more money than I need to but I will spend money if needed. I just want to make sure I only spend it on stuff that needs replacing."

Resistor must have had higher resistance than normal or became intermittently open when it warmed up. I cannot remember for sure now, but aren't they 1.5 ohms or so? Resistors are a lot cheaper and easier to deal with than carbs. Low primary ignition voltage will give a weak spark. Do you have a way to check that?

Anyway, be sure to let us know what the problem was after you get it all fixed. IMO, carbs are much more difficult to troubleshoot and I assume it's the carb when I cannot find anything else wrong.

-Don-

[grouch]

I pulled my carburetor off and tore it down to rebuild. Since I have other vehicles, I took the casting to work to check under the microscope. It looked like a crack in the body near where the venturi assemblies attach. I put some prussian blue high spot indicator on it and there was a web of cracks that one could only see under a microscope. While I was poking the body, the large piece the venturi attached to broke off. I put another unit on it and it's idling now. It's not idling right but the truck has so many modifications that I have to tune it. I'm just glad we don't have emissions testing here. At least when cold weather sets in, I'll have Betty running again.

[Eric]

I pulled my carburetor off and tore it down to rebuild. Since I have other vehicles, I took the casting to work to check under the microscope. It looked like a crack in the body near where the venturi assemblies attach. I put some prussian blue high spot indicator on it and there was a web of cracks that one could only see under a microscope. While I was poking the body, the large piece the venturi attached to broke off. I put another unit on it and it's idling now. It's not idling right but the truck has so many modifications that I have to tune it. I'm just glad we don't have emissions testing here. At least when cold weather sets in, I'll have Betty running again.

Just curious: What type of carb is this? An AFB?

[grouch]

Just curious: What type of carb is this? An AFB?

It's a Holley 2 barrel. I put 20 miles on and have to pull it and replace it. I got a leaker. The engine was running as smooth as it has in years but I started smelling gasoline. With the engine running, a stream of fuel was dribbling onto the intake where the exhaust cross over ports run, hence it's very hot. Nothing like hot gasoline under the hood near ignition sources.

[Eric]

Just curious: What type of carb is this? An AFB?

It's a Holley 2 barrel. I put 20 miles on and have to pull it and replace it. I got a leaker. The engine was running as smooth as it has in years but I started smelling gasoline. With the engine running, a stream of fuel was dribbling onto the intake where the exhaust cross over ports run, hence it's very hot. Nothing like hot gasoline under the hood near ignition sources.

Outside of very high performance/track day type applications, I am not a fan of the Holley carb. It has a very basic/primitive idle circuit, crude choke system and a tendency to blow out power valves - and while it's great at WOT, it is not the best choice for street driving. A Rochester 2 barrel (or Q-Jet/AFB) would probably work a lot better for you.

[DonTom]

"A Rochester 2 barrel (or Q-Jet/AFB) would probably work a lot better for you."

EFI would be even better, of course! ;D

-Don-

[Eric]

"A Rochester 2 barrel (or Q-Jet/AFB) would probably work a lot better for you."

EFI would be even better, of course! ;D

-Don-

But would cost massively more - and involve massively more hassle to install and dial in.

Assuming a good core, one can completely rebuild to "as new" a Rochester 2 or 4-bbl carb for about $100. Bolting it on takes about 10 minutes. Done. Ready to drive. And unless it's a modified/non-stock engine, the OE carb ought to perform very close to perfectly right out of the box, too.

[DonTom]

"But would cost massively more - and involve massively more hassle to install and dial in. "

With my RV EFI conversion, there was only one adjustment, fuel pressure, which took all of a half minute or so. The computer did the rest (after the IC is programmed).

The biggest hassle now will be finding a way for the return fuel line. The item I used to but the gasoline back into the filler pipe is no longer available.

BTW, I think most EFI systems today in newer vehicles don't use a return fuel line. They now have a way to regulate the fuel pressure with no return line.

-Don-

[grouch]

An EFI conversion will run between $1000 and $3500. To go with a 4 barrel, I need to source a kickdown rod assembly for the 318. A 360 will work but they are rare. I've got a 4 barrel intake to put on but it messes up the transmission without the kickdown rod. Since I'd like to get a newer truck eventually, I'll just fix this and keep it until I replace it.