zombie_stomp

I know EGR stands for Exhaust Gas Recirculating. The valve takes exhaust gasses and recirculates them through the intake manifold. This is for emission quality.

I have had a ghost of a problem with my 1982 pickup that showed up when I first got it. There were two main problems. The first was starting. It used to have hard starts so bad that starting fluid would have to be used. I rebuilt the carb and that part of the problem went away.

The other problem was intermittent running. It would not idle without either me pressing on the throttle or the engine being under load accellerating. At higher RPMs under load, it was running ok. Let the foot off the throttle, or light load, it would have very irregular, choppy power delivery.

I haven't tracked this performance condition to any one system, but thought it was an air leak somewhere. I made damn sure my remanufactured carburetor had a really good seal several times. The last time I reinstalled the carb was with a new hand-cut gasket with Threebond on all sides. That was good at first, but the problem came back, basically when it felt like it. Temperature differences didn't seem to be a constant. I changed fuel filters too. Every time the problem came up, the filter was full of fuel and had no large particles. I think the other rece. ntly replaced fuel filter was installed in reverse, but mine was true and correct. I even swapped fuel pumps.

The EGR was something that I had not much experience with. Someone here told me that if it was stuck open during the wrong time, it would suck in too much exghaust at the wrong time, maybe causing the problems I was having. The remedy was supposed to be tapping on it with a screwdriver handle to get the plunger valve to close. I tried that, but mostly got mostly random results from it. Most of the time, the condition would only correct itself after the engine cooled down for a while.

Suggestions? I can provide more information as soon as I have the time to get over the frustration I feel right now and run a few more tests.

I want to know what tests I might want to run. It's difficult to run tests on it when the problem presents itself, because the problem presenting itself is so random. As I said earlier, it ran for at least a month without the problem happening, and I thought it had worked itself out.

I will also come up with a list of things I've done to the truck to cross off any questions before they are asked.

the_supernerd

There is a fuel cut solenoid that cuts fuel to the idle circuit. You can try connecting that straight to the ignition to see if the problem stops. I am not exactly sure how the smog controls on your truck work, but on my truck there is a vacuum switch that shuts off the fuel cut solenoid when decelerating. If that was faulty I could see it causing problems.

You can plug the EGR vacuum line to keep the vacuum system from turning it on. That would rule out any vacuum switches on that system.

There is another system that seems to cut off the idle circuit in the early 22Rs and the 20R engines, but connecting the fuel cut solenoid directly to idle should help determine if that is the problem. I am not exactly sure what that system is, but I could do some research if you think that is the problem.

zombie_stomp

The main part of this problem is that it will not idle properly when the problem happens. I know there are a few electrical devices on the carburetor, and many more vacuum-powered emissions components tied in to the carburetor.

I want to find and check each one until I can prove what might be malfunctioning. It sounds like unless the fuel cut has a variable level that is not correct when the problem is occurring, it might not be the bad part. If it is just an on/off switch solenoid, it would seem unrelated if one of the symptoms is no idle.

If it is on when it it should be off, cutting fuel from the idle circuit, it would not idle. So if it is fuel cut switch related, I may want to look upstream from there to the components that cause it to turn on. I may need to look more into how it operates and at what times and why to gain a better understanding of how it works during my process of elimination testing regimen.

I take it that by the name, fuel is cut when the switch is "on", or electrified.

Is this a common faulty part? After I rebuilt my existing carburetor, the problem continued, so I bought and installed a remanufactured one. The problem happened again. While many of the parts on the reman carb LOOK new, I know that most if not all of them are just run through an ultrasonic cleaning bath, tumble finished, and sprayed with clear coat after assembly. I know that because my choke cut off diaphragm was a little clogged with clear coat when I got it. I pierced that with a tack and was able to manually suck and hear it work.

I want to know if it is common to be a bad part. I can go through the tests, starting with the simplest first.

I did disconnect the EGR vacuum diaphragm line. At the time, the problem was occurring. It persisted. I therefore ruled out the EGR as the cause of the problem.

A while ago, I was replacing vacuum lines and broke off one of the plastic connection nipples on the BVSV. That stands for Bimetal Vacuum Switching Valve. It is right next to the thermostat and is controlled by coolant temperature. I tried gluing it back on, but that failed. My last resort was to cap both lines off, and it ran the same as before without that switch linked into the system, as far as I could tell, nothing in the performance or seeming randomness to the problem had changed.

My Chilton 1970-1988 book does not have an emissions system layout for a 1981 federal and canada model, they start at 1984. But this Bimetal Vacuum Switching Valve has lines running to the vacuum modulator and EGR valve in the diagram that most closely resembles my memory of my emission system.

I pretty much already ruled out EGR as the cause of the problem, by disconnecting and plugging the line that turns it on when the problem was gone. I should mention that when it is happening, SOMETIMES, letting the engine cool down makes the problem go away at least temporarily. If it happens again after cooling down, it is usually after it has warmed up to full operating temperature again. (the other BVSV I have on the engine is one with three vacuum lines tied in. I do not have a picture in my manual with a 3-pronged BVSV like my truck has. I will be looking into a Factory Service Manual to try to track it down, or create my own diagram based on what I have and figure out the logic of my system.

This vacuum system is like a primitive logic controller. There are certain variables that exist while the engine is running under various conditions. I probably need to either figure out the emissions vacuum system completely so that I can understand the logic of it so trhat I don't A)throw a bunch of parts at it to try to fix it, B)delete the emission system completely out of frustration only to find that is was something else causing the intermittent problem, or C) rebuild the engine or replace it completely in vain, since I never pinpointed the probelm in whatever system was causing it. Basically, the easiest and most effective approach is to be meticulous, systematic, and rational; to "get smart" if I want to pinpoint what is wrong.

Wish me luck. The intermittent nature of the problem can ruin my mood in a heartbeat when it occurs!

the_supernerd

Intermittent problems can be the worst to diagnose! I doubt the fuel cut solenoid is bad, but the system operating it could be. Energizing it allows fuel into the idle circuit, and if it is wired backward then it does not work (I know from experience ). The truck will still idle, but very rough. I would start by replacing the BVSV, since you know that is an existing problem. You can most likely find one in a junk yard for cheap. Shorting the fuel cut solenoid to a separate switch or straight to the ignition will help rule out that system.

zombie_stomp

I found a way to test the fuel cut solenoid. It did the problem on and off on the way home. I tried to hook up and test the cut solenoid while it was under the problem condition, but I didn't have the right electrical connections and although I was in the home depot parking lot, I figured I'd save testing for when I got home.

I arrived with the condition in effect, but had to eat first. By the time I got back to start it, it idled normally. So I disconnected the electrical plug from the carburetor and the engine stopped running right away. I got in and tried keeping it running with the gas pedal, and it behaved much the same way as before, but maybe less sputtering. When I connected the fuel cut solenoid, I heard it click on right away. It's good.

The next test will need to be checking if it's getting electricity when the problem occurs. Just because the cut solenoid tested good doesn't necessarily mean there isn't something up with the fuel cut vacuum port. I'm going to look into these two systems and test some more. But not today.

I'm glad to have found something that replicates the condition that I could test.

It may be a long process of figuring out, but at least I could maybe have a switch wired up temporarily until I figure out how to test it. I hope it isn't some impossible hard-to-locate mystery loose connection in the electrical system.