I posted a week or so ago about trying to figure out how to pass a smog test in Idaho on an '84 with the 300 I6, feedback carb, no smog pump... but there is a more pressing issue at hand now.

Over the course of the past week, I noticed the idle getting progressively more rough. Very gradual in onset; also noticed that at idle RPM's would slightly fluctuate. Today I tried to take a quick trip to run an errand and the motor was idling so rough that I thought the engine was going to jerk itself loose of the motor mounts. Popped the hood and it was visibly jerking and vibrating, managed to limp it home.

Later in the day, I couldn't get it to start at all. Jerk, cough, die, etc; but no start.

Misfire I figured. Replaced plugs and wires, but distributor cap that Auto Zone sold me is clearly way too big; tried to tell them, but they insisted that it was the right one. So I'll return that tomorrow and replace that unit.

Anyway, got the truck to start with the new wires and plugs but super rough until warm up, now idling rough ( no variation in idle as I was experiencing before, just rough ) and driving rough ( feels gutless, very little power ). Higher RPM doesn't seem to smooth it out at all.

I have searched high and low for instructions on how to read the EEC-IV code; however, I cannot locate the two-part plug that I need to jump and read with a voltmeter. It's nowhere in the engine compartment that I can see.

Some of the threads I read while searching for a solution instruct the user to "replace all vacuum lines". This is the first carbureted vehicle I have ever owned, so the task is a bit daunting. I can't seem to track down a step-by-step on this, or even a diagram/schematic of what should be replaced.

I did find three screws on the carb. One facing the away from the engine block. It is all the way tightened, if I loosen it, seems like the truck will die. The other two are next to each other on the engine side. Closest to the firewall did nothing on adjustment; farthest from the firewall adjusted idle RPM... so I bumped it up a few.

I would really like to see if the computer can point me in the right direction, but I get the feeling from what I have read that it is a fruitless endeavor to check if you aren't sure the vac lines are in working order.

Any tips? Much appreciated.

 

Assuming you have a 300 six cylinder? Or no? Some v8's had this system also.

 

Sorry about that. Yes, 300 straight six.

 

Grab the carb and try to wiggle it. If it moves, some of the screws may have worked loose, a common problem with these. You have to take it apart a little bit to tighten them up.

 

Thank you Dave. No wiggle or play, very firm.

 

Can you verify that the choke is working? Is it closed when engine is cold, then opens a little when engine starts, then fully opens when engine is warmed up?

If you have an EGR on your truck it could be sticking partially open. That will cause a rough idle and hard start/poor performance (depending on far open it is stuck).

I wouldn't jump right to replacing all vacuum hoses - but you should inspect them without removing them. First, be sure none have fallen off, then flex them some looking for cracks/tears (especially the bottom side).

There are so many things at this point it's hard to know where to start.

I would have suggested not to start turning the mixture screws on the carb - as it is unlikely that they changed position by themselves. Now that you turned them, once you get the main problem fixed you'll need to go back and reset them.

IMO. Good luck.

 

Let me make sure I understand how to check the choke. If I key-on/engine-off and press the accelerator it should close the choke almost all the way, correct? I do know that when it warms up, the choke is open.

Then again, I am assuming that the choke is the flat metal piece the opens/closes on the top of the carb to restrict air flow (first carbed vehicle for me here).

 

Yes. You got it (Ignition key position doesn't matter though). Just trying to rule out various things.

PS. Don't forget to change the fuel filter too.

 

Well, the choke works like it should I think. Pressed the accelerator, heard a click, and checked and saw that the choke was closed.

I happened to have a fuel filter on hand. Went to replace it and the nut that torques the line onto the filter was rounded off. Managed to remove it ok, but in putting it back on, I broke a plastic piece off of a sensor. The sensor has a black rubber line that goes to a nipple that sits on the top right of the carb, almost exactly to the right of the fuel filter.

So I need to replace the fuel line. Should I stick with steel or get some kind of flexible line that uses hose clamps... or maybe better (if it exists) a flexible steel braided line with fittings on each end.

Either way, fuel line is the least of my worries. Any ideas what that sensor is? I am going to try to get the other side of it off of the line and see if there is a part number on it.

 

Here's a picture of the sensor:





Nipple on the top going to carb broke off. The line heads to the top right of the carb, directly right of the fuel filter.

Any ideas what this is? I read L-90982-A2A

 

Looks like the bowl vent solenoid. Is that an electrical connection on the bottom? http://www.theautopartsshop.com/carb...d/micx239.html (example)

Regarding replacing the line. You can get a fitting from the parts store or someplace like Summit that has a short barb on the end then run fuel hose to it. Something like this (but you need to verify the size) http://www.summitracing.com/parts/hly-34-21/overview/

just be sure to protect the hose anyplace where it could touch something sharp or hot.

 

In case anyone down the line wonders, the original part number was D8TE-9B982-B2A, now referenced as CX239. CountryBumkin was correct, bowl vent solenoid.

 

Replaced the fuel line and installed new cap and rotor. Bowl vent solenoid is on the way via mail. If I plug the vacuum tube coming out of the card that would have gone to the solenoid, it seems to run ~slightly~ better, but pretty much back to square one before I replaced the fuel filter.

 

Also, incidentally, I found the connectors to read the engine diagnostic codes. My voltmeter and test light attempts were unsuccessful, so I broke down and bought a Ford OBD-I code reader... the diagnostic light stays solid red no matter what; maybe a byproduct of having all of the smog components missing?

 

After replacing the fuel filter (and line), with the bowl vent solenoid missing, the truck would barely idle. However, I noticed that the PCV valve was leaning a bit on the valve cover and when I pulled it out with the engine running, things got better, at least to the point where I could drive. So I grabbed a new PCV valve and replaced all of the lines.

I am more or less back to square one. Rough idle, rough running. After it warms up, if I plug the line that went from the carb to the bowl valve solenoid, it seems to pick up a bit; but again, still more rough than I am comfortable with.

In summary, so far replaced:
Fuel filter and line
PCV valve (and grommet), and lines.
Plugs, wires, cap, and rotor.

If a new bowl vent solenoid doesn't do the trick, what should I check next?