Jon Posted September 7, 2017 Share Posted September 7, 2017 My 84 F150 with 4.9 L will run only on the gas I pour into the carb. Once it runs out of the gas poured into the carb, it stalls and won't restart (unless I pour more gas in the carb). I've disconnected the fuel line from the carb and cranked over the engine, and the fuel pump appears to be working. I've replaced the fuel filter, but that didn't make a difference. This truck has the feedback carburetor, and I notice that the wires that come from the feedback solenoid (see white arrow in picture below) are disconnected. But I can't figure out where these wires connect to. Can anyone out there verify where these should connect? Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 7, 2017 Share Posted September 7, 2017 Jon - You say the fuel pump appears to be working, but didn't say how you know that. Presumably that means it pumped gas into a coffee can or some such when you cranked the engine. If that is correct the needle in the carb is probably stuck on the seat, not letting gas into the bowl. To unstick that try rapping the top of the carb sharply with a screwdriver handle right above where the fuel line goes in. If that doesn't work after several tries I think you will have to disassemble the carb, and when you have it apart I would replace the needle and seat as well as the gaskets. On the wires, I don't have a 1984 Electrical & Vacuum Troubkeshooting Manual (EVTM) on this site, but I do have a 1896 version. You can get to it via the navigation menu to the left (Electrical/EVTM/1986 EVTM), and on Page 56 you can see a feedback control solenoid with a red wire and a tan/light green wire. Might that be it? If so, you have to think about if you need it connected, and that depends on both whether you have emissions tests as well as what ignition system you have. Do you have an ignition module on the fender, and if so, what is the color of the grommet where the wires go in? Or, do you have a vacuum advance on the distributor? Link to comment Share on other sites More sharing options...
85lebaront2 Posted September 7, 2017 Share Posted September 7, 2017 Jon - You say the fuel pump appears to be working, but didn't say how you know that. Presumably that means it pumped gas into a coffee can or some such when you cranked the engine. If that is correct the needle in the carb is probably stuck on the seat, not letting gas into the bowl. To unstick that try rapping the top of the carb sharply with a screwdriver handle right above where the fuel line goes in. If that doesn't work after several tries I think you will have to disassemble the carb, and when you have it apart I would replace the needle and seat as well as the gaskets. On the wires, I don't have a 1984 Electrical & Vacuum Troubkeshooting Manual (EVTM) on this site, but I do have a 1896 version. You can get to it via the navigation menu to the left (Electrical/EVTM/1986 EVTM), and on Page 56 you can see a feedback control solenoid with a red wire and a tan/light green wire. Might that be it? If so, you have to think about if you need it connected, and that depends on both whether you have emissions tests as well as what ignition system you have. Do you have an ignition module on the fender, and if so, what is the color of the grommet where the wires go in? Or, do you have a vacuum advance on the distributor? Ok, I just looked, 84 could have an EEC-IV system and the 86 EVTM is probably fairly close. I was afraid it might have had the MCU setup which had a potted computer box on the inner fender. Easiest way to see if the stuff is still there, look at the distributor, if it has a vacuum advance then the system has probably been removed, if not then the carburetor may just need a rebuild. Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 7, 2017 Share Posted September 7, 2017 Ok, I just looked, 84 could have an EEC-IV system and the 86 EVTM is probably fairly close. I was afraid it might have had the MCU setup which had a potted computer box on the inner fender. Easiest way to see if the stuff is still there, look at the distributor, if it has a vacuum advance then the system has probably been removed, if not then the carburetor may just need a rebuild. Bill - Thanks. That certainly helps. Jon - Show us some pics of the distributor and the module on the fender so we can tell what you have. Link to comment Share on other sites More sharing options...
Jon Posted September 7, 2017 Author Share Posted September 7, 2017 Bill - Thanks. That certainly helps. Jon - Show us some pics of the distributor and the module on the fender so we can tell what you have. Thanks, guys. I tried rapping on the carb - no luck. It does look like the wires from the feedback solenoid are red and tan (with dots?). I haven't had a chance to look at the wiring diagram yet. Here are the pics: Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 7, 2017 Share Posted September 7, 2017 Thanks, guys. I tried rapping on the carb - no luck. It does look like the wires from the feedback solenoid are red and tan (with dots?). I haven't had a chance to look at the wiring diagram yet. Here are the pics: You have the thin-film ignition system, which means you have a computer running the ignition and trying to control the carb. But, since the feedback control is unplugged it cannot control that, and the computer will have its knickers in a twist. In fact, it is possible that it is in limp-home mode and has your ignition timing locked. If so, your performance could be a lot better. Do you have to pass emissions tests? Link to comment Share on other sites More sharing options...
Jon Posted September 7, 2017 Author Share Posted September 7, 2017 You have the thin-film ignition system, which means you have a computer running the ignition and trying to control the carb. But, since the feedback control is unplugged it cannot control that, and the computer will have its knickers in a twist. In fact, it is possible that it is in limp-home mode and has your ignition timing locked. If so, your performance could be a lot better. Do you have to pass emissions tests? I don't need to pass emissions, I'd just like to get the truck to run. I'll take a look at the wiring tomorrow and see if I can figure out where the wires connect. Based on the diagram, I should be looking for a bunch of red wires that tie together, and the tan looks like it goes into a connector at pin 58. Thanks for directing me to the diagram, I don't have the shop manual for the '84 (I do for the '81, but that doesn't have the feedback carb) and I don't think my Haynes or Chilton shows this diagram either. Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 7, 2017 Share Posted September 7, 2017 I don't need to pass emissions, I'd just like to get the truck to run. I'll take a look at the wiring tomorrow and see if I can figure out where the wires connect. Based on the diagram, I should be looking for a bunch of red wires that tie together, and the tan looks like it goes into a connector at pin 58. Thanks for directing me to the diagram, I don't have the shop manual for the '84 (I do for the '81, but that doesn't have the feedback carb) and I don't think my Haynes or Chilton shows this diagram either. Haynes and Chilton manuals aren't in the same league as the Ford documents like the EVTM and the clips from Ford's Master Parts Catalog like I have on my web site. On the ignition, since you don't have to pass emissions testing you might consider a DS-II conversion. We don't, yet, have a how-to on these conversions on this forum, but FTE does. Go here and scroll down a bit to the Ignition and EEC (Electronic Engine Control) section. Basically the situation is that you have a computer that controls the ignition timing as well as the carb's air/fuel ratio. An EEC system. It can't be happy since it isn't controlling the carb, so probably has the ignition timing locked, meaning there's no advance and that kills the power. But, you can change to a DuraSpark-II system, which Ford used for many years on non-computer controlled vehicles. It takes a different wiring harness in the engine bay, a different distributor, coil, and ignition module, but is pretty well plug & play. The only real option you have to get the truck running well is to make the computer happy, and that requires giving it all the inputs and outputs it was supposed to have. We already know that the carb isn't connected, but what else isn't? Link to comment Share on other sites More sharing options...
JimsRebel Posted September 8, 2017 Share Posted September 8, 2017 I don't need to pass emissions, I'd just like to get the truck to run. I'll take a look at the wiring tomorrow and see if I can figure out where the wires connect. Based on the diagram, I should be looking for a bunch of red wires that tie together, and the tan looks like it goes into a connector at pin 58. Thanks for directing me to the diagram, I don't have the shop manual for the '84 (I do for the '81, but that doesn't have the feedback carb) and I don't think my Haynes or Chilton shows this diagram either. This really sounds like a needle and seat problem in the carb. You can try hooking a hose up to the carb fuel inlet, you should be able to blow a mouth full of air fairly easily. You can lift the top off the carb for a quick look, the float should hang down as you lift it up. As far as the wires on the carb feedback solenoid (white arrow) this is not the reason your truck won't run. My wires are not connected to anything. "Based on the diagram, I should be looking for a bunch of red wires that tie together, and the tan looks like it goes into a connector at pin 58" The computer provides a logic low (GRD) on pin 58 when needed for leaning the mixture. I do not believe the computer gets any feedback regarding whether the feedback solenoid is really working or not. Unless it is waiting for a lower reading on the O2 sensor as it goes lean. Jim Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 8, 2017 Share Posted September 8, 2017 This really sounds like a needle and seat problem in the carb. You can try hooking a hose up to the carb fuel inlet, you should be able to blow a mouth full of air fairly easily. You can lift the top off the carb for a quick look, the float should hang down as you lift it up. As far as the wires on the carb feedback solenoid (white arrow) this is not the reason your truck won't run. My wires are not connected to anything. "Based on the diagram, I should be looking for a bunch of red wires that tie together, and the tan looks like it goes into a connector at pin 58" The computer provides a logic low (GRD) on pin 58 when needed for leaning the mixture. I do not believe the computer gets any feedback regarding whether the feedback solenoid is really working or not. Unless it is waiting for a lower reading on the O2 sensor as it goes lean. Jim Jim - Good input. Given that the timing may not be locked. So, once he gets it running he can determine that with a timing light. Thanks! And I take back what I said about the only option to getting the truck running right is to go DS-II. Let's wait on that until you get the truck running. Link to comment Share on other sites More sharing options...
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