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Eagle 258 Carter BBD hesitation. |
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zeebo76 
AMC Apprentice 
Joined: Oct/09/2019 Location: Washougal, WA Status: Offline Points: 158 |
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 Posted: Oct/18/2019 at 12:44am |
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Hey again everyone. I did a bit more testing after learning that I could read from the diagnostic ports with my voltmeter, and learned that AO and BO for the stepper motor both hover at exactly .86 volts. When looking down the barrel of the carb while the engine was running, the metering pins were stuck fully extended, and from what I've read they should have been flickering in and out rapidly just like the O2 sensor readings flicker. I think my stepper motor is bad, as has been suggested - is there a way to manually operate it just to check if it actually responds to power?
Before anyone says "nutter it", I know that the nutter bypass is very useful for simplicity's sake but AFAIK, if the computerized system works properly it gets far better gas milage than a nuttered car will because it's always optimizing itself for optimum air/fuel. So, I'm wanting to try and fix it. I've been told that the O2 sensor is functional, and all the sensors/switches I could test via the diagnostic ports other than the 4" vacuum switch along with the previously mentioned AO + BO work properly.
Edited by zeebo76 - Oct/18/2019 at 12:46am |
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farna
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Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19692 |
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Posted: Oct/18/2019 at 6:48am |
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Look at your wiring diagrams. You should be able to apply power to the stepper motor and move the pins. IIRC the polarity reverses to change direction and there are only two wires to it. Disconnect from the computer, ground one wire and momentarily power the other while watching the pins. If it doesn't move reverse the wires. Still doesn't move -- motor is bad. Do check the wiring diagram before doing this! I don't have a TSM with electronic BBD wiring handy... You are 100% correct on the Nutter Bypass!! It will make a car that has f'd up emission controls run much better, but it will run even better with the controls functioning properly. If you're going to ditch the emissions controls it's best to get a non-feedback carb (may as well go with a new Weber or Holley 2300) and change the dizzy to a pre emissions model (pre 1980). Then it may run like it should.
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Frank Swygert
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zeebo76
AMC Apprentice
Joined: Oct/09/2019 Location: Washougal, WA Status: Offline Points: 158 |
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Posted: Oct/18/2019 at 10:34pm |
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So I spent a while today trying to power/ground every combination of wire on the stepper motor - no dice. Motor is bad, I believe... I’m hoping that the computer still sends signals to it, so that the replacement I ordered ($90!!!) off amazon will work this time around.
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billd
Moderator Group 
Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Posted: Oct/18/2019 at 10:50pm |
Why? Why change distributor? Run a single vacuum hose from the ported vacuum nipple on the right side of the carb to the vacuum advance. Done. No reason to change the distributor. Run the stepper pins in and pull the plug and there's zero wrong with those BBD carbs. Not a single danged thing wrong with them except all the folks who don't understand them talking bad about 'em. I have owned several cars with them, and have worked on dozens of them. When someone knows what they are doing with them, they are fine. I recently bought a NOS one to have on hand if I ever get this other SX4 rebodied - gotta find a body for it first, though)
Anyway, by running the air pins in and disconnecting - that carb will be just as good as any other with or without that stepper. It's a matter of knowing what to do with it. And if anyone else has worked on it in the past, well, who knows - some gorilla think that tightening the screws a bit is good so a bit more is better - that'll warp and/or distort even carburetor BODIES, not to mention throttle bodies, tops, etc. Air bleeds - we used to tweak those on not just these, but certain other carbs, too, to "adjust" things. It got to the point in the last shop I worked at that people came in and asked for me by name and told the service manager they wanted me to do their "tune-up" (they cited better MPG, better performance, etc.) - the biggest issue I found was that too many who supposedly worked on carburetors couldn't even identify the basic circuits common to any carb. How the heck can they rebuild and tune 'em if they don't know the circuits, when and how they function, and how to ID them? |
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billd
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Posted: Oct/18/2019 at 10:59pm |
Frankly, if things are WORKING, there's not a thing wrong with these systems. It's just that no one knows about them, HOW to work on them, how they work, and refuse to bother with them because the web is full of thousands of things being repeated over and over about how much junk they are. People prefer simple, fast, easy, solutions to learning and fixing things correctly. Hey, these things are trash. I know they are because I keep reading how bad they are.
No wonder my boss used to call the internet the misinformation stupid highway. When tuned properly, and all things are working, they actually do quite well - performance is good (ask my first wife how fast our Eagle wagon got her to the hospital years ago when she went into labor! Man that car could SCOOT and had great take-off from a stop) It's so funny, too - just like kids are taught "Marconi invented the radio" (which is BS) people use the Nutter name because that guy was the first to draw it up and publish it to be widely seen - otherwise all that stuff was being done already, I bet years before he even owned such a vehicle. Nothing magic about it, just stripping the controls out and reverting to a basic 1960s configuration (but with electronic ignition) Frankly, I suggest proper troubleshooting methods, diagnosis, find and fix the REAL problem, and it will be fine. There's a whole lot of these cars out there with full factory equipment still connected, still working, still being maintained, all working fine. I think I even have some NOS emissions stuff laying around for Eagle - depending on year......... I know I have a NOS BBD carburetor here. |
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purple72Gremlin
AMC Addicted 
Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16614 |
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Posted: Oct/19/2019 at 10:38am |
And do you have a TSM? And is your car federal, high altitude or California emissions? Check that too
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farna
Supporter of TheAMCForum
Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19692 |
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Posted: Oct/21/2019 at 6:07am |
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Bill, if I were changing from the feedback system to an older carb and eliminating the smog controls entirely, I'd change the dizzy because the older ones are curved differently than the later smog units. It's not absolutely necessary, the engine will run fine with the smog dizzy. To be honest, I don't know how much difference there is, might not be enough to be worth changing. In general, however, the ignition curve is more aggressive on the earlier units than the smog/feedback units. Hmmm... with modern gasoline being quite a bit different than it was 20-30 years ago, the less aggressive timing might be a plus...
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Frank Swygert
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farna
Supporter of TheAMCForum
Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19692 |
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Posted: Oct/21/2019 at 6:15am |
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zeebo76 -- You can start the engine and probe the wires to the stepper motor from the ECU and see if you're getting voltage. I haven't looked at the wiring diagram, but when you start it's supposed to cycle the needles, so you should get voltage on one or more of the wires at start-up. Might need to have someone inside switch it on/start it. I don't think a remote starter would work -- I believe it cycles as soon as the switch is on, not just on engine start. check at switch on first, if nothing go ahead and start it. BillD probably knows which... I suspect it's switch on. Bill is the resident expert on the emissions and electrical controls of the smogged cars, especially the 83-88 Eagles.
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Frank Swygert
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MIPS
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Joined: Mar/11/2019 Location: Kamloops, BC Status: Offline Points: 347 |
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Posted: Oct/22/2019 at 12:14am |
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Stepper motor is a pulsed device. It will not move in or out if you just give it power. Refer to the below diagram (it's in the mechanics book on the page outlaying the CeC wiring diagram) to verify continuity at either end and the middle of the coils.
 The stepper motors are known to stick if you do not keep the carb clean. The upper pin sits in a portion of the casting that does not easily clean itself of dirt or oil coming in from the air cleaner. It's held onto the back of the carb with four torx heads, watch out for a spring as you remove it.
There's a pretty easy tester you can build that's an LED and a resistor between the phase pin at the diagnostic port and ground. The direction in which they flash indicates which way the stepper motor is moving. Refer to this video - https://youtu.be/b8B6m0SsMEk If you were a liiiitle bit closer I would offer to let you use my feedback tester the next time I'm down on the coast. Edited by MIPS - Oct/22/2019 at 12:30am |
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farna
Supporter of TheAMCForum
Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19692 |
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Posted: Oct/22/2019 at 6:48am |
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Glad someone familiar with these things stepped in!! I have VERY limited knowledge on the electronic BBD...
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Frank Swygert
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farna wrote: