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Thread: Idle Surge - 1984 5.0 Thunderbird, CFI, EEC-III, Duraspark III

  1. #1
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    Default Idle Surge - 1984 5.0 Thunderbird, CFI, EEC-III, Duraspark III

    Hello Gentlemen,

    I've been visiting this forum a lot for a long time now, ever since I first started to love Fox body Fords. This is my first time actually making a post, as I have finally encountered a problem I can't nail down. I've seen a lot of problems get solved on this forum. I'm hoping mine can soon be one of those.

    Here's everything I know so far:

    The Car:

    - 1984 Ford Thunderbird (my second Fox-Bird)
    - 5.0L (302 CID)
    - CFI (Central Fuel Injection)
    - EEC-III (No OBD or self test connector. Limited trouble code ability available by attaching a 12V test light to one of the solenoids.)
    - Duraspark III (Non-adjustable timing. Distributer is basically just a shaft with a gear on one end and a rotor on the other. Computer judges spark advance/retard using a crankshaft position sensor.)
    - Recently redid the exhaust system. Ditched the old pipe and replaced it with some 2.5 inch truck pipe I had lying around. Glasspack muffler.
    - Removed the A/C because it didn't work and was in the way.
    - New air filter, recently changed all fluids and filters (including fuel filter).
    - New ignition switch.
    - Added water temp, oil pressure, and volt gauges.

    The Problem:

    ... is a surging rough idle that occurs only in park and neutral. The rough idle and surge exist at any RPM. If I shift into any other gear the surge stops, the engine smoothes out and any other negative sounds disappear. The car drives like normal (actually it drives GREAT). No stall or hesitation. The surge immediately returns if I shift back into neutral or park. The only other symptom is high NOX in my last smog test. (Test was done yesterday. Everything else tested well within the "green".)

    What I've tried so far:
    - New rotor, plugs, dist. cap, plug wires.
    - Replaced voltage regulator because it looked like it'd seen better days.
    - Checked base timing, all good.
    - Removed EGR and the throttle body and gave both an extremely good cleaning. (EGR looked new when I was done.) All new TB and EGR gaskets.
    - Tested EGR position sensor: good. Replaced o-ring anyway.
    - Replaced all nylon vacuum lines with steel vacuum lines. I got tired of them breaking. There are definitely NO vacuum leaks. Vacuum off the manifold measures at about 17 inches. I'd expect it to be higher, but I think once this surge is gone it will be. No fluctuations in vacuum during surge.
    - Examined the entire wire harness. Fixed any exposed wires or cracked insulation. There are no ground faults or broken circuits.
    - Opened EVERY wiring connector and thoroughly cleaned all of them.
    - Adjusted the curb idle to no avail (if anything, now it surges more).
    - Tested all solenoids, all good.
    - I attached LEDs to the solenoids to see when which were getting turned on by the computer and checked to make sure that they were indeed coming on.

    Everything seems to be functioning normally.

    I reset the computer and then drove it for 15 miles after every one of these changes. Sometimes there is no idle surge after resetting the computer. But then I pull into my driveway thinking it's fixed, shift into park, and start banging my head on the steering wheel because the surge is back again.

    Other than that I've been poking around with a multimeter, unplugging sensors to see what happens, reading A LOT of articles and forum posts and getting really frustrated.

    I wish the car was either EFI, so my problem would be the IAC (there is no IAC in CFI), or a standard carbureted system, so there would be no computer or electronics to argue with (like my dad's 400). Instead I'm stuck somewhere in the middle.

    My current suspect is the electric choke and crank position sensor, as I'm not really sure how to test them (other than sticking a voltmeter on there and going "yup! That's a reading!").

    I'll try to make a video of it and post it to YouTube tomorrow. No promises though, the internets are a bit slow around here.

  2. #2
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    A long time ago when my 84 still had the CFI, I had the same problem. I went through what you are going through now. In a nut shell, I found the wiring harness going to the dist had wires with brittle insulation inside the plastic wire loom that would touch intermittently and cause the problems listed above. That might be it......might not, just my personal experience.
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    is the TPS new?
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    oh wait? does it have one on an 84 cfi?
    ***** Project "EVOLUTION" 1987 Cougar LS & 1985 Cougar Convertible *****

    5.0 HO 306 roller block, machined GT-40P heads, Wiseco dished forged pistons, Eagle forged floating I-beam connecting rods, Lunati pushrods, ARP bolts, Scorpion aluminum 1.6 rockers, Comp Cams Magnum 266HR, Explorer intake, 65mm TB, MAF Conversion, 19# injectors, Ford Racing stainless P-headers, 2-1/2" cat-less exhaust w/ Flowtech Afterburner mufflers , SC AOD with 2800 BDR torque converter, 3.73 T-Lok rear, CHE rear control arms, full 2-1/2" frame w/1" jacking rails & seat supports, Rear disk brakes, Turbine wheels, All original interior w/ floor shift upgrade .......
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    Quote Originally Posted by daminc View Post
    oh wait? does it have one on an 84 cfi?
    It does. I picked this car up off of craigslist for $300. Great deal, but there are a lot of hillbilly repairs that were done to it over the years that I've been going over and making right.

    The TPS looks newer than the rest of the throttle body, but I've never replaced it.

    However, after today I am definitely suspecting my fuel delivery system. I did a pressure test and I was getting 45 psi while the engine was running, but zero psi just before start and right after shut off. I replaced the fuel pressure regulator valve and that fixed that.

    While I had the TB off again, I noticed that the fast idle kickdown felt loose. I opened it up and the vacuum diaphragm was completely worn out. So I replaced that too.

    I then did another idle speed adjustment, this time also adjusting the fast idle, and reset the computer again. Now the car runs like crap in ALL GEARS. So I have somehow either made it worse or just more apparent. But, there also now more symptoms The injectors are pulsing with the surge. They spray a normal mist most of the time but when the car surges the injectors spray out more fuel. I thought that the injectors were supposed to spray fuel at the same rate all the time? Also, does anyone know what color the tops of the injectors are supposed to be? Because these look green and I thought the 302 injectors were blue. I have a lot of injectors lying around from other cars. I've heard of people using CFI injectors in EFI, anyone ever tried the other way around?

    At the same time my throttle kicker actuates a little bit. It had not been doing this before, but it makes sense that it would.

    Also, as far as any wires going to the distributor this is a Duraspark III so there a none except the one from the coil and the plug wires.
    Last edited by crossalchemist; 07-08-2011 at 02:29 AM.

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    I just know that when I do find the problem it is going to be something bonehead stupid obvious and ridiculously expensive. Btw, a new fuel pressure regulator is $100 from CarQuest. Thought I'd mention in case anyone ever ends up needing to find one.

    With a working regulator you should get 39 psi and it should hold that pressure for a good long while after you shut off the engine. My new regulator takes an hour before the gauge drops a little.

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    Also, I figured out how to test the electric choke and it seems to be fine. Mine draws about half an amp while the engine is running which is supposedly normal according the the shop manual I have.

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    Your original post sounds very similar to my currently being ignored issues. Except if I don't warm her up till the needle gets on the blue bar she dies when you put her in reverse. But, since my car rarely idles longer than it takes to warm her up I'm ignoring it till I have the funds to get a code scanner, from there I'll decide depending on the issue whether to go carbed or to just fix the issue.

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    Seems to be a common problem for the 83/84 5.0 and if you do a search you should find several folks asking the same question without a definitive answer. I had/have this problem on my 83 from time to time and I actually recall it doing it when it was still fairly new. I've been collecting some spare electrical parts to swap next time I have the problem to see if anything works. At one point I thought it was fuel related since it would occur more ofter right after I filled up the tank. Don't know if the carbon filter/etc would have anything to do with it or not? It's aggravating and difficult to diagnose when it happens.

    EEC-III is useless for codes. I just picked up a Ford EEC III - EEC IV Training Program 5-Day Technician Certification manual so I should be able to fix anything soon!

    Good luck, keep us posted.
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    An old mechanic friend had a throttle body and intake from an 85 5.0 Tbird laying around which he gave me for the parts. His TPS was newer than mine so I went ahead and swapped them. Now the car will idle, but refuses to idle at less than 700 to 800 RPM. If I set the curb idle any lower than that it starts surging again. However, I think I've at least figured out why it's surging, though still not what's causing it.

    It doesn't feel like a hunting surge where the computer can't find the right idle speed, it feels more like an emergency response. If I lower my curb idle to where 550 RPM should be and then watch the tach I can see that the RPM lowers to almost 550 or 600 and then it surges up to 800 and then slowly goes back down to 600 and then surges up to 800, etc. etc.

    I think that the car is about to stall at low RPM and it reacts by kicking the throttle for a second, then it slowly returns to my curb setting. This is supported by the fact that with the idle set that low the car will not start. I have to set the idle up a bit to start it and then lower it again. Trouble is I can't pass smog with the idle up around 800 (I got a "Idle RPM Outside Manufacturer Spec." checkmark on my smog sheet) and the car can get up to 20 MPH just with the gear engaged, so a slower idle is a must have.

    Another interesting item is that the computer adjusts the timing way off from the base. The base time is 10 degrees BTC, but while it's running it reads as 20 degrees BTC. Is this normal or is my computer really compensating for something?

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