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Thread: EEC III CFI rough idle on cold start

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    What a Luxury car should be. mercurygm88's Avatar
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    Default EEC III CFI rough idle on cold start

    Anyone here intimately familiar with EEC III CFI? The Mark VI has been idling really rough on a cold start for awhile now. I've been ignoring it because 1. I don't drive it that often 2. You give it the tiniest bit of throttle and it goes away until you let off the pedal, one good 1/4 to 1/2 throttle rev and it goes away until the next cold start. It idles just fine when the engine is started warm, the only thing I've tried it adjusting the idle up and down slightly with the adjustment on the throttle kicker solenoid, that doesn't seem to make a difference. It doesn't do it when the weather it cold because the choke takes over. Should I have it set so the electronic choke still engages in hot weather?

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    GMN Regular DerekTheGreat's Avatar
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    Yeah, since these don't actually compensate the A/F ratio when cold, the choke pull-off mechanism should still engage when started cold. Doesn't it have a high speed position and then a lower speed position as it warms up? If so, try and adjust it so it sets to the lower idle speed. EDIT: It may be sweaty hot out there to you, but the engine is still very much cold at those ambient temps.
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    I'm an air-conditioned gypsy gadget73's Avatar
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    Its just a high idle mechanism, might need to engage even in warmer weather. Should be able to loosen it and rotate to adjust how long it takes to drop out.

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    What a Luxury car should be. mercurygm88's Avatar
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    I currently have it set to not engage in this warm of weather. Iíll mess with it and find where it engages and see how it goes.

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    Depending on your results, it might be better off that way.
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    What a Luxury car should be. mercurygm88's Avatar
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    I moved it to where it just grabs the first notch on the choke. It's definitely better now, it wasn't a huge deal anyway just a minor annoyance.

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    With my EEC-IV CFI cars, which mechanically work the same way and just have a smarter brain behind the operation, they want the high idle mechanism to operate even in hot weather.

    The 85 is straight up broken; 5 to 10 seconds of a tiny bit of throttle pedal helps it behave better when allowed to come back to idle. The 84 seems to work fully correctly, and it'll rev pretty high at whatever setting it drops on even in hot weather (haven't looked at it/don't remember, but I think it's the second-lowest setting). Tapping the pedal will then drop it by another setting, and then the final drop comes after a couple minutes of running (which ISTR is done by the computer via vacuum to force it to drop even if the choke thermostat hasn't gotten there yet).

    There is no choke. The CFI unit just happens to use choke-style idle controls and uses a choke thermostat as a form of mechanical timer.

    I don't think it's accurate to say the computer is unable to compensate for cold starts by adding fuel. Adding fuel (and playing with timing) is actually all it can do. The problem is it needs more air, and since this system does not have an IAC or electronic throttle stepper, the ways it is able to obtain more air are kind of archaic.

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    GMN Regular DerekTheGreat's Avatar
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    Yes, no choke, but if I remember right it's still labeled "Choke pull-off mechanism" or something like that.

    I do think it's accurate to say that about the computer, as that was my conclusion with my '85. Adding more fuel when cold is all it would need to do when cold, not more air. That's what a choke does in carb'd car; fuel flow stays the same but it reduces the air flow coming into the carb, thus richening the mixture. Something about being cold and the fuel condensing on the intake runners and dropping out of suspension within the air, science, science stuff I don't fully understand ect. You can get around that by increasing the velocity at which the air/fuel mix flows through those intake runners, which is exactly what Ford chose to do with V8 CFI. You can prove this by taking one of your carbureted cars, disabling the choke such that it's wide open and then starting it cold. Hold the throttle such that once it lights off, it's approximately winging at about 2000 rpm. It'll run just fine. More RPM in addition to more fuel seems nice, as that promotes more oil flow and probably reduces the chance of valvetrain noise.
    Last edited by DerekTheGreat; 07-21-2022 at 06:58 AM.
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    You're correct that more fuel is needed for a cold start, for reasons related to those you listed. However, CFI is already able to add that fuel. It is not able to raise the idle speed by adding air. So the high idle linkage is serving the purpose of adding air, and the computer is going to give it [correct amount of fuel for the amount of open throttle]+[an additional amount of fuel based on the cold temperature].

    Nothing about how the CFI throttle body works allows a mechanical or manual "enriching" function; all that "choke-ish" linkage is doing is adding air (and providing ability for the computer to cancel adding that air re: the pull-off). The computer does the rest.
    Last edited by kishy; 07-21-2022 at 09:55 AM.

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    I'd love to measure the exhaust mixture or look at fuel tables, but my experience and tinkering told me my '85 did not richen the mixture for cold starts or cold drivability. If it did, I'd suspect it would be able to sustain a much lower idle speed despite still being cold. For example, my 1989 K1500 has similar fuel injection set up, only it has an IAC and can enrichen for cold starts. When I start it even in the winter, it starts around 1300 RPM and comes right down to 1000 until it warms up to the point of closed loop operation. I've even unplugged the IAC, still runs when cold. SEFI stuff will run cold too, could be the difference between port fuel injection and traditional induction though. However, my '85 CFI would not idle lower than 1500 RPM when cold, so I compromised and adjusted the pull off linkage crap such that it idled around 1800, I believe the sticker on the fan shroud wanted it to go around 2,200 rpm, just absurd. If I tried to lower the idle while cold, I could hear it start to drop off due to running lean. The only thing I don't have to support this is the hard data of the actual fuel mixture. However, I feel I did a damn fine job tuning the carb on my '69 Plymouth. While I tinkered with that, same type of systems. At one point I had both cars at the same time and that's what helped speed me along to my conclusion about the lack of CFI to provide cold start enrichment.

    However, I'd be convinced otherwise if someone showed me factory fuel tables from an EEC-IV and EEC-III V8 CFI ECM for both cold and hot running conditions. That or maybe you could even hook a wideband O2 sensor to your car and show me what it does cold vs warm at the same idle conditions. Or try this, start your '84 cold. Pop the air cleaner lid and use your hand as a rudimentary choke. See if you can take the idle down without it stalling. I don't know why I never tried that with my '85.
    Last edited by DerekTheGreat; 07-21-2022 at 12:14 PM.
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    The fuel mix is very much influenced by the air and coolant temp sensors. If those are bad though, it won't get the fuel mix right and there is no way for it to correct until the coolant sensor reaches whatever point is required for it to start looking at the oxygen sensors.

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    GMN Regular DerekTheGreat's Avatar
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    I'm sure with CFI they do anything but help enrichen the fuel for cold starts/drivability.

    Although I am going to run an experiment with my truck. Going to let it get up to temp, unplug the IAC and then try and start it & drive it the next morning. If it behaves like my CFI car did, then there's fuel for the fire which suggests CFI does enrichen the fuel mixture for cold starting/drivability. However, with the way my CFI car behaved, it wouldn't even idle in park at less than 1500 RPM when cold before sputtering and dying. My truck already idles at 1000 RPM when cold with zero issues. Riddle me that..
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    Lost and driftin' Arquemann's Avatar
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    My CFI was rich on cold starts, tbh it was rich everywhere
    Seriously though my CFI ran alright when cold, just had to keep it from stalling with some throttle.
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    The longer this thread persists, the more I am glad I've never had a CFI experience.

    *queue rust free CFI wagon at a reasonable price near me*

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    GMN Regular DerekTheGreat's Avatar
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    Oh I'd snatch another EEC-IV CFI car in a flash if I had the cash haha. I'm just genuinely curious and now not so convinced of my previous position. Science will commence! My car ran great once it was where Ford wanted it, just had to fight the brakes with how eager the car was to move when cold. Once it was off the choke-pull-off gizmo & warm, it was great, loved driving it and it was pretty miserly on fuel. Would bark the tires from a stop. Miss that car, may it rest in peace.

    Maybe there was something wrong with my car. Kishy, what's the lowest RPM your '84 will maintain when started cold?
    Last edited by DerekTheGreat; 07-22-2022 at 10:20 AM.
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    Quote Originally Posted by DerekTheGreat View Post
    Oh I'd snatch another EEC-IV CFI car in a flash if I had the cash haha. I'm just genuinely curious and now not so convinced of my previous position. Science will commence! My car ran great once it was where Ford wanted it, just had to fight the brakes with how eager the car was to move when cold. Once it was off the choke-pull-off gizmo & warm, it was great, loved driving it and it was pretty miserly on fuel. Would bark the tires from a stop. Miss that car, may it rest in peace.

    Maybe there was something wrong with my car. Kishy, what's the lowest RPM your '84 will maintain when started cold?
    This is my experience so far as well. Figuring this out was a very minor inconvenience considering how well this thing runs overall. Iím getting about 20mpg overall. Iíve never taken it on a road trip, I donít particularly like pushing it to interstate speeds, 55-60 is where it seems happiest.

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    Quote Originally Posted by DerekTheGreat View Post
    I'm sure with CFI they do anything but help enrichen the fuel for cold starts/drivability.
    Its been known since the beginning of cars that fuel mixtures need to be richer on cold starts, and they had temperature sensors to know when the engine was cold. There was also the ability to add more fuel by lengthening the pulse width of the injector. It would be inconceivably stupid for them to ignore both the input and output control to make the fuel mix fatter for easier cold starts. The one thing this version of CFI lacks is the ability to add more air to go with that extra fuel. The 3.8 CFI cars at the end did have electronic throttle speed control but it never got to the V8 cars.

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    Quote Originally Posted by mercurygm88 View Post
    This is my experience so far as well. Figuring this out was a very minor inconvenience considering how well this thing runs overall. I’m getting about 20mpg overall. I’ve never taken it on a road trip, I don’t particularly like pushing it to interstate speeds, 55-60 is where it seems happiest.
    Indeed. I never drove my '85 far either, unless you count running for an hour or hour and a half a long drive. Those speeds are where my SEFI car is happiest too, well, 55-65. Beyond that, it seems like it struggles but it will do them. Perhaps a bit better than my CFI car did. However, I'm pretty sure my CFI car was a 3.08. 3.23's might just be enough to make a difference.

    Quote Originally Posted by gadget73 View Post
    Its been known since the beginning of cars that fuel mixtures need to be richer on cold starts, and they had temperature sensors to know when the engine was cold. There was also the ability to add more fuel by lengthening the pulse width of the injector. It would be inconceivably stupid for them to ignore both the input and output control to make the fuel mix fatter for easier cold starts. The one thing this version of CFI lacks is the ability to add more air to go with that extra fuel. The 3.8 CFI cars at the end did have electronic throttle speed control but it never got to the V8 cars.
    Yes, I agree with everything you've said. But as I've pointed out, that hasn't been my experience. I don't remember needing to increase the idle speed of my Holley equipped 318 in my Plymouth when I used my hand as a rudimentary choke. Plenty of cold start/first start nonsense out there with carb'd cars which shows the same chit. Those cars are idling much lower than my CFI was able to, hence all my curiosity. If you've been reading my responses, now even I am not so convinced about my original position. I now suspect that they do make an adjustment, just not much of one. Out of genuine curiosity, I mean to try an experiment with my truck and why I asked kishy about the lowest RPM his will run at when started cold, all mentioned in the very response you quoted, but conveniently left out of said quote Perhaps mercurygm88 can try that too. Also try it with his hand acting as choke as he tries to lower the idle. Science + curiosity! I know my SEFI car ran at like 500 rpm when cold, but perhaps being port fuel injected helped it run that low. Not an apples to apples comparison so that probably shouldn't be mentioned.

    I've always wondered why Ford did not add an IAC to the V8 cars but did with the V6 stuff, especially when I learned EEC-IV CFI ran on the panther cars for two years and not just one.
    Last edited by DerekTheGreat; 07-25-2022 at 06:23 AM.
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    Quote Originally Posted by DerekTheGreat View Post
    Kishy, what's the lowest RPM your '84 will maintain when started cold?
    Cold, or like, cold-cold?

    A cold start in weather like we've had lately, it will start on the lowest idle speed setting (e.g. no pedal-push to set the fast idle), but it idles very low and threatens to stall. Never put a tach on it but I'll guesstimate it in the 400s, and it's so rich it'll burn your eyes if you go hang out by the tailpipe. Once it's been running a couple minutes it's happier. Curb idle warmed up is whatever the sticker says under the hood. 550ish?

    In the winter, it needs to race or it just won't do it. Setting the fast idle for 1900 per the book is what I did and that is how it is best behaved. I tried lower and it just wouldn't do it.

    As above - the computer sees TPS and load, and knows a certain amount of gas needs to go in there. It also sees temperature and knows that the temperature acts like a factor; a multiplier, for that amount of fuel.

    When you push the pedal on a carb car, you are doing two things: setting the choke, and setting the fast idle. Despite the same parts being engaged to operate both functions, they are distinct functions that don't actually need to be related. The choke blocks air to create vacuum on certain passages that will now draw in more fuel, enriching the mix, and this happens whether or not the idle is up. The fast idle increases the air flow through the throttle, whether or not the choke is closed. One adds fuel, one adds air. Together, they facilitate the thing to cold start.

    When you push the pedal on a CFI car, you are only setting the fast idle. The choke doesn't exist. All you're doing is giving it more air. The computer is giving it the gas, and not only is it giving it the gas, it's also giving it the correct enriched amount for winter at the high idle speed...which is even more than it would have had to be at curb idle speed.

    I promise you, the computer is doing the enriching just fine. It is literally the only thing it even knows how to do: mix fuel for the amount of air it believes is there at the temperature it believes it to be.
    Last edited by kishy; 07-25-2022 at 10:46 PM.

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    GMN Regular DerekTheGreat's Avatar
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    Yes, both instances! Thank you for the response, a lot of good information. I don't think my CFI car would idle without the choke-pull off mechanism engaged unless it was warm or already hot. In the cold cold, it was just as you experienced- would not do it unless it was screaming away at 1800 or 1900RPM.

    LoL yes, I know all about what you're doing with a carpitator. I did own that '69 Plymouth equipped with a 600 CFM Holley that I bought and installed upon it. Even bought a Holley book so I could school myself on them. I did a damn fine job tuning that thing too, once I figured out how everything worked. Main jets, accelerator pump nozzles & cams, accelerator pump diaphragms, secondary springs, vacuum gauge to assist with tuning blah blah blah. I took all the choke stuff off. As my one buddy who bought it for me to work on said, "Are you a sissy? You don't need it!" I drove that thing around in the dead of winter. However, I never tried the impromptu choke thing on it in the winter, only in the spring/summer. I suspect now that you guys are right in that they need more air when temps are below freezing to prevent fuel from dropping out of suspension within the intake manifold. The stuff I mentioned where the carpitated thing was sustaining low RPM's but cold? All started when it was probably above 70F. Edit: And honestly, it makes sense that they do enrich for cold starts or at least have the capability. Like duh, don't they go rich when you jam the go pedal to the floor? Sometimes my ideas and thought processes are a little less than half-baked.

    I still have not disconnected my IAC on my truck. Too lazy. I will get to it though. Probably when I mow my lawn next as I gotta get gas for all the junk required to maintain it and that's when I put on grungy clothes and intend on getting dirty.
    Last edited by DerekTheGreat; 07-27-2022 at 10:02 AM.
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