EEC III CFI rough idle on cold start

[mercurygm88]

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. 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.

[gadget73]

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.

[DerekTheGreat]

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.

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.

[kishy]

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.

[DerekTheGreat]

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.

[Arquemann]

Fuel atomizes poorly in a cold engine, that's why adding more fuel keeps it running better. Fuel injection doesn't need a choke as much since injectors atomize fuel way better to begin with.
In a CFI system the fuel injectors are far away from the cylinders, so the fuel has more time to condense in the intake, running worse.

With the wideband O2 in my MGM, I can see easily that with a cold engine and no choke, it's running leaner due to poor atomization. Pop the choke on and it runs richer and smoother. Honestly I should've gone with a manual choke.
I've got a (old school) mechanic friend who says that a stock engine with a well tuned carb should start and run in the summer, without choke.
Another friend of mine daily drives a '65 Rambler American, which doesn't even have a choke from the factory, during winter he just holds the throttle cracked for a while until the engine stays running by itself. No unnecessary nonsense is his motto, probably.

[mercurygm88]

Has anyone here ever replaced the vacuum diaphragm that releases the high idle? I noticed mine hasn’t really been working so I replaced it last night and the original was totally disintegrated. What I’m curious about is there was a long spring in there and I’m wondering if it was supposed to be contained in the diaphragm or does that go back in the assembly?

[kishy]

Has anyone here ever replaced the vacuum diaphragm that releases the high idle? I noticed mine hasn’t really been working so I replaced it last night and the original was totally disintegrated. What I’m curious about is there was a long spring in there and I’m wondering if it was supposed to be contained in the diaphragm or does that go back in the assembly?

I have replaced that diaphragm, yes. Its function as I understand it is to allow computer control of high idle - specifically, so the computer can override all of the mechanical bits and drop the idle speed off high idle based on temperature and time values.

The long spring is normal, and you are supposed to reassemble it using the spring as it was before. I believe the spring's function is to ensure the mechanism returns, to prevent high idle from being impossible to set in case the linkage did not return.

[mercurygm88]

I managed to get the whole thing back together and amazingly it works like it’s supposed too.

[sly]

I managed to get the whole thing back together and amazingly it works like it’s supposed too.

Always a plus.