Best Performance Open Loop / Closed Loop?

93gtmustang · Feb 6, 2008

Does a fuel injected 5.0 have the best performance when the engine is cooled off, or when it is at operating temperature. I think the answer has something to do with the computer operating in closed loop or open loop. I'm not sure on this matter, that's why I'm posting this question.
I've read articles where they try to get the engine as cool as possible so that the intake is cool, thus putting cooler air into the motor. Is this to an advantage when drag racing, or do you actually get better performance when the engine is at operating temperature?
Thanks for the help!

vristang · Feb 6, 2008

This could turn into a big can of worms, but I'll jump in anyway...

Performance will be better with cooler intake/coolant temps. Oil still needs to be at operating temps.
The problem is that the ecu will enrich the mixture based on lower ECT (coolant) temps.
For this reason, it is usually recommended that we stick with a 180F t-stat...

Will you get better economy with cooler intake temps???
I have seen evidence against it, but can't say for sure...

jason

347 Pony · Feb 7, 2008

From everything I have ever learned a cooler car runs faster, also it is better for the computer to run in a open loop so it uses all your mechanical settings, when it closes the loop it uses settings programed by Ford. I have always heard it is better to confuse the computer so it stays open. I have always run a 160 thermostat and haven't come across a reason not to yet. I am sure there wil be replies to this with 300 reasons to use a 180 though, its all personal prefference only you know what you like and if you listen to your car it will tell you what it wants.

vristang · Feb 7, 2008

OL vs CL

Open Loop is a fuel strategy used by the ecu during WOT, Cold Start, and some error conditions.
During OL, the ecu will ignore the output of the O2's sensors. Fuel is metered based on the fuel tables loaded in the ecu.

Closed Loop allows the ecu to look at the O2 sensors, and make minor changes to the fuel metering. The ecu always pushes the AFR (based on readings from the O2's) toward stoich.
During CL operation, the ecu will 'learn' what fuel changes need to be made based on what fuel changes have been made in the past.

Here is the part that starts to get a little confusing...
The correction factor that is learned in CL operation, is applied to OL operation.
This is why changing fuel pressure for more power is usually effective for a short time ONLY. After the ecu compensates for the fuel pressure change, the AFR should return back to stoich (or as close to it as the ecu can get).

There are several things that need to happen in order to run in OL.
For a specific period of time after the engine is started, the ecu will run in OL mode.
Switching to CL will occur after a min ECT temp has been reached.
Once in CL, the ecu will return OL when the TPS signal increases to indicate a WOT condition.
Obviously there are other ways to get to OL, but this makes the point..........

The point is...
Tricking the ecu to run exclusively in OL will affect cruising performance as well.
Fuel economy will suffer.
There is an increased chance of 'fuel wash' in the bores... which would lead to premature bore wear. (this depends on other things as well)

Personally,
I don't see any reason to force the ecu to run exclusively in OL.
There are some risks and negative aspects to doing this, and I can't see any potential benefits that would make it worth the effort.

just my take on it though,
jason

93gtmustang · Feb 7, 2008

So ,in a drag racing situation.
Run the car as cool as possible, or run it at operating temperature?

tmoss · Feb 9, 2008

vristang said:
This is why changing fuel pressure for more power is usually effective for a short time ONLY. After the ecu compensates for the fuel pressure change, the AFR should return back to stoich (or as close to it as the ecu can get).

If you have increased the fuel need of the engine the adpative feature will not take fuel out that is needed, so an increase in fuel pressure after a head change and/or intake change will be effective long term - the EEC will not have to increase pulse width as much with the KAM stored lamnda factor. The EEC will then fine tune with the O2s around the new fuel requirements.

vristang · Feb 9, 2008

tmoss said:
If you have increased the fuel need of the engine the adpative feature will not take fuel out that is needed, so an increase in fuel pressure after a head change and/or intake change will be effective long term - the EEC will not have to increase pulse width as much with the KAM stored lamnda factor. The EEC will then fine tune with the O2s around the new fuel requirements.

I agree completely.
I should have been more careful about how I phrased that...

Pushing the AFR away from stoich with fuel pressure is pointless, as the ecu will just use the KAMRF's to bring the AFR back to stoich...

Black1987Stang · Feb 10, 2008

hrspwrjunkie said:
A little trick for the '86-'93 crowd, before you make your pass down the drag strip, turn the key to on, but don't fire the engine for ten seconds, this will allow the computer to sample the Barometric pressure via the BAP/MAP sensor and adjust accordingly. Without doing that, it won't read Barometric pressure, it will just correct for the mass of air provided you have MAF on the car and aren't running speed density.

Wouldn't it do it the first second you turn the key to ON before you get to the crank cycle when turning the key (maybe 1/4 second more like)? I don't see why it would need 10 seconds to read it, the sensor will be adjusted to the corresponding altitude so the instant you give the computer power it will see that voltage right away? someone correct me if I'm wrong, I've been wondering this for a while.

Mustang5L5 · Feb 10, 2008

93gtmustang said:
So ,in a drag racing situation.
Run the car as cool as possible, or run it at operating temperature?

You want the engine at operating temp (coolant, oil, internals, etc) but you want the incoming air to be as cool a possible.

Usually hot engines heatsoak the engine bay so incoming air is heated up as well. This is usually why most people associate a hot engine making less power.

Cooler air is denser and therefore contains more oxygen to make power.

I still love Ford's idea with the 3rd gen lightning that was never produced. They tied the A/C system in with the intercooler. When cruising, the A/C would kick on and cool an evaporator in the intercooler really cooling down intake temps. At WOT the a/c would **** off (therefore robbing 0HP) and the plate would remain cool for about 10-15 seconds for some increased power. When you return to part throttle, the a/c would kick back on and cool down the coil again.

Very cool idea that worked well.

If only something like that for the 5.0 could be made up. I bet guys wouldn't ditch their A/C's as early.

vristang · Feb 10, 2008

hrspwrjunkie said:
The computer will run best when running closed loop because it is recognizing and dealing with changing environmental and engine conditions. In open loop, it has little if any input from the sensors to tell it if it has a change in operating conditions, thus it can't and isn't programmed to correct for operating conditions.

It should be noted that the only sensors that the ecu ignores during OL is the oxygen sensors...

vristang · Feb 10, 2008

hrspwrjunkie said:
... when it isn't running it will have barometric pressure and thus a reference point for current weather conditions. This is also good if you've stopped your car in the mountains or otherwise had a dramatic change in altitude.

I have read this before as well... probably in the Probst book

I'm not sure if this is how the ecu really works though?

I would think the BAP coding would be treated similar to the tps... in sampling is always being done.
I can't see why Ford would only take one sample for BAP, and ignore the sensor the rest of the time

Has anyone looked into this empirically?

jason

mustangfan1990 · Feb 10, 2008

well IMO I personally dont even run a T-stat. When my car is driving down the road the car might run 125 or colder according to my gauge. Now I hear that is not good to do that, but my car is not a daily driver. My O2s are not even hooked up because my car is so low that it ripped the wiring harness to my senosors off. When I am driving my car or even drag racing it, I have no problems whatsoever and it runs strong as hell. My gas mileage isnt all that bad really. I mean its not good, but not bad either. I am not concerned about gas mileage considering its not my daily driver. IMO I would think the car would run better cold.

tmoss · Feb 10, 2008

the SD computer has to use the key on sample to store baro because after that the engine is running and it won't see baro again until the car is turned off again. I doubt it takes seconds.

vristang · Feb 10, 2008

mustangfan1990 said:
well IMO I personally dont even run a T-stat. When my car is driving down the road the car might run 125 or colder according to my gauge. Now I hear that is not good to do that, but my car is not a daily driver. My O2s are not even hooked up because my car is so low that it ripped the wiring harness to my senosors off. When I am driving my car or even drag racing it, I have no problems whatsoever and it runs strong as hell. My gas mileage isnt all that bad really. I mean its not good, but not bad either. I am not concerned about gas mileage considering its not my daily driver. IMO I would think the car would run better cold.

Wow!

All I can say is

WOW!!!!

mustangfan1990 · Feb 10, 2008

vristang said:
Wow!

All I can say is

WOW!!!!

I know I know lol but you would be surprised how good it really does run

Mustang5L5 · Feb 10, 2008

mustangfan1990 said:
well IMO I personally dont even run a T-stat. When my car is driving down the road the car might run 125 or colder according to my gauge. Now I hear that is not good to do that, but my car is not a daily driver. My O2s are not even hooked up because my car is so low that it ripped the wiring harness to my senosors off. When I am driving my car or even drag racing it, I have no problems whatsoever and it runs strong as hell. My gas mileage isnt all that bad really. I mean its not good, but not bad either. I am not concerned about gas mileage considering its not my daily driver. IMO I would think the car would run better cold.

You are damaging your engine running that cold. Engine oil needs to be at a certain temp to flow properly. Running too cold doesn't allow it to get up to proper temp and wear in increased. You may think it runs fine, you are doing a lot of harm in the long run.

Modern fuel injected engines NEED to be run inthe 180-210 degree range for proper lifespan. A cold engine doesn't make more HP. COLD AIR makes more HP

As for running with no O2's? I'd put them back

With is as much money as you have invested into your engine, i don't understand why you would do such a thing.

mustangfan1990 · Feb 10, 2008

Mustang5L5 said:
You are damaging your engine running that cold. Engine oil needs to be at a certain temp to flow properly. Running too cold doesn't allow it to get up to proper temp and wear in increased. You may think it runs fine, you are doing a lot of harm in the long run.

Modern fuel injected engines NEED to be run inthe 180-210 degree range for proper lifespan. A cold engine doesn't make more HP. COLD AIR makes more HP

As for running with no O2's? I'd put them back

With is as much money as you have invested into your engine, i don't understand why you would do such a thing.

I am going to replace the O2s and the wiring it just got ripped off driving down the road...I just got a sided track with me buying the vortech that is on its way.... and I mean the motor has got up to like 190 if I am stuck in traffic, but I turn the fan on and it will drop to maybe 170 but if I am driving non stop it runs cooler....

vristang · Feb 10, 2008

tmoss said:
the SD computer has to use the key on sample to store baro because after that the engine is running and it won't see baro again until the car is turned off again. I doubt it takes seconds.

Mustang5L5 · Feb 10, 2008

mustangfan1990 said:
I am going to replace the O2s and the wiring it just got ripped off driving down the road...I just got a sided track with me buying the vortech that is on its way.... and I mean the motor has got up to like 190 if I am stuck in traffic, but I turn the fan on and it will drop to maybe 170 but if I am driving non stop it runs cooler....

Even 170 is too cold. Put a 180 in it minimum. Too much of a temp swing while driving is bad. Different parts of the engine cool and expand at different rates, so if it's 190 while idling and drops to 160ish when you start moving, things will cool at different rates and cause excessive wear.

795.0pacecar · Feb 11, 2008

hrspwrjunkie said:
I don't have empirical data, but I understand the reasoning behind it, which is the same reason the BAP sensor was deleted in the '94 and later cars, the MAF can read the amount of air entering the engine, which is what really matters, thus the BAP sensor becomes superfluous.

I'm not really sure why they left it on the car, but it does baseline the computer during the initial start if it is sampled during ignition on/no start/no running.

And, yes, this info is from the Probst books.

This isn't entirely true. Ford deleted the BAP sensor in 94 because they learned the barometric pressure could be calculated once the MAF sensor tells the computer the amount of air ingested by the engine.

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