Unplug the coolant temp sensor

[eco]

Your fuel pressure on the eec 4 system isnt real critical as far as making adjustments. It concentrates on regulating air flow. It regulates air flow, while using a fuel pressure thats basicly "set". The o2 sensors will measure the oxygen in the exhaust, not the fuel.

Since the computer in an EEC-IV system does not monitor fuel pressure in any way I can see why it isn't critical to the computer.

But, oxygen is a "leanness indicator" in that the higher the oxygen content in the exhaust the leaner the mixture is and the less oxygen in the exhaust the richer the mixture. Adding fuel to the mixture would yield less oxygen in the exhaust and the O2 would pick up on that and adjust accordingly - right?

 

[blacksnapon]

Since the computer in an EEC-IV system does not monitor fuel pressure in any way I can see why it isn't critical to the computer.

But, oxygen is a "leanness indicator" in that the higher the oxygen content in the exhaust the leaner the mixture is and the less oxygen in the exhaust the richer the mixture. Adding fuel to the mixture would yield less oxygen in the exhaust and the O2 would pick up on that and adjust accordingly - right?

Its only picking up on the amount of oxygen. Oxygen is consumed in combustion. So, if there is anything that makes an incomplete burn (too rich, fouled plug, etc.) thats all it knows. There are holes in the eec4 ability to adjust fuel strategies. Thats why it doesnt pay attention to fuel pressure, too much information! The eec5 is different.

 

[Bob Ayers]

Just to add to what has been thrown out here, the computer has a table assiciated with WOT fuel curves, and part of it is for learning. Over time the computer see's what fuel trims work at various engine loads and rpms and applies this to WOT operation. So because of this the motor will operate leaner in WOT than it will in OL, but it's will still be richer than CL. The last time I has the Tweecer hooked up I seem to remember the motor was running in the low 13's A/F ratio at WOT, but the computer had just been put back in so all it's learning had been wiped out.
In any event, disconnecting the ECT will certainly force OL and a rich mixture, and this will produce more power, but if you leave it this way it will also produce more engine wear over time as the fuel will wash more of the oil from the cylinders.

Not true. The fuel table is fixed at WOT, but on vehicles with knock sensors, the timing table will be "learned" to the point before pinging starts. On vehicles without knock sensors, the timngs tables are also fixed.

 

[conanski]

Not true. The fuel table is fixed at WOT, but on vehicles with knock sensors, the timing table will be "learned" to the point before pinging starts. On vehicles without knock sensors, the timngs tables are also fixed.

I gonna have to agree and disagree with your disagreement, and then I must also correct myself. There is a table for adaptive learning of fuel trims,(actually a table for each O2 sensor on the mustang computers), but it is not associated directly with WOT as you point out. It's values are obtained from closed loop operation, and the resulting values are used for calculations in a number of conditions which can include WOT.

I'll also add that it is typically only the newer distributorless engines that can advance timing to the point of detonation. The control systems from this era don't have this ability for the most part, total spark advance is fixed(based on several tables) and the knock sensor can only remove a fixed amount if it senses detonation.

 

[eco]

Its only picking up on the amount of oxygen. Oxygen is consumed in combustion. So, if there is anything that makes an incomplete burn (too rich, fouled plug, etc.) thats all it knows. There are holes in the eec4 ability to adjust fuel strategies. Thats why it doesnt pay attention to fuel pressure, too much information! The eec5 is different.

The literature that I have indicates that a richer the mixture means less oxygen in the exhaust and a leaner mixture means more oxygen in the exhaust.

I am not a chemist, but the literature that I have indicates that the oxygen in the combustion chambor gets "used up" with the hydrogen and carbons (HC) during combustion. More HC in the mixture means less oxygen out the exhaust an visa versa - right? I have always thought that it was the O2 sensors job to look at this.

This isn't anything that I "know for a fact", but rather what I have read in a book.

I have an oscilloscope and an exhaust gas anaylzer so I am able to monitor the O2 sensor and watch the AF ratio. I will play around with this and see if the O2 adjusts as the mixture is altered once my van is running.

 

[blacksnapon]

The literature that I have indicates that a richer the mixture means less oxygen in the exhaust and a leaner mixture means more oxygen in the exhaust.

I am not a chemist, but the literature that I have indicates that the oxygen in the combustion chambor gets "used up" with the hydrogen and carbons (HC) during combustion. More HC in the mixture means less oxygen out the exhaust an visa versa - right? I have always thought that it was the O2 sensors job to look at this.

This isn't anything that I "know for a fact", but rather what I have read in a book.

I have an oscilloscope and an exhaust gas anaylzer so I am able to monitor the O2 sensor and watch the AF ratio. I will play around with this and see if the O2 adjusts as the mixture is altered once my van is running.

You're close to being right. Still, the o2s only measure oxygen. Lets say you dont have a firing event on one bank, there will be all that unburned, or raw fuel in the exhaust. It will read lean because of the amount of oxygen (the sensors dont pay attention to fuel).

 

[eco]

You're close to being right. Still, the o2s only measure oxygen. Lets say you dont have a firing event on one bank, there will be all that unburned, or raw fuel in the exhaust. It will read lean because of the amount of oxygen (the sensors dont pay attention to fuel).

Yes, but in the context of rich/lean combustion the amount of oxygen will differ and the O2 sensor reading will correspond - right?

 

[blacksnapon]

Yes, but in the context of rich/lean combustion the amount of oxygen will differ and the O2 sensor reading will correspond - right?

You're right in the context that you put it, but it doesn't matter if its burned or not, its just measuring the oxygen. In actuality, using the o2 sensors alone for diagnostics, isn't very accurate. Looking at a combination of data, and other information, is the most reliable.