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Old 10-05-2004, 18:14   #1 (permalink)
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Running rich fix

Not a fix but perhaps someone with an engine using too much fuel could try this idea. I do not use my car much so cannot test it. First the Oxy sensor must be working but not giving enough signal to operate the computer. It should give about .9 volts for a rich mixture, but if it is only .4 then the computer would see that as a lean mixture and not make it leaner. The idea is to put an extra voltage in series to increase that .4 to .8 volts. The computer would then change the mix to lower the Oxy signal to zero - the computer would be reading .4 volt.
Perhaps .4 volts would be too much and .2 would be OK.
The sensor would have to be unplugged and the signal wire cut and either a potentiometer (small trim pots are available) or two fixed resistors connected across an AA cell. The resistors are soldered into the cut sensor wire in such a way as to add the small extra volts. An AA cell would probably supply 1 ma for about 3 months or a mercury perhaps 12 months.
There needs to be a way to test these sensors without expensive gear.
The Oxy sensor output could be measured with a cheap meter if a one transistor buffer was used with a 3 volt battery. Probably $2 and 1/2 hour to solder it together.
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Old 10-07-2004, 15:28   #2 (permalink)
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Re: Running rich fix

The circuit need not be soldered into the signal lead. Because there is almost no current a good connection could be made with pins pushed well into the ends of the cut signal wire. Put a piece of electrical tape over the ends. The positive end of the circuit would be at the plug end and the negative towards the sensor.
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Old 10-07-2004, 17:02   #3 (permalink)
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Re: Running rich fix

using .4V when the afr goes lean the computer will think its fine and keep on going leaner and leaner and leaner and leaner

using .2V the computer will change the AFR from 14.7 to 14.8

if the oxy sensor is "working" but not giving enough voltage then it needs to be replaced.

Oxygen sensors simply will not produce voltage until they're hot, and many perfectly good units are replaced because some technicians test them when the engine is first started, or after it's idled for a while, which allows the unheated type to cool off.

With a cold sensor, the computer realizes it's not getting a signal and will operate in open-loop, holding the mixture at a fixed setting. Since good fuel efficiency and minimum exhaust emissions can only be had during closed-loop, it's desirable to get the sensor hot as soon as possible after the engine is started, and to keep it there while idling, so late-model oxygen sensors are equipped with an electrical heating element.

The EF has a HEGO if its not working properly at idle check the fuse near the coolant bottle.

I believe closed loop afrs cannot be modified on our falcons with the narrow band oxy sensor.

Option one
dont use closed loop like turbotrana

Option two
use a wideband oxy sensor as per my other thread
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Old 10-08-2004, 18:07   #4 (permalink)
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Re: Running rich fix

I think I read somewhere that once warm the ecu will try to lean it out until it reaches .4v. If it's cant do this it goes into limp home mode running constantly rich.

Once heated my oxygen sensor read about .99v at all times so it's been damaged or blocked somewhere. The computer will never be able to get it below .9v so it's goes into limp home mode, using preset amounts of fuel based on throttle possition and manifold pressure.

If I replace the oxygen sensor with a new one, and there is something causing the richness still, the new one will be damaged fairly quickly.

My question is, if the MAP sensor and throttle position sensor and air temp and water temp sensors are fine, what is causing the richness?

Can worn injectors cause richness?

Does low fuel pressure (from a broken fuel pump or fuel regulator) cause richness?

I've asked that last question many times and I've never seen an answer.
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Old 10-08-2004, 19:29   #5 (permalink)
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Re: Running rich fix

problem: leaking injectors
fix: replace them

problem: high fuel pressure
fix: get an adjustable fuel pressure regulator or a new stock one
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Old 10-09-2004, 16:59   #6 (permalink)
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Re: Running rich fix

Con,
About those circuits - we are on different tracks.
You are talking about changing the Ford computer control to give better economy.
I am talking about adjusting the output of the oxy sensor to compensate for variations in its output and changes as it ages.
Adjustment to make the computer control operate as designed by Ford.
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Old 10-09-2004, 17:00   #7 (permalink)
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Re: Running rich fix

Bidju,
Do you know what the fuel pressure is?. It should be about 14 PSI or with the return line blocked about 30 PSI
If the fuel pressure was low the acceleration on a hill would be low or some other noticeable changes. To cause a rich mixture the pressure would have to be high. Just thought that the computer changes the duration of the injector pulse and assumes the pressure is correct.
Cannot understand how the oxy sensor could give an output if it was not working. The computer may not be reading the signal or may not be changing the fuel mix. If you can measure the output with a high impedance meter then try putting the sensor in the flame of a portable gas stove. I tried that test and when the element was red hot the output was around 5 to 7 volts. It dropped rapidly when removed from the flame.
On one of those links there was a note that Mercedes mentioned putting a 1.5V cell in place of the oxy. Not sure why.
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Old 10-09-2004, 18:23   #8 (permalink)
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Re: Running rich fix

ok np how much is a new oxy sensor? i wouldnt have thought it was that much.
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Old 10-09-2004, 20:57   #9 (permalink)
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Re: Running rich fix

doesnt the comp only use the sensor outputs in closed loop mode and when the car is either cruising, very light throttle or idling.
if so it would only cure the richness problem at them points. which now i think of it is the main part you would want it to be leaner for better fuel economy.
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Old 10-11-2004, 17:22   #10 (permalink)
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Re: Running rich fix

Yes but would low fuel pressure cause bad atomisation of the fuel? Or would it be safe to assume only worn injectors cause bad atomisation?

Yes I saw it for myself, I had the oxygen sensor unplugged and it was reading .9v, very slowly dropping.
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