Do AA Chips Adjust Air/Fuel Mix?

[jmciver]

OK, here is the situation. I installed an A/F gauge in my car, the real simple kind that is essentially a voltmeter. Anyway, when I hooked it up to my O2 sensor (I tapped the wire at the harness connector under the car), I did not get the proper reading (according to the Bently manual the out put should oscillate between .2 and .8 volts at idle).

I thought it may have been my wire tap. I disconnected the gauge and put a voltmeter on the signal wire I spliced into the O2 signal. I got a steady .25 volts (even when I reved the engine). So now I am thinking the O2 sensor is bad (after all, it is the original O2 sensor with 76K+ miles on it). I replace the O2 sensor and connect the gauge, still not working properly. I hook up the O2 sensor to a shop O2 sensor tester. It gives what the O2 sensor is reading, however the DME does not appear to do anything with the O2 sensor signal.

The only other thing that I or my mechanic could think of is that the chip in the car (made by AA) is doing somthing with (like disregarding) the signal from the O2 sensor. So my question is, does the AA tuning do something there as part of the performance gain? I am in the process of contacting AA, but wanted to know if anybody else has seen anything like this before. Thanks in advance.

[fourfa]

you're positive you tapped the right wire? one possibility is that you were looking at the heater wire, which is a constant voltage. What did the other wires on the harness show?

[jmciver]

My car has the 4 wire O2 sensor. Grey = Signal, Black = Signal Ground and the remaining White = Heater voltage. That data came from the Bentley manual. I tapped the grey wire.

The funny thing here though is, regardless if I tapped the right wire or not, when my mechanic pluged in his O2 sensor tester to the new O2 sensor, it did not read properly. The O2 sensor was sending a legitimate signal to the DME, but the DME did not respond as expected. When at idle, the system is in closed loop. The O2 sensor signal should oscillate as the DME constantly changes the fuel flow. Based on what the mechanic and I saw, the O2 sensor was sending a signal to the DME, indicating the Air/Fuel mix (which was lean BTW) but the DME did not respond to it. When I revved the engine a bit, DME started to do something, but definately not what I expected to see, especially at idle.

[fourfa]

idle is open-loop. the car should run consistently lean at idle (cylinder temps are low enough to let it be real lean to save gas).

it should go closed-loop right above idle, and stay closed loop until near WOT. sounds like it's working right.

[fourfa]

hmm. a little more research shows that BMWs have been made with both closed and open loop idles. I'm reasonably certain that newer Motronic and Siemens controllers use open loop idle for greater fuel economy.

[jmciver]

You may be right there. My car is a Bosch system covered by the Bently manual and it states that it should be .2-.8 volts at idle. The Bentley does not cover the Seimens system however.

[NickG]

James,

Your car should definately run in closed loop during idle. Accordingly to your findings though, it's not. Now, the programming in the chip can be made to ignore the oxygen sensor and operate in open loop at all times. Hopefully, that's not the case with your car, so let's make sure everything else is operating properly.

First of all, when in closed loop, the O2 sensor's output should toggle between .25v and .65v, with the average around .45v. Lower than .45v means the AFR is leaner than 14.7:1. Higher than .45v means the AFR is richer than 14.7:1.

Since you got a reading of .2v from the O2 sensor at idle, it appears that you've got the correct wire. Have you checked the heater wires to make sure that the sensor's heater is getting 12volts? If it doesn't, the sensor can't reach operating temperature and will not oscillate/respond. This will keep the DME in open loop, although it will also cause a Check Engine light.

Do you have a cooler than stock thermostat in your car? Or is your thermostat stuck open maybe? If the engine's operating temperature is too low, it will prevent the DME from entering closed loop.

If everything checks out, you should call AA and ask them. You DO NOT want to run a chip that disables adaption and closed loop operation on a street car. Besides being illegal, your catalytic converters will be destroyed in short order. That'll be a nice $1000 down the tubes.

[NickG]

Originally posted by fourfa
hmm. a little more research shows that BMWs have been made with both closed and open loop idles. I'm reasonably certain that newer Motronic and Siemens controllers use open loop idle for greater fuel economy.

No, they all use closed loop. Open loop would cause the cats to not operate, which would negatively impact emissions. That's the whole purpose of closed loop operation, to minimize the engine's emissions output. Then fuel economy is considered, and finally power.

[fourfa]

there's plenty of info on the web showing pre-1987 BMWs using open loop idle. Also, many other makes of cars use open loop and have no emissions problems. True, the cats don't catalyse at peak efficiency away from stoichiometric mixtures, but if the idle is programmed right then there may not be any pollution to catalyse. A lean mixture burns very completely (no HC or CO emissions), and NOx only becomes a problem at higher cylinder pressures (idle is as close to vacuum as the cylinders get).

[NickG]

Originally posted by fourfa
there's plenty of info on the web showing pre-1987 BMWs using open loop idle.

Well, your previous comment mentioned 'newer Motronic' systems. I don't consider pre-1987 controllers to be 'newer'. Plus, James' car specifically, being a 1995, does use closed loop during idle.

[jmciver]

Originally posted by NickG
James,

Your car should definately run in closed loop during idle. Accordingly to your findings though, it's not. Now, the programming in the chip can be made to ignore the oxygen sensor and operate in open loop at all times. Hopefully, that's not the case with your car, so let's make sure everything else is operating properly.

First of all, when in closed loop, the O2 sensor's output should toggle between .25v and .65v, with the average around .45v. Lower than .45v means the AFR is leaner than 14.7:1. Higher than .45v means the AFR is richer than 14.7:1.

Since you got a reading of .2v from the O2 sensor at idle, it appears that you've got the correct wire. Have you checked the heater wires to make sure that the sensor's heater is getting 12volts? If it doesn't, the sensor can't reach operating temperature and will not oscillate/respond. This will keep the DME in open loop, although it will also cause a Check Engine light.

Do you have a cooler than stock thermostat in your car? Or is your thermostat stuck open maybe? If the engine's operating temperature is too low, it will prevent the DME from entering closed loop.

If everything checks out, you should call AA and ask them. You DO NOT want to run a chip that disables adaption and closed loop operation on a street car. Besides being illegal, your catalytic converters will be destroyed in short order. That'll be a nice $1000 down the tubes.

I called AA today and they said that their software does not mess with the A/F mix of the car. In other words, my car should do what it is supposed to do at idle, oscilate between .2 -.8 volts (or something like that). I do have a cooler than stock thermostat. In fact, I have a BMW 80 degree racing thermostat (part of my fan/clutch removal mod). But I don't understand how that would be a player here. Especially since my car was at normal operating temp when I had the O2 sensor changed and tested (as indicated by the water temp gauge).

Just a little more background, when I had the old O2 sensor in the car, I hooked it up to the A/F gauge. At idle, I did not even get the lowest LED. When I took the car for a "midnight run accross the bridge" I would just barely see the low LED (lean side) come on, and that was at WOT at mid-high rpms.

[fourfa]

that was just a counter-example to you statement "they all use closed loop," and the pre-87 was the first one I came across.

[NickG]

Originally posted by jmciver

I called AA today and they said that their software does not mess with the A/F mix of the car. In other words, my car should do what it is supposed to do at idle, oscilate between .2 -.8 volts (or something like that). I do have a cooler than stock thermostat. In fact, I have a BMW 80 degree racing thermostat (part of my fan/clutch removal mod). But I don't understand how that would be a player here. Especially since my car was at normal operating temp when I had the O2 sensor changed and tested (as indicated by the water temp gauge).

It very well may be your thermostat. The engine may be running too cold to allow the DME to enter closed loop. (Ignore your temp gauge in the dash; it's useless for any type of accuracy.) That is probably limiting your power potential, as the DME can't 'learn' your engine and modify the fuel maps to match.

Make sure to check the sensor's heater circuit too. It may be the problem here, not letting the O2 sensor heat up and start responding.

[jmciver]

Hmmmm......it just seems weird that my engine may not be performing at it's max potential as you say, but my car seems to perform better now, with all of the mods I have done.

One thing I forgot to mention in the last post. When the mechanic had his O2 sensor reader attached to my car, I did get some indication the DME was at least doing something. Although it was not oscillating as it was supposed to (it just stayed really lean, almost off the scale) when he reved the engine a bit (from inside the engine compartment) the display did indicate a change in A/F mix at RPMs above idle.

I think I will re-verify my wire tap at the O2 sensor again (this time removing the wire tap I used and connecting my wire directly to the O2 signal wire at the harness connector) and see if I at least get the same readings as the shop tool got.

Thanks again for all the help guys. Of course, if anymore insight to this problem can be added, please do.

[fourfa]

3 11 53 6 713 080?

[jww///95]

Originally posted by jmciver
...I think I will re-verify my wire tap at the O2 sensor again (this time removing the wire tap I used and connecting my wire directly to the O2 signal wire at the harness connector...

This is definitely the correct thing to do! I've installed a few of the voltage monitors for o2 sensor in the past, and the biggest mistake you can make is splicing its pickup directly into the pigtail of the o2 sensor itself. With most import cars, the wire is shielded at this point, and if you strip any of it back, even by installing a tap splice, you can seriously alter the signal going back to the ecu. Always tap these connections into the light gauge wire found very close to the computer as this will limit interference with the factory setup.

[jmciver]

I removed the wire tap and just spliced the gauge wire to the signal wire at the O2 sensor under the car. I wanted to tap into the wire closer to the computer, I even took apart the wire loom in the engine compartment to look for the wire, but I could not find it. I know of other people who have tapped right at the O2 sensor on our cars and have not had a problem.

My gauge still did not function properly, When I hooked up a volt meter to the wire I tapped (in the engine compartment), I only got 7mV. After the car warmed up (took about 20 min just sitting at idle) I got a reading of 25 mV (going up to 30 mV when I reved the engine a bit). This is actually pretty consistent with the readings I saw on the tool that the mechanic used yesterday on my car.

Fourfa, could you elaborate more on how engine temp affects the engine going into closed loop operation? The only other thing I have left to try is put my stock chip back in the car, which I will try tomorrow.

[fourfa]

there's a cold enrichment routine, where it runs on rich maps while warming up. this feeds the cats extra fuel to burn to get them up to operating temp faster (in combination with the smog pump that pumps extra air into the exhaust). I assume we're talking about OBDII; I think the OBDIs lack the smog pump.

Some people have used the coolant temp sensor to trick the motor into thinking it's colder than it is, and enriching under boost for example.

[jmciver]

Hmmmm......Well if that were the case, since my engine is running cooler now with the 80 deg thermostat, why am I getting a lean signal on the A/F gauge?

According to the gauge installation instructions, they say to tap the O2 signal wire between the harness connector and the DME and not on the actual pig tail, as I have done since "some oxygen sensors use shielded wire." This does not make sense to me since I only removed a small bit of insulation down there. Is EMI (electromagnetic interference) that great down there? Could EMI be affecting the signal wire that I ran down under the car to the O2 sensor? I have heard of other people doing it this way on our cars with no problem with EMI.

I think I will make one more effort to find the O2 signal wire that goes to the DME, since I will be putting the stock chip back in the car for another test. Any other ideas?