Outlaw952

Hiya. I am new to the Rennlist, but have owned my car for quite some time. Yeah, yeah I know. Anyway, I just installed a Huntley AFPR and VDO pressure gauge on my fuel rail. BTW I installed it in the factory orientation, just took some wiggling to get it in there. Also, I went to the junkyard and bought an extra fuel rail end cap ($10 minimum there) and got it tapped for the VDO gauge at a local machine shop for $20. So all you guys looking for special adapters to do this, just letting you know you can do it yourself for about $30.

I have also installed an Autometer A/F Ratio gauge (electronic) and I adjusted the AFPR to about 3 bar (originally I had it at 4 bar or so because I didn't understand that you needed the vacuum line off, made the car stuble a bit during 4th gear acceleration). It runs fine and all, and the A/F ratio seems to be ok during runs (rich at all times under full boost). The problem I am running into is this. It doesn't matter what I set the fuel pressure to (I havent gone below stock PSI). The A/F meter shows that my car is burning exactly the same "richness" everytime I am under boost, regardless fuel pressure setting I try. Is the ECM not letting it burn as rich as it could? Also, if I disconnect the O2 sensor under the hood, and go run the car, it has considerably more power. Of course, when I do this, the A/F meter I installed doesn't work, it constantly shows that it is in the Stoicometric range. So I was only able to think of a few things: With the O2 sensor plugged in, the chip I have is controlling the A/F mixture to a preset. With it unplugged (and reading Stoic) the chip thinks it is not rich enough and finally starts dumping more fuel in. Or I have a bad O2 sensor, or need an upgraded one. What do you guys think?

Here is my setup:
89 952: Auththority Stage II chip, Linsey manual boost controller (w/ original banjo bolt), K&N cone, ported/polished head, wide fire gasket, 3 angle valve job, Bursch test pipe, HR AFPR. It is running at about 17psi in 4th (sometimes up near 19 if its cold enough).

Before I had the head work done, it had a small blow in the head gasket (blowing a bit of water to cyl #4), the valve guides needed replacing, and the alternater was dragging. Still dynoed at 285hp/335tq.

dlr944

Welcome Outlaw951
[quote] The problem I am running into is this. It doesn't matter what I set the fuel pressure to (I havent gone below stock PSI). The A/F meter shows that my car is burning exactly the same "richness" everytime I am under boost, regardless fuel pressure setting I try. <hr></blockquote>

Great to see a fellow Austinite on the list. Each bar or light on the A/F meter displays a range of A/F mixtures and not an absolute value. If the last richness light is on this could indicate a number of rich A/F mixtures. For example on the ARM 1 if the last blue (rich) is light this could indicate an A/F of 12.5:1 or more. It all depends on the sensitivity and the calibration of the meter.

Perhaps you already know this but one of the best ways to set the fuel curvre is to use a wide band O2 sensor and monitor. Dyno the car using a wide band monitor. Then compare it to your readings (to see how far off your guage is) and then make the necessary adjustments to achieve your desired A/F mixture all the while using the wide band monitor as your reference.

Outlaw952

That makes sense, but I would still expect it to read different,even if it was just a little bit after I make some adjustment. I do plan to get it dyno'd next weekend at Colvin Automotive. Does anyone have any answers to the "weirdness" I am seeing with the O2 sensor? Also, it might be of interest to note that on my A/F meter, more than one of the LEDs is on at once. For example, the meter may have 10 LEDs that represent the "rich" range on it. Under full boost I can expect it to read anywhere from the first rich LED to the fifth rich LED. And it looks like the signal is bouncing back and forth between these LEDs, because the LEDs are pulsing so that the 1st and 5th ones are faint, and the ones in between are brighter, with the middle one being full on. For reference, I have the A/F meter wired directly to the ECM connector, at pin#24. Somewhere I read on the net that this is the correct pin for the O2 sensor output. Do I have it wired wrong?

dlr944

[quote] For reference, I have the A/F meter wired directly to the ECM connector, at pin#24. Somewhere I read on the net that this is the correct pin for the O2 sensor output. Do I have it wired wrong? <hr></blockquote>

Checked the 944 workshop manual and terminal #24 on the DME is the correct pin for the 02 sensor output. Where do you have the meter grounded? Ground loops can cause strange problems. You might try grounding it at the battery if you haven't already.

Outlaw952

I grounded it to what looks like a ground lug underneath the dash. It has two tan wires running to it, both look like about 10 gauge wire, and the lug seems to be a part of the dash frame. I will try running a wire directly to the battery. If that doesn't help I guess the next step is to do the same for the 12V supply?

Outlaw952

OK, tried direct ground to the gauge, no change. Tried direct 12V to gauge, no change. Tried direct ground and 12V to gauge at the same time, made it worse. Ohh well.

Anyone have any ideas why it has more power with the O2 sensor unplugged?

Bri Bro

If the signal coming from the Os sensor is rapidly jumping between say .7 and 1.0v then you have a problem in your O2 sensor or wiring. If it is steady, your A/F Ratio gauge should be looked at. You need a DVM with a bar graph or a scope to see the fast changes.

When you disconnect the O2 sensor you are running open loop and by the sound of it your running richer. This will make the car have more power but it dosn't even begin to pass emmissions.

<a href="http://boards.rennlist.com/upload/powerair_fuelratio.gif" target="_blank">A/F Ratio vs Power</a>

If they use a wideband at the Dyno, it will supply the answer to your question.

<a href="http://boards.rennlist.com/upload/WBO2_d5.gif" target="_blank">Wideband vs standard O2 sensor</a>

aka 951

As mentioned above - you really need a wideband. Do yourself a favor and toss your a/f meter. Apart from stoich, your meter may be a better indicator of battery voltage flucuations than a/f ratios.

Outlaw952

Aww man. But the lights are pretty! Well, the last time I ran the dyno the A/F dropped right down to 10:1 until about 3000 RPM, then it slowly came up to around 12.5:1 or so. Sounds like it is doing fine?
OK I believe you about the usefullness of the meter. So if A/F meters are useless, how come I see lots of people selling ARM1 A/F meters and stuff like that? Seems like a waste of good money to me.

dlr944

[quote] Aww man. But the lights are pretty! Well, the last time I ran the dyno the A/F dropped right down to 10:1 until about 3000 RPM, then it slowly came up to around 12.5:1 or so. Sounds like it is doing fine?
OK I believe you about the usefullness of the meter. So if A/F meters are useless, how come I see lots of people selling ARM1 A/F meters and stuff like that? Seems like a waste of good money to me. <hr></blockquote>

It sounds like you’re running rich in the mid-range 10:1 and fine above 3000RPM. The ARM 1 and other A/F meters are great tools to help to get your fuel curve in the ballpark. But to get a prefect A/F curve for your application you will want to use a more precise tool like a wide band sensor and a dyno. I think many of us use the A/F meters to monitor or eyeball the A/F mixture and to have peace of mind that were not running lean on full throttle.

dlr944

Danno

Also, it might be of interest to note that on my A/F meter, more than one of the LEDs is on at once.

At any one time, the O2-sensor is puting out only one voltage. If your O2-sensor display has more than one LED lit up, it's pretty much worthless.