doug928

Just finished the install of my air fuel meter along with my new RRFPR and I have some very unexplainable readings. First let me mention that I set the fuel pressure to about 55psi at idle and I have the Ott x-pipe and new O2 sensor w/ high flow cats and custom 2.5" exhaust. The O2 sensor for the x-pipe sits in one side of the x-pipe unlike the stock location of between the convergence of the left and right exhaust manifolds just before the cats.

Here's my problem: Upon start up the indicator lights go on and settle at the yellow level for a short while but once I start to drive the readings go crazy. The meter is constantly hunting between off - full lean - to yellow (stoiciometric?). It doesn't want to settle in at any value and looks like a set of landing lights .I am concerned that even when I floor it the display doesn't go to green (rich) and was wondering what the problem might be. I think I am going to reset the pressure to near 60 which is where it was at before I did the change to the RRFPR but I don't have any explaination as to why the meter is constantly hunting. I thought that maybe because of the O2 sensor location I might effect the readings but I don't know.

Any suggestions?

GoRideSno

Doug,
What meter do you have?
What FRP do you have?
Everything you describe sounds pretty normal except that you do seem to be running lean.
The meter will usually hunt. The computer is constantly refining the mixuture. About the only time the lights will stay in one position is when you are at WOT.
The lights normally stay yellow when you first start the car while the O2 sensor warms up.
The postition of the sensor in the x pipe won't cause a problem with your reading though a more acurrate reading could be had if the bung were after the X.
With your exhaust mods it is likely that you will need more fuel.
HTH,
Andy K

doug928

Andy,

Both are from 928 Specialists. I thought it would normally hunt but I didn't think it would go from off the meter lean (no lights) to only yellow with the fuel pressure set at the near the factory setting of (I believe 55psi). I am about to reset it to 60 psi and see if it makes a difference.

Thanks.

GoRideSno

928 specialists sells the ARM 1 so it's probably that. Ok I missed that the lights would actually go off. That is strange. Is it possible you have a short in the wiring somewhere? If it is an ARM 1 then I don't think the lights would actually go off, as in off the meter lean. But it would just give a false reading if it were beyond the sensing capabilities of the O2 sensor.
HTH,
Andy K

doug928

FYI - Just readjusted the FPR to 60 and the arm is not hunting as much - it's still moving too much for me to think all is well but I don't know what else to do for now? Could the MAF efffect the reading if it is not in calibration?

GoRideSno

OK, but there usually realy is a lot of hunting unless at WOT. I've put the ARM 1 on 4 different car's now and that's always the case.

It dosen't seem that you should have to worry about your MAF with what you are doing but it may be a good idea to reset your computer by disconnecting the batery for a few minutes.
HTH,
ANdy K

John Speake

hi doug928
You may have had the mixture so far outside nominal that the O2 loop could not pullit into range. It will only cope with about +/- 6% out of range.

If you have a diagnostic tester, you could adapt the car to the new conditions.(idle stabilisation feature) and it would pull into range

It's only at WOT and when you stamp the throttle that it goes off loop. Then you will get a steady reading, as Andy says.

doug928

John,

If the mixture is in range, I expect a constant fluctuation depending on whether you are flooring the throttle in which I would expect full rich or coming off an accelaration with no throttle and the sensor going into a lean condition. I didn't expect at 55 psi at idle to have a condition where the meter went full lean to just stoicometric since I thought 55psi was close to the factory setting. Now that I have reset it to 60 psi, it's not has bad but still hunts more in the slightly leaner side except when I accelerate. I would have thought that the hunting range would have been narrower and between slightly lean to slightly rich than what it presently is giving me.

Tony

Where do you have the power source tapped from?

If its from the cig. lighter, i had the same thing happen when lean...the red light would go out. I wired it directly to a circut on the fuese panel and it works fin now.

When the car is warmed up, it will hunt. At idle it may do it a bit slower. The LH is constanly adjust the mixture based on your O2 voltage. At WOT it should run near the right side...RICH area. When you let of the gas it will go momentarly rich then shoot imediatly to lean as the idle switch is is back in the circuit.

I know people say that since it is a "narrow" band sensor that it really isnt that good, but IMHO, that little ARM1 has saved me COUNTLESS times in trouble shooting!

http://members.rennlist.com/v1uhoh/arm1air.htm
HTH

Also, i would recomend, disconecting the battery and "reseting" the brain. I had a heck of a time getting my car to indicate correctly when i first added my fender intake back almost a year ago. I finally reset the brain and it cured itself.

John Speake

Hi Doug928
You has made a fair change to the exhaust system, so you are a bit in no-man's land. (unless some other isue has come at the same time as your changes).

Less back pressure may well require a richer idle mixture - but this is not something I can advise on. What is the experience of others you have your setup ? They are known parts.

doug928

Tony,

Yes it is powered from the cig lighter - I will rewire it to another source and give this a try and maybe cure the problem - I guess once I rewire the ARM I will just go trial and error. Thanks for the feedback - now for my new post regarding my flappy .

928ntslow

I had installed the same unit a while back. I spoke to the guys who manufactureed the unit and they said #1, connect the ground (if I remember correctly) as close to the 02 sensor as possble. I ran it to the engine ground at the right side of the block.

At idle, it is steady as a rock, during normal driving, the unit "dithers", which is normal due to the ECU compensating for the different mixture requirement.s given by the AFM or MAF....a closed loop system. My only issue is that at WOT, I get no steady light. This is probably because it is hooked to the cig lighter...a change I need to make.

The important thing to know is that as you drive, watch for the range of which lights the unit dithers to...lean to rich. It should stay in the acceptable range (center) as given in the manual that comes with the unit. It should never go to purple or red while driving normally....only when you lift of the throttle.

Event still, the unit will not tell you exacts of where to keep your PSI. You need to dyno the car for this....something else I have to do.