Porscheman101

I was wondering if anyone else is having problems with the ARC2 fuel controller sold by Huntley Racing with their stage 3 maf. Whenever I come to idle, the reading goes rich and then goes back to stoich, but grey smoke just comes billowing out of my exhaust. It pisses me off. I just cant get the right calibration. Any Ideas with this problem will help me out. Also you could check out my car at this address.
<a href="http://members.cardomain.com/porscheman101" target="_blank">web page</a>

Perry 951

Have you tuned it on a Dyno? The ARC 2 can be a pain to get right. Also, with the cold weather and no cold start enrichment, it really has problems.

Some of us (me included) are trying to adapt the stock inlet air temp sensor into the MAF to make it act as stock in cold weather.

Until one of us has a chance to see if it works, we all are in the same boat.

I would get it on a dyno and tune it there. After that, it should be fine, but you may need to adjust the high **** 2 clicks rich when cold, then back it off the 2 clicks after it warms up.

And welcome to Rennlist. Good to have ya here. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

TonyG

Probably not an ARC2 problem. You're not setup correctly, or you have other problems.

I've had the ARC2 (and still do) on 3 951's and a 911 (and have lots of friends that use them), and they work excellent... but.. we don't live in cold weather (one is in Texas, one in Arizona, and all the rest of us are in So Cal).

Have you had this problem since you installed it?

dlr944

I have to adjust the ARC 2 low setting two clicks everytime I start my car. I've replaced the engine temp senor, new TPS adjusted correctly, the ISV, all the vaccum lines and intake manifold gaskets - still have to turn the low setting up two clicks.

Here's a thread I started concering this topic.

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=000814" target="_blank">ARC 2 - Cool start settings vs. Warm settings</a>

I did add a temp sensor to the DME in conjuction with my 3" MAF. The temp senor I used has the same resistance/temp characteristics as the factory sensor. Unfortantely, it did not make any difference - did not aid in enrichment. Also I live in Texas and still need to turn up the low setting to make it start. Others in my local PCA have the same problem. The voltage output of the MAF during idle might be the source.

tecart

i have this issue, the cure is to leave the low setting 1-2 clicks richer all the time, so when its warm outside you will be running rich at idle, derrick has recommended to leave the low setting like this so you can compensate for the kit not having a cold start enrichment, the problem only is really bad if the temperature is lower then 60 degrees outside and horrible when lower then 40 degrees outside, if its warm outside at initial starts you will not notice a bad idle and have to raise the low ****. I am waiting for someone to add a fix to this and im gonna be first in line to buy the fix for cold starting, anyone reading this email me if you want a customer. Untill then i live with adjusting the low **** when its cold outside, and yes i do live in a colder area then most here who have no problems because the temps never go below 60 outside

IanM

I have the ARC2 Rev.2 version of the Huntley controller, and it's always worked pretty well in conjunction with my Stage2 MAF. I did have a bucking problem after installing my bigger turbo, but I've cured that by moving the MAF sensor directly after the air filter (like the SFR setup), to get away from the vortex in front of my turbos 3" inlet.

My settings (tuned w/ wideband O2 sensor on dyno and street) are 10 o'clock LOW, 3:30 MID, 8:00 HIGH, 1:00 ACCEL. These setting work well, in conjunction with my APE Stg 2 (Ver2.7) chips, 52# injectors, and 2.5 bar fuel pressure. The only problem is at idle when the car is cold, when it runs quite rich (APE chips calibrated for stock injectors, not 52#'ers). It does start okay though, even in the cold. I just have to give it a bit of gas when I crank it over.

I've just purchased a set of Danno's Guru Racing Ver.7 chips, which will be calibrated for my 52# injectors at 3 bar fuel pressure. Hopefully this leans out my idle when cold, and will allow my ARC2 settings to be close to zero (12 o'clock) on all the *****. I'll let you guys know how it works out once I receive the chips!!

Porscheman101

I actually havent had that many problems with mine lately. I just let it warm up untill the reading goes back and forth from rich to cold. And believe me I am starting it in cold areas. Today after school the temp was in the 20's. So there is hope out there.
I will have to see how it runs when the temp is hotter.

tecart

ian please post the results, but are you saying that with your bigger turbo and the maf kit you have and the 52 pound injectors, you cannot adjust and tune your car to run properly to its full power unless you get another set of chips verses just adding fuel and subtracting it with your arc2 controller? I though with the arc2 you never have to buy chips again after you have the fuel cutout fixed with any upgraded chip kit like you have. Cant you just adjust the arc2 to find the bad areas/map that autothority chips have and use Dannos maps as a general rule of thumb to add more high end fuel and take some out in the midrange and then lower some at idle/low setting to fix the richness of the bigger 52 pounders? Isnt that possible to do or do you just want to be the only one with 12:00 on the arc2 all across the board? please let me know why you are switching chips instead of going to a dyno and tuning the arc2 more? Im just trying to see if your just testing or trying totally new ideas

TT

Motronic measures the volume flow directly using the VAF. With this reading it calculates the amount of fuel to inject using the stock injector flow rate. Motronic later adjusts the injector pulse width to account for other parameters (air temp, accel enrichment, cold/warm start, etc.). Problem is that Motronic uses the initial value as an indication of engine load (Ve). This load value is used to set the ignition timing using lookup maps.

If you increase the size of the injectors, Motronic needs to decrease the length of the injections. If you use the ARC2 to fool Motronic into thinking lower air flow to decrease the injector pulse width, it also fools it into thinking the engine is under a lighter load thereby throwing off the ignition timing. You end up with Motronic advancing ignition when it really shouldn't. The Guru chips are setup to reduce the injector pulse width by the correct percentage based against the stock injectors. Only minor corrections are needed for the ARC2 to work with the larger injectors and Guru chips with the beneficial result that the ignition maps are not skewed.

IanM

tecart -
I have dialled in my ARC2 with my APE chips with a wideband O2 sensor, both on a dyno and on the street. I've got it set up VERY well right now, a perfect 12.5:1 a/f ratio under boost, and nice dithering on the ARM1 with 14.7:1 a/f ratio while cruising off boost. Under normal conditions, there's no reason why I'd need to change anything to do with my fuel mapping.

I'm upgrading to the Guru chips for two reasons. One, because when I first start the car (when cold), my car runs very rich. This is because it initially runs in open-loop mode, ignoring the ARC2 settings and goes straight to the fuel maps on the APE chips. Since the APE chips are mapped for smaller injectors, I end up running rich under this condition. Once the car warms up and the ARM1 starts to dither back and forth, my a/f ratios at idle are fine.

The second reason is that the APE chips don't have very agressive ignition advance curves. Danno thinks I'll see a substantial increase in mid-range torque with his chips, due to more agressive ignition mapping. I'll let everyone know how it works out, once I install the chips and do some tuning with the wideband O2 sensor.

IanM

yah, like TT said! So there's a third reason for me to go with the Guru chips!

tecart

yes the timing can be fixed for more power for sure, lets see if that chip change does that for you in any rpm for that matter, you may even boost sooner with better timing maps, please please keep me informed to the testing of that, but as to what you quoted to :

I'm upgrading to the Guru chips for two reasons. One, because when I first start the car (when cold), my car runs very rich. This is because it initially runs in open-loop mode, ignoring the ARC2 settings and goes straight to the fuel maps on the APE chips. Since the APE chips are mapped for smaller injectors, I end up running rich under this condition. Once the car warms up and the ARM1 starts to dither back and forth, my a/f ratios at idle are fine.

I ask how is the car at first start ignoring the ARC2 settings for low/idle on the arc2, i mean if im adjusting the arc2 at first starting the car and my idle is dropping and rising as i try to get a better idle, my car is not ignoring the arc2, and this is way before my arm1 dithers and warms up. I understand you want less fuel at idel with the bigger injectors, but why cant the arc2 fix that? The car will respond to the ARC2 in open loop mode so why is the chip change so necessary, thats what im trying to figure out? Would huntley say that if you get bigger injectors that now you'd have to change the chip so the idle at cold start matches a stock car because the arc2 does not respond in open loop? Why can my car respond in openloop then if i adjust any **** on my ARC2 within the first 10 seconds of cold starts? Thanks for the info Ian

Danno

" I understand you want less fuel at idel with the bigger injectors, but why cant the arc2 fix that? The car will respond to the ARC2 in open loop mode so why is the chip change so necessary, thats what im trying to figure out? "

This seemingly simple question really illustrates the achilles heel of signal-interception and massaging quite well. In order to explain it, we need to examine the algorithm the Motronics DME goes through in order to compute an injector-duty cycle number and the resultant fuel-volume delivered. Then add signal-massaging on top of it.

STEP 1
-------------
Ok, the very first step in the computation is to compute an injector duty-cycle from the incoming air-flow meter voltage cross-referenced with RPM in this VAF-VolumeAirFlow conversion table:


I can't remember which thread I originally posted this, if anyone knows, please let me know because I'm getting a déja-vue feeling like I've been here before. You may notice the flat areas on the sides of the map. These are out-of-bounds areas that typically you would never encounter with a stock car. Such as flowing enough air at 2000rpm to open the AFM enough to generate a 3.0v signal. This is unlikely, so all values above 3.0v are clipped at a 25% duty-cycle. On the other side of the map, at 6000rpm, you'll always be flowing at least enough air to open the AFM and generate 2.0v. So all values below that is clipped at a 10% duty-cycle.

STEP 2
-------------
Once this first look-up is done, an fuel-adjustment table is used to modify the computed duty-cycle. Here are some sample adjustment maps:


As you can see, there's wide variation in the adjustments. This depends upon the car's configuration and its particular flow-patterns.

STEP 3
-------------
If you do a matrix-multiplication between the two tables, you end up with a resulting product like this:


After this point minor corrections are made for air-temperature, altitude and O2-sensor feedback.

------------------------------------------

Ok, with the basics of how the Motronics DME works, let's look at what happens with a signal-interceptor and massager:


As you can see, the signal-massager actually doesn't "adjust fuel", but rather just changes the voltage of the incoming air-flow signal to skew the lookup point somewhere else. This ends up being very dependent upon the chips you're using. A single click clockwise on the MID **** with a certain chip will yield completely different results with another chip because their fuel-maps would be different. Also in general when you skew the look-up point higher up to get more fuel, you also retard the timing. Depending upon how far you have to turn those *****, you may actually lose up to 10-15 degrees of ignition advance (opposite of what you really want to do):


Alright, so what happens at idle? If you look at the look-up point for the first VAF computation, normal idle is around 0.80-0.85v and this corresponds to a duty-cycle of 3%. You'll also notice that the idle look-up point is awfully close to the out-of-bounds region. In fact, it's only one data-point away from the edge.

Let's say you upgrade to 55-lb/hr injectors and then you turn the LOW **** down two clicks to generate a 0.65v idle air-flow. This simulates less flow and a different look-up point is used that returns a 2% duty-cycle. That's fine because you've reduced the duty-cycle by 33% which closely matches the 37% larger injector. However, you've ventured into the out-of-bounds clipped-values edge of the map.

What happens if you upgrade to 75-lb/hr injectors? You can try to turn that LOW **** to lower the voltage all you want, but 0.50 or 0.25v will still result in a 2% duty-cycle from the look-up table. Which is really way too much fuel. To use 75-lb/hr injectors and get the same fuel-volume delivered as before, you need to reduce the duty-cycle by 64% or only 1.4%. This is well below the minimum 2% in that table and you will have 50% too much fuel.

The only way to get around this is to keep the exact same look-up spot on the table as before (no adjusting ANY ARC2 ***** allowed!). Then incorporate a scale-back step in between the 1st VAF-conversion above and the 2nd fuel-adjustment map step. That's what we do with the version-7+ GURU chips. We scale back the computed duty-cycle by -37% for 55-lb/hr injectors, -47% for 65-lb/hr and -63% for the 75-pounders. This preserves the proper look-up location so the same fuel-volume and ignition-advance is used.

tecart

so what your saying is that with 55 pound injectors your arc2 will allow you to get to the proper 2% duty cycle, but any injectors that are bigger like 65 or 72 pounders your in need to change the chip because the map runs out of tunable lookup reference points, because with 65 or 72 injectors the chips map will not allow you to look up a idle fuel duty cycle below 2%? Right? Your saying beside the other benefits of the high or lean end cures of your chip, specifically you chip is mapped for bigger injector that gives a lower injector duty cycle than can be reached with a normal chip, so furthermore i would need your chips new lower injector duty cycle maps and utilize my arc2 to find this lower 1.4 or so duty but since your chip is on target for the size of the injector i can put the arc 2 at 12:00 for the low setting, meaning zero adjustment, right? Also does this mean then if you goto a 65 pounder than goto a 83 pounder, yes once again you need a custom mapped chip for idle, correct. Lastly Ian is running 52 55 pound injectors, if he isnt below the 2% duty cycle needed yet to get a proper mix, why do you both feel changing his chip makes a difference, you state that the concern lies with the big 65 or 72 pounders not the 52 sized ones, right? The only thing i can think of is you both feel that his map should be fine for 2% duty at idle but since you didnt make the chip your just trying to eliminate any possible sources for his high idle, and a custom chip would end the questions to if his map is off at idle right? Or are you saying that no autothority stage 2 chip will allow you to idle properly and get the 2% duty cycle with any arc2 control if you go bigger than stock sized injectors, ie you need a custom mapped chip for idle if you get bigger injectors... This all sounds like get if you injectors, then you must get a new mapped chip, even if you got the arc2. For idle quality of course im talking

tecart

hello