ALFAGTV6.COM

Murray · Post by **Murray** » Fri Mar 25, 2005 12:30 pm

Anybody want to try and explain this one ? (Excuse the length)
I'm in the process of fine-tuning my newly rebuilt 1986 2.5L GTV6 and have come up against something strange.A few years ago I followed Greg Gordon's instructions for loosening the spring on the AFM door to increase richness of the mixture under throttle.At the time I simply released the W spring and rotated the toothed wheel 5 notches CCW.Since then the car ran great and I never touched it again.Today I used Greg's process for verifiying full-throttle mixture by reading the Oxygen sensor voltage.I got readings of .98V and figured with my new engine and new injectors I must be getting more fuel.Followed Greg's suggestions and started turning the toothed wheel CW.Eventually I had to go 24 teeth CW to get my full throttle reading to settle at about .9V.I simply figured that the previous owner must of monkeyed with the AFM and that is why I needed to adjust so much,although I'm puzzled as to why the car had been running so well if it was so rich.I have I high output Jacobs ignition system so the fact that my plugs never looked dark is probably due to that.
Now for the clincher ! I have a Fred DiMatteo modified ECU and until now I had a soft rev limiter somewhere north of 7200 RPM.In the course of adjusting my AFM today I moved the wiper arm counter clockwise to smooth out the idle.When I went for a run I hit a hard rev limit at 6200RPM.The engine cut right out until I backed off.I got out of the car and repositioned the wiper arm clockwise got back in and wound it out to >7000 RPM no problem.Anybody able to explain this one ? By the way I installed a brand new Bosch 3 wire Oxy sensor this AM so that is not a factor in my strange readings.I used two different digital multimeters one is a Fluke so my readings are accurate.Any suggestions would be greatly appreciated.

Greg Gordon · Post by **Greg Gordon** » Fri Mar 25, 2005 12:49 pm

I am not sure why it needed to move so many teeth. Is it the original AFM? Some like the Zat unit are different and 20 teeth on them is about like 6 on the stock AFM. It could be that the previous owner messed with it AND that the spring is worn out. As long as ALL the plugs look good and you get .9 volts throughout the RPM range from the O2 sensor at full throttle then it should be OK.

I have no idea about the rev limit changing. When you move the wiper arm that effects full throttle mixture so I don't like to do it, but I can't see why that would change the rev limiter. Do you think maybe it's a faulty tach issue? You might ask Fred DiMatteo.

These AFMs are wearing out on our cars. The circut boards and spings wear and the units are so expensive new it's a problem.

Murray · Post by **Murray** » Fri Mar 25, 2005 1:00 pm

Hi Greg .No it is a stock AFM for sure.Unfortunately Fred is no longer with us.When you say a "Tach issue" I assume you mean an issue with the E-Z-L ignition module because as far as I know the tach is just a dumb gauge ? All of these unknowns sure make MS. seem more attractive.There is definately some signal from the AFM wiper arm that the ECU or the Ignition ECU is reading and that is why my rev limiter came back because as soon as I moved it back <1/32" the limiter disappeared.

Murray · Post by **Murray** » Sat Mar 26, 2005 10:39 am

Ok part of the mystery is solved.The reason I was getting a hard cutout is that the wiper arm was moving far enough to the left on full throttle that it was moving off the resistor track and I guess this told the ECU to shut down the injectors.Now as far as the strange rich running condition I did some research on the web and found a posting that claimed that on the L-Jet AFM the stock euro spring setting is with the "W" spring 22 notches from the spring's fully untensioned point.I unwound the spring and set it at 22 notches and my Oxygen sensor reading was .96V at full throttle.Cranked it up another full turn (360 deg.) and I get .9V about ideal according to Greg's website.Greg wondered if maybe I had a non-stock AFM so I snapped a shot of it. Anybody got any ideas ?

Jim K · Post by **Jim K** » Sat Mar 26, 2005 12:16 pm

I don't know much about the 2,5v6, but is the US AFM the same as the Euro one? In the 3liter they're different. Not only in calibration, the SPRINGS are different. I've made a little tension-meter tool, that fits the little bean-shaped hole in the plastic wiper holder, so that I can compare the flap tension in different AFM's.
The main thing to remember about the AFM is that it's fully open at about max torque rpm at full throttle. Fuelling from then on is rpm dependent.
Jim K.

Murray · Post by **Murray** » Sat Mar 26, 2005 12:52 pm

Man Jim you put some serious energy into perfecting your Alfa.That tool is brilliant.
I don't quite understand what you mean by "The main thing to remember about the AFM is that it's fully open at about max torque rpm at full throttle. Fuelling from then on is rpm dependent"
If you put the pedal to the metal doesn't the ECU override the AFM entirely ? Maybe that's what you mean and I'm just not getting it !

Jim K · Post by **Jim K** » Sat Mar 26, 2005 1:45 pm

Murray, The AFM flap is fully open at about 3500-4000rpm and more specifically, at the point of maximum volumetric efficiency (greatest air intake/cycle). Since above this RPM air intake/cycle actually decreases, fuel delivery is a function of RPM rather than air flow and follows the delivery map stored in the ECU original program. This is the basic shortcoming of the L-jet, having a lean condition at higher revs in modified engines and NOT the existence of the flap as an 'obstacle' to flow which it isn't (0,017psi pressure drop accross the flap to be exact is nothing, compared to 14,7psi, the atmospheric pressure!). I will leave out the air volume vs mass difference for our discussion-which is another limitation of the L-jet.
'Pedal to the metal' means nothing if the AFM is within its working arc. However, at WOT, the system cuts out the lambda sensor and switches to open loop operation, offering additional acceleration enrichment. I don't know if I answered your question with this little sermon, if you need more info go ahead and shoot-although, I suspect P.Webb would be more enlightening in this subject!
Jim K.

Greg Gordon · Post by **Greg Gordon** » Sat Mar 26, 2005 3:47 pm

Murray, your AFM does look like the stock unit.

Jim that's some device you have made there. Visually the U.S. 3.0 and 2.5 AFMs appear to be the same, but the spring may very well be different, I don't have a tool like that to check.

It's hard to argue with the guy who wrote the book but I thought the AFM was fully open at max horsepower RPM at full throttle. That's what a tech rep at Bosch told me and it made sense to me at the time. Fully open by 4000 rpm? That interesting.

Jim K · Post by **Jim K** » Sun Mar 27, 2005 12:10 am

Greg, this is from many sources, like Watson, Probst et al,(including Bosch manuals)-they all originate from Bosch anyway. I'm sorry but the Bosch rep was wrong. There are even cases where the flap is fully open at 3000rpm! The most important function is to measure air flow at LOW revs and load, thats where precision is required, for emissions and consumption. High power is much simpler to program. Most aftermarket EFI systems do ok at high rpm/power, but low rpm driveability and economy are difficult to set up, hence the need for MAP sensors and the like. The later Bosch systems like hot-wire and hot-film are much better than the L and K series (which were used profusely by VW and Porsche). If emissions consumption and drivability didn't matter much, we could make do with only a TPS pot+rpm sensing and indeed, a few years ago such systems were on sale for performance mods (eg Microdynamics PIC and others).
I once started on a project to monitor flap position in the AFM, but I dropped it as it would only serve to satisfy my curiosity with no possible usable results (too much trouble for nothing, in other words!!)
Jim K.

Greg Gordon · Post by **Greg Gordon** » Sun Mar 27, 2005 9:00 am

Very good information there Jim! I am learing something everyday!

Murray · Post by **Murray** » Mon Mar 28, 2005 1:49 am

Thanks Jim and Greg.I'll allow your information to absorb into my feable brain before I attempt any more "mods".For now I'm seeing about 0.9V when I get on the gas and response is smooth,so I guess I'm OK.The only aspect of this device that I can't stop wondering about is the adjustabilty of the wiper arm.There are even little calibrating teeth built into the "bean-shaped" opening where the tensioning screw for the arm is located.Was there an official Bosch procedure for adjusting this arm and for what purpose.? I guess once I feel I've mastered this little bugger I'll throw it out and go with MS

Jim K · Post by **Jim K** » Mon Mar 28, 2005 7:51 am

Murray, Bosch never encouraged any kind of tampering or adjustment attempts on AFM's (as if we didn't know!). This is why there's no literature on the particular subject. The clockspring and the wiper position adjustment are interrelated. The spring determines the general flap resistance, so that it swings all the way at about max torque and the wiper adjustment the pecise fuelling at idle. You can readily see, that you can have variable combinations of the two for the same wiper position at idle, but only one which will result in proper progression throughout the entire arc travel. Theoretically, you could spend time on a brake dyno and calibrate the unit to a good degree...on a stock engine!!
If you haven't disturbed the clockspring, moving the wiper adjustment (via setscrew) will give leaner/richer mix through the whole range. If you are cat equipped, the system will attempt to correct for this imbalance, which negates your efforts to a large degree....Moral of story: don't *&!$#@ with it! Get an MS or some other system and unlock more power!
Jim K.

Murray · Post by **Murray** » Mon Mar 28, 2005 12:50 pm

Ok Jim I promise I'll never do it.......again ! Thank you.I took a good 200km cruise today and then pulled the plugs.They are a good grey/brown colour so I guess all is well.

MD · Post by MD » Mon Mar 28, 2005 12:52 pm

Great morals Jim !

Jim K · Post by **Jim K** » Tue Mar 29, 2005 3:48 am

Hey, guys, I hope I'm not offending anyone here! Please take my attitude exactly as I intend it - friendly! Murray, seriously I consider we're a bunch of guys made friends through the site- sorry if sometimes the wording may sound different !

Its not meant to!
Jim K.

AFM Weirdness !