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Porsche Crest 86na - Tricking the AFM

I am asking for a friend. Bought a resister from ebay. Does adjusting the afm spring give more power? Any success stories? What was done?

Yes I read the previous threads.
Old 04-30-2003, 08:19 AM
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It will if you're out of adjustement currently. If not all you will most likely do is fail emissions in the future if you mess with it.

BTW, what is this "resistor" that you mentioned?
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Old 04-30-2003, 09:07 AM
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Quote:
Originally posted by Scott R
It will if you're out of adjustement currently. If not all you will most likely do is fail emissions in the future if you mess with it.

BTW, what is this "resistor" that you mentioned?
ebay has 20hp for 2 dollars. Many auctions.

How sensitive is the spring? If I was going for 5% richer.
20notches?
10 notches?
5?
1?
How many notches on that ring anyhow?
Old 04-30-2003, 10:01 AM
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1 notch would be about 1~2% But the second you move it you will know. You will get the famous "idle shudder" when you let the gas off. Or you will start to burn black/brown smoke out the back on heavy accl.

Best just not to mess with it, you're not going to see any real gains by messing with it.

20HP from a resistor huh? Not to sure about that.
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Old 04-30-2003, 10:18 AM
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yah i didnt and still dont really believe it does much but my gullable buddy bought one off ebay for his 2nd gen DSM non turbo, put it in and it did actually make a difference. It tricks the car into thinking its cold still or something which puts more fuel in i think. Pretty lame if you ask me....
Old 04-30-2003, 12:31 PM
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hey look!! someone's selling Snake Oil!!.. wow cool......
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Old 04-30-2003, 07:36 PM
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Quote:
Originally posted by Roastin944
yah i didnt and still dont really believe it does much but my gullable buddy bought one off ebay for his 2nd gen DSM non turbo, put it in and it did actually make a difference. It tricks the car into thinking its cold still or something which puts more fuel in i think. Pretty lame if you ask me....
in thread 'What could cause a rich mixture?' you moved it clockwise or counter clockwise? One click or more? The correct direction was not clear in that thread. Thanks
Old 04-30-2003, 07:48 PM
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counter clockwise standing in front of the cart is "rich" the metal conductor that looks like a pointer will track from left to right, right is rich.
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Old 05-01-2003, 05:37 AM
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Saw this thread and just had to jump in.

What your buddy bought on eBay is actually a "Performance Chip."

It's just an Eraseable Programable Read Only Memory, or EPROM integrated circuit "chip" that has been "programmed" with a new set of "maps" for the engine management computer, or DME.

These new maps make some small adjustments, or "tweaks" to the fuel, ignition timing, engine load data and in some cases the REV limiter settings the DME uses. The power gains are real, but a chip won't compensate for a tired engine, so make sure the engine is in good mechanical condition.

As for "tweaking" the AFM spring, you can, but you run the risk of running lean if you don't have the skills, knowledge and proper tools.
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Old 05-01-2003, 04:48 PM
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Quote:
Originally posted by Porsche944
Saw this thread and just had to jump in.

What your buddy bought on eBay is actually a "Performance Chip."

It's just an Eraseable Programable Read Only Memory, or EPROM integrated circuit "chip" that has been "programmed" with a new set of "maps" for the engine management computer, or DME.

These new maps make some small adjustments, or "tweaks" to the fuel, ignition timing, engine load data and in some cases the REV limiter settings the DME uses. The power gains are real, but a chip won't compensate for a tired engine, so make sure the engine is in good mechanical condition.

As for "tweaking" the AFM spring, you can, but you run the risk of running lean if you don't have the skills, knowledge and proper tools.
Wrong! they call it a Timing Advance resistor. Thanks Scott R.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2413355734&category=42604

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Old 05-01-2003, 05:33 PM
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That is the same scam I saw about a year ago...........

Read his profile.

ITS a joke.

20HP ROFFFFFFFFFFFFFFFFFFFFLLLLLLLLLLLLLLLLLLLLLLLLLL

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Old 05-01-2003, 05:49 PM
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Thats what I was getting at. Resistors! Ha! Snake Oil is right Frank.

Now, where did I put those muffler bearings...
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Old 05-01-2003, 06:43 PM
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I think that my AFM is adjusted incorrectly. When I was looking around my engine area I noticed the the AFM cover was loose. What is the stock setting on the AFM? I would like to check to make sure that mine is correctly set.
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Old 05-01-2003, 11:59 PM
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OK, I stand corrected, and this is definately "Snake Oil."

The temperature sensor in the AFM is there to give the DME incoming air temperature information, and this temperature directly correlates to air density.

Cooler air is more dense than warmer air, which equates to more Oxygen molecules (Oxygen atoms like to travel in pairs) per unit volume of air.

Replacing the sensor with a fixed resistor will cause the engine to run lean when cold (cold starting problems?) and run rich when warmed up (wastes fuel, excessive carbon build up, possible CAT failure, early O2 sensor failure).

As for adjusting the AFM, it can be done, but you need an exhaust gas analyzer, wide band O2 sensor, and a dyno if you want to do this with the AFM installed. On the other hand, there are firms that will sell you a "remanufactured" AFM ($$$$!) as well as firms that can "recalibrate" the unit (Again $$$).

If you want to get "In the ball park," you can use a digital volt meter to measure the O2 sensor output while you adjust the AFM spring tension.

For a late model engine ('85.5 and later) you need to disconnect the O2 sensor and disable the Idle Stabilizer and conncect a Dwell/Tach to the coil primary (green) wire.

Connect your DVM to the O2 sensor output and ground. Set the DVM to read 2 volts DC. Start the engine and let it come up to normal operating temperature.

With the cover off of the AFM you will see a black plastic "gear." Use some white paint or correction fluid to mark the initial position of the gear. With careful application of a flat tip screwdriver the "gear" can be shifted one tooth at a time in either direction.

As you move the "gear" watch the DVM. As the fuel/air mixture goes lean, the DVM will indicate a higher voltage(More free O2 in the exhaust gas). As the fuel/air mixture goes rich, the DVM will indicate a lower voltage (less free O2). What you want to shoot for is slightly above 0.5 volts but not much more than about 0.7 volts.

What you are doing here is setting the AFM so that if the O2 sensor fails the DME will set the mixture on the rich side to prevent detonation (knock/ping). HINT: If you measure the voltage on the DME side of the O2 sensor with the sensor DISCONNECTED, you should see about 0.45 volts. This voltage represents a lean mixture condition and is used by the DME to compensate for an invalid O2 sensor input.

As you go through this "adjustment" you will note that the engine RPM will vary either up or down, so you need to use the Idle Speed By-Pass screw on the throttle body in order to maintain 850 RPM. You will also note that there is a very narrow span (just a few clicks either way) where the engine will idle smoothly.

Once you feel confident you have the AFM set, connect the O2 sensor (leave the DVM connected to the sensor output), and enable the Idle Stabilizer.

If your adjustments were successfull, the engine should idle smoothly at 850 RPM, and the DVM reading should swing, or dither across 0.5 volts DC.

As a final check, take the car to an emissions inspection station and have the CO (Carbon Monoxide) level checked. This test is performed by inserting a sensor in the exhaust system upstream of the CAT (944 exhaust systems have a test port for this), disconnecting the O2 sensor, and removing the vacuum line from the Fuel Pressure Regulator.

If the AFM and DME are working properly, the reading should not be above 0.6%. If the reading is low, the technician should turn the AFM by-pass screw IN (richer). If the reading is high, the AFM by-pass is turned out (leaner).

HTH
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Old 05-02-2003, 05:14 AM
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