Date: Sat, 19 Feb 2005 17:31:02 -0800
Reply-To: Mark Keller <kelphoto@TELUS.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@TELUS.NET>
Subject: Re: AFM ADJUSTING
Content-Type: text/plain; charset=us-ascii; format=flowed
Adam H. Behle wrote:
>Ok, so today I hooked up my multi meter to the o2 sensor and drove around to get various
>readings. The lowest voltage I could get back was around 650 millivolts while cruising. If I
>tightened the spring anymore the mm would start to go crazy and give negative readings, etc. It
>was as if the AFM was ultra sensitive and sending out too much info in too great a range for the
>mm to pick up. Idle in this position was "lopeing" around 1000 rpm +/- 150 rpm. The good
>news is it definatly is not running as rich as it was.
>
>Any ideas how to drop the millivolts further? Or is my AFM too far gone to salvage? Thanks again
>for all your help, Adam
>
>On Fri, 18 Feb 2005 18:17:05 -0800, Mark Keller <kelphoto@TELUS.NET> wrote:
>
>
>
>>Adam H. Behle wrote:
>>
>>
>>
>>>Thanks for the AFM info. I recently have had idle problems and rich running conditions with
>>>
>>>
>my
>
>
>>>87 Westy. I tried checking everything per Bentley, replaced vac lines, grounds, etc. Swapped
>>>
>>>
>out
>
>
>>>idle stabillizer unit with a good one, tested oxy sensor per your instructions, and replaced all
>>>
>>>
>the
>
>
>>>usual tune up items with no luck. Finally gave up and took it in to my mechanic. He checked
>>>
>>>
>the
>
>
>>>fuel pressure and swapped the ECU, but no luck. Finally swapped the AFM and said it fixed it.
>>>
>>>Before shelling out $550 for a new one or $200 for a rebuilt unit, I wanted to try re-aligning
>>>
>>>
>the
>
>
>>>AFM track/arm and cleaning the unit, which ended up doing nothing. Then I tried tightening (I
>>>think) the spring by turning the wheel counterclockwise about 6 clicks and it worked! Great
>>>
>>>
>idle,
>
>
>>>lots of power, better than it has ever been before-BUT it is running extremely rich. Tailpipe is
>>>really sooted up, nauseating smell and fumes, etc. Interestingly, mileage seems to have only
>>>decreased 1-2 mpg.
>>>
>>>My qustion is...do you think I can get my AFM back into whack by performing your adjusting
>>>technique, or do you think it is too far gone and I should cough up the cash for a rebuilt one?
>>>There are paint marks where the spring was originally, but the engine would not keep an idle-it
>>>would get progressively worse the more clockwise the spring wheel was turned. Any help from
>>>anybody would be greatly appreciated-thanks! Adam
>>>
>>>On Tue, 15 Feb 2005 16:09:56 -0800, Mark Keller <kelphoto@TELUS.NET> wrote:
>>>
>>>
>>>
>>>
>>>
>>>>Hi Marc,
>>>>
>>>>I would so love to show you how to fix your van in person. I've have
>>>>written quite a bit about tuning the fuel injection system. You of
>>>>course may have other issues, but if your willing to read my procedures,
>>>>they will help you pinpoint what works and what dosen't.
>>>>
>>>>
>>>>First thing is how are you with using a digital volt meter? If you have
>>>>one this is a key piece of equipment.Ok, there are two ways to get the
>>>>detail instructions, 1. search vanagon.com archives of the vanagon list
>>>>under author's name contains, just enter kelphoto. That should pull up
>>>>every thing I've written years 98-2003 are the ones you want. 2. Sam
>>>>Walters has saved most of my articles, and may send you the complilation.
>>>>
>>>>Just to get you thinking let me say some things about the Vanagon ECU.
>>>>What it does know. Air flow, Air temp, water temp, amount of hydro
>>>>carbons in the exhaust stream, if the engine is at idle or wide open
>>>>throttleor WOT. What it dosen't know, but belives to be at a specificed
>>>>value. Fuel Pressure and timing.
>>>>
>>>>
>>>>What corrupts the ECU's perception of it's world. Bad grounds, wrong
>>>>fuel pressure,wrong timing (not too likely), vacuum leaks, bad wireing
>>>>harness, wires and or connectors. Faulty sensors. Poor contacts of the
>>>>microswitches. Other issues are if the idle circuit is not working
>>>>properly, but note this circuit is only relied on when warming up a cold
>>>>engine. A warmed up engine will idle fine with it disconnected, which
>>>>rules out another failure point. i
>>>>
>>>>So the critical path according to liklyhood of failure is to check the
>>>>fuel pressure. Then ensure ALL of the connectors are clean and tight.
>>>>Then check the high failure items. Temp II sensor, the wire from the O2
>>>>sensor to the ECU, common short, and a intermittant one at that. The AFM
>>>>is a variable. Carbon is used to determine resistance, and does wear
>>>>thru where the wipe arm sweeps, visual inspection is telling, look for a
>>>>white mark where it should be black. Other things are the ilde and WOT
>>>>microswitch connuity
>>>>
>>>>So if I were there, the first thing I would do is to disconnect the O2
>>>>Sensor, and connect the DVM to the sensor lead, and start the engine.
>>>>The voltage should show in the first minurte or two, if not the O2
>>>>sensor needs attention first. Remove it, heat the sensor tip with a
>>>>propane touch. This will accomplish two things, it will clean the soot
>>>>off, two see if it will now generate voltage. The voltage should be
>>>>between .3 and .7 volts. The ECU ignores the O2 until the TEMP II
>>>>begins to registers, just as the temp guage touches the white block,
>>>>then the ECU goes to open loop. Email me whenever you like
>>>>
>>>>Mark Keller
>>>>91 Carat
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>Adam,
>>
>>Yes you should try to recover your old AFM, mines at 240,000 miles, one
>>track adjustment an works fine.
>>
>>It's a common misconception that the AFM controls idle. The AFM spring
>>adjustment should only be done while the O2 sensor is disconnected and
>>you are driveing the van and monitoring the O2 sensor via a digitial
>>voltmeter. A good test area will include a couple of miles of level
>>and continueous grade so you can see how well the AFM spring and Flap
>>interrelate with load on the engine. Perfection is to have the voltage
>>in the low range ie .3 ish when at cruise, and .84 ish when on grades.
>>
>>Once the spring tension is set, then look at my procedures for setting
>>the idle. Bypass the idle control circuit and then you need three
>>things: a working microswitch at idle, Adjustments to large air bypass
>>screw for RPM, and the allen screw adjustment for idle air bypass on
>>the afm which controls mixture. You basic have to do a spiral
>>adjustment, first RPM, then mixture and so on. Repeat until the idle is
>>steady at 840 Rpm or 860 Rpm I forget which it is off the top, and the
>>o2 sensor is at .5 volts. While the O2 dosen't read CO level O2
>>voltage approximates CO in percentage, So .5 volts correlates to
>>something in the range of 5% CO-- according to Probst "Bosch Fuel
>>Injection"
>>
>>So in short Don't bother with idle adjusment until the spring tension is
>>set.
>>
>>Mark
>>
>>
>
>
>
Hi Adam,
Good job getting out there and testing. How was the power on grade?
Were you able to get any readings other than .65 Volts. It should drop
to nil In a decceleration the with rpm above 1700 RPM and the Idle
Microswitch on, ie your off the gas pedal as the ECU cuts all gas to the
engine. Does the O2 sensor readout reflect this? Did the O2 voltage
show richer/higher volts on grades, How many clicks or teeth did you end
up moving?
Just for clarity you do have the O2 sensor disconneted from the ECU.?
What type of wire are you using to carry the signal from the O2 lead to
the front of the van. Microphone wire works best. And The O2 Sensor has
to be clean, normally I wouldn't say this, but your trying to run down
erratic behavior and you did say that your were running extremely rich.
Wouldn't hurt to clean it with the propane torch. No exhaust leaks
either. Sorry, but I had a van come in for this procedure and he had a
major leak at the two into one collector. As a result the O2 input was
usless.
For the moment lets ignore what the DVM was reading, Remembering the
"spiral" therory, go ahead and make 1st approximation adjustment to the
idle. Engine warm, Idle circuit by passed.That is plugs removed from the
controller per Bently and plugged into each other and the idle air motor
disconnected. Turn large air bypass screw to drop the Idle rpm. Were
kinda flying blind without the O2 data, so if the RPM drop cause it to
stall, I 'd leave alone until you get the O2 sorted out, and the spring
tension right on the road test portion.
Mark
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