|
|
Year(s): '86 - '91
Model/Type: 2.1L Digifant models
Symptom(s): Stumbling stuttering during long drive. AFM static Air flow Sensor Modification
The addition of a capacitor to the air flow sensor wiring may help with intermittent miss. (The mechanic at the dealership says this will also cause stalling after being driven awhile and will not restart for about 30 minutes. Runs fine when restarted.) A 22uF/25 Volt tantalum capacitor can be installed.)
1) Remove the connector from the air flow sensor.)
2) Pull back the boot on the connector for the air flow sensor.) Remove connectors 2 and 4 from the hardshell connector for the air flow sensor.)
3) Cut the connectors of the ends of the wires, strip the ends of the wire and connect the '+' side of the capacitor to the #2 wire and the '-' side of the capacitor to the #4 wire.
4) Crimp on new power timer connectors on the #2 and #4 wires and reinsert them back into the hardshell connector.
5) Reconnect the airflow sensor connector) Connect a ground from the metal part of the air box to the empty 6mm ground connection point on the right cylinder head.
6) Solder the + side to wire #2 and the negative side to #4. wrap the bare wires in electrical tape, then slide the boot back up over everything, this seals everything in well. This information was made available to me through the many helpful Vanagon people on the web. Also note the added ground wire.
Another variant of the installation which begins with a testimonial:
This does work, cleared my probs immediately, so far for 14months now. My only recommendation is that when installing simply pull back the rubber boot exposing the 4 wires that go to the connector. Find #s 2 and 4 and simply nick them for a 1/2" or so to expose the bare copper. Pry the wire out of the insulation by pushing a nail/knife under. Then solder the capacitor right across the bared loops of copper. No 15cm leads, no fighting with connector lugs etc. Use some electrical tape over the solder sites then tuck, everything neatly back inside the rubber boot.
(1) The capacitor I used was a 25Volt 22microfarad tantalum type. I read of mention of the stuttering problems not being completely solved with 10ufd size, quoted from a LIMBO article (via email) maybe? NOTE: it says to use #2 as positive, #4 as negative !!! I used it this way. Any electrical geeks wanna tell if it makes a diff in this application? Prolly. Tim Smith '87 non?stuttering Syncro
(2) Getting the polarity right is certainly key, as a backwards one will get leakier and leakier (electrically) and finally short. If there's enough power in the circuit, an aluminum capacitor will blow its can off (until the spoilsports put a crease in the top so now it just peels open) and a tantalum will squirt a tiny jet of molten tantalum in some random direction. David Beierl ? Providence, RI http://pws.prserv.net/synergy/Vanagon/ '84 Westy "Dutiful Passage" '85 GL "Poor Relation"
Details on the capacitor for this fix.
(1) I bought a tantalum 22MFD 35VDC capacitor cost me $4.50, the tantalum types cost more other types. The capacitor needed is a 25 volt 22 microfarad tantalum type (cost me .41 cents).
(2) Tantalum is just another type of electrolytic capacitor, it uses different material. Most electrolytic capacitors use aluminum. The difference is tantalum in place of aluminum. The higher the voltage the better off you will be also. Go with the 35Vdc rating. This will handle any transient spikes. Also because of the various temperatures located there, there will also be variations in the capacitance. Bill
(3) Response to someone who said polarity didn’t matter. I beg to differ. Tantalum capacitors are polarized. They have a marking to show the positive connection. The actual symbol for identification can vary but it is there. Have a look at any comprehensive parts catalog and it will identify the positive connection. Regards, Indulis
(4) Responses to a person whose fix had stopped working:
(a) The problem with your 22mF/35V capacitor is that it's failed, not that it's 35 volts. My guess is that the heat in the engine bay took it out. Use the highest temperature spec available. There is a special "automotive" spec, with reason.
(b) Capacitors have limits as to the amount of voltage it can handle across its plates. Thus, the rating givin' specifies the MAX dc voltage that it can withstand before failure. As a rule of thumb, you should always use a higher rating when designing circuits.
(c) I suspect that the electrolytic (tantalum) capacitor was breaking down. Heat has a definite reaction to capacitors. This depends on the temperature coefficients. An example would be 100 ppm/C for a 1 micro farad capacitor calculates to 1 degree Celsius rise in temperature, the capacitor will decrease by 100 Pico farads. Yes, temperature vs capacitance is inversely proportional
NOTE: If you have opened your AFM and know what you are doing, the cap can be soldered to the terminals in the AFM which are marked. The plus connection
of the cap is soldered to terminal 2, and the minus connection to terminal 4.
See Comments on this entry (F.W.I.W.)
|
|
|
