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Rewiring the Mass Air Flow Meter Sensor Connectors
 The
V12 engine uses two Mass Air Flow (MAF) Meters. One is used for the left bank of cylinders, the
other is used for the right bank. What you must keep in mind is that the MAF on
the left side of the engine feeds the right side bank of
cylinders, and the MAF on the right side feeds the left bank of cylinders.
Mercedes Benz used a wire insulation
material that was unsuitable for the high-temperature environment of an engine
compartment. Rumor has it that it was developed to be biodegradable in an effort
to be environmentally conscious. Unfortunately, the insulation degrades in the
car. This seems to be the case with many different types of MB models around
1992 to 1995. The insulation begins to break down and crack. If the problem is
not addressed, the insulation will eventually fall off the wires and cause short
circuits. Insulation failure in the MAF wiring bundle can cause rough idling
and/or surging problems, among other things. At the least, this could cause all
sorts of caution lights to light up on your dashboard. At the worst, it could
cause an engine fire. In my car, I got an intermittent Check Engine (CE) caution
light. Pulling fault codes from the onboard computers did not really point to
anything specific.
One way to determine the condition of
insulation quality is to do an Insulation Breakdown test. To do this requires
specialized equipment though, something that most people don’t have in their
garage. In addition, there are some very sensitive electronic components that
could be damaged by performing such a test. The best way to examine the
condition of the wires is to visually inspect them.
This page describes the problem I had,
and what I did to fix it. Note that I did not replace the entire wire lengths in
this project. The insulation on the wires in my car was only damaged near the
high heat areas. I spliced new wire into the existing wire. Doing this avoided
the need to pull the module housing and all modules out of the car. This
write-up does not include steps to pull out the module housing.
Tools needed:
- X-Acto knife with sharp blade
- Flat blade screwdriver
- Wire cutters / strippers
- Soldering Iron, along with flux and
solder
Parts needed:
- Solder splices
- Raychem Heat shrink tubing,
1/4" ID
- Raychem Heat
Shrink tubing, 1/2" ID (#DR-25)
- Two stainless steel hose clamps,
sized for approximately 1/2 inch diameter.
I chose to use 5 different colors to help keep the
5 wires
identified. I used the same colors for both left and right MAF harnesses, so I labeled
the wires to make sure I didn't mix them up. However you decide to proceed, here are the lengths you need;
- M22759/11-20 wire in 8 foot lengths
for the right MAF
- M22759/11-20 wire in 15 foot lengths
for the left MAF
I used Military grade wiring for
this as it is can withstand high temperature. It is rated for a conductor temperature of 200° C, and the insulation is able to
withstand a constant temperature of 260° C. The wire number series is
M22759/11. The -20 designator is the wire gage size. 20 gage is comparable
to the original metric size of .75 mm.
The color designator is also a
number, and is placed at the end of the wire and gage number. So for
example, M22759/11-20-6 is a 20 gage wire with blue insulation.
It is assumed that you know how to
solder well.
If not, find a friend who knows how to solder to help you.
Possible Wire Suppliers:
Whitmor / Wirenetics
27737 Hopkins Ave
Valencia, CA 91355
800-822-9473 |
Sea Wire and Cable,
Inc.
P.O. Box 647
451 Lanier Road
Madison, AL 35758
800-633-7210 |
Galaxy Wire and Cable
420 Babylon Road, Suite D
Horsham, PA 19044
888-425-4454 |
RDS Wire & Cable
225 E. Gardena Blvd
Carson, CA 90248
310-323-7131 |
Dearborn Wire
250 W. Carpenter
Wheeling, IL 60090
847-459-1000 |
Sheathing Supplier:
Varflex
512 W. Court Street
Rome, New York 13440
Sheathing Data
I used Varflo (size 3), which according to their literature is good to
130° C. I personally tested it to 190° C, and it withstood the
temperature without any problem. I would suggest you use something with a
200° C rating or higher.
Adhesive / Sealant data:
Dow Corning 3145 RTV (Room Temp
Vulcanizing) Gray
MIL-A-46146
Available from:
Ellsworth Adhesive Systems
Germantown, WI
800-888-0698
Approximately $18.00 for a 3 ounce tube.
| CAREFULLY cut the
sheathing of the MAF wire harness open. You must go slowly and with
caution so as not to cut into the wires within the sheathing. The
sheathing is pretty tough stuff, so be patient.
Cut the sheathing approximately 4
inches, and carefully pull out the wires inside it.
If the insulation is not cracked,
you are in luck! Place the wires back inside the sheathing, and secure the
sheathing with electrical tape. Check the other side as well to be sure.
|
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| If they look like mine
did (cracked insulation), you're going to need to rewire.
Examine closely,
especially near the connector.
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| Remove the MAF wire
harness connector by twisting the lock ring in the direction shown. Pull
the connector away from MAF.
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|
#1 Remove the rubber weather strip
off by pulling straight up.
#2 Remove both left and right plastic covers by
twisting the retaining tabs 90 degrees.
#3 Release the retaining clips on
the wire harness tray covers, and remove the covers.
|
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| With the covers off,
you will be able to see more of the wires. The MAF wires are routed into
the tray at this point. |
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| More shots
of the wires in the tray.
Notice the wire bundle with the
label on it? This is the wire bundle for the injectors. A previous owner
replaced it. It looked brand new.
You should remove the wrapping
around the harness to expose the wires. The wrapping may hide smaller
cracks.
You can see more cracked
insulation in this photo.
|
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| You now need to follow
the wires back toward the module box. The photo shows the module box
circled.
In my car, there was a point
where the insulation was not cracked anymore. This is where you need to
cut into the wires to splice in the new wire.
Don't cut into anything just yet.
Measure the length of wire you will need to replace for each MAF. Add at
least two feet to this length for a little safety slack.
|
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| This photo shows how
the wire bundle runs.
It was in this area that I was
able to cut into the old wires. Remove
the wrapping around the bundle, and gently separate the MAF wires away
from the bundle. |
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| Good electrical
technicians will stagger splices to eliminate the risk of short circuits
in case the splices fail. So keep this in mind when you cut into the
original wiring, as well as when cutting the new wiring to fit.
Examine each wire, and determine
which wire needs to be cut back the furthest. Cut the remainder of the
wires accordingly to accomplish the staggering.
In my case, it was difficult to
determine the original wire colors. They were faded with age. I labeled
each matching wire as I cut it. You must keep track of this so that you
know which wire goes where
when wiring it all back up.
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| We're in the thick of
it now.
Remember to identify the wires
properly with tape!
Make sure you also know which MAF
the wire goes to if you're doing both at the same time.
The Left MAF wires run inside the
tray along the firewall, and then "merge" with the Right MAF wires.
|
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| This is the Right MAF bundle. Notice the goop someone in the past tried injecting to
seal up the cracks in the insulation! Obviously not a good way to fix
this.
I met a friend from Germany over
the internet, and he told me that this "fix" was really intended
to prevent chaffing and excess movement in the wires. The purpose was to
secure the wires so that more insulation would not fall off, and not
necessarily act as an insulator.
|
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| Now we need to
disassemble the connectors.
Gently pry the retaining ring
away from the connector using a flat blade screwdriver.
|
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| The retaining ring is
off.
|
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| Using a sharp new X-Acto
knife, CAREFULLY start to score the connector along the mold line. Make
repeated passes to gradually increase the depth of the cut. Do NOT try to
do this in one pass!!
PLEASE be careful, as a slip
could mean a trip to the hospital.
Note that this group of
photos shows the retaining ring in place. You should have already taken it
off. I did not discover that it popped off until later.
|
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| Keep working at
scoring the two halves apart...slowly but surely.
Work your way around the
connector.
REMEMBER!!! The cleaner and
better you do this, the less chance of destroying the connector!
I cut the wires off the
connector in this bottom photo to make it a little easier.
|
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| You will get to the
point where you will be able to insert a flat blade screwdriver between
the halves as shown.
CAREFULLY, gently, and slowly pry
the halves apart in various places. Do not force the halves apart in one
spot, you can damage the plastic. Keep prying in different spots to get
the entire seam to split.
|
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| The halves will come
apart as shown.
|
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| Pull the connector
pins and wire bundle out of the connector.
|
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| In case something
breaks, these are the part numbers I saw on the pieces.
If you do need to buy a
connector, order part number 140 540 00 81.
|
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| Unsolder
the old wire from each of the connector pins. Make sure all the old solder
is removed from the pins.
|
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| Solder a new length of
wire to each connector pin, and place the pins back into the connector.
Keep track of the pin number for
each wire. The pinout is as follows;
Pin Position # Original Wire Color
Pin 1
= All Brown
Pin 2 =
Red stripe
Pin 3 =
Purple stripe
Pin 4 =
Green stripe
Pin 5 =
Black stripe
Form the new wire so that the
wire rests relaxed in the wire grooves of the connector.
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Cut a 2 inch length of 1/2
diameter Raychem heat shrink tubing, and slip it over the wires. Heat
shrink it in place as shown.
Cut a 12 inch length of the
Varflex sheathing. Insert the new wires into the Varflex.
|
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| Apply silicone
adhesive to the outer edges of the connector, as well as the
area where the Varflex sheathing will be.
|
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| Carefully move the
Varflex sheathing so that the end rests in the bundle opening of the
connector. While holding it all together, assemble the back cover to the
connector trapping the wire and Varflex securely.
Don't let the red wires confuse
you. This is a new photo to illustrate this step better.
|
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| Gently
clamp the connector halves together with just enough force to keep them
together. Do not squeeze too hard. Wipe off the excess adhesive, and allow
to dry for at least 24 hours. Remember, this adhesive cures using moisture
in the air. Elevating the temperature will not help it cure faster. Thick
cross sections of adhesive will take longer to cure. I also installed a
small stainless steel hose clamp onto the round portion of the connector
where the wire bundle comes out. This helps hold the connector together
while curing. I left it on to add strength to the area after cure.
|
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| Once it's
fully cured, assemble the retaining ring back onto the connector. I
painted the arrow white on mine so I could see it better. |
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| Place the newly wired
connector on the MAF sensor. Route the new bundle into the wire tray.
Determine where to cut the new wire so that it can be spliced into the old
wire.
Remember to stagger the cuts.
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| Once
you've cut the new wires to their proper lengths, strip back about 1/2 of
an inch of insulation from the ends of the old and new wires.
Place a 1 inch long piece of 1/4
inch diameter shrink tubing over one of the wire pairs.
Twist the wires together, and
solder them. Move the heat shrink tubing over the solder joint and heat
shrink in place.
You can use electrical tape
instead of heat shrink tubing, but make sure you buy a good type. One that
bonds to itself and seals up would be excellent.
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| Once you have all the
wires connected and soldered, lay them neatly back into the wire tray.
Secure the wire bundle with nylon tie wraps, or several wraps of
electrical tape. It's always a good idea to keep the wires tightly wrapped
to prevent chafing.
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| Install the wire tray
covers, making sure that you're not pinching any wires.
Install the weather stripping and
the two plastic covers.
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| Connect the
MAF connector to the MAF. Make sure you feel a slight snap to be sure you
twisted the connector on all the way. You're ready to fire it up!
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