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Old 11-02-2011, 12:35 PM
Registered User
Join Date: Nov 2011
Posts: 1
w108 2.8l fuel mixture adjustment

hi guys, i recently found that my car runs rich ( smell of gas while driving). ive gone over the WRD which was stuck from the car sitting for a long time and also the cold start valve is working properly. Now with those issues aside i wanted to know if someone could walk me through the air and fuel mixture process. I tried to lean out the fuel from the back of the IP and close up the air bypass a bit but still the smell of fuel.
Also i noticed that when i push on the brakes while in park the car will rev up. Is that a sign of too much air through the bypass or not enough? Also How much air should be coming through the bypass?
Any helpful hints forr me to get this job done would be appreciated.
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Old 11-03-2011, 08:18 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
The first thing that you need to check is the fuel enrichment during warm-up.

Make sure the fuel/additional air shuts off after warm-up.

Remove the screw on filter & make sure that when warm, that there isn't any suction there.
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Old 11-03-2011, 01:28 PM
Brian Ostosh
Join Date: Mar 2007
Location: San Diego
Posts: 504
smells of gas

Does it smell of raw unburnt (leaking)
burnt exhaust? (mufflers, trunk seal)

There are lots of leak potentials, check rubber connecting hoses front
to back and underneath by the tank and elect pump. and in gas fill door. even the tank sending unit can leak and be fixed cheap, or just replace all that for fun, (and future safety) cheap and easy work.

Then determine whether smell is cold or warm motor,
then after a full tune-up and valve adjustment, and compression test.
then can start to adjust MechFuelInjection pump idle circuit.
Then the activating connecting linkages.

Great cars, great motors, no mystery's
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Old 11-10-2011, 09:55 PM
Join Date: May 2009
Location: Brick, NJ
Posts: 48
Idle Change when pushing on brake pedal

I'm no expert, but I don't think the engine RPM should change if you step on the brake pedal. The brake booster vacuum should be a closed system. I can't explain your fuel smell.

I ran into a weird situation with my 250SE 108 where this same situation happened and it turned out the seal between the booster and the master cylinder was leaking.
I didn't understand the connection between the brake application and the RPM increase until I started the car one day and was getting clouds of smoke out of the tailpipe, (I initally thought it blew a head gasket!)then there was no fluid left in the master cylinder reservoir. The booster seal failed and over time got worse until the engine vacuum sucked all of the brake fluid into the engine. I figured this out when I saw that the little plastic bottle in the booster vacuum line had fluid in it. I blocked off the booster line and restarted it-no more smoke. I replaced the seal and the master cylinder. The car idles and has run perfectly ever since.

Again I'm no expert....
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Old 11-10-2011, 10:27 PM
Registered User
Join Date: Apr 2006
Posts: 442
First thing to check is that the injection pump linkage/ rod allows the IP to return all the way at idle. Pop the rod off the linkage by the valve cover and make sure that all is in adjustment correctly.
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