4.5 fuel mixture - Mercedes-Benz Forum

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post #1 of 7 (permalink) Old 05-13-2008, 09:00 AM Thread Starter
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Vehicle: 1972 280 se 4.5
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4.5 fuel mixture

anybody know how i can improve air/fuel mixture? im getting about 3 miles per gallon, and its killing my wallet!!
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post #2 of 7 (permalink) Old 05-13-2008, 08:51 PM
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Check the cold start injector to make sure it's not leaking. Make sure the other 8 aren't stuck open either. There could be quite a load of crud in there. What is the condition of all the spark plugs?

Then do a search on 'djet' to see what others are doing. You can also check the service manuals on W116 index: Mercedes-Benz S-Class - 280S, 280SE, 280SEL, 300SD, 350SE, 350SEL, 450SE, 450SEL & 450SEL 6.9 on checking and adjusting.

Near Manassas Va. '65 220S, 2006 Ford Crown Victoria Police Interceptor, '99 Volvo V70, '72 350SL 4 speed

Not part of the in-crowd since 1952. It's BRAKES not breaks. You break a bone, use brakes to stop your car. /rant

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post #3 of 7 (permalink) Old 05-14-2008, 08:00 AM
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You might want...

Add a can of "Seafoam" to 1/2 tank of gas and then run the car until the reserve light comes on, then refill as normal. You can find it at Kragen/Shucks, or AutoZone, etc.

Seafoam has quite a following over on the W210 forum and elsewhere. It will help get the "crud" out of the injectors and intake system.

Good luck,

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post #4 of 7 (permalink) Old 05-14-2008, 11:23 AM
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These engines have air temp and coolant temp sensors. If the brain doesn't get the right resistance from these, it can go pig-rich.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #5 of 7 (permalink) Old 05-15-2008, 10:36 AM Thread Starter
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my manual says to check the pressure sensor and replace if needed. also pressure regulator and adjust or replace?? are these issues anyone has incurred?
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post #6 of 7 (permalink) Old 05-15-2008, 05:51 PM
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The "pressure sensor' is that device on the firewall that is connected with a hose to the engine and has a plug connecting to the loom. Get a second hand one from somewhere and just swap it over to make sure it's OK. it uses engine vacuum to determine the engines fuel requirement so that hose must also be OK.
But you cannot just guess your way through a Djet by swapping stuff over. there is a right way and wrong way to fix injection .
Start by tuning the ignition so it is PERFECT .
Replace the fuel filter with a new one. And any of the rubber hoses by the tank.
then do a pressure test on the engine. Average pressure at the cold start valve is 28PSI. More than that and the pressure regulator(s) has failed or the return line to the tank and in the tank has become blocked.
Theres lots more to check but that should get you on the way.
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post #7 of 7 (permalink) Old 05-08-2010, 03:22 AM
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The seafoam website also talks about putting it straight into the crank case and PCV....anyone try that? I'm tempted to give it a shot from what I've read on other forums.

Former MB: "Miss Juliana" - 1972 280SEL 4.5
Current MB: 2013 C250
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