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Old 11-25-2005, 09:13 PM
Registered User
Join Date: Nov 2005
Posts: 3
1977 280E Fuel probs.Undrivable!

Hi Guys,

I am in the process of getting '77 280E 123 model running again.

I'm having trouble with hesitation and lack of power making the car to be undrivable.

It seems to get the worse as the engine gets warmer.

Idles fine when cold and seems to rev ok with a bit of a miss here and there.

Once a bit of heat gets into the motor the idle drops and turns lumpy and it just doesn't want to rev.

I detached the warm up regualtor from the block and disconected the electrical conection.

To see if it would make any difference.It seemed to idle properly for a bit longer and could be driven under 15 klms per hour for about 5 -10 minutes.

Then returned to a lumpy idle and and no power/stalling condition.

I checked the voltage to the fuel pump when cold and got 11.5V and when it was warm i had 10.5V is this normal? would this be enough to send the pump lazy and reduce the flow of fuel? and cause these problems?

Thanks for any help.


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Old 11-25-2005, 10:49 PM
t walgamuth's Avatar
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 35,538

it smoke black when it is running badly?

my 280e had a bad warm up compensator which made it run very rich.

if it is smoking black that might be the prob

tom w
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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Old 11-26-2005, 01:51 PM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
I always thought the pump needed at least 11.5 volts to work right. Try jumping 30 and 87 on the FP relay and see if that improves the feed to the pump and the running problems. If so, then that would mean the relay is going bad.

You should also check the EGR valve. They can cause a massive vacuum leak when the engine warms up.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 11-29-2005, 01:50 AM
Registered User
Join Date: Nov 2005
Posts: 3
Thanks Guys,

The car doesn't seem to idle too rich no black smoke anyway.

I have a gut feeling the Warmup regulator is the culprit.

C taylor- Could you please tell me where I can find the FP relay?

It's a 1977 280E w123 RHD model.

Thanks heaps. Jeremy

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