500SEC Fuel system problem - PeachParts Mercedes-Benz Forum

hitwtom · #1 09-13-2007, 08:08 PM

I'm having some problems with my newly aquired 1985 500SEC. It starts right up and will idle about 500-600 RPM, when I press on the accelerator everything seems fine until I get to about 1000-1100 RPM then the engine seems to choke and want to die (lack of fuel?). The car had been sitting for about 2 years so I drained the fuel tank, removed the fuel pump, filter, accumulator? pressure regulator? and tank screen. Cleaned everything and got a new filter, checked the fuel pump while I had it out and put it all back together. Still have the same problem. Also the throttle position unit? (circled in the picture) makes an awful lot of noise (clicking) when the key is turned on or when running. I'm new to the gasser world but I've got 2 MB diesels. Thanks in advance

Lander91 · #2 09-13-2007, 08:33 PM

When you try and accelerate does the engine stumble and struggle to rev up, can you rev the engine while in neutral?
P.S thats the cruise control actuator not the TPS

hitwtom · #3 09-13-2007, 08:49 PM

Quote:

Originally Posted by Lander91

When you try and accelerate does the engine stumble and struggle to rev up, can you rev the engine while in neutral?
P.S thats the cruise control actuator not the TPS

It is doing this in "park" If I put it in "drive" I can idle out the driveway.

cdplayer · #4 09-13-2007, 09:41 PM

Check the condition of your distributor cap. Actually take it off and look for cracks. Could be just that simple.

ctaylor738 · #5 09-13-2007, 09:51 PM

It sounds like the warm-up regulator to me. It suppies enrichment on warm-up and acceleration. A common casualty of extended sitting. If you put a gauge on it, I predict you will see high control pressure.

CamelotShadow · #6 09-13-2007, 10:59 PM

My 83 500 sec was only used 300 miles in 4 years.
I have noticed on a restart of a hot engine
Actually hot restart was a bit troublesome
as it didn't start right up
I also noticed a lumpy lobbiness to the engine in park idle after the hot restart...

Could this be related to sitting?

Thanks

PS When cold starts right up
idles 1000 in park
but goes down to 650 in drive.

Engine is otherwise pretty smooth & strong

Thanks Again

ctaylor738 · #7 09-14-2007, 05:59 AM

It could be from sitting, but also from age and mileage. Your injectors may be getting weak and losing pressure, your accumulator the same.

Your idle speed is where you should be with a cold engine. Could be the idle relay, or the temp sensor at the back of the engine.

hitwtom · #8 09-14-2007, 01:58 PM

Quote:

Originally Posted by ctaylor738

It sounds like the warm-up regulator to me. It suppies enrichment on warm-up and acceleration. A common casualty of extended sitting. If you put a gauge on it, I predict you will see high control pressure.

Where is it located, and what does it look like?
Thanks,

ctaylor738 · #9 09-14-2007, 04:32 PM

It's on the front of the intake manifold. It has two lines from the fuel distributor, a couple of vacuum connections at the bottom, and a two prong electrical connection.

hitwtom · #10 09-18-2007, 10:08 PM

Thanks Chuck, I removed the air filter housing and did some cleaning with carb cleaner. The air flow sensor? (large round air intake) was very gummed up. After a good cleaning, I could rev it up to about 2000rpm. Squirted some cleaner in the vacuum lines of the warm up / acceleration regulator. Was able to rev it up to 3000rpm. Is the vacuum fitting on top a vent? Or am I missing a line somewhere?

CamelotShadow · #11 09-18-2007, 10:20 PM

Is this the warm regulator?

I'd have liked to have seen a pic under the air cleaner assembly

I took my filter out yesterday & cleaned some debris out from under it.

I noticed on the lid over the part with the tubing coming out that the lids was sooty ther so I wiped it.

I'd be curious to see whats under the assembly

Glad that seemed to help your porblem.

ctaylor738 · #12 09-18-2007, 10:50 PM

hitwtom -

The fitting on top is just a vent.

4-speed · #13 09-19-2007, 02:58 PM

The item circled is the cruise control actuator. the CC amp is under the steering column.

hitwtom · #14 09-20-2007, 02:09 PM

Update, after some more cleaning, and checking vacuum lines (I thought MB diesels had a lot of vacuum lines) It will now rev to 3000 at start up without much problem. After about 30 seconds it's like a governer kicks in and speed drops to 1700-2000. If I drop back down to idle it will rev to 1700-2000 but not much higher. If I shut the car off and let it sit for a few min. it will do the same thing all over again. Any more ideas?

Thanks 4speed, I've got the cruise control unplugged for now until I can get everything else working properly.

sublettd · #15 09-21-2007, 08:56 PM

Chuck,

Have you got a diagram/picture of where the coolant temp sensor is located? The car is the 500SL (Euro).

Thanks!

Quote:

Originally Posted by hitwtom

Update, after some more cleaning, and checking vacuum lines (I thought MB diesels had a lot of vacuum lines) It will now rev to 3000 at start up without much problem. After about 30 seconds it's like a governer kicks in and speed drops to 1700-2000. If I drop back down to idle it will rev to 1700-2000 but not much higher. If I shut the car off and let it sit for a few min. it will do the same thing all over again. Any more ideas?

Thanks 4speed, I've got the cruise control unplugged for now until I can get everything else working properly.