88' 500 SEC w. KAT - stalling on acceleration - Mercedes-Benz Forum
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post #1 of 13 (permalink) Old 12-22-2018, 10:17 AM Thread Starter
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Unhappy 88' 500 SEC w. KAT - stalling on acceleration

Hello Guys,

I have a rather big problem with my euro 500 SEC. The car stalls when I'm trying to accelerate - I know it sounds funny but this issue makes car totally undrivable in regular traffic. I've done a video that shows the problem - english subs are available if You want


The car itself sat unused for 9 years because of gearbox malfunction. Gearbox was rebuild, the engine started after putting in it new pumps and some fresh fuel. It can run on idle for hours... but trying to move it a little bit faster almost always ends like in the video.
So far I've resoldered the fuel pump and idle relays, fuel pumps are new, fuel filter is new, ignition coil is new, rotor and cap are refubrished. Today I resoldered the OVP - the video was made before I done it, had no chance to test if it made any difference.

I will be grateful for any good advice...
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post #2 of 13 (permalink) Old 12-22-2018, 11:39 AM
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Ckeck all your throttle linkages for proper movement.

Make sure the throttle body is moving properly and the throttle body switch is functioning.

Verify that the air flow meter is able to move freely and is adjusted to specifications.
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post #3 of 13 (permalink) Old 12-22-2018, 06:53 PM
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Plugged cats? Is this after it warms up? Can you rev the motor that fast when it's in idle?

1991 560 SEC Euro
1986 420 SEL
1985 500 SEC (US)
1983 500 SEC (Euro)
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post #4 of 13 (permalink) Old 12-23-2018, 02:07 AM Thread Starter
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Originally Posted by corellian corvette View Post
Plugged cats?
I hope not - car has got single catalytic device, I've had to buy a used one because whole section of exhaust with converter was cutted off. As far as I know - this would be the least plausible cause of stalling...

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Originally Posted by corellian corvette View Post
Is this after it warms up?
The video was made when the car is around 60 - 70 degrees C. Will have to check how the car behaves after when it's totally cold, and how it is when it's around, and above 80 C.

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Can you rev the motor that fast when it's in idle?
Well, when in idle it revs without any problems. Faster, slowly - anyway you want. But when you want to drive off a little faster - bam! - it dies.
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post #5 of 13 (permalink) Old 12-23-2018, 07:33 AM
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Towards the end of the video when you drive off from the side of the house there is an unusual sound when it dies? High pitch like a squeal?
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post #6 of 13 (permalink) Old 12-23-2018, 02:31 PM
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When the engine is idling in park and you go around the back and listen to the fuel pumps are they making a steady humming noise with no variation in sound.
Or do they appear to change pitch (sound) as if they are cycling up and down versus a steady hum.
Stalling under load indicates the pumps are clogged (even though they are new) from fine rust sediment in the tank that gets past the tank strainer.

I have had this happen to me some years ago with brand new pumps as well
The engine would die under any load but happy to idle a rev with no load in park.

Its because the pumps are just supplying barley enough system pressure and can't maintain it once the engine comes under load and it stalls

Remove the pumps and on a bench set up a supply of kerosene from a container and reverse the connections from a 12v power supply so the pumps can be flushed in reverse direction to remove the sediment
Your fuel tank will need flushing properly to remove all the rust scale from inside it and that involves removing the bottom strainer.
If you don't do this the pumps will clog up again

That is my theory anyway as to the stalling under load

Of note i ended up also installing a large in line canister filter between the tank and the pumps to prevent the pumps getting any fine particles in them and it worked a treat and never missed a beat after some 9yrs later of owning the car.
Pic below of the in-line filter installed
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87 White Euro 500 "ECE" 265hp SEC
88 Black Euro 560 "RUF"300hp SEC
89 Blue Euro 560 "RUF" 300hp Hydro SEL

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post #7 of 13 (permalink) Old 12-31-2018, 09:20 AM
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I am having basically the same problem but even worse: see here: https://www.benzworld.org/forums/w12...ling-when.html

Maybe that will give you some useful information. I would try to check your duty cycle first and that will give you a slightly better idea of what is going on as well. See here: https://www.benzworld.org/forums/w12...y-cycle-3.html

A pressure test could tell you if it's the fuel pumps being clogged, right? Something on my list to do.
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post #8 of 13 (permalink) Old 01-02-2019, 10:39 AM Thread Starter
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Quote:
Originally Posted by KRH View Post
When the engine is idling in park and you go around the back and listen to the fuel pumps are they making a steady humming noise with no variation in sound.
Or do they appear to change pitch (sound) as if they are cycling up and down versus a steady hum.
Stalling under load indicates the pumps are clogged (even though they are new) from fine rust sediment in the tank that gets past the tank strainer.

I have had this happen to me some years ago with brand new pumps as well
The engine would die under any load but happy to idle a rev with no load in park.

Its because the pumps are just supplying barley enough system pressure and can't maintain it once the engine comes under load and it stalls

Remove the pumps and on a bench set up a supply of kerosene from a container and reverse the connections from a 12v power supply so the pumps can be flushed in reverse direction to remove the sediment
Your fuel tank will need flushing properly to remove all the rust scale from inside it and that involves removing the bottom strainer.
If you don't do this the pumps will clog up again

That is my theory anyway as to the stalling under load

Of note i ended up also installing a large in line canister filter between the tank and the pumps to prevent the pumps getting any fine particles in them and it worked a treat and never missed a beat after some 9yrs later of owning the car.
Pic below of the in-line filter installed
Quote:
Originally Posted by 000ooo000 View Post
I am having basically the same problem but even worse: see here: https://www.benzworld.org/forums/w12...ling-when.html

Maybe that will give you some useful information. I would try to check your duty cycle first and that will give you a slightly better idea of what is going on as well. See here: https://www.benzworld.org/forums/w12...y-cycle-3.html

A pressure test could tell you if it's the fuel pumps being clogged, right? Something on my list to do.
Thank You both guys, and anyone else who shot me with his hints on my problem
I've decided to put my car in mechanical workshop, as I'm a bit out of time lately and the weather is ... well it's the middle of winter here in Poland, and my garage is not heated... I will tell the mechanics, what I've done so far and what is my diagnosis - probably rust sediment on the bottom of fuel tank or blocked exhaust and let them do their job. The fuel pumps make a rather steady kinda cycling "hummm" without pitch change. Hopefully the workshop crew will come with good solution of the problem... we will see...
Ahhhhh I'm missing my good old EFI 560 SEL in moments like these
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post #9 of 13 (permalink) Old 01-02-2019, 01:59 PM
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Quote:
Originally Posted by Evilaseq View Post
Thank You both guys, and anyone else who shot me with his hints on my problem
I've decided to put my car in mechanical workshop, as I'm a bit out of time lately and the weather is ... well it's the middle of winter here in Poland, and my garage is not heated... I will tell the mechanics, what I've done so far and what is my diagnosis - probably rust sediment on the bottom of fuel tank or blocked exhaust and let them do their job. The fuel pumps make a rather steady kinda cycling "hummm" without pitch change. Hopefully the workshop crew will come with good solution of the problem... we will see...
Ahhhhh I'm missing my good old EFI 560 SEL in moments like these
Let us know what they find, hopefully it will help me figure out my issue as well. An EFI conversion sure would be nice.
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post #10 of 13 (permalink) Old 01-18-2019, 10:57 AM Thread Starter
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The problem is still not solved. Mechanic got sick and even hasn't started any diagnostics. I needed to take the car from the workshop because I have an reservation in a body shop, I've waited long so I can't miss my place in body shop queue. When the body work will be done, I will surely return to solving the stalling issue.
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