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91 500SL
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4 Posts
Discussion Starter #1
91 500sl. Starts and runs fine for a few miles then starts sputtering and usually dies. Most times will start right up again. Replaced fuel filter and OVP relay. Still have the same problem. Understand that this model does not have a fuel pump relay. Any ideas or suggestion welcome. I really need to get this car running again and don't have a lot of money to just replace parts and hope.
 

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Greek God of the R129
SL500-500SEL-190E
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8,366 Posts
You are asking/looking, for the fuel pump relay?

Of course, it does.

It is integrated in the MAS module.

It is located in the module compartment.

Regards,
aam.
 

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91 500SL 37k,90 300SE sold, 91 300E sold , 92 300E137k ,02 Kia Sedona ,I know..... its a Mini van.
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8,119 Posts
have you looked at the distributor caps and rotors? CSP may be at fault also, test it for 800 ohms, can be done without removing, 2 min job.
 

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91 500SL 37k,90 300SE sold, 91 300E sold , 92 300E137k ,02 Kia Sedona ,I know..... its a Mini van.
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8,119 Posts
Also check FPR, may have a bad one, there's a clear tube at the bottom of it, look and see if you have fuel in it, if you do, bad diaphragm.
 

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Outstanding Contributor
R129 500 SL 1991
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892 Posts
91 500sl. Starts and runs fine for a few miles then starts sputtering and usually dies. Most times will start right up again...
I have same model /year, but need more info.
Any fault codes? Keep ignition on after engine dies and check codes. (They reset when you turn ign off).
Does it die just at idle, or on throttle, or both? (Can you keep it running with the throttle?)
Has it stood (dormant) for several months prior to this problem?
Yours is the KAT version?
Do revs rise at idle to 900/1000rpm before engine dies?
Can you smell gas fuel just before it dies?
Do you hear a click from engine compartment when you turn off and reset the ignition after it has died?

Reason of further questions:-
Clicking noise can indicate faulty fuel pump relay, and because this is incorporated in the MAS module as Albert said, possible faulty MAS controller. You can read codes from MAS. "Fuel pump relay (circuit 87) not functioning" indicates faulty MAS. When you reset the ignition, error clears, and you can hear a loud click from MAS unit when relay resets. This could be why you can restart right up again. You can remove MAS and clean terminals. Sometimes this works. I blanket soldered the PCB which seemed to fix mine. (I had fuel starvation at high revs - different to your problem).

Faulty FPR (fuel pressure regulator) doesn't maintain fuel pressure when ignition turned off, and also dumps unmetered fuel into inlet manifold. Symptoms are difficulty starting, particularly longer you leave (~24hrs), and lumpy idle on start up. Usually clears on throttle.

Because it starts right up again, probably not FPR or distributor caps, but worth checking and cleaning anyway. Known issues, but not aligned with your symptoms.

Revs rising would indicate air leak (if you have the KAT version).

As engine dies after warmed up, most likely heat related in electrical component, or maybe over fuelling due to loss of vacuum to switchover valve.

Possibly CPS (crankshaft position sensor) but usually not that critical on older CIS systems, I believe.

If you can keep it running on throttle, this would indicate fuel mixture issue. Maybe leaning out when hot, but probably not likely because it starts right up again.

I think this is error code territory.

Regards
Rob
 

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91 500SL
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4 Posts
Discussion Starter #7
I have same model /year, but need more info.
Any fault codes? Keep ignition on after engine dies and check codes. (They reset when you turn ign off).
Does it die just at idle, or on throttle, or both? (Can you keep it running with the throttle?)
Has it stood (dormant) for several months prior to this problem?
Yours is the KAT version?
Do revs rise at idle to 900/1000rpm before engine dies?
Can you smell gas fuel just before it dies?
Do you hear a click from engine compartment when you turn off and reset the ignition after it has died?

Reason of further questions:-
Clicking noise can indicate faulty fuel pump relay, and because this is incorporated in the MAS module as Albert said, possible faulty MAS controller. You can read codes from MAS. "Fuel pump relay (circuit 87) not functioning" indicates faulty MAS. When you reset the ignition, error clears, and you can hear a loud click from MAS unit when relay resets. This could be why you can restart right up again. You can remove MAS and clean terminals. Sometimes this works. I blanket soldered the PCB which seemed to fix mine. (I had fuel starvation at high revs - different to your problem).

Faulty FPR (fuel pressure regulator) doesn't maintain fuel pressure when ignition turned off, and also dumps unmetered fuel into inlet manifold. Symptoms are difficulty starting, particularly longer you leave (~24hrs), and lumpy idle on start up. Usually clears on throttle.

Because it starts right up again, probably not FPR or distributor caps, but worth checking and cleaning anyway. Known issues, but not aligned with your symptoms.

Revs rising would indicate air leak (if you have the KAT version).

As engine dies after warmed up, most likely heat related in electrical component, or maybe over fuelling due to loss of vacuum to switchover valve.

Possibly CPS (crankshaft position sensor) but usually not that critical on older CIS systems, I believe.

If you can keep it running on throttle, this would indicate fuel mixture issue. Maybe leaning out when hot, but probably not likely because it starts right up again.

I think this is error code territory.

Regards
Rob
It will die at 20mph in the side street or at 80 on the interstate. Sometimes you can keep it running for a few seconds with the throttle other times not. It acts like fuel starvation not flooding but will almost always start right back up.
 

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Outstanding Contributor
R129 500 SL 1991
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892 Posts
It will die at 20mph in the side street or at 80 on the interstate. Sometimes you can keep it running for a few seconds with the throttle other times not. It acts like fuel starvation not flooding but will almost always start right back up.
It sounds like you have a faulty MAS controller. Read codes.
MAS module is dead easy to locate. It's got MAS written on it! :)
Next to OVP in engine compartment, under plastic cover (5 screws), top left as you look from front of engine.
Turn knurled knob to release metal clips to extract MAS module.
Good luck!
Regards
Rob
 

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91 500SL 37k,90 300SE sold, 91 300E sold , 92 300E137k ,02 Kia Sedona ,I know..... its a Mini van.
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8,119 Posts
CSP= crank shaft position sensor, I've hear they act up when bad and can shut the engine down when they get hot, but they need to cool down for restart, you say yours starts back up right away, so may not be issue here. I would test fuel pressure before buying an expensive part, rule it out.
 

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Premium Member
92 500SL
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30 Posts
I have a 92 500SL that starts easily and idle fine...However, after about 5 mins I put it in gear it will die and will not start...new plugs, coils, wires, caps...I got a code "11" (Crankshaft position sensor failure) but remember that 'Poundy' said that when engine is off you will get that code anyway)..anyone have ideas? I will restart and run after it cools off...
 

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‘91 300SL-24 R129
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7 Posts
Did anyone find the culprit? I have the same symptoms on my 300SL-24. It stalls at load when the engine is at operating temperature. It dies and it starts right over.
Also the fuel pumps start making a buzzing sound like they are failing, but they are brand new (driven 250 km).
 

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Outstanding Contributor
'03 SL500, '03 SL55, '97 SL320, (2) '91 300SL, (2) '91 500SL, '00 S500 -- all for sale
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4,173 Posts
Also the fuel pumps start making a buzzing sound like they are failing...
According to M-B noisy fuel pumps can be caused by a partial blockage of the screen at the inlet of the fuel distributor.
 

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300SL-24 1992 White;BMW X3-3.0 E83 2005 Blue;190E-2.6 1992(sold); BMW 316-1.8 E30 1983(sold)
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227 Posts
Did anyone find the culprit? I have the same symptoms on my 300SL-24. It stalls at load when the engine is at operating temperature. It dies and it starts right over.
Also the fuel pumps start making a buzzing sound like they are failing, but they are brand new (driven 250 km).
Check & clean the distributor and rotor would be helpful. Mine is 300SL-24 and met the smar problem twice.
 
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