m103 intermittent issue
Thread Starter
Newbie
Joined: Jun 2025
Posts: 4
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1990 300se
m103 intermittent issue
I have an intermittent problem: The car (1990 300se, Canadian Spec) )dies if I blip the throttle too quickly. If I increase it slowly, it shakes/vibrates.
Maybe unrelated but the car starts well when cold (or in cold weather) , when hot, I need to help it by depressing the gas pedal to start.
Last weekend the problem happened at a stop sign and the car refused to start up until i let it rest for a good 30 minutes. Did anyone encounter this and if not, where would you start looking?
Maybe unrelated but the car starts well when cold (or in cold weather) , when hot, I need to help it by depressing the gas pedal to start.
Last weekend the problem happened at a stop sign and the car refused to start up until i let it rest for a good 30 minutes. Did anyone encounter this and if not, where would you start looking?
Junior Member
Joined: Dec 2006
Posts: 43
Likes: 4
From: London
300sel- w109 .1971
103 engine
For starters replace the fuel accumulator and filter . If it restarts when engine has cooled is a sign of failed fuel accumulator. Low fuel pressure gives varied fault symptoms.,hence 'for starter'
Thread Starter
Newbie
Joined: Jun 2025
Posts: 4
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1990 300se
Edit: I will order a fuel pressure regulator and I think there is a "damper"? too? while I am at it.
Last edited by Spaceman80; Jun 28, 2025 at 10:55 AM.
Junior Member
Joined: Dec 2006
Posts: 43
Likes: 4
From: London
300sel- w109 .1971
Ok, the fuel filter is new so I will order an accumulator. This reminds me of my 1986 bmw 728i e23, BMW made a small hose/kit with a checkvalve to address hot starting issues. However I am not too optimistic because while the hot start issue is always there, the misfire and stall is occasional and intermittent.
Edit: I will order a fuel pressure regulator and I think there is a "damper"? too? while I am at it.
Edit: I will order a fuel pressure regulator and I think there is a "damper"? too? while I am at it.
Been through all that with my 300se , a Euro model .
Thread Starter
Newbie
Joined: Jun 2025
Posts: 4
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1990 300se
as the fuel pressure decreases and due to vapour lock, issues like misfires, a occasional bang in manifold may manifest itself leading one to think there are additional issues. Step by step will resolve all issues fueling being first
Been through all that with my 300se , a Euro model .
Been through all that with my 300se , a Euro model .
Thread Starter
Newbie
Joined: Jun 2025
Posts: 4
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1990 300se
Status update
Today the car started well from cold as usual , i hooked up a multimeter and took a look at the duty cycle values from the x11 connector. Red on pin3 and black on pin2. With ignition on but no running engine i get 69.9% which confirms my ecu is capable of giving diagnostic codes through duty cycle values. At full operating temp, the percentage hovers around 20% and varies which I think indicates normal operation at idle. The car ran fine without misfiring today. Still has a hard time restarting when hot. I am waiting for delivery on the fuel accumulator and will be running some more tests.
In general, how likely are the valve stem seals to be bad on the m103 engine? I put a paper in front of the exhaust pipe and it "flutters" as if there is sucking action in there sonwhere instead of only blowing exhaust out.
In general, how likely are the valve stem seals to be bad on the m103 engine? I put a paper in front of the exhaust pipe and it "flutters" as if there is sucking action in there sonwhere instead of only blowing exhaust out.
Junior Member
Joined: Dec 2006
Posts: 43
Likes: 4
From: London
300sel- w109 .1971
Today the car started well from cold as usual , i hooked up a multimeter and took a look at the duty cycle values from the x11 connector. Red on pin3 and black on pin2. With ignition on but no running engine i get 69.9% which confirms my ecu is capable of giving diagnostic codes through duty cycle values. At full operating temp, the percentage hovers around 20% and varies which I think indicates normal operation at idle. The car ran fine without misfiring today. Still has a hard time restarting when hot. I am waiting for delivery on the fuel accumulator and will be running some more tests.
In general, how likely are the valve stem seals to be bad on the m103 engine? I put a paper in front of the exhaust pipe and it "flutters" as if there is sucking action in there sonwhere instead of only blowing exhaust out.
In general, how likely are the valve stem seals to be bad on the m103 engine? I put a paper in front of the exhaust pipe and it "flutters" as if there is sucking action in there sonwhere instead of only blowing exhaust out.
103 engines do have an issue with valve stem seals leaking as they age . Effects the spark plugs with oil deposits .
A leaky fuel accumulator always require long cranks to fill in the fuel.and start the engine till the time accumulator is replaced. Expect all kinds of starting issues.
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Newbie
Joined: Aug 2025
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W126 300SE euro
Ok, the fuel filter is new so I will order an accumulator. This reminds me of my 1986 bmw 728i e23, BMW made a small hose/kit with a checkvalve to address hot starting issues. However I am not too optimistic because while the hot start issue is always there, the misfire and stall is occasional and intermittent.
Edit: I will order a fuel pressure regulator and I think there is a "damper"? too? while I am at it.
Edit: I will order a fuel pressure regulator and I think there is a "damper"? too? while I am at it.
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