I’ve been having a problem starting my ’94 C280. Here’s what’s happening: When the car sits overnight it will start on the 1st try without any problems. After sitting for a while the next restart results in the engine starting briefly, then dying. The only way I can get the engine to continue running is by flooring the gas pedal. When I do this I can hear the Rpm’s rise and the engine will continue to run. I’ve checked the over voltage relay and I’ve got the updated one. Any ideas on what to replace / check next? I checked the archives and although the OVR is mentioned there is not too much on this type of warm start problem.

Thanks

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1997 C36 Designo Red
1999 SLK230 Sport
1999 Honda CRV 5-spd

1990 Acura Integra (given away!)
1995 Mazda Miata Merlot SE (sold)
2003 Honda Element EX 4WD (sold)
1994 C280 - (sold)
1985 190e 2.3 5spd (sold)
1991 Yamaha FZR1000 (sold)
1994 MB S420 (sold)
1994 BMW 318ica (sold)
1991 Mazda Miata BRG SE (sold)
1989 Fiat Spyder (Died!)

Is the "Check Engine" light on? If so you need to scan for codes to see what might be the problem. If no engine light I would guess the fuel pump relay.

Did you check the OVP's fuse?

I also agree about the fuel relay... which is the 2nd most common problem to the OVP for stalling problems.

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Sounds like a fuel pressure leak down problem. It could be the fuel pressure regulator, the fuel pump or check valve. If the pressure leaks down after the warm egine is stopped, the fuel in the injector manifold vaporizes and you get vapor lock. Vaporized fuel cannot atomize and won't burn. So, you continue to crank and crank the engine until the pump eventually pumps fresh fuel at the correct pressure to the injectors and the engine starts. Or, you leave it sit overnight, the manifold cools and the fuel condenses back into a liquid and it will start. Check your fuel pressure. It should be about 44psi running. Check it after you shut the engine off. It should hold at least 30 psi. If it leaks down in a short time, that's your problem.

Here's an update. Took the car to the dealer who said after a quick check that the OVR and O2 sensor needed to be replaced. He said that after he replaced the OVR the car started fine but indicated a O2 sensor fault. The dealer wanted to charge $95 for the OVR and about $198 for the O2 sensor. I said thanks, but that I'd buy the parts myself.

I ordered the OVR for $49.50 and will be replacing it this weekend as I've not gotten a chance to use the car - I live in NYC. I believe the OVR replacement should do the trick. I'm SOO glad I have an alternative to getting parts from the dealer!


Thanks for everyone's help!

__________________
1997 C36 Designo Red
1999 SLK230 Sport
1999 Honda CRV 5-spd

1990 Acura Integra (given away!)
1995 Mazda Miata Merlot SE (sold)
2003 Honda Element EX 4WD (sold)
1994 C280 - (sold)
1985 190e 2.3 5spd (sold)
1991 Yamaha FZR1000 (sold)
1994 MB S420 (sold)
1994 BMW 318ica (sold)
1991 Mazda Miata BRG SE (sold)
1989 Fiat Spyder (Died!)

Here is an update. I replaced the OVR and it had no effect, still have the warm start problems with no check engine light on. Time to plan my next attack. David mentioned the fuel relay, perhaps I should replace it. ARJAY - how do you check the fuel pressure?

Any other suggestions?

__________________
1997 C36 Designo Red
1999 SLK230 Sport
1999 Honda CRV 5-spd

1990 Acura Integra (given away!)
1995 Mazda Miata Merlot SE (sold)
2003 Honda Element EX 4WD (sold)
1994 C280 - (sold)
1985 190e 2.3 5spd (sold)
1991 Yamaha FZR1000 (sold)
1994 MB S420 (sold)
1994 BMW 318ica (sold)
1991 Mazda Miata BRG SE (sold)
1989 Fiat Spyder (Died!)

It also very well could be the fuel pump. I have been hearing more and more about fuel pump failure lately. But I heard that the fuel relay is a more common failure, but heard different recently. Hopefully a tech will write on this one.

(Corey, I'll reply to your email shortly.)

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

To check the fuel pressure you need a fuel pressure gauge. You can purchase one from any auto parts or store. There is a fitting on the fuel supply manifold (tube that supplies fuel to the injectors). You remove the cap and screw the adaptor for the pressure gauge onto the fitting. Start the engine and read the pressure. Then stop the engine and read the pressure and leave theengine stopped and the gauge connected for about 30 minutes. The pressure should hold without dropping for at least 30 minutes. If it drops rapidly or is too low, you may have a faulty pressure regulator, fuel pump, or check valve. The pressure regulator has a vacuum line that runs to the intake manifold. If the regulator is bad, it can leak fuel through the diapragm into the manifold and further the problem by "flooding" the engine after sitting for a while.

Arjay,

You were 100% correct. My problem was traced to a faulty pressure regulator. It was replaced today and my car is back to normal.

Thanks!


Gotta love this site

__________________
1997 C36 Designo Red
1999 SLK230 Sport
1999 Honda CRV 5-spd

1990 Acura Integra (given away!)
1995 Mazda Miata Merlot SE (sold)
2003 Honda Element EX 4WD (sold)
1994 C280 - (sold)
1985 190e 2.3 5spd (sold)
1991 Yamaha FZR1000 (sold)
1994 MB S420 (sold)
1994 BMW 318ica (sold)
1991 Mazda Miata BRG SE (sold)
1989 Fiat Spyder (Died!)

Great news! Glad I could be of help.