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  #1  
Old 03-05-2010, 10:24 PM
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Join Date: Mar 2010
Location: Georgia
Posts: 6
Question Rough idle and white smoke...

Hello all. I will apologize in advance for the novella.

My problem is with my 87 300SDL Turbo. Things began when I let my fuel level get down into the reserve (ca. 2 gallons...I know I know). I filled my tank with fuel at the BP that I always go to (and have never had a problem with product). I drove approx. 1/2 mile and the car died. There was no warning (ie stuttering, shuddering, etc.). It just stalled. After I killed the battery from trying to start it, I had the car towed to my house. I ruled out a bad batch of gas by taking a sample and letting it sit for 24 hours. Nothing separated out. Thinking I simply clogged my fuel filters after letting my fuel level get to low (again, no chiding necessary), I replaced my in-line primary filter.

*A side note: before I replaced the primary, my dad (in an attempt to "help") blew air through the old primary filter down the hose and into the fuel heater, at which point I saw fuel/air being forced out around the fuel heater o-ring.*

After replacing the primary, I started the car. It would start with the pedal depressed to the firewall, but ran at very low rpms. It would run only with the pedal depressed; if I removed my foot to let it idle, the car stalled. I restarted and let run for 10+ minutes before the rpms finally came up. At low rpms, the engine is rough, but smoothes out at 2000+ rpms.

*Another side note: at this point (in another attempt to "help") my dad revved the engine up to the point that a huge plume of black smoke came out of the exhaust. White-ish smoke then followed. In all honesty, I can't remember if the white smoke began before or after the black exhaust.*

Next, I replaced the secondary fuel filter, filling it with fuel before tightening the bolt (learned that one from this forum-thanks!). The car now starts with pedal fully depressed and will idle on its own, albeit a very rough idle at around 600rpms. If revved, the engine smoothes out at 2000+ rpms as before. White smoke is present at all times, but is worse (thick and billowing) at lower rpms.

By reading multiple posts here, I come up with a few ideas on the culprit, but would appreciate any advice on what to check as well as what to do next.

1. The rough idle makes me look to either
a. air in the line (considering how notorious the self-priming engine is for not being fully self-priming.)
b. an air leak (possibly around the fuel heater o-ring?)
c. or a fuel burning problem

2. The white smoke makes me cringe for obvious reasons:
a. a bad head gasket: is it possible that the engine revving to the point of putting out black smoke could have blown my head gasket? (Full disclosure: my car throws oil at high rpms)
b. if I'm lucky, the white smoke confirms a fuel burning problem

I am going to bleed the fuel lines of air through the injectors (thanks again to the forum for that info), and if there is still air, I'll view the fuel heater o-ring as a problem, but I have no idea how to go about checking a fuel burning problem.

Any thoughts and advice will be welcome.

Caitlin
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'87 300 SDL Turbo 230K "Bessie (the tank)"
'79 450SL 64K
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  #2  
Old 03-05-2010, 10:33 PM
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Join Date: Mar 2010
Location: Georgia
Posts: 6
P.S. In regards to a blown head gasket, I have checked the fluid level in my radiator reservoir and it appears to be at an appropriate level (ca 3/4 - 1 inch from the top of the reservoir) My oil also appears water free.

Caitlin
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'87 300 SDL Turbo 230K "Bessie (the tank)"
'79 450SL 64K
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  #3  
Old 03-05-2010, 10:37 PM
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Join Date: Jan 2002
Posts: 18,355
Rough idle could be an air leak. I'd pursue that solution first. I think that engine also has an electronic idle control.
The white smoke is not good. If it were grey smoke that went away as the engine warmed up, it could be unburned fuel. But white smoke is an indication of a failed headgasket. What does the smoke smell like?
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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  #4  
Old 03-22-2010, 01:11 AM
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Join Date: Mar 2010
Location: Georgia
Posts: 6
Kerry thanks for your reply. After replacing the fuel heater o-ring, I zeroed in on some sort of fuel burning problem...turned out to be a bad batch of fuel (with complications, ie. the o-ring). With a tank clean and an injector clean (for good measure), Bessie runs like a top. Many thanks to the forum for past and present advice available here.

Caitlin
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'87 300 SDL Turbo 230K "Bessie (the tank)"
'79 450SL 64K
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