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  #1  
Old 07-18-2003, 08:59 PM
cincuenton
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'77 450 SEL (German spec): Vapor Lock?

Right to the point: Car is excellent, 1 prior owner. 64K miles. Well mantained.

But I got it 9 months ago, at which time original owner had only put on 10K miles in last 10 years. But kept maintaining it throughout. Garaged, etc. 59K at time on clock. Since then, about 5K more.

Gradually, but over last 2 months, I have a loss of power (not stalling; just power) when I press too hard on accelerator. Sometimes more than others. But it has been progressive. Now, iit is the heat of summer and I'm here in Miami, so I ask you. Does this sound like:

a. vapor lock.
b. bad plugs.
c. bad wires.
d. bad fuel filter.

What do you think? anybody with this kind of symptom on this vehicle?

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  #2  
Old 07-18-2003, 09:29 PM
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Join Date: Jun 2001
Location: oregon
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450 SEL

It doesn't sound like vapor lock.
maybe fuel pump,fuel filter?
new plugs wouldn't hurt and are cheap.
inspect the wires,any cracks?
you can run the engine at night and look at the wires,see any sparking?
the problem with a mercedes with that low of miles is that it hasn't been driven enough.

good luck,great car !
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'78 240D
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  #3  
Old 07-18-2003, 10:36 PM
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Plugged fuel filter would be my first thought. All that dead gas sitting there all that time ain't good for the filter, nor the tank, especially someplace as humid as Miami.

Change the filter and run a bottle or RedLine or Techron injector cleaner in the next couple of tanks of fuel and see what happens.

And DRIVE it! These cars die if not driven till they are all warmed up and the fluids circulated properly at least once a month.

If you are going to let it sit with fuel in it for weeks or months at a time, get some fuel stabilizer and put it in the tank. It will prevent algae growth in the water you will surely collect, and will prevent the fuel going "dead" while it is sitting.

The detergent and dye added to gasoline don't burn worth diddly, so letting it sit for long periods of time results in the volatile part of the fuel evaporating, leaving you with thin diesel fuel in the tank. Won't run worth diddly until you get good gas in it.

You won't get vapor lock on this car, it has a high pressure electric fuel pump and the fuel circulates.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #4  
Old 07-18-2003, 10:54 PM
cincuenton
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Thanks, Peter. Driving it steadily now.

What I need to do is go visit my daughter in Gainesville (350 miles of I-75) when she gets back to school. that'll do it. And 350 coming back!!

I'll tell you. This car is SOLID. Not like my previous model, a 420 SEL which was a W126.
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  #5  
Old 07-18-2003, 11:00 PM
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Fuel filter, check fuel pump output with the new filter, fuel pressure check.

I suppose it's possible that you have an ignition problem, but that usually causes more trouble than fuel delivery. I suspect you are going lean with loss of power form fuel starvation.

However, when it is doing it, look behind for black smoke -- it's possible it's going over-rich from low fuel pressure.

I had a 75 Audi Fox with K-Jetronic, and in the winter the blowby would freeze in the air mass meter, causing it to add more and more fuel until it would flood out, blowing black smoke. When it finally stalled, sitting on the side of the road for a while would cause the ice to melt from the engine heat, and it would run fime. Finally managed to get to a garage once when it was running badly and looked in the mass flow meter. I disconnected the blowby line, cured the problem. Screwy.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #6  
Old 07-19-2003, 07:15 AM
cincuenton
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Peter...thanks again.
No. no smoke of any kind, under any conditions. Car uses no oil. There's only DRY soot on the inside exhaust pipe tips.
no drips. No smells. Totally dry. My first experience in an older Benz where I could categorically say this.

Sometimes, as I told you, the problem doesn't every appear. But when it does, when I ease off on the gas some, it will accelerate plent. but with a heavier foot, it kind of half cuts out.

Strange, no?
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  #7  
Old 07-19-2003, 07:28 AM
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I'm inclined to agree about the filter, but I suppose the fuel pump could be the problem too (a distant second I'd admit). When you turn the key to run (before you turn all the way to the right to crank over the engine) you should be able to hear the fuel pump for a second or too as it primes the system. If it runs continuously, it's on the way out. As I type this, I also seem to recall that the orginal fuel distributors on these M117s had problems leaking, and were replaced with an updated aluminum version. That bears checking on yours as well - actually it seems like a better candidate than the pump given your symptoms.
Hopefully though, its just the filters, and you can enjoy this beautiful car.
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82 300 SD
77 450 SL (gone)
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  #8  
Old 07-19-2003, 04:45 PM
cincuenton
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Tjohn:

Actually, I ran out to car - kept radio off and fan. Turned key to "on". I didn't hear anything.

Went to back of car. I know how electric primer sounds. Have had other MBs. No sound. Certainly, it's not over-running.

But IF .....the electric primer is not functioning, due to contacts or fuse or soemthing like that, could that cause symptoms? But be advised: Car always starts, and doesn't stall - regardless of outside temp. It cranks about 2-3 seconds before catching, but within normal limits.

Any thoughts?
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  #9  
Old 07-19-2003, 06:59 PM
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Fuel pump relay.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #10  
Old 07-20-2003, 11:03 AM
WANT '71 280SEL's Avatar
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I currently have the same problem except on a 1989 Volvo 240DL. A mechanic told me that it MAY be the air mass sensor. Bought a used one and it still did it every once in awhile.
David
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2000 Honda Accord V6 137k miles

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  #11  
Old 07-21-2003, 08:22 PM
firestormer
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Peter,

I may have emailed you about a similar problem.

In my case, the symptoms are excellent engine behavior and great power through the gears when cold. As indicated T passes beyond 40c, things start to get rougher. Beyond 50c, poor instant throttle response develops, but if only partial throttle is used after warm-up, eventually I can go as fast as I want. As speed increases, it will gradually accept more and more throttle as power demand to maintain that speed gets matched.

Its as though it is too lean when expecting normal response after warm-up. When cool, I imagine the CS valve is keeping things just rich enough.

In my email I asked what the sequence of things are with the CIS as it warms?

Mark Shinnick
www.mastertimer.com
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  #12  
Old 07-21-2003, 09:35 PM
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Location: Evansville, Indiana
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Mark:

K-Jetronic (no feedback system) has a warm up regulator that enriches fuel while the engine is cold. Controled by engine temp and a heater (so it won't stay on forever in really cold weather), it is a "contolled leak" that is closed by a thermovalve. Lowers the differential pressure in the fuel distributor, I think, and so enriches the mixture until the vavle closes. There is also a thermo valve that adds extra air for increased idle speed.

Your problem may simply be that the fuel mixture was set with the engine cold, so it is too lean warm.

You will need to measure the CO in FRONT of the catalytic converter, if you have one (or two) -- if this is necessary, there should be a port for the probe. You cannot, alas, set the mixture very well "by ear". The adjustment is a 4mm allen socket between the mass air sensor horn and the fuel distributor.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #13  
Old 07-22-2003, 12:47 AM
firestormer
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Peter,

I set the thing for optimum emissions while hot last week. Emissions great, performance sucks. Sound familiar?

So, it looks like I need to get richer. I need to test this anew.
I will richen things slightly, and look for improved throttle response equating to the cold running performance….will report back.

Mark
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  #14  
Old 07-22-2003, 11:36 AM
mapab
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Quote:
Originally posted by tjohn
I'm inclined to agree about the filter, but I suppose the fuel pump could be the problem too (a distant second I'd admit). When you turn the key to run (before you turn all the way to the right to crank over the engine) you should be able to hear the fuel pump for a second or too as it primes the system. If it runs continuously, it's on the way out. As I type this, I also seem to recall that the orginal fuel distributors on these M117s had problems leaking, and were replaced with an updated aluminum version. That bears checking on yours as well - actually it seems like a better candidate than the pump given your symptoms.
Hopefully though, its just the filters, and you can enjoy this beautiful car.
In position "run" as you call it, i.e. ignition on, the fuel pump does not prime on a k-jet from 77. The cast iron distributors were improved later with aluminium ones but they don't usually leak to the extent that would cause the described symptoms. How's the hotstarting - is it always easy or do you have to crank and crank? The resulting vapour lock could be caused by many different parts of the FI system and a diagnostic procedure needs to be followed to discover the faulty component. If a new fuel filter does not solve the problem I'd recommend investing in a fuel pressure gauge. Only 2 weeks ago it helped me to solve the hot starting problems in my 6.9.

Adam
'77 6.9

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