'79 450 SL - Vapor Lock or Fuel Accumulator ?

[money markets]

My '79 450 SL has many of the symptoms others have described in this forum. Difficult to start at first, much easier to start after the car has been running awhile. The longer the car has been turned off, the more likely it will take 5 to 7 seconds to crank the next time. Once it starts it runs rough for a few seconds and then is fine. In the past 6 months my mechanic has replaced the Starter and Fuel Distributor, cleaned the fuel injectors and replaced the fuel injector seals. I've tried the suggestion of turning the ignition on and off rapidly to pump cooler fuel, but no luck. Any idea if this is more likely Vapor Lock or a worn out Fuel Accumulator? I like my mechanic but this one has stumped him, so any suggestions on how to diagnose would be great (plus the problem never seems to act up for the mechanic).

[Mark Herzig]

By 1979, I don;t think vapor lock was a huge issue. The hard start after warm could be the accumulator not holding system pressure... Replacing the accumulator would be prudent as it is a preventative maintenance item. What mileage do you have? Also, what is your running temperature in general? I'm wondering if your fuel mixture/timing is off.. My '79 runs at slightly over the 80 degree mark just like clockwork.

Also, check all the plastic vacuum/leak lines. I replaced a lot of them as they get brittle and snap in two. The Maintenance CD has schematics of how these lines connect with the fuel injection and egr systems.

Sorry for the potention cognitive dissonance, but it's likely that your fuel distriubutor did not need to be replaced. Conventional thinking is that the distrubutor is routinely mis-diagnosed and the problem lies elsewhere. This is a $1400 mistake.

[money markets]

Thanks. My mileage is 103,000. My running temperature is about 175 degrees. My mechanic has said that my fuel mixture is a little rich, but first I need to clear out the carbon build-up before he adjusts it. Once that is done, will the running temp. go down? For better or worse the Fuel Distributor job was only about $800 w/a rebuilt Bosch part, as my mechanic is also a Bosch parts distributor.

[maheath]

Vapor lock and fuel accumulator problems would show up as hot starting problems, not the cold starting problem you describe.

i'm not familiar with the 450 engine, but I'd start with the ignition system first. Have you checked the distributor cap? plug wires? plugs?

Did your mechanic check the fuel pressure? If he did all that work without hooking up a fuel pressure gauge, I'd find a new mechanic. The fuel distributor would be the last part I'd suspect. It could be leaking injectors or a leaking cold start valve.

[diggad]

Hello everyone,
I was frustrated with exactly the same problem for about four or five months with my 1980 450sl. About ten seconds or so of turning over without firing, then a few rough stutters when oil pressure built up, then off she would go. It would seem to happen especially if I left the car for a few days without driving it. Once I was driving regularly, it would settle down, especially if the engine was still warm on startup.
Replaced the fuel accumulator, and heart warming engine warbles are instantly mine every time!!! Do it now!!!!!

I believe the accumulators do have a tendency to leak over time. Mine was, after all, over twenty years old... All the best.

Daniel

[4NDELIT]

How much did it cost for the part? Is it a DIY job, or should you take it to the shop?

[tjohn]

The fuel accumulator is with the fuel pump and fuel filter, underneath your car just behind the passenger rear tire. They run around $125 bucks. This is very DIY, if you don't mind a little gas on your clothes. This is the pesky critter right here:

[PCM84]

I'm just trying to get a picture of how much fuel I'm going to get on myself and how one actually replaces the accumulator...

Thanks. PM

[tjohn]

the actual process. You unscrew the cover over the accumlator, clamp the hoses on either end, unscrew the hoses from the accumlator, unscrew the bracket holding the accumulator, and it's off. You won't get much gas on you if youre carefull - the main thing is to keep in out of you eyes. You should be able to reuse your clothes after this job, as long as you clamp the hoses down good.

Good Luck

[PCM84]

Thanks... is the accumulator actually under a cover out of sight?

I'll go look behind my passenger side rear wheel.

Also, any thoughts on a source for the part?

[PCM84]

I just went and looked... is the accumulator behind the two fuel pumps? Under the plastic cover that protects all three... I was imagining it to be about three inches max... but it's more like six to eight inches long and pretty fat?

[jr811]

If I"m not mistaken, their is a pressure value on the end of the fuel pump - I had trouble several years ago with my 1979 450SL on warm starts - I replaced this value for about $9.00 and fixed problem

[Max J. Sandler]

I own an 86 560 SEC and an 87 560 SL. The SEC starts on half a turn hot or cold. The SL cranks for about 2 seconds before starting, longer when hot. In and effort to cure the problem, I replaced both fuel pumps (got a good deal on e-bay), and the fuel accumumlator. This was after replacing all of the injectors and the fuel distributor. The problem is better, but the SEC still starts instantly, even after sitting for a week or two. This is one of the great mysteries of the Universe.

Max J. Sandler

[PCM84]

So... can someone describe the exact location and relative size of the fuel pump, accumulator and fuel filter... are these three grouped together? It looks to me like on my 86 560SL there are three fuel devices huddled together near the passenger wheel...

I've ordered a new accumulator... my 560SL is embarrasing to start when it's warm!

[RickM]

Jim,

Where did you get the Pressure valve?

Thanks