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560SL
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Discussion Starter #1
Hi Guys -

Any thoughts on this situation would be appreciated. My 560SL drives fine - but there's an issue with starting. On both cold and relatively warm starts, the engine ignites buts I can't actually move the car, and the vacuum/economy gauge goes to the middle of the dial. If I wait 30 seconds to a minute with the car in park, the dial slowly moves to the left and eventually I can move the car.

After some consultation and research, I believe I've narrowed it down to an issue with the fuel accumulator / fuel pressure on the basis that:

a) it's a start-up issue, suggesting a problem with fuel supply, since it self-corrects once the car is going for a bit
b) the car's been checked for vacuum leaks, and fuel accumulator problems can cause vacuum leaks...

The smart thing to do would probably be to take the car to a good mechanic and have them try and diagnose it, but I'm thinking of just buying a new fuel accumulator and having it installed and seeing if it works. Is that an OK idea? Should I at least do a fuel pressure test first? Is this easy to do on a 560SL?

Any other thoughts?

Thanks in advance
 

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It Is What It Is, Dude
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a) it's a start-up issue, suggesting a problem with fuel supply, since it self-corrects once the car is going for a bit

Is it primarily a warm start condition? That's the typical FA symptom.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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Hi Guys -

Any thoughts on this situation would be appreciated. My 560SL drives fine - but there's an issue with starting. On both cold and relatively warm starts, the engine ignites buts I can't actually move the car, and the vacuum/economy gauge goes to the middle of the dial. If I wait 30 seconds to a minute with the car in park, the dial slowly moves to the left and eventually I can move the car.

After some consultation and research, I believe I've narrowed it down to an issue with the fuel accumulator / fuel pressure on the basis that:

a) it's a start-up issue, suggesting a problem with fuel supply, since it self-corrects once the car is going for a bit
b) the car's been checked for vacuum leaks, and fuel accumulator problems can cause vacuum leaks...

The smart thing to do would probably be to take the car to a good mechanic and have them try and diagnose it, but I'm thinking of just buying a new fuel accumulator and having it installed and seeing if it works. Is that an OK idea? Should I at least do a fuel pressure test first? Is this easy to do on a 560SL?

Any other thoughts?

Thanks in advance
I don't know enough about the 560 to comment except to second what Al said. There is no physical connection between the FA and any vacuum source.

Question, though. How does the brake pedal feel through all this? Hard as a rock or normal as any power brake car?
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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What year 560. The '88 and '89 have a diagnostic port.
 

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I was having similar issues with "pulsating" engine speed when warm, and I replaced the whole fuel delivery system, including the accumulator. But all the experts here said the accumulator was like the source of that particular issue.
 

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560SL
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Discussion Starter #8
Rowdie - it's an '88...where's the diagnostic port?
Nobbie - I never tried the brake pedal through this. I'll get back to you
Abiby - I can't remember where I read this, but somewhere online I read that a fuel supply/pressure is can cause the vacuum gauge to move. In other words, it's a symptom that might be consistent with a fuel accumulator problem...

is there any easy way to confirm or diagnose this further?

Thanks again guys
 

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82 380SL 96 SL500 03 SL500
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Checking fuel pump pressure and fuel control pressure is simple, but you'll need a pressure gauge set compatible with bosch fuel injection systems. The complete instructions are in the manual, for which a link is in the stickies.

A quick & dirty way to check the accumulator is to clamp off the fuel return line from the accumulator to the tank or fuel supply hose (can't recall which). Then drive it. If the symptoms change... you probably have an accumulator problem. Downside is the possibility of that line leaking afterward, but IMO if it does, it's past due for replacing.

I'm still certain it isn't related to your vacuum leak, which you most certainly have. Keep in mind the leak can be in a component and isn't necessarily in a hose/fitting.
 

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It Is What It Is, Dude
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I can't remember where I read this, but somewhere online I read that a fuel supply/pressure is can cause the vacuum gauge to move. In other words, it's a symptom that might be consistent with a fuel accumulator problem...


If a failed accumulator is causing a stumbling fuel starvation / low pressure issue at start up the vacuum reading will fluctuate due to the stumbling and hesitation, not because of the accumulator leaking down while the system was static. That is a secondary symptom.
 

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Discussion Starter #11 (Edited)
Thanks Abiby

If there was a component causing a vacuum leak, wouldn't it be present after start-up? This problem seems to self-correct...that's why we thought it was a fuel pressure problem causing the appearance of a vacuum leak, since the fuel pressure would be normal after driving for a few minutes, whereas a vacuum leak would continue to be present? Hmm...

Isthisdave - that's exactly what I was told. The vacuum gauge moving is a symptom of a fuel supply / mixture problem
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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Thanks Abiby

If there was a component causing a vacuum leak, wouldn't it be present after start-up? This problem seems to self-correct...that's why we thought it was a fuel pressure problem causing the appearance of a vacuum leak, since the fuel pressure would be normal after driving for a few minutes, whereas a vacuum leak would continue to be present? Hmm...

Isthisdave - that's exactly what I was told. The vacuum gauge moving is a symptom of a fuel supply / mixture problem
Check your brakes. The vacuum booster is a BIG vacuum draw. If it's pooched, it MIGHT be a cause of your problems.
 

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1988 560SL (California Model)
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Rowdie - it's an '88...where's the diagnostic port?
Diagnostic port is on the driver's side of engine bay approx half way back. IIRC has a cover on it. Only minimal info can be received and it's not like the port on modern cars.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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I bought the one Len Sokoloff made. Befor I found out the '86 does have the port. I gave it to someone but can't remember who.

The port does have a cover. It is a rectangle. Not the round one. Reno described the location. It looks the same as the one in the PDF but is in a different location on the 560SL.
 

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Discussion Starter #16
Thanks for all the input guys. I will try and get the brakes checked out, do a fuel pressure diagnosis and ultimately change the fuel accumulator as discussed. I will report back on this thread how it goes.
 

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1987 560SL, 1998 SL500
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Before you take it inot a shop, or order an expensive accumulator, I would try at least one test. Since it real handy, pinch the hose coming out of the small end of the accumulator, and make a jumper wire with two alligator clips on one end, and one on the other. Pop the cover off the battery, and the rubber boots off the two fuel pump terminals, not the brown wire, the other one. connect the two to the fuel pumps, and then the other end to the positive terminal of the battery. You should hear the pumps run quite nicely. If not, disconnect the factory wire off the pumps. this should deliver plenty of fuel to the system, and if the engine does not start and run, it's an ignition/vacuum problem.

This will supply full pressure and flow to the system, with the excess going to tank thru the pressure relief valve in the engine comp. when I did this to my poor running, intermittent quitting 560, all was better. And this was after 2 new fuel pump relays.

this is free, and might put you on the right track immediately.
 

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Discussion Starter #18
Wanted to close the loop on this thread - it took me much longer to get into the shop than I thought but have finally done so. We ran a smoke test, and deep in the engine, whiffs of smoke were coming out in the engine. I'd been told by another shop in the city that there was no vacuum leak, but they hadn't run a smoke test...

So it seems like the first thing to do is take care of the vacuum leak. The shop did not think - contra to other input I got - that there was any fuel supply issues or fuel accumulator problem

I've booked in the car to get the vacuum leak sorted this week. I'll post more info on this then...

Incidentally, the shop's smoke machine was a real Mcgiver creation - made up of jam jars and the like (see pic). Did the job though
 

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