I phoned the Benz distributors and is asking me a whopping R4000 for a part that's roughly $600. It would be cheaper for me to import one myself.
But looking at this system I have tried making sense of the accumulator's function, I can only see that it was meant to smooth out the pump operation or account for hiccups or spikes and to maintain a smooth running pressure. Like a capacitor in a circuit or a mechanical balloon, a 4K balloon.
Both my secondhands does that when the motor runs, they just don't seal properly making fuel return overnight.
My guess is because the res is leaking it causes a vacuum opening the pressure compensation valve on the motor fuel distributor side allowing all the fuel to run back trough the feed line.
Can anyone see any reason why I can't just fit a standard non return valve into the fuel line hose going from the fuel filter to engine right after the fuel filter?
Well at least until I can get a replacement that fits my pocket.
Quote from: George on 13 July 2011, 04:19 AM
I phoned the Benz distributors and is asking me a whopping R4000 for a part that's roughly $600. It would be cheaper for me to import one myself.
But looking at this system I have tried making sense of the accumulator's function, I can only see that it was meant to smooth out the pump operation or account for hiccups or spikes and to maintain a smooth running pressure.
Both my secondhands does that when the motor runs, they just don't seal properly making fuel return overnight.
My guess is because the res is leaking it causes a vacuum opening the pressure compensation valve on the motor fuel distributor side allowing all the fuel to run back trough the feed line.
Can anyone see any reason why I can't just fit a standard non return valve into the fuel line hose going from the fuel filter to engine right after the fuel filter?
The valve should halt fuel excaping the res since it's creating a vacuum seal and won't inhibit the function of the pressure comp on the distributor since it's only function is to keep fuel volume shrinkage/volume from messing arround.
Well at least until I can get a replacement that fits my pocket.
Is this a K-jet car you are talking about?
Where are you located?
Here in South Africa I have supplied several club members with accumulators, and for the W116's the total cost is something like ZAR1250 each.
In JHB, this is for a 126
WHich W126? Some use the W116 style accumulator for ZAR1250, most use the smaller type and it is a lot more expensive - ZAR2200 or so.
It had the larger one but without the second inlet in front. 1980 280se 126.022
It's still alot of money for a disposable component, in what way will the car suffer without it or if there's a checkvalve on the fuel filter outlet? The leaky components still offer fuel spike damping to the fuel pump. The check valve could extend their usage unless it causes other problems.
There is already a check valve on the pump outlet (or there should be, at least). That check valve may have failed.
Question - are you sure the accumulator is the problem? Fuel pressure can leak away out of :
a) check valve
b) accumulator
c) one or more injectors
d) cold start valve
e) base of fuel distributor.
The pump valve is tested OK and with the disconnect test on the resevoire, it's leaking some fuel when the engine is running but not squirting.
I have tested the car start problem with clamping it's exit hoze before turning the motor off at night. It started easy the next morning in one go.
The car runs OK with it it just doesn't start that well.
looks like your car needs A000 476 08 21.
Approx ZAR1550.00 all incl.
Fuel accumulator holds a volume of fuel under pressure and also maintains pressure in the fuel line running to the fuel distributor. This prevents fuel in the lines vaporising in hot climates, it also means fuel under pressure is available for engine start rather than pointless cranking as fuel pressure comes up.
koan
In answer to your original post, the accumulator does two things - smooths out the pressure flow when the pump is running, and holds the system pressure high for a few hours after the (hot) engine is stopped, preventing fuel vaporisation. Note that the pressure does drop to near zero after that, but by then the engine is cold, so there is no chance of vaporisation. Additionally, a cold start with the system pressure at near zero is not an issue, as no air is admitted to, or fuel lost from, a healthy system, so the system remains full of fuel, and the pump can raise that fuel to the required system pressure level in well under a second.
A faulty accumulator makes warm/hot starting difficult, but a cold start should still be perfect. If it's not, then there is a different problem than the accumulator, or another problem in addition to it. (Had this exact issue with my 116, new accumulator fixed it, with no other changes to the fuel system)
Edit: Just like Koan said!
I think you are right, all theory had to fly out the window this afternoon. I tested the second hand replacement I fitted yesterday and it does not even have a drop of fuel coming out the back with the motor and running even after having used the car to drive to work today.
So there's something else that might still be amiss here, it struggled starting this morning and this afternoon on the way back from work.
What bugs me is the old one was leaking and the test I did a few days ago clamping it's leak/atmospheric hose going back to the damper did make the car start off the bat after standing over night. Proving that if I could stop the fuel return through the exit/leak that the car would start easy, and it did.
I guess maybe it was just one time luck. I'll do the test again to try and disprove the accumulator. I did get a second one from the secondhand merc shop again on the way home so now I have a second one for spare.
Paid R100 for each but there's no guarantee on how long they will last.
Quote from: George on 13 July 2011, 01:22 PM
So there's something else that might still be amiss here, it struggled starting this morning and this afternoon on the way back from work.
This is cold starting is it?
Warm starts are OK?
Does it backfire in the inlet manifold if the throttle blipped after a cold start?
When warmed up how does it run?
koan
Warm starts are OK.
It has to heat up to about 50degrees celcius before the throttle can be pushed normally but there's no obvious backfiring just a engine dying away effect if you push it while it's cold.
When it runs it's doing OK or have been running OK but this morning it was rather lazy, it's an automatic gearbox, If I push the pedal down to trigger full enrichment it did not respond with it's usual power. Something else must have died in this past week.
atm it's behaviour when warm has been pretty random, one day it was a loose plug wire, the next the plug wires are OK but something is not 100%, then in the afternoon it would be OK again with seemingly normal power at low speeds and good power at full throttle.
The clamp test failed to give me the same results this morning so that means there's more issues or a new issue has presented itself now, the accumulator is no longer leaking so it's time to move on.
I think a full fuel injection inspection and minor service is in order.
Have you checked ignition timing and the vacuum plumbing associated with the distributor?
A compression check would be worth doing.
koan
Will do that next. Need to get a pressure gadget first.
Really struggled this morning getting it started.
Eventually I unhooded the air filter cabinet and just pushed the air plate down and then left it to return.
Then after that I'd try starting and there would be an enourmous response from the engine, I repeated this and this broke the cold spell and the engine started. So what came to mind is an air issue.
I then did an investigation into the choke/idle controll circuit and found that the high start idle setting is not working or not kicking in.
I did the test of unhooking the tube to the decel circulating air valve and replugged it, According to the manual this should provide the high idle effect for a few seconds but it did nothing.
The bugger is a bit hard to reach under the car but I got to it and just unhooked one of it's hozes. Oil came running out!!
What could have gone wrong here? I can only assume this came from the air filter cabinet because it's oily. Maybe someone thaught it would make it better if it's oiled.
I allso tested the Aircon cutover circuit by removing it's tubes from it's cutover switch and connecting them to each other, there's no idle increase for that either. What's worse is the tube that's used to controll the aircon bypass valve has a vacuum on it??!! Could be busted and now the car is sucking air through the control?
(http://mb.bolinko.org/15/warsztat/silniki/M110/m110%20-%200471-1.jpg)
I tested the cutout valve and found that someone put little ball bearings in it's valve switch tubes. Removed em, tested the cutout and everything is fine if I connect them together the car dies so it's working. Dont know if the bearings blocking the tubes on the valve switch was a fix for some other problem but I guess I'll find out.
Quote from: George on 16 July 2011, 07:40 AM
Really struggled this morning getting it started.
Eventually I unhooded the air filter cabinet and just pushed the air plate down and then left it to return.
Then after that I'd try starting and there would be an enourmous response from the engine, I repeated this and this broke the cold spell and the engine started. So what came to mind is an air issue.
When you pushed the plate down you may have heard the injectors spraying, that would give you some extra fuel and an engine start.
Sounds like whatever controls cold start enrichment is not working. If it was standard K-Jet I'd say warmup reg but I think you said earlier it was KE-Jet.
Quote
I then did an investigation into the choke/idle controll circuit and found that the high start idle setting is not working or not kicking in.
I did the test of unhooking the tube to the decel circulating air valve and replugged it, According to the manual this should provide the high idle effect for a few seconds but it did nothing.
The bugger is a bit hard to reach under the car but I got to it and just unhooked one of it's hozes. Oil came running out!!
If the decel circulating air valve is same as the coasting boost valve on my engine that won't be the problem. Mine wasn't working for awhile, I gave it a bit of a flush out and it now works. All it does is boost revs for a 2 or 3 secs AFTER the engine has started and effectively opens the throttle a fraction when coasting, reducing emissions.
koan
The plate was pushed down with the car not started and couldn't remember hearing anything.
The car started first go this morning without doing anything. I think it might be the pool of oil that might have caused an air seal in the rubber tubing.
I did clean the valves and tubing yesterday before putting them back, even though the valves seem to be busted the car started easy this morning, where it was impossible yesterday. Holding my thumbs it wasn't just a one time thing.
It makes sense to me, as this is the only place air get's to a cold engine apart from the normal idling tube. I can't operate the fuel pedal when starting so everything is up to these valves to give air when the plate is in it's normal closed position.
There's still no idle difference. The car works up from a 500 rpm to 900 rpm as it get's to normal temperature. Switching the aircon on and off has no effect.
I'm going to try and get a complete set from the secondhand place as I can't seem to find a part number or online references to either these two valves. I think I'll also get the aux air valve while I'm at it.
The cold start enrichment is definitely working, my car usaully get's 3-5 seconds of effective cranking because of it but then when it runs out there's nothing to carry the flag further and the car is expected to run on normal warm idling. This would allso explain why I need to try in one minute or so intervals, so that the heat from the start can dissipate causing the cold start to activate again, improving my chances.
Replacing the valves fixed the problem.
On a really cold/bad start you can hear a faint popping sound like when pushing in an empty soda can from the valve. it makes a ping ping sound.
Quote from: George on 22 July 2011, 03:54 PM
Replacing the valves fixed the problem.
Which valves did you replace?
koan
The Auxilary valve, I think this valve was still OK.
The Aircon valve, this one was pulling a vacuum through it's control port, clearly busted.
The aux circulating valve.
I think the startup pressure comp will need a service too but at least the nightmare's over and she starts. That circulating valve are litterally keeping the motor from dying by giving it little shutters of air.
Quote from: George on 23 July 2011, 12:59 PM
The Auxilary valve, I think this valve was still OK.
The Aircon valve, this one was pulling a vacuum through it's control port, clearly busted.
The aux circulating valve.
Did you replace them one at a time and try the engine?
So you would know exactly which valve was the problem.
koan
No, I had enough physical contortion exercise as it is.
I took everything out to avoid revisitation, I allso washed and inspected the tubing and it was not like I was going to wait 5 hours to try each component. All that I could determine is that it was an O2 starvation at startup.
With all those small cristmas gift socket gift sets my father in law got through the years I managed to assemble weird things that could reach weird places.
The car still has a 5 minute warmup time before I can drive it, so the warmup pressure compensation might need some attention next.
What I figured out with this exercise is that alot of desighn goes into making things unnoticed' or smooth. This can be contrary when you compare testing components vs driving the car. So the compensator would just make the car start and go.