1980 350sl Starting and idle problems - Page 2 - PeachParts Mercedes-Benz Forum

willsandbills · #16 08-27-2012, 07:20 PM

My car was registered on 1 jan 1980 so its really a 1979 production model. Does that make much of a difference.?
Checked out the fuel pump relay, interchanged it with another of same p/n and no difference.
I only have 3 relays , all the same p/n all located just above the fuses, its confusing as most articles refer to many more relays.
Question, there is a much bigger relay mounted to one side, any idea what that is?, I can take a pic if the site allows it ?
BTW thanks for the link to the european manuals, its excellent

willsandbills · #17 09-04-2012, 05:56 PM

Been busy checking as much stuff as i can.
~Fuel pump and relay all ok. WUR resistance is 30 ohms, also checked filter in WUR and its clean, 12 volts is there when fuel pump running.
Two problems spotted.
1 no voltage at cold start injector, if i put 12 volts directly to cold start injector it operates fine and sprays petrol, just dont know why no voltage there when starting.
However ,main problem is I still cannot start car, problem appears to be low fuel pressure, if I look at fuel pressure going in to fuel distributor it is very good but at fuel injector it is obviously poor. ( sorry no fuel gauge to be exact)
The fuel dist is brand new from previous owner, so that should be ok.
Wondering where to go next ??
willie

Frank Reiner · #18 09-04-2012, 07:49 PM

I'm afraid that you are going to need a pressure gauge soon (100 psi range).
The basic pressure test is performed by connecting the gauge to the control pressure line on the top of the fuel distributor (FD). System pressure should be approx. 70 psi. with a cold WUR.

In the short term you can perform this check: 1. Remove the plug from the safety switch on the air meter (it is located just forward of the FD, towards the right side). 2. Disconnect fuel lines at two or three injectors. 3. With the key on the pump should run continuously, and there should be a small fuel flow at the disconnected lines. 4. Press down on the air flow sensor plate; the fuel flow at the disconnected lines should increase. Turn off key.

If there was no flow at the lines, or it did not increase, it is a symptom of a rather worn pump. The pump must deliver at the pressure established by the pressure regulator in the FD.

As a check of flow, remove the return line from the FD, connect a hose which you can direct into a container, and run the pump for 30 seconds.
Output should be approx. 1 liter/30 sec.

For other checks, see the post of 08/25 by meltedpanda.

willsandbills · #19 09-07-2012, 06:00 PM

Thanks for help so far, pulled two injectors, removed safety valve and pressure out of injectors seems pretty good, no gauge yet to be precise , but looks good.
A question?? i am unable to find the auxiliary air device, I see it mentioned in all the literature but I cannot find it.

willie

Frank Reiner · #20 09-07-2012, 07:10 PM

The aux. air valve will be found to the right of and a bit aft of the distributor.
There have been a couple of types fitted over the years, but they are all characterized by having two hoses of about 1 inch diameter; the inlet hose connects to the air guide under the air flow sensor plate, and the outlet hose connects to distribution passages in the upper portion of the inlet manifold/plenum.

On the matter of starting, now that you have determined that you can cause fuel flow at the injectors by pressing down on the sensor plate, have you tried starting by having someone crank the engine while you depress the sensor plate a bit? That gambit provides extra fuel while cranking.

willsandbills · #21 09-08-2012, 03:11 AM

Thanks, I had found that air device, however i was looking for one like is shown in the cis manual, ie one that has two wires going to it also. The one i spotted in the car just has the two large hoses like you say.
Does this mean that i do not have one with an electrical connection ?

Also will try to stary as you suggest.

Removed distributor and rotor, contacts somewhat grubby and cleaned all ,no change

willie

Frank Reiner · #22 09-08-2012, 12:30 PM

The device which you found, is in fact the aux. air valve. It is a thermo-mechanical device, i.e., when cold it is open to supply additional air, and with increasing engine temp it closes. There are two types; yours which is heated by engine temp, and an electrically heated type. The electrically connected device to which you refer may also be an idle speed control valve (ICV), which is driven by an engine control unit (ECU) to maintain programmed idle speeds. It was used in model years subsequent to yours.

The aux. valve can be removed, cleaned with a solvent such as spray carb or brake cleaner, and tested for function by applying heat to its base. At 20C. or below it should be completely open, at 70C. closed.

You had noted earlier that you did not have power at the cold start injector. If you will follow the wiring from that injector, it will lead to the thermo-time switch. That switch responds both to engine coolant temperature and to internal electrical heating. If defective no power will reach the cold start injector. When cold, the switch should have continuity.

willsandbills · #23 09-08-2012, 02:06 PM

Thanks again, i will dismantle it tomorrow, I was mistaken with the cold start injector, there was no power to it at ignition position, however when i go to start car there is power there for a short while.

I did not try your previous suggestion yet as was away today,

One more question, i pulled out the drivers side carpet and the thick foam underneath was all wet, i had tried to dry it out but decided to rip it out, it was stuck to floor.
Two questions if I may?
1 is it possible to buy a replacement or will i have to make it u from carpet underlay
2 is there a known problem of water getting in here, everywhere else dry and the floor looks ok, ill try firing a hose of water at the floor perhaps ?

willie

Frank Reiner · #24 09-08-2012, 06:15 PM

Re: Wet Floor

The floor foam and carpets are generally available from a number of aftermarket suppliers. Have look in some of Body and Detailing sections of this site.

Two leak areas for which MBs are notorious:
1. Windscreen seals (the rubber gasket).
2. Clogged drains in the cowl (scuttle?) fresh air intake area.

The Gulf Stream does make it all emerald, eh?

willsandbills · #25 09-08-2012, 06:26 PM

im afraid it rains a lot here, think of seattle but worse and much more damp.

the fresh air scuttle is fine, i think maybe the windscreen rubber could be bad, how do i check? put the hose on the bottom of windscreen???

thanks again

irshmerc · #26 09-08-2012, 08:16 PM

Hi, how you doing

The clogged drains Frank spoke about, one either side just infront of the windscreen, if you remove the grilles and poke around with a length of wire, an old coat hanger is handy, you should be able to remove any old ****e thats wedged down in there, hopefully that will sort the problem, much easier and cheaper than the windscreen or maybe even the heater hoses.

Good luck

willsandbills · #27 09-13-2012, 07:10 AM

the aux air valve was removed, it does not close fully at 70 degrees c i need to go to 80 or more. I know this as i have lost some of the skin on my lip blowing thru ( wont do that again)
so do you think its faulty? i can get a s/h one i think

Re leak, channels ok but found a small leak through a grommet in wiring loom, dripping down to a place behind accelerator pedal could have been there for ages, fixed now and will monitor.
A small bit of debris came out of the chanell under door but seems minor.

Have now got a s/h WUR which i will try if you do not think the aux air valve needs replacing
willie

meltedpanda · #28 09-13-2012, 10:25 AM

IIRC the aux valve needs to close completely. I know it does on mine

Frank Reiner · #29 09-13-2012, 02:14 PM

Re: Aux air valve
If the aux. valve does not close completely, the result will be a somewhat high idle speed; the aux. valve is simply a temperature controlled throttle bypass, and has the same effect as the driver manually holding a bit of throttle.

Earlier in this thread a check of return fuel flow was suggested; have you done that? See my post of 09/04.
If flow volume is low, turn your attention to pump, accumulator, and filters.
If flow volume is OK, a check of pressures, both system and control, is in order.

willsandbills · #30 09-13-2012, 03:26 PM

yes i did all that ( with the exception of not having a pressure gauge as yet) fuel flow is there and when pushing down on the big round flap ( with safety sw discon, there is a really good increase in fuel flow)
To re cap a bit, would you say that the fact that the aux valve does not close fully till 80 degrees c is a cause ti replace it.

thanks again Frank