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  #1  
Old 08-23-2012, 05:11 AM
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Angry 1980 350sl Starting and idle problems

Hello from Galway in Ireland.
I have just bought a 1980 350sl in pretty good shape.However it has a problem that i reckon the previous owner spent a good bit of money on and did not fix.
If I leave the car for more than 2 days it takes 15 mins of turning over to start. On the other hand once started it will start easily.
When started it will not idle happily and if put into drive will be inclined to conk out, with carefull revving I can stop that but it means I really cannot drive it safely.
Things that have been relplaced as far as i can see are:" the coil, plug leads,distributor top, fuel distributor ( i think that is what it is called, a multi sided metal item with all the fuel lines going in to it , its just under the air filter . I asked a local mechanic to look who is familiar with older mercedes and he said there was nothing obvious.
So any help appreciated, i just ordered the haynes manual and the injection system book by Probst,

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Old 08-23-2012, 07:00 AM
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Quote:
Originally Posted by willsandbills View Post
Hello from Galway in Ireland.
I have just bought a 1980 350sl in pretty good shape.However it has a problem that i reckon the previous owner spent a good bit of money on and did not fix.
If I leave the car for more than 2 days it takes 15 mins of turning over to start. On the other hand once started it will start easily.
When started it will not idle happily and if put into drive will be inclined to conk out, with carefull revving I can stop that but it means I really cannot drive it safely.
Things that have been relplaced as far as i can see are:" the coil, plug leads,distributor top, fuel distributor ( i think that is what it is called, a multi sided metal item with all the fuel lines going in to it , its just under the air filter . I asked a local mechanic to look who is familiar with older mercedes and he said there was nothing obvious.
So any help appreciated, i just ordered the haynes manual and the injection system book by Probst,
Start with a compression test. This eliminates basic issues like low compression, stuck valves, etc.

Then check the ignition timing.

Next, connect a vacuum gauge and make sure the vacuum is around 20 and steady at idle.

Let us know your results.
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  #3  
Old 08-23-2012, 10:53 AM
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It almost sounds like you're not getting fuel to the cylinders at first. I'd suggest a fuel pressure test. One of the first steps in doing that test under these circumstances is to "jumper" the fuel pump relay, as it only comes on for a second or two until it receives a signal that the engine is started.

It sort of sounds like you are not getting and holding the fuel pressure in the system. This could be due to a bad pump, bad accumulator, bad fuel pressure regulation, or a restricted line(poss clogged fuel filter?).

There are also small filter screens in the fuel supply and injector lines that may have gotten clogged.

It sounds like you are 'starving out' the engine from lack of fuel.

Just a wild guess, over the 'net, from thousands of miles away; take it for just that.
Scott
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  #4  
Old 08-23-2012, 11:55 AM
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thanks Scott

i think a fuel line pressure meter is needed, any tips out there for a goo link to one? thanks smiffy6four and radiotek willie
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  #5  
Old 08-23-2012, 11:17 PM
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Search for a K-Jet fuel pressure gauge. K-jet is short for K-Jetronic, the designation Bosch gave that particular generation of fuel injection system. My '75 is a D-Jet, an earlier generation of FI system, but my guess about your problem is from info gathered hanging around here and at The Other Forum.

Best wishes,
Scott
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  #6  
Old 08-24-2012, 12:28 AM
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Quote:
Originally Posted by RadioTek View Post
Search for a K-Jet fuel pressure gauge. K-jet is short for K-Jetronic, the designation Bosch gave that particular generation of fuel injection system. My '75 is a D-Jet, an earlier generation of FI system, but my guess about your problem is from info gathered hanging around here and at The Other Forum.

Best wishes,
Scott
x2. I have a 300ce with CIS and have had numerous vw/audi's with the same mechanical fuel injection. If the fuel distributor has been replaced, then it sounds like it should be a fairly simple fix. From what you describe, it seems like bad injectors that are gradually leaking when the car sits, so that when you're ready to cold start there is no fuel in the lines. It might be useful to pull a couple of the fuel injectors for inspection to rule these out.
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  #7  
Old 08-24-2012, 05:02 AM
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help with some points raised pls

I have not had a classic car for years so gotta go and buy some tools now,hence ill be a little slow in getting back with results, but really gratefull for responses.
When I turn the key to position 2 should I hear the fuel pump whizzing?
Can I substitute the window opening relay for the fuel pump one?
If not which contacts do i short out?

Any recommendations for articles on the site to read ?

Willie
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  #8  
Old 08-24-2012, 07:30 AM
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I am not that familiar with this site. There is a collection of posts regarding trouble and repairs specific to the 107 on another.
The Encyclopaedia Germanica Volume 107 (aka EGv107) - Benzworld.org - Mercedes-Benz Discussion Forum
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  #9  
Old 08-24-2012, 07:45 AM
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All good answers, guesses and suggestions.

No you can't use a different relay for the fuel pump.

Here's the online MB service manual. Though this is specific to US models, it should be relavent to your problems, including how to short accross the fuel pump relay.

Model 107
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  #10  
Old 08-24-2012, 12:49 PM
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Re: Fuel Pump Relay
The FPR part # should be 001 542 02 19 (stamped or printed on relay)
The window relay is part # 001 542 02 19
Ergo, they are interchangable!
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  #11  
Old 08-24-2012, 01:45 PM
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Quote:
Originally Posted by Frank Reiner View Post
Re: Fuel Pump Relay
The FPR part # should be 001 542 02 19 (stamped or printed on relay)
The window relay is part # 001 542 02 19
Ergo, they are interchangable!
Yes. It is a rotw model so different from U.S. 450 of the same year.
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  #12  
Old 08-24-2012, 04:07 PM
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i'd start with injectors as a culprit , presurize and then see if they loose pressure rapidly ( bad) or slowly ( good) with engine off.
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2015 Porsche Cayman - Elizabeth
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99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
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19 BMW X5 - Heaven on Wheels
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  #13  
Old 08-24-2012, 04:09 PM
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I don't know anything about the K-Jets, but on a D-jet, I would look at the cold start injector if it wouldn't start after sitting for a few days. It is sort of like the choke on an old car. I think the K-Jet has a cold start valve, so perhaps look at that ?

If it cuts out once started and you have to work the accelerator, then maybe it is running too lean at idle. I don't know how you adjust that on a K-Jet, but if you go down to the K-jet section on the link Rowdie provided, it may be there.
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  #14  
Old 08-25-2012, 09:08 AM
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Out of the KJet manual

Engine does not start/starts hard cold:
1. Sensor plate or plunger not moving freely:
Remove air filter and gently apply pressure to the sensor plate. If the plate does not
move, there may be an internal problem. Look for any possible cause for the binding
externally. If this fails, remove the fuel distributor and have it repaired or replaced by
a qualified repair shop.
2. Auxiliary air valve does not open:
Remove the hoses from the valve and verify that the valve is open. If not check that the
electrical connection is good and that there is voltage present with the ignition on.
3. Electric fuel pump not operating:
Check the fuel pump fuse and the pump relay, if both are good check voltage at the fuel
pump, if good replace fuel pump.
4. Thermo time switch defective:
Disconnect the connection to the cold start valve. Put a test light across the terminals.
Run the starter, the light should stay on for a few seconds, depending on the temperature
of the engine. If the light does not work, check for voltage on the yellow wire between the
starter and the Thermo switch. If there is voltage to the switch and the light does not
work, replace the Thermo time switch.
5. Cold control pressure out of tolerance:
Check the control pressure Regulator. Check the voltage at the connector to the
regulator - at least 11.5 volts. With power off and the connector off, check for continuity,
if none replace the regulator.
6. Injector leaking, opening pressure low:
With the engine not running pull the suspected injector and look for any leaks. If leaking
replace with it new injector.
7. Injected fuel quantities not equal:
Suspect that there is an injector problem. Pull each injector and test for quantity of fuel
injected into a measuring container. Run the engine for a short time for each injector.
Compare the amounts of fuel. Replace the injector that is not operating correctly.
8. Basic idle setting incorrect:
Check the speed and adjust as necessary.
9. Fuel Accumulator and/ or Fuel Pump Check Valve:
These keep pressure on the system.
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2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #15  
Old 08-25-2012, 10:38 AM
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2. Auxiliary air valve does not open:
Remove the hoses from the valve and verify that the valve is open. If not check that the
electrical connection is good and that there is voltage present with the ignition on.

The '80 350 does not have the electric AAV. It is the older style. Just so you don't go looking for an electrical connection to test.

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