1980 350sl Starting and idle problems

[meltedpanda]

A non fully functioning avv will cause an idle hunt. I know this from experience. It should close fully when engine temp rises. This allows the idle to settle. Without full closure air is introduced and the idle will surge.

[Frank Reiner]

The late closing (or non-closing) aux.air valve may cause drive away problems associated with hunting as described by panda. Given all that you have accomplished so far, if you still have starting problems after a layover of a couple of days, I think you will need to get some definitive pressure information. The difficult starting after layover points to rather rapid leakdown of residual pressure. There are three areas where that leakdown can occur: 1. check valves in the injector nozzles, 2. accumulator diaphragm, 3. "push valve" in fuel distributor.
It's good that you have the Probst book; just about all the analysis procedures are covered.
Incidentally, you now know how to circumvent the starting problem; pull the plug on the safety switch, and run the pump until pressure comes up. It will start much more readily.

[willsandbills]

is this one sufficient
Basic Fuel Injection Tester, Bosch CIS STRTU447C BRAND NEW! | eBay

I think you are correct in saying that it is fuel pressure dying away, I kept turning the starter motor until it started and now for 4 days in a row in starts no problem, however i reckon if i leave it for 3/4 days it will be back to the same problem.
If you think this pressure gauge is ok ill order immediately

[Frank Reiner]

Have a look at this source also.

http://www.specialtauto.com/mercedes-parts/index

CIS Fuel pressure test kit.
Professional quality

This is a must for testing the fuel
system for correct operation.
For the Bosch K Jetronics
99.95

[meltedpanda]

have you read my post here
http://www.peachparts.com/shopforum/sl-forum/260122-auxillary-air-valve-djet-who-knows-does-close-completely.html

you may want to try it ...carefully..

[willsandbills]

many thanks agian to all who helped,its ben a long hard road, but in summary. Stripped down to inlet manifold and gaskets were all damaged, so that was a good sign, replaced them. Removed all injectors , all spraying well and correct amount of fuel. Then replaced wur, still having starting problems. So next fitted tie wraps to all hoses and cleaned all.
However the thing that fixed it was replacing the distributor.
Now starts perfectly and runs like a dream, HOWEVER, one little problem left that I need a comment on.That is , if I let engine heat up and then restart, no problem, if i let engine get cold, no problem. However if i start and leave car for about 10/15 mins it takes a lot of cranking to start.
my assumption is that when cold the cold start injector is doing its job so thats ok, but when left for the 10 mins it is relying on the fuel pump to send fuel and that seems to be a problem. As i have never had the car before all this i need clarification on one thing please ? when I turn on the ign key (not cranking yet) should I hear the fuel pump running ?? because i do not and that is I think my problem area, but I would like to be sure before i go tracing the circuit.
Apologies for long winded summary, but nearly there and would appreciate any help. willie

[meltedpanda]

CSV will not fire above a "cold start" temp or should not. I would no that out , it could be leaking or fireing when it should not. Test it during that 10 -15 min. Turn key to spin pump, it shoulf not realease fuel

[willsandbills]

thanks will do, to clarify: when i turn key should fuel pump spin up?

[meltedpanda]

yes you should hear it , then again on a later model like yours , not a 100% sure

[Frank Reiner]

All K-jet systems have a fuel pump timer incorporated at some place in the pump electrical supply. The most frequently seen is in the pump relay; when a running engine signal is received from the ignition, the relay remains closed. When the engine stops, or has nor been started, and the key is on, the timer allows the pump to run for 1-2 seconds only. Although I have not encountered one, I understand that one version did the timing in a master relay that is separate from the pump relay (the master relay controlled the ground of the pump relay), which is the case with the D-jet system.
So yes, you should hear the pump spin up when the key is turned to "2".

[willsandbills]

Been in bed for 3 weeks with flu, no xmas dinner etc.
So been at the car today, to summarise
Starts PERFECT every time from cold.
Runs like a watch
If i kill engine and restart immediately, no problem.
If i let warm up for a few mins , then kill engine, leave for 5/10 mins , it will only start after a good bit of cranking.
if I leave to get cold we are back to starting perfect.
When i turn key to the position before cranking engine, there is no fuel pump activity, i also put a volt meter on fuel pump and no voltage there.
The three relays are all the same part number , so i moved them around and no change , i can hear relay coming on when ign sw turned.
There was a post to say short pins 1 and 2 in relay socket to hear pump, i did that but engine began to turn over.
Not sure where to find Master relay mentioned in last post.
Should i try to put a direct 12 volts to the fuel pump with a switch and simulate the two seconds of fuel pump activity?
willie

[meltedpanda]

after your rule out fuel delivery

hot start issues on K JEt

lost of rest pressure
improperly adjusted airflow sensor
leaking injectors
leaking cold start injector
incorrect control pressure

any or all or a combintion - check each one

[rowdie]

Hard warm/hot start after sitting for that period of time is a common symptom of accumulator failure. The accumulator maintains fuel pressure in the system to facilitate warm/hot start. If the diaphragm is leaking you loose pressure too quickly. Engine warm the cold start valve doesn't provide fuel.

It can fail at any time. I had to replace it on my '86 560SL with 60,000 miles. Then had to adjust the AF mixture because some idiot had adjusted it to help with the hard hot start.

[meltedpanda]

Rowdies post= Rest pressure.
Said much more elequently -

[willsandbills]

The accumulator looks new, but i think i can borrow a friends one to test.

The one thing I know for sure is that when i turn ign key I am not getting any 1.5 sec of fuel pump running, as this car is newish to me i cant swear that it should do it ( its a 1979) but all the books seem to say it should.

The FP relay is ok so that points me in the direction of the ECU unit ? what do you think?
willie

PS thanks for replies