Ok, thanks! :-)
Actually I think that the reistance of the coolant temp sensor is within that range, but I can always try again.
What do KOEO mean? Is it during startup?
I guess all of the current mesurments are is done when engine is started up from cold...

Thanks again!

Key On, Engine Off. It gives you the base current for the EHA.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Aye, then I know....
I will try tonight! :-)
Thanks!

I tested the current at the EHA and it was 19.9, engine off ignition on, about 7 mA directly after startup. 20 seconds later it was approx 4. When engine was warm it was fluctiating at about -3.5 mA (between -3.1 and -3.8 or something like that) (indicating that the lambda sensor was compensating for a rich mixture, right?) and I left it there since a little rich mixture would make cold starts easier according to another thread at this forum.

Also last night (a few degrees below freezing point) the engine was easy to start.

This morning however, it was in the garage (temperature about 5 Celcius (ca 40 F if I make a guess)) and this time it took a few second of cranking, then the idle rpm slowly rose to the warm up idle at approx 950 rpm....

I will exchange the fuel filter, I have bought a new one. But might the OVP relay or the fuel pump relay have anything to do with the strange behaviour at just over and at freezing point temperature.

By the way.... I did also connect a button (installed under the steering weel, hardly visable!) to a relay that I connected to the the cold start valve, will try to use it the next time the car doesn't start easily (to test if this is the problem).

Thanks! :-)

So now I am back to thinking the problem is in the power to the cold start valve.

From the wiring diagram - the coolant temp sensor sends resistance reading to the CIS/E, which relays it to the fuel pump relay. Fuel pump relay decides to power start valve.

So, possible problems:

- flakely reading from coolant temp sensor tells fuel pump relay not to send power to start valve

- bad wire from CIS/E control unit to fuel pump relay (tells fuel pump relay coolant temp sensor reading). Green/Blue from Pin 9 of CIS/E to Pin 2 of fuel pump relay.

- fuel pump relay bad (cold start valve circuit)

- bad wire from fuel pump relay to start valve

- bad start valve ground

I think you need to have the test equipment in place to measure voltage to the start valve when the problem occurs. Based on what you have already tested, the fuel pump relay is my prime suspect now, with the temp sensor in second place.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I agree with you, although the two last suggestions are probably not the right ones. The resistance between battery minus and the ground connection the valve is 0.3 ohms, the resistance between fuel pump relay and positive connection at valve is also 0.3 ohms. Not perfect connection, but not source of a very large "voltage loss" at load either.

I mostly agree with the suggestions that its about bad wirering or bad fuel pump relay or something like that, since the problem seems to "come and go". The cold start valve is working (i can hear it work so to say if i shortcut it (engine off, using the accumulated fuel pressure) or use my newly installed start valve button button I can hear a "click" from the valve and also the sound of gasoline being sprayed (if you understand what I mean). The wire from the computer (control unit is perhapps a better word for it) to the relay is good (?), I have tested it before (if its not a loos connection making it work sometimes and sometimes not).

The resistance between the temp sensor and ground is, if I remember this right, ca 4-5 kohms at 0 C, freezing point, (but Im not very sure about this value, haven't checked this for weeks) and about 180-190 ohms at working temp (87 C) (the latter is a little to low, I know that). Might this small deviation be the cause of all of this???
When I connected a 10 kohm resistance instead of the temp sensor the valve sprayed for several seconds (tied this out to open air, just to test if it was a fine spray or not).

Tried to disconnect the temp sensor, and then the engine was impossible (almost) to start if warm, probably due to flooding of fuel due to open cold start valve, and starts only with gas pedal to the floor... Then I got an idea!... Since the engine also sometimes starts easier with pedal to floor when i try to cold start it another question arises... Is it probable that the computer tells the relay to "over use" the cold start valve (using it to long time) thereby flooding the engine with gasoline (that is, the problem is to much gasoline instead of to little)??? And that THIS is my cold start problem... (I hope not)...

Many thanks to the answers so far, I have got several ideas about what to look for from you...

Last night I left the car outside just to test wether it would be hard to start or not. This morning it was very hard to start, took four tries including one where I used my button for 2½ seconds (0 degrees C) - guess its not because the cold start valve is not actuated then... this time I know that it was actuated since I did it myself....
Strange...
Eventually I floored the gas pedal and then after a few seconds of cranking it started...

/Ola

btw: i have a new ovp relay waiting for me at the post office now so i will fetch it after work and hook it up... Most probably i will need another fuel pump relay ta, I will try to get my hands onto one of those to... however they are quite expensive new so I will try to find a good used one...

Were you able to get a reading on the voltage to the start valve when it didn't want to start?

Maybe the valve itself is flakey?

BTW - my friend Jim Freeh, who bought my 300E last summer, is having this exact problem, and he has not been able to figure it out either. He has an "extra" 300E and he has swapped all the components in the loop withouth success in isolating the problem.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Mine sounded very simliar...



Now in the last few months- it starts and then dies cold or hot. I cannot be sure-but I think I smell fuel on occasions.

I was leaning toward testing/replacement of the FPR?

I can by pass the fuel pump relay and try a cold start. temp sensors are in spec. Seems to start fine when it's below 0 C.

It's better after an airflow sensor plate adjustment.


Michael

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

I will try to do such an adjustment... Thanks for the tip!
By the way, what is an airflow senor plate adjustment?? It not the CO-screw you mean, right??

There is specifications for the position(centering of the airflow plate) in the venturi. It must be ccncentric with the bore and then must have the zero adjustment.

it's procedure 07.3-1665 in the manual.

Michael

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Never measured that for som time now, but it looked like it´s withins specs, but I will be forced to check that again....

Is there a check list of things to verify(?),

I feel like I'm arbitrarly testing components.

Can someone tell me what the test proceedure is to tell if it's a fuel pressure regulator vs EHA?



Thanks,


Michael

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

High again, new questions bringing this thread back to the top...

I did replace the fuel filter the other day, and now I have a problem with "walking" idle... sometimes it's normal and suddenly it can go up to 1200-1500 rmp or so... being there for som time... I did a new CO adjustment using the EHA current and it got better, however still wanting to be high from time to time... I have just tried a few times)... When I changed the filter the car was washed as well, might it be a problem realating the new filter (better fuel pressure) or might it be maiost disturbing the engine?
Any ideas anybody ;-)

BTW: I have only cold started the car once since then, and then it started just fine, although the idle was to high....