mercedes w126 420sec cold start problem

[grober]

fixable??? fuel pump relay 003 545 25 05 - Mercedes-Benz Forum

 

[Firepants78]

already asleep when I got the idea ... after all, I could connect it to the starter motor,

maybe stupid question where is the starter motor in my car?

Regards Maciej

 

[Firepants78]

At night I found if someone would want
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1988/420SEL/WIRING%20DIAGRAMS/3168.pdf

Ordered a new relay because the diagram shows that there is no other option than spoiled relay.

 

[Firepants78]

resoldered all pins, and still nothing has changed , I'm waiting for the new relay, I hope that it will solve the problem,

 

[Firepants78]

I found more Diagrams

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1989/420SEL/SYSTEM WIRING DIAGRAMS/

 

[Firepants78]

I have another questions ... sorry
I'm looking now cold start valve gasket, i found one on ebay but in US :-(
Maybe someone know where I can buy that gasket or maybe somehow replace gasket by silicone paste for example

Regards Maciej

 

[grober]

Any decent motor factor should have suitable gasket paper-- failing that a corn flakes packet is pretty good. You can to cut one to a suitable shape [ carefully-- small embroidery scissors often found in supermarkets sewing section are useful for this ] using the old one as a guide or the flange of the valve. Coat both sides with suitable gasket cement and you should have no problem.

 

[neilrr]

IME FPRs either work or they don't, they are on or off, no halfway stage.

If you can hear your FP spooling up when you turn on the ignition then the FPR is working & I'd say a new one is a) not the solution to your problem & b) a waste of money.

 

[Firepants78]

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1988/420SEL/WIRING%20DIAGRAMS/3168.pdf

according to above diagram I'm guessing that coil from cold start valve is malfunction, if kick down works fuel pump works that is only one option I guess.

 

[E55BOF]

If the engine runs OK once it has started, then the FPR is serviceable to that extent. It may well have no fault, but we don't know. If the cold start valve works when +12V is applied to it, the problem is somewhere in the circuit between the relay and the cold start valve.

In the short term I'd try hard-wiring the valve direct to the +12v supply on the starter motor solenoid, as has been suggested; sounds like a very viable demon bodge (not botch...) to me. If that works, the only downside that I can see will be that the cold start valve will always add extra fuel, even on a hot start, but of course, will stop doing so as soon as the starter motor stops. I can't see a problem; does anyone have any other views?

 

[ianrandom]

The cold start valve does add extra fuel each time even on hot starts. Just for longer or less long, depending on temperature.
So that fix could work for now.

Have you tried a different injection ecu, just for kicks? The one near the idle relay but a lot bigger, in the passenger footwell. Just a thought.

 

[Firepants78]

New relay installed and no changes
I give up, you have any ideas?
or could someone help me locate the bloody starter please?
I want connect that valve to the starter motor is always something more than nothing, but first i must to FIND HIM

 

[neilrr]

See post 28.

Take it here - Star Motor Services

 

[Firepants78]

So I now think, what makes the relay knows the engine is cold or warm, maybe there is a chance of a temperature sensor, lie to the relay.
maybe someone could send me guidelines which one it is, and where to look for, it is easy to leave a car to a mechanic but it always costs a fortune,

 

[Firepants78]

neilrr - maybe you have any idea, what that can be?? If you was sure is no relay then what??

 

[grober]

Looking at your various wiring diagrams it would appear the 12 V supply to the start valve from the starter comes into the FUEL PUMP RELAY via violet white wire and departs via a violet green wire to the injector. You might want to test if you have 12V on the violet wire when the starter is turning over and 12v out on the violet green. If you do then you need to test continuity on the violet /green wire from the relay to the injector and continuity of the brown injector wire to earth.
If as I suspect you have difficulty with vehicle electrics you have to entrust the car to someone who has the necessary experience.

 

[neilrr]

FP,

I don't know what the issue is, it could be quite a few things.

Before you throw any more parts / money at it talk to a good MB indie with experience of these cars & sound them out. They'll all tell you they really need to see the car to diagnose it but they will at least be able to tell you how much that diagnosis will cost, what their experience of the W126 is & whether they think they can fix it.

Most indies are quieter in the afternoon after about 2ish & will have more time to talk to you then.

 

[Firepants78]

measured the resistance of temperature sensor,

cold 0.365kΩ
hot 1.112kΩ

it seems to me that is not working properly.

 

[ianrandom]

Not sure about the resistance values but the sensor is cheap and easy to change so maybe try that.

I'll second neilrr's idea about Star Motors, they'll have it diagnosed in no time. But will probably need it booked in, they are always very busy. Know the 126 inside out though, which makes it quicker and therefore cheaper..

 

[mejermy]

Dug this out of my W126 archive. Should allow you to check the sensor resistances.