85 - 190E

I have an 85 190e 2.3 that will start and die immediately
I took out the fuel pump relay and bypassed it and the car runs great without the relay.
I bought a new fuel pump relay and it did not fix the problem.... I have checked all wires going to and from the relay location and I have main power and key-on power to the relay.

Can anyone tell me if there is another input to the fuel pump relay that might affect the relay not starting the pump?

My shop CD notes an RPM input solenoid going to the fuel pump relay but does not show location, does anyone know where to find it.

Has anyone heard of a similar problem?

Any suggestion out there would help ...I do not have a Benz tech in my area so I am on my own.

Thanks
Eric
85-190E

autotech.ca

hello Eric

you are right on the money, there is other inputs for fuel pump control...

there is a green wire with a yellow tracer refered to as TD, you will find a connection near the diagnostic connector (two wires joined with a screw)

you should have a RPM signal at this wire, but keep in mind this could be difficult to test due to meter internal impedance, using a oscilliscope is best.

this TD signal wire originates at the ignition module and is spliced off to the fuel pump relay, A/C compressor control unit, tachometer and the CIS control unit, any one of these could be affecting the signal.

HOW IT WORKS
you will notice on the fuel pump relay 9 connections

power
ground
+ power to fuel pump
start
coolant temp
cold start injector
kickdown switch
TD signal
overload relay connection

autotech.ca

oops

the important one to worry about here is the TD signal
because in your case, it starts runs then quits, by pass the relay to the pump and it stays running

so when you turn the key to the start position the fuel pump relay gets 12 volts at the start wire and the pump is powered for a short time just to start the engine until it can pick up a TD signal.

after the engine starts the relay wants to pick up the TD signal to keep the fuel pump powered, if there is no TD or a bad signal the relay will not feed the pump.

so pay close attention to the TD signal, this is a RPM signal and is probably used in the event of a no spark condition, if there is no spark the engineers figure lets not fuel the engine.

and remember where the TD branches to, the A/C compressor, tachometer, fuel pump relay and the CIS control unit.

in other words your A/C compressor unit, tach, or CIS could be interupting the TD signal. this circuit is low impedance and a multimeter could affect it operation.


good luck
L

85 - 190E

Great thanks for the help. I will have a look at the TD signal and post results..
Eric

autotech.ca

I hope it helps

good luck

rogerdugans

Holy thread resurrection, Batman.

A friend of mine has a 190e with a similar problem:
starts ok, runs rough if at all in cold weather (stalls out when in gear).
Runs better in warm weather but still has occasional problems.

He plans on replacing the fuel pump, and asked for my help (pretty decent "shadetree" mechanic) so I began with google- and here I am.

From the info in this thread it would seem to me that there are some possibilities to check FIRST....

I am looking for any and all info that may help:
how-to related links
specific things to check
Mercedes maintenance info.

Anything that might help.

Thanks in advance