Petrol Pump fails when warm starting

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Bender Boy - 06 Dec 2006 08:12 GMT

Hi, I have a 1990 124 200TE. When the engine is warm and I try to start
the car, the petrol pump sometimes doesn't kick in. I'll wait a few
minutes and then try again and it will start. When I hear the
'whirring' of the petrol pump as I turn the ignition switch I know it
will start. When I don't hear the pump I know it won't start. I also
cuts out occasionally when driving along.

I've had a new Petrol Pump Relay fitted (the one with 'kickdown'
written on it) and a new overload protection relay. The car always
starts from cold?

Any ideas would be appreciated.

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macdrone - 06 Dec 2006 09:19 GMT

> Hi, I have a 1990 124 200TE. When the engine is warm and I try to start
> the car, the petrol pump sometimes doesn't kick in. I'll wait a few
[quoted text clipped - 8 lines]
>
> Any ideas would be appreciated.

It could be a relay but first i would turn the fuses or replace the due
to corrosion. Then I would replace the ignition switch, not the
tumbler(lock) just the switch in back.

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Bender Boy - 06 Dec 2006 09:49 GMT

Thanks for the reply

I have turned the fuses in the past but this didn't work. I hadn't
thought of the switch part of the ignition. Have you known of this
problem before and is the switch difficult to get to?

Thanks again

> > Hi, I have a 1990 124 200TE. When the engine is warm and I try to start
> > the car, the petrol pump sometimes doesn't kick in. I'll wait a few
[quoted text clipped - 12 lines]
> to corrosion. Then I would replace the ignition switch, not the
> tumbler(lock) just the switch in back.

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Jens - 07 Dec 2006 23:49 GMT

Fuel Pumps get power directly from the fuel pump relay, which will
switch on as follows:
- for 1 second when you put ignition key to "run" position
- when you put ignition key to "start" position
- when ignition key is in "run" position, and when rpm is above 500

The fuel pump relay also has coolant temperature signal input from the
ECU. I don't know what it does, but it is likely that it will shut down
the fuel pumps if temperature is too high (I don't see what else it
should be there for).

So, you may get a wrong temperature signal, or the fuel pump relay
reacts wrongly to the input. That could explain your situation.

Bender Boy skrev:

> Thanks for the reply
>
[quoted text clipped - 20 lines]
> > to corrosion. Then I would replace the ignition switch, not the
> > tumbler(lock) just the switch in back.

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Tiger - 08 Dec 2006 22:13 GMT

It can be the ignition switch that is bad. What happens when you starts the
car? Does it run rough for a while? If yes, then you got hot start
problem... vapor lock... which requires you to replace a few seals in the
fuel distributor.

If not, then it is probably ignition switch or fuel pump.

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macdrone - 10 Dec 2006 01:44 GMT

> It can be the ignition switch that is bad. What happens when you starts the
> car? Does it run rough for a while? If yes, then you got hot start
> problem... vapor lock... which requires you to replace a few seals in the
> fuel distributor.
>
> If not, then it is probably ignition switch or fuel pump.

The switch is up under the dash (2 screws and remove plastic) then
reach up and there it is.

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