1989 300SE intermittent start problem

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Rob. Smith - 11 Apr 2006 08:31 GMT

Hello
Got a slight funny (and I don't think its the immobiliser).
If I have run the car (used it- got it warmed thro), and then stop for
a couple of mins, it just doesn't want to start up (turns over and
doesn't 'try' at all). If I wait a little while longer, It will start
OK (still slight hesitation/stumble, but then fine).
One thing I've noted is that if I switch the ignition on and off
during this problem, I don't hear the fuel pump run its prime cycle.

So,
Could it be a dodgy pump relay?
Does this happen (anyone heard of it)?
Where is the fuel pump relay (UK spec car)?
Can I get it apart and fix it or is it sealed for life?

Cheers... Rob.

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Roland Franzius - 11 Apr 2006 10:44 GMT

Rob. Smith schrieb:

> Hello
> Got a slight funny (and I don't think its the immobiliser).
[quoted text clipped - 10 lines]
> Where is the fuel pump relay (UK spec car)?
> Can I get it apart and fix it or is it sealed for life?

Seems to be the famous soldering problem of the pump relay. The simplest
way to cure it: Make a direct connection of fat copper wire from relay
foot to the outer contact. The thin printed copper connection isn't
capable leading away the heat from both the hot electromagnet and
corroded relay contacts.

It will help too to change old worn pump and closed fuel filter to
reduce pump current to normal.

Signature

Roland Franzius

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Tiger - 11 Apr 2006 16:48 GMT

That's the classic fuel pump relay failure due to age. Change to a rebuilt
one or a new one will solve the problem.

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T.G. Lambach - 11 Apr 2006 19:04 GMT

Hi Rob,

When the motor cranks but fails to start, does it act differently if you
"step on the gas"?

If so, I'd suspect leaking fuel injectors, if not, either the fuel pump
or the over voltage protection relays - or the ignition coil.

Cool the coil with an ice bag to test it - hot coil - no start vs.
cooled coil - start. Or, no difference, coil OK.

I once spent a lot of $$ on my then 280E's fuel pump when the cheap
battery, that I bought to "save money" was too weak to do anything more
than crank the engine.

Tom

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Rob. Smith - 11 Apr 2006 19:56 GMT

Hello All

Thanks for the responses.

To answer your Q's Tom,
There appears to be no difference if I step on the gas. It just cranks
away pretty quickly.
The battery is a quality item, with a lifetime gaurantee (can you
believe a UK manufacturer actually offered a lifetime gaurantee on a
battery as long as you kept the vehicle. The one on it is now the 4th
the original owner bought. Guess I'll have to buy one next time).
I understand your point about cranking volts and enough to overcome
the voltage sensing relay, but since I don't hear the pump prime cycle
run, I'm reassured (by a negative result) that the battery is OK.

Ignition coil > Worth a try. I've got some aerosol freezer that will
do a quicker job on the coil. I'll give that a coat of looking at.

In response to the other comments From Roland and Tiger
I'm going to investigate the fuel pump relay also (If I can find it)!.
I'd hope to repair mine since they seem to be about £60 to buy.

Cheers... Rob.

>Hi Rob,
>
[quoted text clipped - 12 lines]
>
>Tom

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