1989 300SE intermittent start problem

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That's the classic fuel pump relay failure due to age. Change to a rebuilt one or a new one will solve the problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.