Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Plus8 fuel pump relay

Any chance it is next to the pump?

John

I note your ?? After the comment about ECU picking up the relay earths. This is not at all uncommon ECU’s are often used to switch on and off earths to components as it’s much cooler to switch on earth on and off than feeds.

Heat is the enemy of control modules so manufacturers soon learnt to use the ECU to switch earths on and off this is the case with fuel injection on Motronic systems for example. Less arcing and all that ;-)

BR
Colin

Have you ruled out the 2 "non original" ones you mention behind the dash on the left.

That's the area where the original ECU was probably fitted so why have you discounted them?

Thanks all for your input. It turns out my pump is it the tank, and the relay is one of two between the glove box and Omex ECU. Both the relays are RIPCA 2746 and don't appear to have Diode protection, so I think I need to buy some Bosch 0332014112, or an equivalent.

John.

1999 Plus8

John/Jads, seems you have found relays and still have issues relating to identifying which of the two is controlling the fuel pump...? I know next to nothing about ECU`s used in cars or the theory behind switching earths as opposed to the the live, but if all the earths are black as was the norm pre ECU, then I can understand you may not be able to follow the more usual method of identifying individual switched circuits by using the colour code of the wires...? Which may have from the following link been a white wire with a purple tracer..?

http://www.mgb-stuff.org.uk/colourcodes.htm#:~:text=In%20the%20United%20Kingdom%20the%20British%20Standard%20BS-AU7,a%20thin%20line%20trace%20of%20a%20different%20colour.

I am also interested to know why you want to fit a relay with a Diode...Is the diode to quench the spark across the relay contacts......? Or is the diode across the relay`s coil connections, to suppress the coils back EMF when it is in the process of de-energising ( switching off) to avoid upsetting the ECU internals...?

Diode relays are advised to quench back emf which can be damaging to electronic components in ecu.

Hi George

Diode relays were introduced to help prevent back EMF to the ECU. The switched Earth effect can be seen when you connect a battery or jump leads. Much smaller spark from the earth side of the battery than the feed.

At Volvo we stopped teaching wiring colours years ago and worked from pin numbers because of wiring colour change issues (we had the advantage of also having a BOB - Break Out Box- fitted between the ECU and multi pin connector which helps massively).

Not what I joined the trade to engage with but just what the industry evolved into, give me a gearbox to overhaul any day.

BR
Colin

Hi DJ, thanks for your response, I was aware of the back EMF issues, though wondered if the diode was to protect the ECU from the coil, or the contacts in the relay from the back EMF when the pump was switched off..

Colin, in all my years of blowing things up with AC and DC, I never came across anyone or anything that suggested breaking the DC Negative created less of a spark....Duh..! As they say, every day is a school day, thanks for the education chum.. and look after yourself WELL..

Yes, but some ECU's have the diodes built in and so can use relays without diodes.
Cheers
John

I know which relay it is as removing it stopped the pump, on mine it's on the right looking forward. I was told to look for a white wire with purple trace but I couldn't find one. I'm fitting Diode type relays for the reason Colin explains and thus reduce the risk of ECU damage, especially as a replacement Omex 710 is circa £1000 plus re-mapping !!!

John.

1999 Plus8