Fuel pump + ECU fuses blowing simultaneously

[Magnum]

Hi All

I have a lovely hot-rod consisting of a 1972 car with 1985 engine and running gear (standard motronic ECU retained), but need a  little bit of advice please (or your experiences please).

I was returning from a weekend road trip where the car had run flawlessly when suddenly the car cut out whilst driving at steady pace up a pass - first inspection revealed both the ECU & fuel pump fuses had blown (presumably simultaneously), which I quickly replaced and off we went. This occurred again five minutes later but at steady pace on the flat, however, on replacing both fuses again we managed to get home without further incidence (although I kept things sensible - ie kept revs down to about 3000rpm).

It's a little confusing for an auto-electric numpty like me, but can I reasonably assume, as both fuses blowing simultaneously, that this is possibly alternator or voltage regulator related. I wasn't gunning it on the two occasions the fuses blew - perhaps 4-4,500 rpm, but the problem didn't recur whilst keeping revs down.

Any suggestions really welcomed and equally thoughts on how to test without removing alternator etc.

Many thanks 

[Roy M]

Got to say that sounds odd doesn't it. I suppose first check is the fuse ratings then battery voltage whilst running to check alternator output. Once you have these post them on here. The only part I can think of common to both circuits is the DME relay but you may not even have one depending on your setup so more info there would be useful as well.

Lovely car btw

[Magnum]

Thank you Roy - she's a great car, love her dearly!

The fuse ratings are correct I believe - well she's been perfect for the last two years so I'm sure fine. I will check voltage at both low and highs revs and report back.

I do have the standard DME with the Motronic and also considered this is a common element - I think I should open the (relatively new) DME and have a look for anything unusual before reporting back. 

Many thanks 

[SilverWT]

Roy M is referring to the DME relay, not the DME box itself.

Fuses blow to protect the wiring when there is an excessive power drain, e.g. when there is a short to earth due to failing components, or chafed wires.

I would start with the DME relay and wiring to fuel pump.

Mark

[Magnum]

Thanks Mark

Without me being clear, I was on the same page (bit of luck involved!). Thank you -  I'll also ad checking to the fuel pump wiring to the list (and perhaps extend the scope of that check too).

Cheers