car cranks but doesn't start

[pyro-rwd]

I've posted this on a couple of other forums and basically got the only useful answer from Wayne, so I figured I'd post here.

I needed to jump a car, and in a rush, connected my RED strut tower negative mount with the positive clamp, and the BLACK jump box on the passenger side firewall to negative.

I saw some sparks, and after, all electronics work, the car cranks, but won't start.

The main relay (3rd and forward most out of 3 in aux panel) is toast, pins black, plastic melted. I'll be replacing that.

I cannot check DME codes because the check engine light will not come on at all, but of course the DME get it's power from the main replay, which is dead.

When the DME is plugged in, ignition ON, only 1 pair of pins show a voltage of ~1.8V out of the main relay socket and that's it.

If you were to guess, what should I look at except what's said in the bentley and of course, the main relay and DME?

Thanks.

EDIT: Also, do these relays carry any protection or are they just switches?

[BMWCowboy]

Sounds like you fried the DME~

[pyro-rwd]

Yea, just replaced that relay, 5 prong. Still no dice...

Time for a new DME...

[wludavid]

Relays will provide a very limited circuit protection. Typically they are rated at around 20 Amps, and will burn up above that. That's enough to fry a lot of electronics though, and they are not designed to do a quick burn like a fuse.

[pyro-rwd]

Took a look at the next 2 relays in the panel, they both seem to have blue discolored pins and the bentley dme pin 36 to ground test isn't making the main relay click, even with a new relay.

Can you guys please take some guesses?

[pyro-rwd]

Also I know that, bridging pin 36 and ground in the DME harness connector (with DME removed) does NOT operate the main relay (it's supposed to according to Bentley).

No voltage at fuel relay; fuel pump does not operate if you use a jumper; due to no voltage at main relay.

Also part of the positive box jump box thing at passenger side doesn't supply voltage. The small part with 2 5mm looking wires does not, where as the big 10mm multiple wires on the right side of it do.

However, when car is put in gear, it moves while starting. I would assume you need ignited fuel to move the car?

[pyro-rwd]

Fixed it!

It was the fusible link that got taken out in that jump!

Thanks for the help.