Think you're good at wiring?

[DaveSmed]

I have a real funny feeling your main relay either has a dead leg, or isn't where it belongs.

The main relay is called a "double 87" which means when it is energized, it supplies power to two separate terminals under the relay simultaneously.

99% of Bosch style 5 pin automotive relays (with the same terminal layout, and same form factor) instead have an 87 and 87a. This supplies power to one pin when the relay is energized, and one when denergized. Like when you unplug the DME.

The main relay also helps control the fuel pump. There are more questions as to why its working as the fuel pump relay shouldnt allow it, but jumbled relays could even explain that too. The fuel pump relay is a very specific BMW terminal layout, but again, same terminal layout and form factor as the much more common relays.

[accident]

we swapped the main relay with a running car with no change

[DaveSmed]

Damn this is a good one. :p


In theory, all the car should need to start assuming proper function everywhere else is power on pin 27 and engine crankage.

As far as proper operation of pin 27, take a look at C101, it's the round plug located on the firewall next to the fusebox and brake booster. The top half of that plug is the engine harness. Pull back the rubber boot and take a look for a solid green wire, located in pin 7. Check the voltage with the key on, C101 connected, and the DME installed.

As far as engine starting, with pin 27 jumped to battery, check the Red/blue and Red/white wires for power at the main relay (relay connected of course) Both should be battery voltage. Also, check voltage at Fuse 11 while cranking.

[accident]

all of those wires have power with the coil jumped directly to the battery. we didnt check fuse 11, however

[DaveSmed]

In that case, give this trick a shot too with the fuel pump relay. Check power at 11 with this in place, and try to start the car.

[accident]

it's pushing gas while the motor is cranked.

[DaveSmed]

So, Fuel pressure, Spark, Injector pulsing, and still no start unless you crank a bit with the DME unplugged.

Makes no sense. Pop the fuel hose off at the regulator, and verify fuel comes from the regulator NOT the hose when cranking like normal, with the jumper.

[accident]

fuel comes out of the regulator, that's where we tested it at. i think it's a pressure issue, but we cant figure out where. we changed the fuel filter and the FPR and still no dice

[DaveSmed]

Pinch off the return to dead head the pump and give it a try.

[LB.Motoring]

We will be trying new stuff Monday. Thanks for the tips. Keep them Coming! :)

[NigelStu]

If its potentially a fuel pressure issue (did you guys measure this yet?), and fuel was looking nasty (comment from other thread), you could have a clogged line or blockage at the pick-up in the tank.

Crap that got dislodged and is now floating in the tank could have got caught somewhere. I had this issue on my 510. It sat for years before I bought it and inner tank rusted a bit. Adding fuel and driving it around the track loosened stuff up, and kept clogging up filters. Granted that car was carbed and not FI, but I ended up having run issues where on long straights, it would loose power or die. Blockage was enough that with long, high fuel demands (like a long straight, full throttle for >15 seconds), not enough fuel was flowing and it would starve. But on/off throttle would keep enough fuel in the float bowl to keep it running. IF you are having a similar prob, its much more severe blockage where the pump can build some pressure at the rail, but only until the car starts using fuel.



Other than attaching a fuel pressure gauge at the rail and seeing what it does, the only real way to test this theory is to pull fuel from a different source or bypass the blocked lines. If that fixes the prob, go after the lines/tank until you find the blockage.



another theory is that your tank is not releasing vacuum (I have less confidence in this one) and the pump is not able to pull hard enough to get the fuel out. Easy test though... take off the fuel cap and listen for a suction sound. and then try to start the car with the cap off.

hope this helps...

[DaveSmed]

Bump? Hoping its running?

[Len013091]

This may sound redundant, but does the check engine light turn on in position 2? The green wire you described sounds like the 13 button immobilizer wire. If the relay box has failed and doesn't complete that circuit, the car will absolutely not start. CEL won't come on either.