fuel problem

[ryderb1474]

I just put a new alternater on it. Still having the same problem so I got on ebay and ordered another ecu. Will see what happens thursday when it gets here.

[ryderb1474]

I put a new alternator on a couple days ago. I've decided it has to be the ecu so I got on ebay and ordered on. We will see thusday if I'm right if not I'm gonna set it on fire in front of my house......

[ryderb1474]

Got the new 173 eco in today and for some reason it STILL won't start. I'm running out of ideas. Anyone have any other ideas I would really appreciate it.

[Rtheriaque]

I'd suggest a disciplined troubleshooting approach. As you're experiencing, throwing parts at a problem can be very expensive and very ineffective. If you have a simple broken or shorted wire, you could replace virtually every part on the car and it'll still be nothing but a BMW lawn chair.

You've established that you can get power to the pump by jumping it, but the car still wouldn't start. Step one is correcting the pump power issue. Trace wiring between the relay and the pump.

Once you've got power flowing correctly to the pump and you have fuel pressure, you may find the vehicle starts. If not, you can check for power and pulses to the injectors, the fuel pressure regulator, etc.

[mr ilia]

Have you jumped the fuel pump to see if it is working? Just do direct connection to the battery.
Also, make sure your electric plug to the fuel pump is good and tight and working...I remeber waiting day and have trouble shooting no start issue, when the issue was bad connectop to the fuel pum AND it was discovered by me by accident.

[ryderb1474]

Ok. Here is what's going on. Previous owner hooked up battery backwards. I have replaced the batt. Checked the fuse link in trunk. Its goood. Replaced alternater, cps, all relays 173 ecu, and checked all fuses. With key in the on position the check engine flashes and doesn't stop. Engine cranks no fuel and no spark. I have jumped the fuelpump and it works fine. Is there anything else tall can think of before I go crazy on this thing?

[jlevie]

Okay, since a different DME made no difference and since we know that reversed polarity was applied to the car, use the trouble shooting guide that follows to identify the cause.

For the engine to run the following conditions must be met:

Power on DME pins:
27 Start Input
18 Un-switched Power input
37 Power Input from Main Relay

Ground on DME pins 2, 14, 19, 24

Timing data from the CPS on DME pins 47 & 48 from a rotating engine

To have spark power must be present at the coil positive and ground pulses
from the DME's pin 1 must reach the coil negative. Power to the coil is
controlled by the ignition switch via C101. When checking for spark, use the
output lead from the coil to eliminate the distributor, rotor and plug wires.

To have injector firing power must be present at each injector and ground
pulses from the DME's pin 16 (Bank1) and pin 17 (Bank2) must reach the
respective injector bank. Note that the injectors are wired as two banks of
three. With cylinder 1,3,5 being bank 1 and 2,4,6 being bank 2. Power to the
injectors is controlled by the main relay. Injector firing is best checked
with a noid light.

The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30. The DME will ground pin 85 to turn on the
relay and power the pump(s) via pin 87. Of the above, only the fuel pump power
is fused. So if the there's power at pin 87, but not at the pump, check fuse
11.

The main relay and DME pin 18 receive power from the smaller of the two wires
that connect to the battery's positive terminal. That wire incorporates an
in-line fuse. When the DME is presented with a start signal, it grounds the
main relay pin 85 and furnishes power to the fuel pump relay, injectors, and
DME.

Troubleshooting:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If
the CPS is dismounted, the resistance can be seen to change from about 500 to
540-560 ohms when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 1mm), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

The engine will start and run (if poorly) with only those connections to the
DME in place. The other signals from Cylinder ID, AFM, temp sensor, etc., are
necessary for proper operation. But they won't prevent the engine from firing.

IMPORTANT:

A power check means seeing a voltage within about a tenth of a volt of what
you measure across the battery terminals, which should be at least 12.6v on a
charged battery.

A continuity check means seeing less that 1 ohm of resistance.

An open circuit means seeing a resistance of at least 100k ohms.

A good quality auto-ranging digital multimeter will make these tests much
easier.

[ryderb1474]

Cool. Thanks. I will spend this weekend sorting it out but it is difficult not having a second pair of hands to help. Not a very big e30 following here and have not been able to find a mechanic that can work on it.

[ryderb1474]

Looks like I will be sending it to a mechanic tomorrow. Electrical problems are out of my league.....

[ryderb1474]

Does anyone know if its possable to pull an engine code when the check engine light won't stop flashing?

[dnguyen1963]

Try disconnecting the negative cable from the battery for a few minutes...

[FLG]

Just follow Jims instructions, all you need is a multi meter...its very simple.

[ryderb1474]

Having a mechanic come by this evening to give me a hand with it. Wish me luck......

[ryderb1474]

SHE LIVES!!!!!!!! so, how about Autozone sold me the WRONG 5 prong main relay. I would have never thought to look at that again. Now I can move on to the turbo build!.

[mr ilia]

Good to hear you figured it out!