Fuel pump relay question

[JPlue]

Couldn't find this through searching, but it's yet another fuel pump question... I've determined that my pumps are ok through jumping my relay terminals, but they don't activate with just the relay. I've tried swapping the relay but still nothing.

The part that confuses me is that when I key on the relay does not click, but it clicks twice when I key off...Has anyone run into this before? Also, what would cause the relay to not get activated? CPS maybe? Any help would be appreciated

[Pennyw1se]

Could be your main relay or your ECU.

[JPlue]

testing recommendations?

[jlevie]

The DME only engages the fuel pump relay when it sees timing data from a rotating engine. If the relay doesn't close when you crank the engine, check for spark. No spark and no fuel pump operation will be:

no timing reference data to the DME
no power to the DME
bad DME
damaged wiring harness or relay socket

If you have spark, check to see if power is present to the relay coil, whether ground to the coil is supplied by the DME, and whether power is supplied to the relay contacts when cranking the engine. If all are present, check the fuel pump fuse and/or replace the relay and check continuity from the relay to the pump.

[E30SPDFRK]

The DME only engages the fuel pump relay when it sees timing data from a rotating engine. If the relay doesn't close when you crank the engine, check for spark. No spark and no fuel pump operation will be:

no timing reference data to the DME
no power to the DME
bad DME
damaged wiring harness or relay socket

If you have spark, check to see if power is present to the relay coil, whether ground to the coil is supplied by the DME, and whether power is supplied to the relay contacts when cranking the engine. If all are present, check the fuel pump fuse and/or replace the relay and check continuity from the relay to the pump.

Pretty sure his coil is dead. We're getting 12v to the terminals but only 8 coming out of it. I didn't think of the correlation between that and the ECU.

Could that be causing his weird relay issue?

[jlevie]

I'm not sure what to make of that statement. What coil are you referring to?

[JPlue]

I'm not sure what to make of that statement. What coil are you referring to?

my ignition coil

[jlevie]

The coil if fed switched 12v power and is grounded by the DME for each spark impulse. If switched power is present and the DME grounding pulses are present when cranking the engine and there is no spark, the coil is bad. If the DME's ground pulses aren't present, see above.

[JPlue]

would the impulses be something we can see with a multimeter, or would I need to get a hold of a lab scope to test that?

[jlevie]

A meter probably isn't going to tell you much. An LED test light might give you a clue as to whether grounding pulses are present. But to really tell what is going on you need a scope.

[JPlue]

I have a friend with a known good coil, I'm gonna try swapping that in first and see where it leaves me.

[StereoInstaller1]

Coils are a pretty tough thing, they hardly ever fail compared to several other items in the ignition chain.

Why do you think you have no spark? You said you weren't getting fuel pump. The fuel pump is ECU controlled, but the power for it comes from the main relay.

Have you downloaded your electrical troubleshooting manual? If not, go to www.wedophones.com and find "manuals" then "automotive" then "BMW", that might help a bit. They are intended for the pro, so they don't exactly hold your hand, but the info is there.

[JPlue]

Yeah it's kind of a dual problem. My relay isn't activating when I key on, and we also tested my ignition coil and found no spark. My friend gave me a bunch of his old m20 parts including a known good fuel pump relay and 173 ecu, so tonight I'm gonna swap those in to see if there's any change

[jlevie]

Rather than throwing parts at the problem and hoping for a favorable outcome, properly diagnosing the problem will yield results quicker.

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

Power on DME pins:
27 Start Input
18 Unswitched 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 fronm 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.

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 to 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 & 47, which should be 500-560
ohms. If the CPS is dismounted, the resistance can be seen to change
from about 500 to 540-540 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 0.040"), 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 batter 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.

[JPlue]

ok, here's what we have so far. There is no ground from the dme at fuel pump relay terminal 85. dme pins 47 & 48 had 519 ohms of resistance. the other dme powers and grounds that you said to initially check were ok. without a lab scope I couldn't really check the dme pulses to the ignition coil. Any suggestions what to check next? Also, the 173 dme didn't make a difference. is this because the 173 doesn't work with a 87 year, or could that indicate a problem independent from the dme?