Hi everyone,
I am in the process of installing my rebuilt M20B25 in a 1987 325is and have run into some starting problems. My issue appears to be the fuel pump relay not switching power to the pumps. I have done some research on multiple forms and was hoping I could get some assistance with the troubleshooting.
I found the below noted guide and have made my way down the list, as documented below. My conclusion is the DME is not grounding pin 85 on the fuel pump relay, thus the relay is not closing. Could anybody shed some light on this issue?
Of note, I have tried using a completely different DME and have come across the exact same problem;
“For the engine to run the following conditions must be met:
Power on DME pins:
27 Start Input (Checked 12.5 v)
18 Unswitched Power input (Checked 12.5v)
37 Power Input from Main Relay (Checked with DME plugged in, 12.5v)
Ground on DME pins:
2 (Checked Grounded)
14 (Checked Grounded)
19 (Checked Grounded)
24 (Checked Grounded)
Timing data from the CPS on DME pins 47 & 48 from a rotating engine:
(Checked, stationary 512 k/ohms, rotating engine 1200 k/ohms)
To have spark, power must be present at the coil positive
(Checked, 12.8v)
and ground pulses from the DME's pin 1 must reach the coil negative
(Continuity confirmed)
Power to the coil is controlled by the ignition switch via C101
(This is the coil itself?)
When checking for spark, use the output lead from the coil to eliminate the distributor, rotor and plug wires.
(12v at coil output lead. Coil, distributor and plug wires all new with the rebuild)
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.
(I have jumped the fuel pump relay points 30 and 87 closing the circuit and functioning the pumps. Still no ignition on turn over, but fuel was smelled from spark plugs when removed which indicates the injectors are functional)
The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30.
(When key is ON, 12.5v to 86 RD/WT and constant 12.5v power to 30 RD.)
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.
(When key is ON, there is NO power at 87, therefore no power at the fuse. This suggests that the DME is not grounding pin 85 to turn on the relay? Suggestions as to why?)
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.
(Confirmed continuity on coil neg to DME pin 1 and ground is open)
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 540-540 when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.
(Checked at 512 k/Ohms)
3) Check for continuity from DME 36 to main relay 85 (DME pin 36 to 85 GN continuity confirmed) and from DME 3 to fuel pump relay 85. (DME pin 3 to 85 BR/GN continuity confirmed)
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.
(Pin 18 has 12.5v, Main Relay 86 RD & 30 RD has 12.5v)
2) With the key on, verify that power is present at DME pin 27 and pin
18. (Pin 27 and 18 confirmed 12.5v). Power to pin 18 is from the main relay and there should be power to the injectors and fuel pump relay.
(12.5v confirmed to fuel pump relay 30 RD, 86 RD/WH, 85 BR/GR... There is NO power to 87 GN/VI leading to the fuel pumps)
3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).
(No voltage found on DME pins 2, 14, 19, 24)
4) Verify that power is present at the coil positive (12.5 v confirmed at coil) and at fuel pump relay pins 30. (30 RD 12.5v confirmed). 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.”
Thanks!
I am in the process of installing my rebuilt M20B25 in a 1987 325is and have run into some starting problems. My issue appears to be the fuel pump relay not switching power to the pumps. I have done some research on multiple forms and was hoping I could get some assistance with the troubleshooting.
I found the below noted guide and have made my way down the list, as documented below. My conclusion is the DME is not grounding pin 85 on the fuel pump relay, thus the relay is not closing. Could anybody shed some light on this issue?
Of note, I have tried using a completely different DME and have come across the exact same problem;
“For the engine to run the following conditions must be met:
Power on DME pins:
27 Start Input (Checked 12.5 v)
18 Unswitched Power input (Checked 12.5v)
37 Power Input from Main Relay (Checked with DME plugged in, 12.5v)
Ground on DME pins:
2 (Checked Grounded)
14 (Checked Grounded)
19 (Checked Grounded)
24 (Checked Grounded)
Timing data from the CPS on DME pins 47 & 48 from a rotating engine:
(Checked, stationary 512 k/ohms, rotating engine 1200 k/ohms)
To have spark, power must be present at the coil positive
(Checked, 12.8v)
and ground pulses from the DME's pin 1 must reach the coil negative
(Continuity confirmed)
Power to the coil is controlled by the ignition switch via C101
(This is the coil itself?)
When checking for spark, use the output lead from the coil to eliminate the distributor, rotor and plug wires.
(12v at coil output lead. Coil, distributor and plug wires all new with the rebuild)
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.
(I have jumped the fuel pump relay points 30 and 87 closing the circuit and functioning the pumps. Still no ignition on turn over, but fuel was smelled from spark plugs when removed which indicates the injectors are functional)
The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30.
(When key is ON, 12.5v to 86 RD/WT and constant 12.5v power to 30 RD.)
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.
(When key is ON, there is NO power at 87, therefore no power at the fuse. This suggests that the DME is not grounding pin 85 to turn on the relay? Suggestions as to why?)
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.
(Confirmed continuity on coil neg to DME pin 1 and ground is open)
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 540-540 when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.
(Checked at 512 k/Ohms)
3) Check for continuity from DME 36 to main relay 85 (DME pin 36 to 85 GN continuity confirmed) and from DME 3 to fuel pump relay 85. (DME pin 3 to 85 BR/GN continuity confirmed)
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.
(Pin 18 has 12.5v, Main Relay 86 RD & 30 RD has 12.5v)
2) With the key on, verify that power is present at DME pin 27 and pin
18. (Pin 27 and 18 confirmed 12.5v). Power to pin 18 is from the main relay and there should be power to the injectors and fuel pump relay.
(12.5v confirmed to fuel pump relay 30 RD, 86 RD/WH, 85 BR/GR... There is NO power to 87 GN/VI leading to the fuel pumps)
3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).
(No voltage found on DME pins 2, 14, 19, 24)
4) Verify that power is present at the coil positive (12.5 v confirmed at coil) and at fuel pump relay pins 30. (30 RD 12.5v confirmed). 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.”
Thanks!
Attached Files