just did engine rebuild, wont start, no spark????

[custom e30]

first time i did this, everything going good but i have no spark, what could it be? this is a m20b25

[shiboujin]

cps

[custom e30]

what is cps

[shiboujin]

crank position sensor.

honestly, your description of the problem leaves very little to go by. So I just threw out the usual suspect.

[custom e30]

ok thanks ill check it now

[custom e30]

everything is connected right, i checked my coil and it is getting power but its not sending power out to the coil cable to the cap and rotor, so is the coil just bad or can something else be wrong

[shiboujin]

well then shove in a new coil! or a new cps. Go go! NOW!

[xwill112x]

its defintily your flux capacitor sheild leaking.

[Van Westervelt]

Make sure all your turn signals work. Thats what did it for me last time. lol

But seriously, throw in a new coil, and make sure you have it wired in properly.

[jlevie]

everything is connected right, i checked my coil and it is getting power but its not sending power out to the coil cable to the cap and rotor, so is the coil just bad or can something else be wrong

The coil gets switch power from the ignition switch and fires when the DME grounds the coil. There are a number of possible reasons whey the DME might not be firing the coil.

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.

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.

[custom e30]

yea im not good enought to know what the hell im doing for all that, could i have connected something wrong or backwards when i put the engine back in??

[custom e30]

ok i played around with some wires and all the sudden spark is back, but still wont start, couldi have put the gas lines backwards

[txtorquemade]

Not to sound like an ass, but If you could get your wiring messed up, guess you ought to figure you could get fuel lines, grounds, sensors not connected properly. Do you have a Bentley manual?

Are you saying, your getting spark to the plugs themselves, and no fuel? Or what?

[Kershaw]

if you pull the plugs, do they smell of fuel?

[custom e30]

i had a bad crank sensor, its running now and a beast it is...