No start, no spark. Totally stumped.

#1

'87 325is. Cranks fine but won’t start due to no spark. Previously intermittent issue but now won’t fire at all. Has fuel. Replaced the following:
Crank sensor (original tests ok)
Coil (swapped from running car)
Motronic brain (swapped from another car)
Distributor cap, rotor, wires all recent. Removed cap and still looks new, no carbon traces, cracks, etc.
There are 15-ish volts at the coil with the ignition on.
Timing light hooked to the coil wire shows no activity, nor is there any at the plug wires.
Extra ground strap has been run from the engine to the chassis.

I’ve checked connections, checked fuses, swapped relays and pretty much everything else I can think of. This is a Spec E30 race car so it does have a master cutoff switch, but I can’t see how that would effect this while providing full power to the starter, dash, etc. The car was running for a couple of years since the build but the no-start began acting up in the past year. I want to get this wretched thing out of my garage and since it drove in I feel compelled to get it to drive out.

#2

Check the fusible link on the small wire that is connected to the battery.

#3

on the 87’s there is a connection around the ECU/glovebox, a flat 3 wire plug, I would unlug that and clean it or it may have a rig in there…

Al

#4

Here you go…

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 & 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.

  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

  1. Power to pin 18 is from the main relay and there should be power to the
    injectors and fuel pump relay.

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

  2. 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.

#5

Thanks Yoda Levie.I hit the print button and put the correspondence in my “engine don’t run” file.

Mine would not start at CMP last November and Yoda-guy Chuck Taylor saved the race weekend by disconnecting/reconnecting the big circle connector,wiring harness bundle at the fuse box. Problem solved.

Thanks to Chuck, you, and all others that help us with this hobby.

RP

#6

Jim’s post is probably the most helpful post ever made on this forum.

Al

#7

I just want to know if that was a copy and paste from a previous post or Word document or if he sat there and typed that out. Great work Jim.

#8

I wrote this up to help out another fellow racer a while back. Since we were corresponding via email and the car wasn’t where he had access to email it made sense to put it all in one document. I didn’t spend a lot of time writing it, but I have polished it a bit since. I have a similar sort of document on idle problems that I’ll share:

Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn’t eliminate the
possibility. Only a smoke test will really work.

Once the possibility of intake leaks is eliminated, the ICV needs to be
removed and cleaned with carb cleaner until the vane inside moves freely. When
the ignition is switched on you should be able to feel vibration from the
ICV. If no vibration the ICV is bad, there’s a problem with its wiring or
connector, there’s a problem with the TPS, or the DME (or Idle Control Module
(ICM) on an ETA car) is faulty.

For the DME (or ICM) to control idle, the idle switch in the TPS must work
correctly. The switch should close when the throttle stop is 0.020-0.060" off
the idle stop screw.

The fuel system should be tested via the suite of tests in the Bentley manual
as invalid rail pressure can be a contributor to idle and starting problems. A
simple injector check is to pull the injectors, jumper the fuel relay to run
the pump, and see if the injectors are leaking. You can also point the
injectors into a towel, remove the coil wire, and crank the engine to see if
all of the injectors appear to be spraying in a similar fashion. The best
approach to possible injector problems is to have the injectors cleaned and
flow tested. Since raw fuel can or will be released in these tests, have a
fire extinguisher handy.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

The AFM can be a contributor. If the vane doesn’t move freely or the
resistance track is worn the DME may be receiving invalid data from the
AFM. And if someone has fiddled with the bypass air adjustment the DME may be
unable to stabilize idle. The bypass air adjustment should only be adjusted
per the procedure in the Bentley and with an exhaust gas analyzer. And even
then everything else associated with engine management has to first be
operating properly. If the AFM becomes a suspect, replacement with a good used
unit is the best approach.

Improperly adjusted or malfunctioning valves will affect idle and starting. As
can compression issues from ring or cylinder wear. A valve adjustment is
called for every 15k. A useful diagnostic is to run compression and leak down
tests on the engine. And aged ignition wires, plugs, distributor cap, or
rotor can cause problems. Insulation does break down with time and heat. And
since the youngest E30 is going on 19 years old, if the ignition system is
original or the plugs are old replacement is indicated.

Although not usually a problem, a bad DME temp sensor is a possibility. That
generally won’t cause an unstable idle, but can cause hard cold or hard hot
starts and/or a rough idle. As can problems with the timing reference sensors.

When all other possibilities have been eliminated and idle or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

#9

So, Robert hits the print button, again.

Thanks, Yoda Levie. Your helpfullness makes this an enjoyable hobby.

Regards, Robert Patton

#10

is there a way to sticky/archive the advise of yoda levie?

#11

Solved. Main relay (most forward relay of the 3 in the auxiliary panel). Thank you all my BMW home boys who chipped in with good advice. B)

#12

I still have a problem, no spark and the only thing that didnt check out is I have no power to pin 27 with the key on but I have the plug out of the DME to test. Is there a way to test the relay out of the socket to verify that its working? I may just go and buy a new relay if that fixed ddavidv’s problem.

#13

Pin 27 is the start input to the DME and that signal causes the main relay to close, which powers up the DME. Pin 27 is fed via C101 from the ignition switch. That circuit also supplies power to the coil positive. Check for power at C101 pin 7 and back towards the ignition switch.

Edit: I just saw your thread in the Engine forum. On an 87 the Start signal to pin 27 is via a three wire connector. 88 and later cars route the signal through C101.

#14

It was the pig tail wire, plugged it in and it started right up. thanks for a great step by step writeup that will be going into my “take to the track” book for sure.

#15

I used this to narrow down my no start issue to a crank sensor continuity issue. The sensor itself is alright but the wiring from the sensor to the ECM isn’t. Thanks for putting the guide together.

#16

Dumb question…At the harness end you’re certain you don’t have CPS wire mixed with spark sensor wire? It’s a good idea to mark one of those so they can never be confused.

#17

Looking for some help troubleshooting a no-spark condition. Car ('88 SE30) had been running fine, then died on the out lap last weekend - just shut down all at once. Cranked just fine, but would not restart. Heavy rain and lots of standing water, so I initially assumed something had gotten wet, but when I got to the paddock, everything under the hood seemed dry. Initial troubleshooting showed no spark, and I was only getting ~6V at the positive terminal of the coil. Swapped the main and fuel relays with no change. Disconnected the positive lead and jumpered 12 V to the coil with no change. At that point, I had missed qual and the race, so I punted and loaded up.

Today, I started troubleshooting using Jim Levie’s guide. For the most part, everything looks good. I checked pins 47 & 48 with the CPS installed, and got 558 ohms, but did not try the ferrous object with the CPS unmounted. However, I did swap in a new CPS with no change.
The only test that failed was the final one. With the key on and DME connected, there was only 4-6 volts at the coil. Also, the fuel pump relay had battery voltage at pin 30 with the key off or on. According to Jim’s guide, that power should only be present with the key on. Finally, I found that with the DME disconnected, I did have 12V at the coil with the key on.

Any idea of next steps?

Thanks,
Cliff

#18

Did you swap the ECU yet?

#19

Nope - didn’t have a spare. I’ve got one coming and should have it by the weekend.
I’m betting that’s the issue, but figured I’d see if anyone had other ideas.
Thanks,
Cliff

#20

Confirmed - ECU was the culprit. Started right up with the replacement installed.
Thanks,
Cliff