pro-3 car ignition problem

[e30evolution]

Thanks in advance for any response to this question.

We have had this issue on our car for the past 3 years and have not yet found the cause, or remedied it.

Under load the ignition coil will intermittently cut out and cause the car to stumble, costing precious seconds each lap! We have done numerous things to try and repair the issue, have also spent hours on the dyno trying to track this problem. Today I had a great idea about what it could be, and will try it tomorrow.

where r3v comes in.... basically I want to put together a check list of things to check and go over everything to make sure it is up to par. Anything from check the fuses to make sure the cat isn't clogged would be helpful for my purposes (even thou the car has no cat and only 8 fuses of which none have anything to do with the engine.)

[backtrail69]

Where are you getting your power for the coil? OE it comes from the fuel pump relay (I think, may be 02 sensor relay). I have had problems with MS before with cutting out under load because of interference with the crank signal. I fixed it by using a shielded wire and routing it away from HT ignition leads and my coils.

[e30evolution]

painless harness and modified engine harness.... no more stock relays.
Problem was there before we put the new body harness in.
DME's KAM and Switched power are hooked up to constant power. and ignition coil is hooked up to the kill switch.
(i believe the fuel pump relay is the same as the o2 heater relay)

We do have some wires running above the ignition wire cover... water temp/oil pressure/temp all for instruments though, not the computer

[backtrail69]

I would just make sure that the shielding is all there for the crank trigger and the shield is grounded well.

Is the car only cutting out at high rpms or just load based?

[e30evolution]

very intermittent and random, but seems to be under load at WOT... during the EIP race it didn't happen at all... during the pro-3 race it was happening every lap

We have tried 2 engine harnesses.... we haven't changed the injection harness... but that wouldn't cause an ignition cut.
We had all the insulation off the stock harness and we re wrapped it... all the shielded parts looked good.

[PiercedE30]

How did you go about determining it was ignition cutout?

[e30evolution]

inductive pickup on ignition wire.... also the tach signal would drop to zero despite obvious engine rotation.

[Hallen]

I really wish I had a better idea to help. It sounds like you know what you are doing though.

The only thing I can offer is some thoughts.

It might be related to heat, g load and/or vibration in my mind. I think this because it sounds like it does not happen on the Dyno. Nowhere but race conditions will you see the loads, heat and vibration at high levels.

This suggests does suggest bad components, but it sounds like everything has been replaced.

What is different than stock? (a lot I know). But if you look at components and wire routing for the stock setup and compare that with what you have now, maybe you can get some clues where you are picking up interference or vibration issues that you wouldn't face with the car stock.

Edit:
Another thought.
I have worked with a lot of electronic devices that get used in extreme heat and cold situations. One thing we find is that when you have lousy solder joints and traces on circuit boards (like you find in older Bosch products) you will have problems with heat, cold and vibrations. At a certain point, the bad solder joints and or traces will cause open circuits that will cause strange problems. But when you go to test for those problems, everything works great because you are not seeing the same external conditions. So, maybe the problem is in one of the printed circuit boards like the ECU.

Sorry, that is pretty lame stuff, but maybe it will spark (no pun intended) an idea with you.

[jlevie]

This sounds like it might be a loss of CPS signal. Causes of that include a bad CPS sensor, wrong air gap, loose or failing harmonic balancer,, failing DME, or wiring fault. I've been struggling with the same issue for a while and the long story of the search for the cause is below... You might get some ideas of things to check from it.

10/09/2007

The car is an early production (06/87) 325is. I replaced the 153 DME
with a 173 well before this started happening and it ran fine for a
couple of track weekends. When the problem first surfaced it might
happen once in a while. But with time it has progressed to happening all
the time.

Around 5400-5800rpm the engine experiences a sudden and complete loss of
power. It seems to occur at higher rpm at the beginning of a track
session, when the engine is relatively cool, and at lower rpm once
everything is good and hot. From the driver's seat it feels as if the
ignition was briefly switched off and there's no stumbling, misfires, or
loss of power prior to the event. If I persist through the cut-off(s)
the engine will pick back up and run to the redline.

I have noticed that the CEL will come on just before the event and when
it happens the tach will drop a lot more would be appropriate for the
loss of speed from coasting. On occasion I've seen it briefly go to
zero. The CEL is so consistent with the loss of power that it can be
used as a shift light. And the CEL will extinguish as soon engine rpm is
reduced by an upshift or by accelerating through the cut-off region. It
doesn't appear to matter whether the critical rpm is reached at WOT or
at partial throttle. Having to short-shift at 5200-5300rpm on the track
is a major irritatant...


In an attempt to solve this problem (and fix other problems) I've:

1) Replaced the O2 sensor (new OE part)
2) Swapped in a known good AFM
3) Swapped in a known good 173 DME
4) Replaced the injectors (new OE parts)
5) Replaced the crank position sensor (new OE part)
6) Replaced the TPS (new OE part)
7) Replaced the main & fuel pump relays (new OE parts)
8) Replaced the coil (new OE part)
9) Replaced ignition wires, cap, & rotor (new wires & OE parts)
10) Cleaned all grounds and primary power connections
11) Replaced intake manifold gaskets & all hoses
12) Verified proper operation of the DME temp sensor
13) Proved there are no leaks in the brake booster
14) Replaced the oil filler cap and dipstick o-rings
15) Eliminated the evaporative control system
16) Acid cleaned & sealed the tank & replaced both pumps (new OE parts)
17) Replaced FPR (new OE part)
18) Checked C101 for corrosion
19) As of 10/28, replaced the alternator

With all of that done and other routine maintenance (timing belt,
filters, valves adjusted, plugs, etc), the engine runs better than it
probably has in quite some time. And I now have a nifty collection of
good spares. But nothing I've done has had any affect on the problem.

I have proved that the used AFM and DME are good by installing them in
another E30 and they behaved perfectly there.

A scan of the DME showed Fault 1 & 3. The only reference in the TIS (for
an M40/42) says that the first code would indicate a short in relay 1
(fuel pump relay) or in the control lead to DME pin 1 and would only
occur when at least one additional final stage is faulty. The latter
fault occurs when shorts or breaks occur on either fuel injector
bank. Injector shutdown could explain what's going on, but it shouldn't
affect the tach. So it isn't clear whether those codes are a result or a
cause.

The only thing I can think of to do at this point is to ohm out wiring
to the DME. A high resistance in the power or ground connections or to
the fuel relay or injectors might be be a possibility.

10/20/2007

I've ohmed out all power and ground connections to the DME, coil, and
injectors. Nothing remarkable there. But in checking power connections I
did find that there's about 4.5ohms of resistance to the hot side of the
coil, which means the ignition switch isn't quite healthy. Just for
grins, I bypassed the ignition switch to feed power directly to the coil
and DME "Start" input, to no affect.

Now I'm thinking that the prime problem may be Code 3 (injector fault
for 1,3,5). If that fault, and only that fault, happens after a single
event I'm inclined to figure out a way to bypass that part of the
harness (even though it ohms out) to see if that fixes it.

10/21/2007

Now I know what it is. The car is possessed by demons. To fix it I need
a young priest, an old priest, and a large jug of Bavarian Holy Water...

In trying to see if the injector fault code was repeatable I did several
runs where I cleared the codes, duplicated the problem, and scanned the
DME. The reported fault codes were completely random and different each
time. It is possible that CarSoft (all I have available) is
mis-diagnosing the DME, but if it is correct something is scrambling the
DME at high rpm. Alternator perhaps?

As a next step I'm going to rig something up to allow in-car disconnect
of the alternator and see if that changes anything.

10/28/2007

Since I had an alternator that just needed new brushes, I swapped
alternators after fixing the spare. That didn't eliminate the problem,
but it may have moved the event higher in the rpm band. It was happening
at about 6k and the CEL would come on a couple of hundred rpm below the
event. More testing is going to be needed to see if it really has moved
higher.

A "stomp test" only pulled up 1262, which is an idle speed control fault
and may be related to the CEL that occasionally comes on while the
engine is idling or during a long down hill closed throttle run. But
that code can also be set by a stall above 600rpm. So it might be
related to this problem. I didn't scan the DME with CarSoft this time,
so I don't know if it would agree with the "stomp test" results.

I'm running out of the possibilities. The only thing I can think of to
do now is to ohm out all of the wires in the engine harness. But I don't
understand why a problem there would be rpm sensitive and not also cause
cause problems at other engine speeds.

11/16/2007

I found the spec for the CPS air gap (.040") and discovered the CPS was a lot
closer to the crank wheel than the spec calls for. I adjusted the gap, but
that made the problem slightly worse. So it is looking more and more like a
problem with the wiring harness and specifically the CPS signal wires. Perhaps
there's some damage to that circuit or the CPS connector that is attenuating
the signal. That would be consistent with it only occurring at high rpm and
with the problem being worse when the air gap was opened up. I'll have to
catch up on work around the house before I can dive into diagnostics on the
wiring harness.

I know the head needs freshening, but before I pull it I want to run a
compression test and see if more engine work is warranted. If I haven't found
and fixed this problem by then I'm inclined to replace the engine harness
while the head is off and it is easier to get to the harness where it runs
under the intake (for grand problems, grand solutions).

03/13/2008

I found other information that says that the air gap should be .012-.028. I
re-adjusted the CPS, which made no difference at all. I am seeing a pair of
fairly consistent codes after an event (misfire on cyl 7 and injector failure
on both banks). The first would be a coil or coil interface problem and the
latter could be a wiring or injector interface issue. But then, both could be
caused by a CPS or power fault. For grins, I tried disconnecting the cylinder
ID connector and saw that the DME did register that failure. It had no affect
on the problem, but it would appear that the signal is valid. Likewise for the
engine temp input to the DME.

I've pulled the boots on "interesting connectors" to look for corrosion, but
haven't found anything suspicious. I noticed that when one of these events
occur that the MPG gauge drives to 40mpg concurrent with the tach drop. That
may imply that the DME is not supplying injector pulse width info to the
cluster.

I think I need to find out whether the CPS signal is going away, or whether
power to the DME is being interrupted. I think the check needs to be done at
the DME.

03/23/2008

Power to the DME is good. I probed to wire from the code relay (ignition on
signal) and the wire from the main relay (DME power) using a test light as an
indicator. The light never flickered or dimmed during an event. Therefore I'd
say power isn't an issue.

03/27/2008

One more thing that isn't a cause. I pulled the harmonic balancer and
inspected the rubber mount. It was fine and the balancer was tight. A "fork
lif"t upgrade is in the works. I've found an 80k mile engine and harness. I
just need to fiond some time to pick up same and do the swap.