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:
- Replaced the O2 sensor (new OE part)
- Swapped in a known good AFM
- Swapped in a known good 173 DME
- Replaced the injectors (new OE parts)
- Replaced the crank position sensor (new OE part)
- Replaced the TPS (new OE part)
- Replaced the main & fuel pump relays (new OE parts)
- Replaced the coil (new OE part)
- Replaced ignition wires, cap, & rotor (new wires & OE parts)
- Cleaned all grounds and primary power connections
- Replaced intake manifold gaskets & all hoses
- Verified proper operation of the DME temp sensor
- Proved there are no leaks in the brake booster
- Replaced the oil filler cap and dipstick o-rings
- Eliminated the evaporative control system
- Acid cleaned & sealed the tank & replaced both pumps (new OE parts)
- Replaced FPR (new OE part)
- Checked C101 for corrosion
- 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) and saw normal system
voltage at each. I monitored each wire with a test light while driving the car
to repeat the problem. The light never flickered or dimmed during an
event. Therefore I’d say power to the DME isn’t an issue.
03/24/2008
I think I saw a DC level appear on the CPS signal during an event. That could
be as a result of chaffed wires in engine harness. It seems a stretch that
both DME’s would have that fault, so the harness is now my prime suspect.
03/25/2008
I found what should be a good harness, still wrapped around a 140k mile engine
that was running great before the car it is in was rear ended. So I’m
summoning the young priest, old priest, and a large jug of Bavarian holy water
and swapping engines and the harness. I’m tired of screwing with this and I
want to race the car at Roebling. The fresher engine should mean that I can
defer the head rebuild and such and I suspect it’ll make a bit more power. It
will almost certainly burn less oil (a track weekend is 2-3 quarts).
I’ll pick up the engine sometime next week…
04/12/2008
Work has gotten in the way of picking up the engine and harness… But I know
one more item that isn’t the cause. I pulled the harmonic balancer to see if
its rubber mount had failed. That could cause the problem, but the harmonic
balancer looks fine. No signs of cracking or separation.
5/21/2008
I finally picked up the new(er) engine and started prepping it for
installation. While looking for an oil leak in the vicinity of the cooler (the
leak was because the fitting was separating from the cooler) I saw that the
harmonic balancer was wobbling around. For grins I swapped in the balancer
from the new engine. The wobble was less and that raised the cutout to around
5800rpm and make the problem less frequent. I’m onto something now…
Placing a web-cam and a headlight in the engine bay and running up to the
problem area clearly showed the harmonic balancer wobbling around. More
importantly I could see that the crank bolt was wobbling (worn bearings, most
likely). At the point that the cut-out occured the harmonic balancer was
wobbling like crazy. I’m thinking that the wobble is disturbing the CPS signal
to the point that the DME just gives up. We’ll see what happens when the new
engine is in.
6/6/2008
With a prodigious expenditure of effort I got the new engine & transmission
installed in time to go to Barber for the NASA event. Setting the engine on
the mounts at 9am Friday morning. Only to have the shifter break too late to
be able to effect a repair. The good news is that the harmonic balancer and
crank bolt run dead true. Ah well, I did have a good weekend
instructing… Note to self, don’t ever let an early 911 driver trail
brake. Exciting things are gonna happen!
6/14/2008
The new(er) engine seems to run great. I’ve flushed the cooling system as the
car the engine came out of was an auto with a leaking tranny cooler and there
was a good bit of oil in the cooling system. I’ve fixed the shifter and as
soon as I check out the front driver side strut (the shock collar may be
loose) I’ll see if it will run to the redline.
6/15/2008
Cautious optimism abounds! I’ve done a good dozen runs to the redline in 1st,
2nd, & 3rd without once having an “incident”. Sticking a pipe on the crank
bolt with the old engine mounted on my engine stand, I could detect motion in
the front main bearings! That could easily explain everything.
I’ve gone all over the left front strut and still can’t explain the noise I
hear on occasion when the suspension travels. Everything seems tight so I’m
not gonna worry about it for now.