960 cuts out/stalls

I'm having issues with my 1994 960 where all of a sudden sometimes I'll
lose some engine power and it'll become rough whereas other times it'll
stall(in kinda a weird way, I'll lose all responsiveness and the tach
drops to 0 at which point it all the dash lights come on indicating the
stall). After it does this the car won't start again unless you turn
the ignition all the way off and then back on. If you do that it starts
back up no problem...otherwise it just cranks and cranks and won't
start. After restarting it will run again and maybe not do it again, or
maybe it'll do it a few seconds later. Its very inconsistent, some days
this happens repeatedly, others not at all. It seems to happen under
light acceleration. My mechanic has looked at it several times and it
will either never reproduce for him or he's not able to figure out
what's going wrong. At one point just to try something we replaced the
ignition control modules but the problem still persists. I've actually
gotten pretty good at popping the car into neutral, and turning off the
ignition and back on...sometimes if I do this fast enough I don't even
have to turn over the engine to have it restarted, it'll just be started
already. But it doesn't seem very safe and I'd like get it fixed. Any
clues? Thanks,

Micah

 

The part about the power dropping and the tach going to zero (I presume you
are saying the tach reads zero although the engine hasn't quite stopped
turning) is a familiar symptom of trouble with the ignition "power stage."
Unmounting the power stage, cleaning the mounting faces well and applying
heat sink compound from an electronics or computer store typically corrects
the intermittent. Anyway, it's cheap and easy enough to try! The power stage
is the only ignition component I know of that can cause the fade-away. More
often I think of fuel delivery.

If it isn't the power stage getting hot, (particularly if you are saying the
tach seems to follow the engine speed faithfully) I would suspect either the
fuel filter (debris that falls to the bottom when the pump shuts off ) or
the old standby, an intermittent fuel pump relay. Many people have
resoldered the circuit board in the fuel pump relay with good results, and
careful examination in good light often reveals any cracks in the solder
around the leads.

Mike

 

Additionally, what about problems with the ignition switch and related
wiring?

Disconnect and reconnect the computers' main plugs.

Being that it restarts immediately I don't think it is a failing
component but a bad connection AT some component or alond a wiring
harness.

If a fuel filter clogs it can stop a car, but it usually takes a
minute or two with the car not running for the filth to settle to
allow fuel flow again. The immediate restart that he is expeiencing
rules that out, generally. (BTDT with a Ford PU- ended up a rusty fuel
tank. The rust would clog the filter, and when it stalled out the rust
settled and the truck would restart.)

I wonder if the computer is setting any codes that could be read in
the OBD?

I might also suggest replacing the fuel pump relay(s), and removing
the fuses, cleaning all connection points in the fuse box, and
replacing the fuses.

That should keep the mechanic busy for a bit.
__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"

 

Typically, ignition failures cause the engine to turn off very suddenly,
while fuel supply failures have a short fade-out... longer at light
throttle. But that is only an indicator and shouldn't completely exclude the
other system. The tach is a great clue, because if the tach drops like a
stone while cruising down the road we can say it is definitely ignition.

I won't argue with that at all, because the electrical inputs to the ECU can
definitely cause fade-away failure.

I agree that it usually takes a while for the filters to uncover - longer
than the second or so to shut off and restart the ignition. But it could
happen.

The OP said nothing about a "check engine" light, which offers a few clues.
Fuel pumps quitting don't normally set the light (I don't know why), and
ignition failures from the power stage on also don't.

 

My '93 960 had similar symptoms a few years ago. It wasn't too long before
the car would not restart. A little probing with the multimeter indicated
no signal at either power stage module. The computer had to be replaced.
Ouch! I miss my 740's.

 

Sounds like my problems with my 1994 850.

Cruising along and bah-zip, coast to the side and wait twenty minutes
or so. Alternately, I'd be making short trips and the car won't start.

Cam position sensor having a heat-fault was suggested and that cost me
$400 for the same results as before. I've also had the fuel shutoff
relay/selenoid/switch posed as an alternate (co-worker had this with
the honking big diesel pickup and seems similar) and someone suggested
disconnecting the computer so that the memory resets (beein suggested
in this thread as well...)

 

Yeah, I'll be driving along, lose engine power(some or all), but as I'm
still coasting with plenty of speed the tach steadily drops down towards
0. The mechanic had replaced one other part first before the ignition
control modules, but I couldn't find my work order and wasn't sure what
it was when I posted. I checked on the car and it must have been the
power stage as it looks new and recently replaced. The weird thing is
that when the power stage was replaced(I presume), the problem did go
away for a number of weeks, but eventually returned. Also, my mechanic
did indicate when he was able to reproduce the problem once he had some
diagnostics of some sort that told him it was a ignition problem, not a
fuel problem. Sorry for leaving out some information, this problem has
been going on for months, so its easy to leave out some details.

I'm not sure about the comments about a loose connection. Usually once
the car starts missing or I lose power the only way to get the car
running normal is to shut it off then back on. I would think a loose
connection would give me mort of a cut out/cut back in kind of symptom.

I'm not sure where that leaves me. I've kinda been wondering if it is
indeed the computer(as rgarrett suggests), but I'm not any kind of
expert and would just be guessing. Any additional thoughts? Thanks for
your feedback,
Micah

 

The symptom went away for a few weeks when the power stage was replaced, eh?
My interest in the mounting is renewed! If the mechanic cleans under it and
mounts it with heat sink compound (not factory standard, but recommended
here) I think you just may have a solution. If not, at least it rules out a
major suspect pretty cheaply. And the tach behavior really sounds like a
power stage overheating.

Mike

 

Another problem in the same area is that each power stage grounds
separately on either side of the motor mount and sometimes one or the
other will work loose.

Bob

 

Solution?

Have you resolved your problem? I'm experiencing the same things in my '95 960