Big problems with 89 Voyager - please help

Hello everybody,

I have a 89 Voyager, 130k miles, with the 3.0L V6 engine and 3-speed
automatic transmission.
Recently the car became hard to start. Two days later the engine died
when idling at a redlight. Back home (engine still runs, but not good) I
checked the codes and the SBEC gave me a 54.
So I started checking the photoelectric pickup assembly. I checked at
the distributor-to-harness connector. Power is good (8.9 Volts), ground
is good (3 Ohms from the connector to the battery ground) and the signal
line delivers a beautiful digital clock signal (measured using an
oscilloscope) while the engine is running. I cleared the codes, but
after operating the engine, the "54" is back.
During my examinations, I also noticed that every 10 seconds or so, the
a/c compressor is engaged for about 1 second - although a/c is set to
OFF at the control panel! The SBEC did not do this all the time ...
after 2 minutes of 1-second-runs, it stopped ... and came back some 10
minutes later.
I disconnected the a/c clutch from the harness, thus forcing the
compressor to stay off. Now it is even more noticeable that there's
something going wrong. Whenever the SBEC tries to engage the compressor
(it can't do this due to the disconnected clutch), I can hear a clicking
sound (some sort of solenoid or relay) coming from the front left corner
of the engine compartment. Also engine idle speed is raised to about
1300 rpm during that 1-second-run.
What the hell is going on? Any suggestions will be very much appreciated.

Markus

 

Code 54 is "No fuel synch pickup signal". That'll certainly cause hard
starting and stalling. Even though you may have a perfectly good signal
out of both the low-rate and high-rate pickups in the distributor (you
tested both, right?), the computer may not be seeing them properly,
sometimes due to a faulty wire or corrosion at the 60-pin connector at the
engine computer.

Are you sure it's actually set to "off"? If you've got the Defog button
pushed, it'll run the A/C compressor regardless of the compressor
pushbutton position, and if your A/C system is low on refrigerant, it'll
short-cycle. That is one mechanism by which such a symptom could be
observed. Another is -- again -- corrosion or faulty connections at the
engine computer. Another is an internal computer fault.

The SBEC did not do this any of the time. An '89 has a SMEC, not an SBEC!

You're hearing the A/C clutch relay, which is usually drowned out by the
louder click of the A/C clutch itself. The idle speed increase is normal
when the A/C clutch is engaged, to compensate for the compressor's load on
the engine. All you have to do is figure out why the computer thinks
you're requesting A/C.

DS

 

Ok, of course I ckecked both of them and both clocks are there. I also
measured the voltage at the clock lines at the distributor harness
connector with ignition turned on: both read at 4.8 volts, thus telling
me that that I've just seen the voltage which arises on an open digital
input with internal pullup resistors. So the 60-way SMEC connector must
be good.
Note besides: if I disconnect the distributor from the harness while the
engine is running, it dies immediately.

I'm absolutely sure that it's set to "OFF". If I set it to "NORMAL", a/c
runs smooth without any short-cycling. My a/c system is in perfect
condition, as it is serviced twice a year by an a/c professional.

You're right, sorry for the typing error!

So how can I figure out who the hell is the cause for that intermittent
a/c cycling while the system is turned off? I already disconnected the
vacuum hose which runs from the power brake booster to the a/c control
panel (I remember that my Chevy van did funny things with the a/c some
time ago and it was just a defective vacuum fitting at the control
panel). But that did not change anything.
The a/c clutch is operated directly from the SMEC (unfortunately I don't
have schematics for the SMEC, only for the SBEC, which has a different
pinning layout). Can you tell something about the the signals going into
the SMEC which are responsible for operating the a/c?

Thanks a lot for your help,

Markus

 

Ok, so I started cleaning the throttle body, which is something that's
never wrong. I also cleaned the AIS motor. I saw that the pintle was not
in its retracted position (<= 1 in), so I twisted back the pintle.
I also checked the distributor harness. I was able to see the 2 clock
signals which run from the distributor to the SMEC. I could also verify
ground and power (+5V) at the distributor harness... The distributor
signals seem to be ok, when I pull the connector from the distributor
harness while the engine is running, it instantly dies, as this engine
does not have a camshaft or crankshaft sensor (I believe).

After having the throttle body cleaned and the AIS motor pintle
retracted, the car is easy to start now. Looks like that was the
stalling problem. Although I cleared the codes, I keep getting that
f***cking 54! And the "Check Engine" does not light up!

I also still have the problem that the computer kicks in the a/c
compressor now and then, although it's turned off. After looking at the
schematics, I found out that the a/c control panel simply grounds a wire
when the user selects a mode which requires compressor support. This
wire then runs thru the high and low cutout pressure switches and the
ambient temperature sensor switch and then it ends up at the 60 way SMEC
connector. Now if ANY of those switches would open the line, the
compressor should not engage anymore. So I simply pulled the connector
from the high pressure switch. No change, the SMEC continues to run the
compressor now and then (but always just for a second or two).
Currently I'm driving with the a/c set to "Defrost", just to override
that intermittent compressor engaging. This car has no cycling a/c and I
dont' want to ruin the compressor. When I do this, there is no on/off
problem. The compressor runs all the time (of course I had to reconnect
the high pressure cutout switch).

But what the hell can I do to track down the problem? Given the case
that the SMEC is faulty, can this be diagnosed by hooking the car to the
dealer's diagnose system?

Could it be a vacuum problem? Or something around MAP or EGR? How can I
do some "it cannot be this sensor" troubleshooting?

Any suggestions will be greatly appreciated,

Markus