I just got a 20V 850 Wagon (70k miles) towed it home and it won't
start...seems that there is lots of fuel at rail but I don't see a lot
on plugs. The plugs were heavily fouled with black crud when I first
pulled them. There is good spark. I supect the injectors are not
firing...any ideas on how to make this happen...I have been reading the
many postings on this subject and it seems that cam sensor has come up.
I have been cleaning up grounds but they don't seem that bad...would
the cam sensor do this? Where is the cam sensor located? Can it be
bypassed to verify that is the problem?
thanks
PS I have red many postings and I love the helpful tone of this group.
The cam sensor is bolted to the rear of the exhaust cam housing (T40 x2)
behind the bracket for the upper torque mount. The cam sensor signal
must be present for the fuel control system to trigger either the fuel
pump relay or the injection control circuitry to produce spark. If you
can find a used motor in the junkyard try to find a used sensor with the
all metal body as opposed to the one with the black plastic cover that
you have.
However before changing the cam sensor blindly, pull and record any
diagnostic trouble codes (DTCs). Install fresh plugs--single prong
copper type plugs if it's a turbo, multiprong plugs if it's normally
aspirated. Be aware that for cold temperatures there was a service
upgrade for the turbo hose routing if that applies. And the use of
multiprong plugs was an attempr to overcome cold starting issues in the
non-turbo. Additionally the nonturbo will gas foul the plugs if started
and stopped before the motor has had a change to warm up.
Check the vacuum hose from the fuel pressure regulator for fuel or
intermittent leaking.
Both these problems are more frequent that a cam sensor failure. Which
by the way will not leave a code unless the failure occurred while the
engine was running. Most times the failure is during an attempted start
and no code is written.
Check at the coil for spark. At 70K it's likely that the ignition cap,
rotor and wires are original.
If the first look over for obvious no spark, and liquid fuel leaks
yields no results, disconnect the O2 sensors and the MAF and see if the
car will start. Both of which should have left codes in memory. If not
you'll pop some codes but they can be reset later; Cf. brickboard.com
<740 FAQS> <OBD> for details on mastering the pushbutton diagnostic
panel. It's the same as on later 960's. If the motor starts, plug the
MAF back in. If it stalls the MAF is bad. If it runs, but poorly, it may
still be bad but check some other things first. Also plug the O2 sensors
back together to see if there is any change.
Check the coolant sensor wiring for integrity. Check the resistance in
the sensor. It should not be a very large number. If it's bad it will
leave a code. If the resistance is very high it's telling the control
unit that it's about -40* or something and the motor will flood.
If none of these pan out try to borrow a "noid" light from a parts store
or buy one to fit a Bosch injector. I think Harbor Freight sells a kit
for $10 on sale. If the control unit doesn't flash the noid light then
either try and get a scope reading on the cam sensor wave form or just
swap in a new one. If the waveform looks correct compared to the spec
pattern then replace the control unit. If the wave pattern is absent
replace the sensor. If you have gotten the all metal body drsor then
just bolt it in anyway it's a better piece.
Now as long as the timing belt was correct when you began, and the motor
has compression, and none of the control fuses are blown, and there is
actually gasoline in the tank, and the fuel pump and injection relays
are OK, you get good fuel pressure (~3 Bar = ~43 psi) and mice haven't
been eating the wiring harness (a wiring harness is better than sex to a
mouse) then there's no reason the motor shouldn't run.
Bob
