94 850 20 valve Wagon

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

 

If this car has the same UK type dual ECU's (fuel and ignition) then the CPS
is *not* required for the engine to start. Only the Siemens and Motronic
single ECU cars need it for start up.

I would guess you have flooding and or lifter pump as your problem.

Tim..

 

Thanks Bob for the thorough reponse.

Oh I did have to add 2+ litres of oil to bring it up to "full" is there
an engine low oil safety that must be reset?

 

On this side, I'm assuming by your header that you're in Ontario, only
the 83's had a low oil level sensor, simple float type, that leaked, was
unreliable and removed under bulletin and in later production.

Always check the oil cold before the motor has run. In an older engine
that may have been susceptible to sludging from infrequent moneral oil
changes or exclusive short trip driving, nearly a quart of oil can
"hang" in the cam tray before draining to the sump. A 94 should have the
red handles dipstick (as opposed to the day-glo orange dipstick). The
red stick = 5.3qt (5.0 l) sump capacity with filter, the orange 5.6qts
(5.3 l).

BTW the clearing sequence command from the test panel causes the control
unit to load a capacitor discharge command. The second press is the yes
answer to an "are you sure?" dialog, to which the box replies memory
registers polled, all zeroes found, execution successful.

Bob

 

I have the 850 inside in my shop where it is warm and is level...the
previous owner did not check things like oil level and tire
pressure,she told me last time she tried it wouldn't start (december).
I checked the fuel pressure in the header and it showed 45psi. I
pulled a plug and saw a good spark (multi prong volvo plugs in pretty
good shape). I cleaned the plugs and tried with no combustion. Pulled
several plugs and it didn;t appear to be flooded...plugs were quite dry
and I couldn't see or smell fuel in the cylinders. will try with the
noid on the injector tommorrow if I can pick one up. I tried to get a
OBD1 code reader but couldn't find one...for the volvo...so I can't
access codes unless they are internal to the speedo head?

The cam sensor has a large metal cover over the rear cam ( under
torque bracket). I have an oscilliscope that I can hook up to the cam
sensor...am I looking for a step function? should I just connect tot
he output from the sensor or does it receive an excitation voltage thru
the connection.

I am flying blind here since there is no volvo dealer within 200km of
me and I don't yet have a manual.

 

Under the hood, clipped on the control unit compartment, next to the
windshield washer fill spout, you'll see a pair of sockets marked "A"
(black) and "B" (gray) underneath their protective covers. There is a
flylead attached to the A socket. Each of the sockets has numbered
holes. To query each system insert the flylead as follows:

A1--Transmission Modes available: 1,2,3,4
A2--Fuel system " 1,2,3,4
A3--ABS " 1,4
A5--TCU/CEM (turbo control unit)" 1,3 "
A6--Ignition " 1,2,3
A7--Combined Instrument " 1,3,4,5,6
B1--Climate control " 1,2,4
B2--cruise control " 1,2,4,5
B5--SRS " 1,4
B6--Power Seat " 1,4

With the key in the run position, marked II, on the lock cylinder face,
depress the push button on the A socket in one second intervals while
the flylead is engaged in one of the above numbered sockets. Each press
of the button increments the query option by 1, so that pushing the
button 5 times with the flylead in A7 would open mode 4 in the
instrument cluster if it were ECU equipped. The LED would flash at 2Hz.
You would then enter the code 1 push, pause 5 pushes, pause, 1 push,
wait, to reset the service reminder light. Once the code was accepted
the LED would flash rapidly for 1 second to acknowledge the change, the
service light would be reset.

Mode 1 is always a "query for codes".
Mode 2 is ask the control unit to ask for a switch response and then it
responds back if the switch make break was detected.
Mode 3 is always "devices operated by the control unit".
Mode 4 is always "clear retained codes and respond with all clear if all
registers reset to zero."
Mode 5 is always "query for variable parameters and report values as
set".
Mode 6 is always "reprogram the values of variable parameters set in the
device previously queried in Mode 5".

So to find out if there were any fuel system codes present plug into A2,
push the button one time and record the code. There are three available
memory registers, so repeat the process three times. Do the same thing
again in position A6 and record any codes. Then report back.

Check the codes against the list here:

http://www.brickboard.com/FAQ/700-
900/EngineOBDCodes.htm#LH24FuelInjectionFault

or

http://makeashorterlink.com/?O25712ABC

Same as above without the wrap. Bookmark this page.

Please list the VIN here, replacing the last six digits with x's so I
can tell which systems we're specifically talking about. And we'll go
on.

Bob

 

Bookmark this as well, make a copy for the car if you don't have one:

http://new.volvocars.com/ownersdocs/1994/1994_850/94850_1.html#contents

http://makeashorterlink.com/?12A75ABC

Although this is froma 940 manual the socket pictured as 17/11 at thr
URL below is what you're looking for.

http//:www.autoelectric.ru/auto/volvo/940/1993/940-93.htm

Bob