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.

Reply to
Greg
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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 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

Reply to
User

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..

Reply to
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?

Reply to
Greg

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

Reply to
User

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.

Reply to
Greg

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:

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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

Reply to
User

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

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this is froma 940 manual the socket pictured as 17/11 at thr URL below is what you're looking for. http//:
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Reply to
User

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