I have an 850, I think the EZ-129K type system that gives no spark. I have another 850 that ran right up to the point of the moment the timing belt broke, so I think it would be reasonable to assume all the ignition components function. I have switched into the no-spark 850 these items:

1. coil
2. crank position sensor
3. camshaft position sensor
4. ECM (middle one in the case I think) but did go back to the original one when this made no difference.
5. tried a different coil high tension wire

All connectors look clean and wiring shows no damage anywhere that I can find.
All grounding straps I could find look great.
Car cranks over fine, dash lights come on as they should, the distributor rotor is turning indicating the timing belt has not given up.

This may or may not be related, but the data link connector led comes on when I push that button with the key on and the probe in socket #2, but I get no response.

Does anyone have suggestions for this seemingly elusive problem>?

Thanks for this tip about my 850 with no spark. My manual doesn't have much for wiring diagrams (Chilton seems almost, but not quite useless.) It also does not mention relays.




Relays 101 thru 104 near the fuses are stamped with the numbers, but the remaining three identical cubes have no numbers on them. However, the stamped cubes look as if they are counting in a clockwise manner, so I surmised position 106 is the middle cube. I did replace it with one from the parts car, and do have power at the coil, but still no spark, nor did I get a code working either.




So I'm still puzzled about all this.

Did you find the Volvo Wiring book? It's terrific!

There's an ECU and Powerstage modules
and don't forget to check your grounds carefully.
Many circuits are switched with the ground side. (Thus you see +12 but
it still doesn't work since the ground is not being switched on)
I would confirm that the power stage is getting +12 AND the switched ground
from the module, measure everything at the power stage input connector.
Go from there...

Do you have other electrical issues?

Bill

Hi Bill,

Thanks for the leads as to where to get the wiring diagrams. I, hopefully,
will have time this weekend to get them printed. We do have company here
tho too, so I'm not sure if I'll get a window of opportunity. The Data
connector, besides not having a spark, are the only two electrical issues
I've noticed... Who knows though, with more investigation, I may discover
something else!

Thanks again, and I'll keep you posted as to what I find. As a double
check, I measured the crankshaft probe resistance and it is right in the
middle of the desired range. I realized the ignition module was the far
right unit, so I traded the one from the parts car into mine, without
creating a spark, so that doesn't seem to be the problem. I'll keep
learning more, and checking more as I get time.

Jim

I looked at the wiring and see a commonality with no spark and a dead OBD.
Its relay 2/31 powered by the ignition switch and marked #106 in the main relay box.

relay 2/31 supplies +12VDC to the power stage pin 3 you can try to measure it there.

Happy hunting, Bill

Hi again.

I did a bit more detail. When I initially measured battery voltage at the
coil, I checked the primary connection at the coil. I went back out just
now and pulled the wiring connector at the power stage and checked those
pins. I had battery voltage on the middle pin, zero on either outboard pin
with the key on, and with that still had battery voltage at the coil's
primary circuit. (Not sure which is #3 as depends if the wire bail should
be up or down when counting, and then I see in the manual for other
connectors, such as the camshaft position sensor connector, they show
counting pins up from right to left when the wire bail is up.)

I also pulled that middle relay and reinstalled with the key on, and upon
doing that, did hear a somewhat familiar click from somewhere under the
hood.

I also checked out the coil per the Chilton's manual, which said checking
ohms from high tension to primary I should have 5 to 8K (I had 6K) and
primary circuit to ground I should have half an ohm, I had about 0.1; but
the lowest scale my meter goes on is 0 to 200, so I would guess my meter is
not accurate at such a low reading.

Do you know what function the power stage serves? I am contemplating
putting on an older 12 volt coil from the 70's to see if I get a spark
there..

Thanks again for any help.

Jim

Hi Bill,

Thanks for this tip about my 850 with no spark. My manual doesn't have much
for wiring diagrams (Chilton seems almost, but not quite useless.) It also
does not mention relays.

Relays 101 thru 104 near the fuses are stamped with the numbers, but the
remaining three identical cubes have no numbers on them. However, the
stamped cubes look as if they are counting in a clockwise manner, so I
surmised position 106 is the middle cube. I did replace it with one from
the parts car, and do have power at the coil, but still no spark, nor did I
get a code working either.

So I'm still puzzled about all this.

One other thing is that after the car had been running there always was a
sound, humming or buzzing, coming from under the cover where the throttle
cable connects to the intake. I can't remember for sure if that used to
come on also whenever the key was turned ready to start the car. However,
it doesn't make any sound. I do hear the fuel pump come on when the
ignition switch is initiated.

Such grief; most of the time the 850 is a great car!

Jim

Hi Jim,

For openers, go here and get the 1994 850 wiring diagram:
www.matthewsvolvosite.com/downloads/1994_850_wiring_diagram.pdf

I'm not sure if it's complete or not, there being multiple sites that offer
the Volvo 850 wiring diagram (my 1995 book is 41MB)

The Volvo wiring diagram is terrific, system diagrams and component locations.
Look in the index for multiport fuel injection EZ129K

and find the ignition parts on the lower right portion of the schematic.
You will see that there's an ignition module (ECU) and a power stage.
and it should be much easier for you to troubleshoot. Everything is carefully
documented.

The index explaining component ID starts at page 200 in my book. It helps to print that out so you can understand the schematic.

The schematics page is followed by a parts location page

They will have a pictoral showing what pins are what.

Soon you will ignore that Chilton's :-)

Bill

"One other thing is that after the car had been running there always was a
sound, humming or buzzing, coming from under the cover where the throttle
cable connects to the intake." - that is the idle control motor, and it should always be running when the key is in position II or III.

Sorry, I am not good with electrics.
--
My back feels better when I sit in a Volvo seat