My wife was driving down the highway in her 960 and it started chugging and wanting to stall. after going through the engine i realized that 3 of the coils are not working. i swapped one of the other coils with one that is is not working and it still did not work in that position. I read through the forum and it seemed that everything pointed to one of the two Ignition control units being the culprit so I followed the wire coloring and replaced the one I believe to be controlling these three coils. still not working. The engine will idle on the other three cylinders very rough, and i can unplug the three unworking coils with no change. the position of the coils that are not functioning are from the engine firewall towards the front of the car: #1, #3, #4. Any suggestions here?

You might try swapping out the other power stage, maybe you did not do the correct one?

How do your spark plugs look, how old are they?

Another thing, is there any stored codes, is the check engine light on?
Not all codes will light the dash lamp though, so you must still check for codes.

So since you have swapped coils, and changed out the power stage, then I would start with the injectors, do you feel them clicking at idle? Then check the spark plugs. I don't have my volvo fault guide with me now, I have a '94 and there were some small changes in the '95 year, but there is a relay for the both the ignition and injection systems, the part is the same and maybe swapping relay, located near the front driver side fender shock tower, gray boxes. That is if the '95 had them.

Inspect the wiring on the head top, move it around while idling, see if that changes any thing, the wiring is prone to cracking insulation from engine heat.

The wire connectors under the hood of this vintage are not very weather proof, so cleaning and tightening connectors may help here, it should be an annual maintenance item.


Dan R '94 964 360,000 miles (126,000 miles on a new engine)
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DanR

Sorry to hear about your problem, I have not had this, but I have a wiring diagram for my 1997 965. Here is what I can tell you, hopefully there are close.

Coils for cylinders 1-3-4 are driven by Power stage module 1. Power stage module 1 (and 2) are driven by the "Engine Control Module Unit behind left dash" that is from the wiring diagram. Additionally, pin 2 GRN/RED wires are the +12V that should be present on each plug, it appears they have a common source. Pin 1 is the signal from the Power stage module.

My 1997 is equipped with the MOTRONIC 4.4 version. I don't know what version the 1995's had it may be the 1.8 version. Someone else will chime in here, but maybe it is a starting place for you.

Best of luck, and post back when you are hitting on all cylinders.

Fred

Three coils not firing is almost certainly a power stage module issue. Make sure the ground is good and clean and, as has been suggested, swap the modules to be sure you replaced the correct one.
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Dale

Thanks for the quick response guys. Ok, so tried swapping the power stages around and no matter where i put the new one, the same three coils will not function. here is something i noticed along the way. i checked the wire colors on each coil, and found colors for each three on the power stage that is controlling them. according to what i see, here are the coils and the power stages they are connected to (im calling power stage module 1 the front and ps2 the rear, underneath byt the firewall) :

coil 1 = c1
ps 1 = power stage 1 etc.

firewall

c1 O PS2
c2 O PS1
c3 O PS2
c4 O PS1
c5 O PS2
c6 O PS1

front
of car


So this doesnt make sense to me, because the coils that are not working are these three:


c1 X PS2
c2 O PS1
c3 X PS2
c4 X PS1
c5 O PS2
c6 O PS1


BTW, I replaced the plugs, no change. I havent pulled any codes becuase I do not have a handheld to plug in, but i am guessing the codes would come back as misfire on the cylinders mentioned.

It appears you have a problem further "upstream", since all the hardware "downstream" from the Engine Control Module seems to be functional. The wiring, connector to the Engine Control Module,and the Engine Control Module are all suspect now.

Good Luck.

Fred

Ok, so I have had no luck figuring out the problem so I ended up taking it to someone to do diagnostics. He tells me that it has no compression on 3 cylinders, bad engine. I told him the story, that she was just driving along on the highway and it stalled out and asked if it could instantly lose compression on 3 cylinders like that, he said yes, could be many things to cause it internally. I just want to make sure I cover all possibilities before I tread down the path of a used engine or part the car out. Is there anything here I could be missing?

I find this hard (impossible) to believe. I would double check the compression myself to verify.

Did they ever pull the codes? Was it a P0113 or P0115? You may have a bad ground or power wire to that Power Stage. Too coincidental.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100