My long deferred maintenance on my 94 940(195,xxx miles) finally caught up w/me! Friday night on the way home my wife calls me frantically to announce the Volvo had stalled on her way home. She was able to immediatley re-start but it died numerous more times during the the rest of the 20 minutes ride home. Once or twice it took some extended cranking but it did get her home(not a fun cell phone conversation!). Anyway, I had failed to change spark plugs since 150k and w/my 75-80mph highway driving every day, the gaps were huge and plugs were spent but working. I would imagine this hastened the demise of the Power stage or maybe the RSR. But being that I have never changed the Fuel Pump relay or the crank sensor...WHO KNOWS! So I ordered all the above from FCP Groton last night:) I will begin installing them one by one and testing thereafter to determine which is the current culprit. I know, I know, I should meter this and test that(actually I did check for codes and it was clean) but like I said these are parts which at 195k, owe me nothing and should be changed anyway. In case anyone is already guessing I changed the FPR and both the in tank and under car fuel pumps last summer, so they should all be good. No evidence of rich running, and tach drops immediatley to zero when she stalls....my money is on the power stage. Any bets? I should get the parts tonight or tomm and I will post the results.

I have now driven to work the last two days with not even a blip of trouble.
Clearly the Power Stage/Ignition Module was the culprit.
Thanks Matt

Last night armed with the proper fuel pump relay I continued my experiment. R/R the Fuel pump relay, start car ran for 5 minutes in driveway in park then
stalled out in same manner, tach to zero. R/R RSR, start car, ran for 5 minutes in driveway. Feeling confident I had it licked, I proceed to take her around the block approx 1/4 mile and car stalls out. I drive home(stalling 1 more time along the way). R/R power stage, start car, chug a couple beers while letting it run for 10 minutes in driveway. Take her for run around block.
LIKE A CHAMP!! I decide that my beer intake at that time precludes a spirited highway sprint so I sit and watch and listen. Pending further time and testing, it appears the power stage was the culprit. Whatever "heat conducting grease" may have been there from the factory is long gone and is now replaced with some whitish dry corrosion on the back of the unit. So two questions for the field(if anyone is still following). I cheaped out and bought the "Hugo"
aftermarket unit from FCP, if as anticipatyed this does solve the problem should I replace this with a genuine OEM unit? And I want to go back in and add the missing "heat conducting grease", anyone know where to get some?
Thanks
Matt

computerparts stores sell this "grease" on tube, same as used when mounting comp. processors.
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V70 2,5T -98

I understand your concern about the quality of aftermarket replacement parts vs original equipment. I think often times parts that weren't really bad in the first place get replaced with parts that are actually worse. I think that's the case with some u-joints I put in a few years ago. I had the driveshafts out to replace a leaking pinion seal, sloppy output shaft seal, and center carrier bearing and bushing. I figured since it was all apart I would replace the u-joints just as preventative maintenance, and I used non-Volvo parts. Now, about 20,000 later, the drive train is starting to growel a bit when decellerating at low speed. I don't know whether it's the u-joints or not, but if I had it to over I would have left the originals in place.

But anyway, back to your car - good news if you indeed fixed the problem! But consider this - what if you took the original power stage and cleaned up the mounting surfaces and applied a fresh coat of heat trandfer grease (or whatever they call it) and reinstalled it? Would it then work OK, or is the component still shot from previous overheating? It might be interesting to try it - between cold ones.

Hi All
I tested Spooks theory last night re: the CPS. Started car(started fine) ran it to temp, shook the heck out of the wire, from connection all the way to sensor. Nada. Then I was gonna replace the Fuel Pump relay. But quickly came to realize FCP sent me the wrong one. They sent the large white rectangular and it appears per the FAQ's that the 94 and 95 940 w/b230fd used a blue square one(front row second from right). Sh!t!!! I am picking up the correct one from local Stealership on the way home($33). Grrrrr, to be continued....

UPS delivered parts at 7pm. Was well into 4th can of liquid demotivation. Will
install this evening and post results Thursday.

I vote for the RSR. I have had several of these fail, in various ways, often much like what you described. I have never had a problem with any of the other components you mentioned. (though replacing them as preventitve maintenannce is not a bad idea, assuming the new parts are of OEM quality)

Another point in favor of it being the RSR is that they do not set a fault code when they go bad.

The power stages are pretty tough, if the incredibly eroded caps, rotors and plugs, and deteriorated plug wires I've replaced on various cars (that were still running, more or less normally) over the years. I once bought an 86 that seemed to run just fine, but when I pulled the plugs I found that three of them were broken internally, with the terminals and part of the copper core just sitting loosely in the hollow insulator. They were SplitFire, which, having seen that, I will NEVER buy, or recommend to anyone.

If it were the RPM sensor, it probably would have thrown an error code. But you saw no codes. So I'll say it ain't that - at least for now.

Since you don't know for sure if you lost spark or not at the time of failure, I'll say ignore any ignition components - at least for now.

So now I'm down to the RSR and Fuel System Relay..... Let's see, you aren't going to let me pick TWO possibilities, are you? So I have to pick one or the other. Hmmmmm, decisions, decisions.

Wellllll, let's see. The weather is getting warmer so it's getting hotter under the hood which could cause the RSR to fail, while the the fuel relay is inside the car and she likely had the A/C on which means it wasn't exposed to that much of a change in environment. Plus, the RSR is easier to access for R&R. So hey, it would be a quicker fix if it WAS the problem.

OK, that's it. My first choice is that she ran it out of gas. (Just kidding) I vote for RSR.

Outstanding! I personally am torn between the RSR and the Power Stage, due to my admitted dereliction of the spark plugs and the stress the increased gap would have placed upon the coil and therefore the Power Stage...but I am a rookie! I will say I was bummed with the no codes, I always forget how rudimentary the OBDI system truly is. Thanks.

You need to carry a spare spark plug with you so that you can check for spark when it's in "full failure mode". That would cut the list of possible culprits in half.

I thought the same thing but it trully seems to re-start again almost immediately virtually every time. So I have a hard time making the failure last long enough to test...

I vote for none of the above. Have you ever changed your fuel pump?

Yup, as I mnetioned, both in tank and under car, last summer. Good thought though:)

Dear mmal231294,

May this find you well. I vote for the crank sensor.

To test it, wiggle the wire, while the engine is running. If the engine stops, you've found the culprit.

Hope this helps.

Yours faithfully,

Jay E.

Hi Spook
Long time no hear! Hows things? I will certainly attempt, as you suggest, the wiggle on the CPS first to see if you were correct. Thanks
Matt