Hi,
Another guy on in the forum and I have been having trouble with our 940 turbos with intermittent cutouts. We pretty much nave the same symptoms, they are as follows:

-engine cutout while stopped or driving slowly. No sputtering or bucking just cuts right off. Takes a very long time to restart. (traffic tie ups, much shouting)

-occasional cutout while traveling at highway speed. Though the car restarts on its own (without me doing anything)within 10-15 seconds while still coasting.

-tach needle doesn't budge until engine fires up when starting. Someone had said that it should move slightly while the engine is turning over. I don't think mine ever did.

We both have decided to start replacing things until the problem is solved. My question is, what are the most likely culprits? Someone please correct me if I'm wrong.

1. check for loose wires under hood.
2. check/replace Fuses for good connection.
3. check/replace Fuel Pump Relay.
4. check/replace Fuel Injection Relay.
5. check/replace Fuel Pump.
6. replace RPM Sensor.
7. replace Ignition Module.
8. replace Coil.

Lastly, can anyone tell me what the Power Stage is?(A part? A group of parts?, Ignition Module?, Ignition amplifier?, something else?) It may be a stupid question but I just don't know.

Thanks,
john

My money is on the FPR. Resolder for $0 per the 700/900 FAQ. If the problem persists, replace RPM sensor, as it is cheap, and the original (white vs. yellow stripe) is known to be a problem. If it still cuts out, you could have heat-related power stage failure. Try pulling it and clean/replace silicone in heat sink before buying a new one (see 700/900 FAQ for info). You can also swap the supression relay with the fan relay (black relays near strut towers.

Good luck. It can be aggravating and expensive to cure drivability issues.

OK, I found at least two cracked solder joints on the Fuel Pump Relay. I resoldered all the joints though. Just got back from a meandering two hour drive with no cutouts, though I'm still not sure that it's fixed. The thing I did notice was that the relay was fairly warm once I got back home, is this normal? It was by no means hot to the touch, but it was definately more than luke warm.
john

Had the same problem 5 years ago with wife 760 turbo wag. 1989,
Dealer fixed for me. was fuel inj. relay intermittent. no rhyme or reason to when would cut out, Local volvo repair guy tried about 5 times to fix NG. Dealer kept overnight and mech drove home etc. But was relay for sure,
Frank , florida

I had the exact same problem that I just solved. The car was a 93 940T. Had the same stuff, intermittant stall when warmed up, sometimes would start right up, and same junk you describe.

It is worth it to resolder the fuel pump relay, because it will probably need it sooner or later. This was not the cause of my problem.

It was the RPM sensor. Check your engine's codes, if the RPM sensor is your problem, the computer should have a code stored for it. Let us know if you get any error codes.

Hope this helps!
Greg

The only time it threw a code was one of the times it cutout on the highway and then restarted on its own. 1-4-3, Knock sensor signal fault. I had that replaced but the problem remained.

No codes have shown up since. Which brings me to another question. Is it possible for something like the RPM sensor or the ignition module to go bad and not set a code, even though there are codes for both of them?

john

I'm not sure about the code question. I'm sure anything is possible.
Did you take a look at that fuel pump relay yet? Do that as soon as you can.

Does the stalling seem to be heat related? I'm asking because my stalling was only when the engine was warmed up. Most of the time, RPM sensor problems tend to be heat related. If you do solve your problem and it is not the RPM sensor, just be advised that the RPM sensor will probably start to give you problems sooner or later.

Greg

Obviously check the coil wire and any other loose connections under the hood and in the fusebox.

THe fuses must be good, but can be intermittent.

Most definitely replace the RPM sensor. Carefully extract the old one from the bellhousing bracket. Douse it with silicone spray if you can't get it out of there (engine cold) and wiggle it gently until it comes out. Break the bracket and you're up the creek. That part is SO inexpensive compared to the engine's total dependence on it, that it would be silly not to. You'll probably find the old one fouled with debris and corrosion.

If that isnt' the culprit, often the fuel pump relay is the one. On a 91, you should be able to hear that one click (and the fuel pump run for a second or two) when you turn the key from OFF to ON, before starting. If it doesn't do that while you're stalled out, it could be the problem.

Power stage is possible as well. Can be intermittent. I'd follow the first two as the most likely, then go on to the power stage. You can even pull the RPM sensor and LOOK at the thing before deciding to replace it. A good one should be clean and not corroded. Wire should be intact, no splits in the insulation.

The fuel pump shouldn't work intermittently as a fault of the pump itself.

--
Chris Herbst, near Chicago, IL. 93 940, 91 240, 90 240, 88 740, 87 240

It would be important to know if you are loosing fuel or spark. If you lose spark (read pulses at negative terminal of coil) the tach will go to zero immediately even though the engine rpm may still be winding down. This is because the tach signal comes from the same point on the coil. For the same reason you should see a slight nudging of the tach while cranking. If tach signal is there then you almost certainly have spark unless the coil is bad but they usually do not go intermittent. Power stage, ignition amp and I think ignition module differnet words for same thing. This is what sends above mentioned pulses to the coil. If no spark then prime suspects would be power stage and RPM sensor.
If spark OK then its fuel. Start by resoldering the fuel injection relay. That is your prime suspect. There are instructions in the FAQ section on how to jumper out the relay to apply power directly to the pumps.
Thats my .02 cents worth.

Good Luck

david,
If it is in fact fuel related and is the fuel injection relay it seems to me that it would make sense that it takes a while to restart since there's no gas in the line, but shouldn't the car sputter a little before cutting out, kind of the way it would if it were to run out of gas. Yes? No?

john

No, it will cut off within seconds. A fuel injection system will react very different than an old carburator engine which will sputter and die slowly as the fuel empties from the float chamber. On a FI car the fuel pumps must maintain the line pressure at about 35psi, when the pump cut out fuel pressure drops immediatly and no fuel can spray from the injectors. The gas stays in the line but at ambient pressure. Once the pumps decide to start again pressure builds immediatly and she will run. An intermittently bad solder joint can give the exact problem you describe.
Yes they do run pretty warm.
Hope you have it fixed!!

On 740T cars it's on the engine compartment wall lhs near the four firecracker-lookalike ballast resistors for the injectors. It's a solid state device on an aluminum heat sink.

I think the 940T still has a B230FT engine and associated electronics...very likely should be the same part.

I wouldn't be surprised if it's the ignition module...I had the same problem on BOTH my 87 760T a few years ago and the 90 740T last year.....looks like the 91's are up to bat!

jb,

Do you remember roughly what the modules cost and it sounds like they are easy to replace, did you do it yourself?

john

I keep looking for the button to push on my manual screwdrivers...if I can find one that hasn't been boogered up as a pry bar...

Two more additions.

In my case, the first four times it cutout, it started right back up. Since then it has taken a pretty long time to restart.

And although this has some relevence, I don't know if the tach needle drops the instant it cuts out, since most of the time I'm either sitting still or going pretty slow.

Hope this sheds a little more light.

john

I'm going through a similar problem with my '87 740 turbo except mine totally died. I have now come to the conclusion that it is the power state; located on the inner front fendor just above the battery, drivers side. I priced the part at a Volvo dealer it is $127. Through an independant parts house I found it for $87. I just gave them the Bosch part number which is stamped on the power stage. I priced it on Saturday but didn't make it to the parts house until after they closed. Looks like I know where I will be 1st thing tomorrow morning!

If I had to trouble shoot it again, the first clue that I would look for would be the tach moving while cranking. No tach equals no spark which limits the problem to the coil, hall sensor; which I do not believe your car has, the power stage or ignition control unit. I believe your car has an RPM senor on the bell housing which reads from the fly wheel. If the tach moves, start checking the fuel delivery.

The FAQs have several articles on trouble shooting which are excellent. Look at the section No Start Check List. Someone put alot of effort into writing a well thoughtout proceedure. The only comment I have is that the people that wrote the articles have a much high level of understanding the electronics than I do. I really had to analyze what the tests were accomplishing i.e. what did each test eliminated as a possible problem.

Good luck!

I had mine at a shop a few weeks ago, they told me that it would be much easier to diagnose if it had died completly. As it was, the mechanic keep it for twp weeks, driving it home at night, and it never cut out once on him.
As far as the tach moving while cranking, it doesn't budge at all until the engine actually starts. And most of the time it starts just fine. It's only after a cutout that it's tough to start. Maybe I should find another Volvo owner and see what theirs does when starting.

Thanks for the advice,
john

I have an 87 760T which I'm having the same problems with that you are. Extremely frustrating!! Intermittent stalling at any given time. Have replaced fuel pump relay, radio interference relay (#1323592-1), timing belt, plugs, and injector wiring harness. Still the problem exists. Last night it stalled continually and finally refused to restart at all. She spent the night cold and alone on the interstate !! Started right up this morning when I got there. Tach moves slightly while trying to crank. I'm stumped as to whether it's fuel related or electrical. I don't always hear the fuel pump motor run for a second while trying to restart. I've visually inspected the power stage and noticed 2 or 3 little pits on the aluminum side. I think I'll replace it next. Let me know what you find out please. Thanks. Susan

Susan,

One of the things that people had been asking me was whether the tach dropped to zero as soon as the engine died or did it gradually drop down due the the fact that the engine was still turning. If it dropped immediately, it was supposedly electrical. If gradual, it was supposedly fuel realated. I was never sure which mine did because it typically happened while I was at a fairly low idle (driving slow or while sitting at a stoplight/sign). When it did cutout on the highway I "think" it dropped slowly, but in ever case of a highway cutout it would restart on its own while still coasting.
So far I've replaced only the Fuel Pump Relay and the RPM(speed)Sensor and "SO FAR" it hasn't cutout again "YET". If you're tach is moving while cranking than it doesn't sound like the RPM Sensor, but who knows. After I replaced mine, the tach needle still doesn't move so I'm holding my breath. The only other things I have in mind to change next if the problem continues are the Power Stage and the Coil.
I also hear conflicting information on which parts tend to die either intermittently or all at once. It would be nice to know for sure, if that's possible.

john