I got this car a few weeks ago from the original owner. Just 140k miles and well-maintained, it's a great little car. But a week or so after I got it it stalled as I was driving down the road. Since then it has stalled once or twice a week. If I wait a few moments I am able to get it back running again.

I saw a page by a Volvo guy called Dave Barton saying he had this problem and changed a couple of relays - one for the fuel pump and one called the 'radio noise suppression' relay and the problem went away. I went to buy the fuel pump relay but the guy at my Auto Zone told me that it couldn't be the problem. He said if the fuel pump relay was bad the car wouldn't run sometimes and then stall and then run again. So now I'm back at square one.

Anyone heard of this problem?

 

I should add that I pulled a check engine code of 1-4-4 which says 'no load from fuel injection relay', which is how I got thinking the relay might be the problem. But maybe something else can cause that(?)

 

there's a 'radio suppression relay' under the hood on 740/940's. this relay powers the fuel injectors and idle air controller valve. if it has problems, your engine stops. I'd swap yours with another 7/9 and see if the problems swap too, then you know its a bad one.

I don't like or trust cheap generic relays, so much of them are chinese junk now. the real Volvo relays are made by Stribel (logo is an S in a circle with two curve lines like )(

see Volvo Relays for the details on this 'radio suppression relay'

 

Wow, so it actually could be the radio noise suppression relay. I read that it was a possibility but thought it sounded too minor to be the culprit. I'll get a new one - a real one - and see if that does the trick. Thanks.

 

the name is confusing, for sure.

the 240 originally used a double relay, one half powered the ECU and injectors, and the other half powers the fuel pumps. on the 240's, the relays were scattered all over the place behind the dash, the fuel injection+pump relay is behind the glovebox.

when they designed the 740, they centralized all the relays in a panel forward of the ashtray, which put them directly under the relay. the electrical noise of the injector pulses got into the radio, especially on AM. so they added a 3rd relay under the hood thats turned on by the ECU half of the main fuel injection/pump relay, and powered the injectors off this so the high current pulses would stay far away from the dashboard, hence the name Radio Suppression Relay.

 

Most likely, Crank Position Sensor.

 

Aw crap.

I was just becoming convinced that the radio suppression relay was the problem, and now I get a second suggestion. Well that stinks.

Mind elaborating?

 

Word of mouth diagnosis is certainly a hit and miss proposition but the symptoms you describe most often are caused by a bad CPS. Then FI relay, etc. Not that it couldn't be any of many other things.

 

well, the radio relay can easily be tested. unplug an injector, key on, and there should be +12V on one of the pins of the injector plug (the other pin will be 'floating' so not have any consistent voltage on it). if not, the radio relay isn't supplying that power, which either means its a bad relay, or its not being told to switch on... to check if the ECU is being switched on, verify you can get error code 1-1-1 (normal) out of the diag box in jumper 2.

the CPS, the standard failure mode, which most often leaves it erratic, is the insulation on its cable disintegrates, hiding back there behind the head baking in the heat. a visual inspection will tell you if its bad.

if it looks like this, whooops!

 

I wouldn't go by looks alone. I have seen them look all pretty but do just this "now and then" stalling. I guess they heat up, resistance changes? Don't know how to test them, best to replace with a good one and see what happens.

 

Would a bad CPS throw a 1-4-4 code as stated in the second post? Given that code, I would still suspect the radio supression relay. You can try re-soldering the joints in the relay if you have a soldering iron. Typically the solder joints crack over time due to vibration and cause intermittent connections. Just pop the top off of the relay and inspect the circuit board. Touch up any joints that show signs of cracking.

When the CPS starts to go bad, usually you get intermittent stalling after the engine warms up. If it gets to the point shown in Pierces picture you'll have a hard failure. I would inspect the CPS and only replace it if it has cracked and flaking insulation.

 

Alright guys, thanks. Think I'll just change both and see if it stops happening.

 

Oh didn't see your post, but good point. That code did seem to indicate a fuel injection issue which would seem(?) to point to a relay as being more likely. I'll do that one first.

By the by, I've worked the last 20 days straight trying to finish a project, which is why I haven't had to time fiddle with the car. I have been able to steal away a few moments here and there to do this research, which has been very helpful. Tomorrow, finally a day off

 

I am new to this forum, so first of all: "Hi"

I also have a 92 740 Turbo with the intermittent stalling problem.
I at this point would refer to it as "The curse"....

How it stalls:
It all started when I'd go 60mph on the highway and hit traffic. After slowing down quickly the car chokes and has no power when I want to accelerate again. Flooring it sometimes help, sometimes it doesn't. Car will usually restart after 2-5 minutes and drive ok.
Lately it stalled after driving ~1hr on the highway, on the first traffic light after the highway. The light is on a hill with a curve.
Down the road is a stop sign (with a hill and a curve), the car stalled twice in a row exactly at the same spot.

What I've done / checked / replaced so far:
- Fuel Injection Relay replaced
- Radio Suppression Relay replaced
- Crank Shaft Sensor (RPM relay?) replaced
- MAF checked
- Idle Air Control Valve checked
- Vacuum hoses checked, some replaced
- Ignition Control Module (Power Stage) replaced
- Break Booster check valve replaced

Car is still stalling. Great!

I've a distributor cap and new rotor ready, but not yet installed.

Sooooo:
I am willing to do one last attempt, I need this car, and I don't want to give up. But it's getting pretty annoying.

My next step would be fuel delivery: Pre-pump, Main Fuel pump, Fuel Pressure regulator and seal, fuel pump check valve and pre-pump filter sock.
For good measure the fuel sending unit?

Could be the ECU?

Any advice appreciated!

Thanks!

 

could be the turbo air path. my 92 740T had all kinda weird running symptoms when the big elbow hose that goes between the MAF and the turbo air intake got squishy on the bottom (turbo) side. make sure there's no leaks on any those big air pipes or the intercooler

re: idle air controller...
start and warm up the engine, shut everything off (ac, lights)... if you unplug the idle air controller, the engine idle should be about 500 rpm, while plugged in, it should be about 700 rpm and quite steady. also, there's a test called "DTM 3" with the diagnostic box by the left strut tower which will cycle the IAC on/off/on/off, so if you hook up a piece of clean vinyl hose, and blow gently through it, you should feel it go on/off/on/off.

see, Engine and OBD Diagnostic Codes and read the sections on DTM 3 in jumper 2... note it also tests the electric fans, and other actuators, so be careful.

 

Thanks Pierce,

what are you thinking of my fuel delivery theory.

That hill + curve makes me think clogged filter sock?

I'll definitely check the turbo air path!

 

it could be the transfer pump and/or sock and/or pickup hose, especially if it does it mostly with a low gas tank, but is fine above 1/2 tank. a bad transfer (tank) pump can also make the main pump noisier, as it has to work extra hard. my experiences with main pumps is when they fail, the car won't start, but once its running, they usually keep going.

re: the fuel pressure regulator, *usually* they fail via the diagraphm leaking, and when that happens gas comes out the vacuum port on the back of the regulator. unplug the vacuum hose from it, start the car, is fuel squirting or dribbling out? (KILL THE ENGINE QUICK IF IT IS!).

 

Thank you!
Truly appreciate it!

One of the mechanics at my garage, mentioned that he would hear a very subtle noise from the pre-pump...I can't hear anything, but that doesn't mean much.

I think that's what I'll try next.

thanks again!

For what it's worth:
I had ongoing problems with my speedometer, that I could not get fixed, replaced the instrument cluster and what not, nothing would help.

Since I've the new ignition control module, the speedometer works fine again...

 

huh. the speedo isn't connected to the ICU in any fashion.

 

Yup. You are right.
This morning I drove the car to the shop (to get the fuel pumps done)
And speedo is dead again...
Must have been a coincidence, that it worked after I put in the ICM.

It is also raining like crazy here on the East Coast, and the speedo clearly doesn't like that.