I've got a 1996 Volvo 960 w/2.9L engine 182K Miles. This car has one fuel pump(In-tank).
About a month ago it started occasionally having "spells" where it would sputter and/or stall when I hit the throttle but only occasionally. Between "spells" it ran PERFECTLY at any throttle setting. It had "spells" with increasing regularity. Eventually it became "cronic" to the point that it wouldn't even idle. I was stranded. When I came back to the car it started fine and I was able to limp 10 miles home as long as I didn't give it too much throttle.

I put in a new fuel filter and but the problem returned in a day. The car has progressively gotten worse to the point that it will start and idle but I can't give it much throttle or it will stall and eventually it sputters and stalls anyway. It "appeared" to be fuel starvation initially.
I've got a OBD-II device(ELM327) and previous to this problem have had a Check Engine fault with the "Air Injection Unit" but that code had been showing months and it stayed cleared a few days each time I cleared it.Since it started showing long before this problem I don't think it's related, but I'm open to being corrected.

When monitoring live data I'm seeing misfires in the cyclinders when it's sputtering/stalling and The "Closed Loop fuel system" reports an "O2 Sensor fault" but no more detail.
The only hard fault I've ever seen was in the Air Injection System I mention above. It's not come back since I cleared it at the start of my troubleshooting efforts after limping the car home.


I hooked up a fuel pressure guage...Here is what is happening:
The pressure is 42psi constant at idle - Normal.
If I give it throttle the pressure instantly goes up with it but it never makes it to 50 psi.
If I hit the throttle quick the pressure snaps up but it stalls or almost does.
If I give it throttle slowly it'll rev up to near redline and the pressure creeps up with the throttle. In anycase - too much throttle makes it stall.

It seems like anything that makes the fuel pressure flirt w/50psi causes it to stall. I mean it almost looks like there is a overpressure safety switch at 50psi. Does this make sense?

The only fuel related repairs it's had in the last 10K miles has been the fuel rail and the filter I put on it.

Thanks for any advice you guys might offer,I appreciate it...

 

Unplug the mass flow sensor and see if it idles good. It will not rev good but if it idles like a champ most likely the MAF is bad.

 

Thanks! I'll try it as soon as I get home from work today.
I would like to ask for clarification on the test procedure. It will idle fine for various periods after starting before it starts to develop a problem. I assume the proper test would be to wait till the problem includes a rough-idle and then unplug the MAF to see if it smooths out the idle?
I guess I could also unplug the MAF right away and see if the stalling problem is the same with it unplugged. That in theory would show it's not working.

Thanks again for the advice. My wife is on my butt to get her car going. I've not done any "work" on the car in her eyes because everything I've done so far has been diagnostic she wants to see some parts ordered

 

I know the feeling.
Yes if it is running crappy unplug it and see if it gets better.

 

OK - That was informative....I think.
If I unplug the MAF and start her up...She idles fine...Pretty much indefinitely. It did eventually gently slow and die after several minutes - almost as if it was just idled too low.
If I start it with the MAF plugged in - it starts acting up immediately and stalls within a minute or two - unplugging it after a stall-episode initiated didn't seem to help. It would still finish stalling...and need a certain recovery period before it would start again even with it unplugged.
If I start it unplugged and then plug it in while the motor is running the engine immediately starts stalling.


I paid attention to live data while it was running with the MAF plugged in and the MAF was showing a reading and even seemed to respond to me hitting the throttle. It also showed a stable reading w/no throttle was used. This was noted during the initial breif test period when it was running with the MAF plugged in.
Overall - the MAF appeared to be a definate negative influence.


SO - On the assumption that you or someone else will confirm that it does appear to be a bad MAF - Should I get a used w/warranty OEM Volvo one for $40 or a new AFTERMARKET for $80?

Another note - someone mentioned that it might be the sock on the fuel pump. Correct me if I'm wrong but wouldn't that have been shown on the pressure test? The pressure NEVER dropped below 40 during the whole test - even as the engine stalled.

I of course won't hold it against anyone if the MAF doesn't solve it. I'll still be WAY ahead of a repair bill. I'm looking forward solving this mystery.

 

I would try the used OEM one for $40.00.
I have a feeling it is the MAF. But I could be wrong. Also maybe try cleaning the idle motor as well.
One more thing I just thought of. With the car running use either carb or brake cleaner and spray around the intake and see if the idle changes.

I would not even consider the fuel pump at this point. The pressure would have dropped if it was the pump.

 

Ok...The MAF is on the way. I found a new Bosch for a reasonable price so I took the plunge. We will see if it does the trick.

I should start a pool...I think your "feeling" is correct. If not - at least I'll have a new MAF along with a spare.
So if the problem continues with the new MAF - where would you go next? It'll take a week or so to get it. Plenty of time for speculation

I had to get rid of a 2003 Toyota Corrolla that cost $400 a month + full coverage insurance and got the 960 w/title in hand. I'm thinking I can afford LOTS of parts to keep the 960 up before it becomes more expensive I've alread put a new AC compressor/dryer, all new brakes and assorted lights and lenses into it and did a complete fluid swap with the tranny. The previous owner did the fuel rail, radiator, alternator, battery, tires and who knows what else before selling the car to me for CHEAP.
I'm a first time Volvo owner...My other Car is a Honda Ridgeline(2006) I bought new in better times.
I can say that the car looks much newer than an 1996 inside and out...but it feels much less "new" when driving it Maybe the Ridgeline has spoiled me but I've already got 67K on it.

 

Try checking for the intake leak like I said in the post above and try cleaning the idle motor.

Hopefully it is just the MAF and thats it.

I kind of hear you on the 960 ride. I love the way the 850's ride and I think it is a ton smoother than the 960.

See if you can check for those leaks then let me know.

 

I'll do as you say tonight...but since I've got your ear: Is the "IDLE MOTOR" that air pump thingy on the passenger side of the engine that sounds like a gas-turbine when it kicks in? Is this the same thing as the "Air Injection Pump"? Is it an emissions thing or does it serve a purpose beyond making the EPA happy?

 

The Idle motor is in the induction hose just before the throttle body. It is a cylinder looking thing with 2 ports on it.

The Air pump is used to divert Hot exhaust air back into the motor to help the car warm up faster.

They are 2 totally different things.

 

It finally came in today and I popped it on....No joy...It still does basically the same thing. Maybe a slight improvement but it's hard to tell as the severity varies.

I'm wondering about that "O2 Sensor Fault" in the fuel system I see when I do the live data. It's not throwing a check engine light but does show when looking at the live data.

I've had O2 sensor problems on other vehicles but it never caused a drivability problem. Should I be looking at that more closely? Actually the only option I think I would have would be to buy another one and stick it on there to see...Correct?


Any other ideas where I could go with this?

 

It is possible it is causing the running problem I have seen that before as well.

 

Solved the problem finally.

It was one of the ignition amplifiers. Found one on ebay for $10 used for testing purposes. I took a 50/50 shot and swapped the easiest one first(front) and it runs like a dream at any temp. I'll be ordering two new ones now that I know they are known to fail at 150-180K miles(this car has 182K)


Thanks again.

 

Glad all is good now.