Hi!
I recently bought an 850 2,4l 20v (non turbo) with 105.000 miles. I bought the car in Sacramento and drove around with it just fine until recently. I went on a road trip to Canada where the problems started.
It began on the highway at about 60 MPH on a hilly road. The motor started bucking and the RPM reader went up and down. It felt like the motor wasn't pushing for a short time and then came back. Sometimes so hard that the automatic transmission switched gears down and then up again.
My impression is that this problem occurs more likely with humid weather, for example when we drove down the pacific coast. When we came back to California and drove a bit inland where it is warm and dry the car drove as nothing ever happened before.
I first thought it could be the automatic transmission as it felt like pushing down the clutch of a manual car but concerning the weather dependence it must have to do something with the ignition / electric parts, right?
Do you have any advice which parts I should replace? The problem is I cannot reproduce the problem where I live because it just drives normal here. Maybe start with the spark plugs and/or distributor? Or can it be related to air problems so I should check the butterfly damper or sth else?

Another smaller problem is with the AC. It sometimes stops working when it is hot and I drive at slower speeds, in the city for example. On the highway with higher speeds it tends to be better. The car has ECC. I should probably check the refrigerant first, right?

 

I would replace cap rotor, plugs and wires first

 

Did you run through 'Stage 0'? If not, that's a good place to begin.

 

Ok, thanks for the advices!
I'll try the plugs, cap and rotor first. I think I'll try to clean the cap and see if that changes something.

 

Regarding the AC problem; does the radiator cooling fan come on when the AC compressor is engaged?

RE: the running issue; if the tach goes wacky could be the engine speed sensor, camshaft position sensor, or I've heard bad ABS modules can also cause this... Any problems with the ABS?

Did you say the engine problem only happened at partial load; i.e. when you gave it more throttle, it then ran better?

 

I'll check the cooling fan tomorrow and will try the broomstick test soon.

Yes, when the bucking started it would disappear when giving more throttle. I didn't get any bucking when giving full or almost full throttle.
I also noticed that the bucking stopped after giving almost full throttle. It would then run normal for the next couple of minutes even with reduced throttle.
The ABS error light came on about 2 times during the last 3000 miles but after switching the engine off and on again it was gone. Would the sensor problem be in accordance to the extreme weather dependency?

 

?? Is your AC clutch not engaging at all? Thought you said it only didn't work at slower speeds? I was just asking, with engine cold, start the car and let idle. Turn on the AC; the compressor clutch should engage and the cooling fan behind the radiator should come on (does it?).

I've never seen ignition problems go away under more load; not that a stage0 (and plug wires) shouldn't be done, if due, but don't think that's your running problem (could be wrong though..). The ABS modules on these cars have a known issue with bad solder joints; heard it can make the tach go wacky but wouldn't think it could cause an engine running problem..

It's possible but not common. Were you at elevation when it acted up? I'm thinking MAF or MAP (if at elevation) but just guessing now..

Was there a direct correlation between the tach going wacky and the engine running bad? When you sped up (and the engine started running better..) did the tach also start working properly?

 

AC:
Yes, the clutch is engadging when tested it in the morning when the motor is cold but I've read about problems when it gets hot and the gap got too big that it isn't engadging properly. Anyhow, the cooling fan didn't turn on when I switched the AC on, so I guess that's my problem. The compressor gets too hot and the overheat protection turns it off then, right?
Any advices on what to do now?

Bucking:
That's strange, I thought it could be correlated to the ignition. Doesn't the air/fuel mix gets compressed more when giving more throttle so that an ignition is more easy, even with a tiny spark?
It was on elevation between 0 (at the coast) and about 2000 feet. That's all the elveation difference I drove since it appeared.
Yes, the tach going wacky and the bucking seemed directly correlated. Yes, when speeding up the tach went normal as soon as the engine went normal.

I've heard about the ABS problems with that car but it's hard to imagine that it can affect the ignition, but who knows? Can this be repaired or does it have to be replaced? I mean I can solder, but that's probably a lot of solder points there, right?

 

The ABS is pretty easy to repair yourself, there's a great write-up to read:
http://www.matthewsvolvosite.com/for...lit=ABS+module

You can also check with Matty Moo (http://www.matthewsvolvosite.com/for...rofile&u=13052) over there who can fix it for you.

I started to do it but gave up because one of the 4 bolts was rusted pretty good and I wasn't able to pull the module - so I saved the repair for another day...

 

Yeah; ck out this thread. You likely have same issue but suggest you troubleshoot it as described in post #4.
https://volvoforums.com/forum/volvo-...ser-fan-55607/


No, much higher pressure at wide open throttle inside the combustion chamber than at idle or cruise; higher pressure requires higher voltage to jump the spark plug gap. So consequently your ignition system is under the most stress (and most likely to break down..) at wide open throttle, especially while pulling a hill.

Are you sure you're CEL is working (and not on)? The direct correlation between tach and misfire would point me to either engine speed sensor and/or cam sensor... but typically either sensor failure would set a code.

vjaneczko answered that one..

 

Thanks for the ABS thread aneczko and for the A/C thread gdog, I'll try that soon!

I can confirm that the CEL light is working. It was off after driving around for many miles with the bucking car. Then I read somewhere that I could try how the motor behaves when disconnecting the MAF sensor. I did that and logically, the CEL light turned on. It now stayed on sinced that even after reconnecting the MAF sensor.
The problem is I can't read out or reset the engine error codes with the LED OBD method as I seem to have the motronic 4.4 which doesn't give out the engine codes. I've read that I could order an USB connector and use the VOL-FCR software. Can you confirm that? Anyhow it would surely be only a faulty MAF code.
I think I'll first try new plugs and maybe have a look at the throttle valve? I've read that it could be needed to turn the screw there a bit because it tends to get hammered in after many miles? What do you think? But then it shouldn't be that much dependent on the weather, right?
Can I test if it is ignition related by putting a bucket of water on the running engine? I need to somehow simulate the bad weather because we don't have it here and the motor is running smooth ever since entering california again

 

Not familiar with the s/w; what MY is your car? Have you ckd under the hood for the pre-OBD2 DTC connector? If it's there you can read out the codes manually by monitoring the LEDs..

You can but I wouldn't do that!! Try misting the plugs wires with a spray bottle of H2O. If they're the originals I would just replace them...

 

It's a 1996 model. Unfortunately I don't have the LED and the fly wire under the hood and the OBD LED method works for ECC and cruise control but not for the engine.

Ok, then I'll rather try misting instead of the bucket.

Update:
I checked the relais and it's faulty. As soon as I tapped it the fan turned for a short time. Any hints where to get a cheap new one?
I also noticed that the compressor was cycling on and off every 10 seconds. The engine was cold, fan to min, temperature to min. This is not normal right? Maybe I should also check the freon?

 

Fcp has the relay for $35..
1993-1997 Volvo 850 Cooling Fan Relay
or you can take it apart and try to clean the contacts yourself..
and yeah, sounds like you may be low on freon too.

While at it, pick up some OEM plug wires while you're there..
1993-1997 Volvo 850 Bougicord Ignition Wire Set

 

Thanks so far and some more news.
I opened the relay and it looked clean and good. When closing the switches in the relay manually the fan went on. One is for low speed the other for high speed, right? At least it acted like that.
As I understand the big red single wire is always at 12V. So in order to activate the relays therer must be 0V (ground) at the inputs. But here's the problem I think. Both inputs were at 12V. After a while when the engine got hot one input went to 0V and activated the fan. But when the inputs are low/high they are not dedicated for A/C and engine but rather both come from the ECU, right? Any advices what I could check next?

 

From post #10 of this thread..

"Yeah; ck out this thread. You likely have same issue but suggest you troubleshoot it as described in post #4.
a/c condenser fan"

 

I did that and found out that the relay is working, so must be something else. Anyhow, I didn't know where A1,B1,B2... are supposed to be as it is not written on the relay.
I think I'll first do a recharge or bridge the low pressure switch because I've read too low pressure or a faulty switch can also lead to the fan not working properly.

Sorry to only discuss the A/C problem but as I said I can't really test the main problem (bucking) because it is running good here.

 

I bridged the low pressure switch which caused the compressor and fan to run continously. So I went to buy some freon.
I just filled in an 18 OZ r134 can. The pressure was around 20 PSI at the beginning. During recharging it went up to around 40 PSI. When the can got empty it dropped back to around 25 PSI. The compressor doesn't cycle that often now but still about 2 or 1 times per minute. Could it be leaking or do I just need another can? But is it plausible that it could still hold 20 PSI with a leak? Or should I try a freon with leakage sealing?

 

Update:
The bucking rarely appeared in the last time so I couldn't really try what would happen if I would disconnect the MAF for example.
I got my OBD2 cable though and read out the following codes with VOL-FCR:

EFI-121 Mass air flow (MAF) sensor signal
EFI-514 Engine cooling fan (FC) Low speed signal
ABS-443 Pump Motor Electrical or Mechanical fault
CI-221 Vehicle speed signal missing

I reset the codes and the CEL went away. It's still off after about 100 miles of driving since then.
I think the 1-2-1 came up because I disconnected the MAF to try how it would run. I'm going to check if any codes come up the next days and I'll have a look at the MAF connection to make sure it is OK.
Concerning the ABS fault, which pump is meant and what could I check? Or could it be the bead solder points in the ABS module to cause this error?