Got a good one going on with our 95 850 Turbo sedan with 196K. I think we have a turbo overboost problem. The car starts and runs normally, idles fine, and overall drives great. Today, under moderate acceleration, the boost started coming on stronger than usual, and builds smoothly, but quite a bit faster. Get on it a bit more (Like if you were in a hurry to pass someone) and the turbo takes off! It will peg the dash gauge needle (I know, it is not very accurate) then the boost will cut out and the car will bog and lose about 500 RPM. Stay on it and it will repeat the cycle (boost like hell, cut out, boost like hell, cut out) until you back off on the accelerator.

No check engine light, but I pulled the codes and got a 4-1-4 out of socket A2 (Turbo boost pressure too high) When I reset the code, I hear a low bzzzt/hisss sound come from the top of the motor for about 2 seconds. Code comes right back if you get on it hard and cause the boost/cut out cycle. Reset the code and you get the bzzzt/hiss again.

Overall, no weird sounds, lights, smells, etc... Car runs great except for wanting to boost like crazy when you get on it. I can drive it without using the turbo too much, and it is fine, but what fun is that!

I did a search but no luck. What do you think, wastegate issue, boost control valve,????

If anyone has had this before or can give me a good place to start looking......

Glenn

 

check the hoses going to the TCV and from theTCV to the wastegate. might be a leaky hose.

tech, the man with the plan, should be able to help.

 

Until Tech comes back. This is a procedure for 4-1-4. The buzzing noise upon clearing the code, as far as I know, is normal as my 850 used to do the same.

This procedure seems to require a couple of special equipment.

Code 4-1-4 (Charge Pressure Control)
1) Turn ignition on. Leave MAF sensor connected. Connect
voltmeter between MAF sensor connector terminals No. 2 and 4. If
voltmeter reads .1-.2 volt, go to step 3). If voltmeter does not read
.1-.2 volt, go to next step.
2) Turn ignition off. Ensure MAF sensor and ECM connector
terminals are clean and tight. Repair as necessary. Reconnect
connectors. Turn ignition on. Connect voltmeter between MAF sensor
connector terminals No. 2 and 4. If voltmeter reads .1-.2 volt, source
of code was poor contact in MAF or ECM connector terminals. If
voltmeter does not read .1-.2 volt, retest using new MAF sensor.
3) Turn ignition off. Connect breakout box and check grounds.
See COMPUTERIZED ENGINE CONTROLS in I - SYSTEM/COMPONENT TESTS
article. Disconnect ECM. Turn ignition on. Connect voltmeter between
breakout box pin No. 42 and ground. If battery voltage is present, go
to next step. If battery voltage is not present, check wiring between
ECM terminal B42 and Transmission Control Module (TCM) terminal B1 for
an intermittent fault.
4) Turn ignition off. Check Turbocharger (TC) control valve
and ECM connector for contact resistance or poor contact. Repair as
necessary. Reconnect TC control valve and ECM connectors. Turn
ignition on. Using Volvo scan tool in Diagnostic Test Mode (DTM) No.
3, check that TC control valve ticks. If TC control valve ticks, go to
next step. If TC control valve does not tick, retest using new TC
control valve.
5) Turn ignition off. Check hoses between TC and TC control
valve, and hose between TC control valve and pressure servo for
wastegate valve for obstruction or kinks. Also check that TC control
valve is not blocked between Red and Yellow connectors when valve is
activated. Valve should be open between Red and Yellow connectors when
not activated. If hoses and TC control valve are okay, go to next
step. If hoses and/or TC control valve are blocked, repair as
necessary.
6) Turn ignition off. Remove hose from pressure servo.
Connect Manometer (999-5230) and Pressure Tester (998-5496) to
pressure servo. Pump up pressure to about 46.6 psi. If pressure servo
fully opens, check pressure servo setting. See procedures in the
I - SYSTEM/COMPONENT TESTS article. Replace wastegate valve pressure
servo. If pressure servo is not okay, retest with a new pressure
servo. Replace wastegate valve pressure servo.


JPN

 

Gents, I appreciate the starting point. Right now my manuals are packed as we are going to be moving to a new house in the next couple of weeks. If you happen to have any pics or location for the TCV, TCV hoses, and wastegate, I would be appreciative. Right now we are having a snow/rain storm type of day, so I doubt I will be looking too much at the car today, but tomorrow is a different day!!

Thanks

 

 

TIPSP

Many thanks for the GREAT diagram!!!

The rain/snow let up for a few minutes today and I was able to do a couple of quick checks I looked at the vacuumhoses going to the turbo and they look fine, and the connections to the MAF look good too, but I may have found an issue. I moved the pressure regulator rod by hand to see if it was free and it was, but when I let it go, it moved back but did so quickly and a small hiss of escaping air came from the regulator. Almost sounded like a leaky diaphragm in the pressure regulator. I was able to repeat this every time I moved the rod.

I went over to the wife's 01 XC 70 and moved the pressure regulator rod by hand on hers, and it moved freely as well, but each time when I let it go, it moved back slowly and without the hiss of air.

I'm thinking the pressure regulator on the 850 is bad for the above reason.

What do you think?

 

Sounds like the waste gate is leaking. Do you have some kind of setup that you can add pressure to the waste gate valve? If so then try that and it is does not move then you know it is the wastegate valve.

 

Hmmm, I have a hand vacuum pump , but that adds vacuum not pressure. I could try my hand tire pump. It has an adapter for a small hose fitting. I will try that today.

Thanks

Glenn

 

Sounds like a plan let us know what happens.

 

Will do. It is still snowing/raining here, so....

If it does turn out to be the wastegate valve, do you know where I could find one besdies a dealer? I looked at all the usual palaces (Groton, IPD, Myswedishparts, etc...) and no one lists them.

Glenn

 

Maybe try to find a used one for now.

 

Quick question. WHen I get a chance I want to swap the turbo control valve (the vacuum operated solnoid valve with the three vacuum hoses going to it) from the wife's 01 XC 70 to the 95 850 to eliminate it as a cause of the boost issue. Are these parts identical or are they different because of model/year/etc...?

Also, from looking at it, the valve is located near the air filter box on both cars, am I correct about that?

Thanks,

Glenn

 

I think they are different electronically.

 

Just an update, I have a friend who has a 95 850 who will be coimng over this weekend. We are going to swap over his turbo control valve (which is working fine) to our car to see if that heps. I figure it cannot hurt. Just the same, besides making sure I mark the threee vacuum lines to be sure they go the right way, is there any hidden gotcha's I should know about. It looks like a pretty straight forward swap.

 

It's straight foward.

 

Hi TIPSP,

Would really appreciate if you could also share the TCV and all the hoses diagrams for
S60T5 simillar to what you have just shared for 850. Thanks.

 

Just an update. We FINALLY got time to swap the boost controller and it worked. I now have a new one in there (took 15 munutes tops to install) and the cars works fine now.

Glenn

 

Nice!

 

Glad all is good.

 

TIPSP thanks very much for posting the parts book turbo vacuum lines. I have an 850 with overboost I just bought cheap and the lines are all messed up. Now I see why there is overboost!