96 850 Turbo Low power after half throttle

T64me · Post by **T64me** » 10 Oct 2014, 17:34

I recently purchased a 96 Volvo 850 Turbo with 166,xxx miles. I bought it real cheap because it did not run well. At first it would not get above 30 MPH. I just completed a full tune up (fuel filter, spark plugs, cap, rotor, spark plug wires and air filter). The car runs much better now. Codes are cleared (had misfire codes before). However, when I press the pedal more than half way down, the engine starts to stumble. When in park the car revs fine - sounds good. It just does not have power when driving - especially after half throttle.

Anyone have any ideas?

Post by **tryingbe** » 10 Oct 2014, 17:51

I know you said

Hoses and clamps look intact/tight.

Did you take off every hose to check for tear?

T64me · Post by **T64me** » 10 Oct 2014, 17:55

Tryingbe, you are awesome!!!! Thanks, I will take a closer look. I can't thank you enough for the fantastic post!

T64me · Post by **T64me** » 10 Oct 2014, 20:59

Tonight I followed tryingbe's advice. I removed all of the intercooler hoses then cleaned and inspected them. I reinstalled them. The car seems a little better, but it is clearly not performing as a 850 Turbo should. It will make it to 50 miles an hour now, but it still does not like to go past half throttle. There is no check engine light. The factory boost gauge needle just barely gets into the white area. Any suggestions would be appreciated.

Post by **scot850** » 10 Oct 2014, 21:53

I'm having similar issues, where my car seems to run out of boost above 50kph. I have changed the TPS which was a Volvo part and it is known to slowly degade which prevents the turbo from being able to raise boost. Also check the 3 pipes that lead to it as they degrade and crack with age losing pressure or vaccuum. This prevents the TPS fromallowing boost also. Another fail point is the turbo compressor boost valve (CBV). This has a diaphram which can split with age, again reducing boost pressure at higher boosts. I am waiting to get the boost pressure profile checked to see if the CBV s holding pressure. My car runs Rica software and runs upto 17psi, so this is critical . I'm also waiting to have the fuel pressure checked before and after the fuel filter is changed to make sure it is fueling ok. There is another boost pressure measuring sensor on my car in the pipe leading from the intercooler to the throttle body which I understand verifies what boost is getting to the ETM. Not sure if/where the 850 has one of these.
Finally these cars are very fickle what electrical ignition parts thy use. Use Bosch for rotor and distributor cap, Bougicorg wires and I only use Volvo turbo plugs. Other guys recommend other brands but I stick to what I know works.

Then you can check all the pipes and parts in the evap. system for leaks and function.

Hope this helps.

Neil.

T64me · Post by **T64me** » 10 Oct 2014, 22:15

Thanks for the input Neil. I will replace the vacuum lines leading to the TPS tomorrow.

Does anyone know if there is any way to test the TPS or the CBV to see if they are faulty?

I will also check the fuel pressure at the fuel rail. I think I have heard that is should be about 44 PSI. Is that accurate?

Any additional suggestions would be appreciated.

T64me · Post by **T64me** » 11 Oct 2014, 12:17

I just checked the fuel pressure at the rail and found it to be 10 psi. As the car was running, it slowly crept up to 20 psi where it leveled off.

https://www.dropbox.com/s/v681awyhg6j91 ... 5.jpg?dl=0

I am not sure if it matters, but the fuel pressure gauge I rented did not have a fitting for the Volvo fuel rail so I had to connect to it like this:

https://www.dropbox.com/s/udq35yrxxrwlz ... 7.jpg?dl=0

I had always thought fuel pumps were either good or they did not work. Is it possible that the fuel sock on the pump is plugged and only allowing half as much pressure as it should have?

I also noticed that by the time I turned off the car and returned to the fuel pressure gauge under the hood, the pressure had dropped back to 0. I would have thought the system would have held pressure for a while. This is not the case with this car.

I would be interested in feedback from others - do you think this is what is causing the car to not have power above half throttle (fuel starvation)?

Thanks in advance for constructive input.

Post by **tryingbe** » 11 Oct 2014, 16:40

Fuel pressure should be around near 43psi.

I'd start by testing the voltage at the pump, if it is near 12 volt, I'd replaced the fuel pump and fuel filter.

http://www.volvotips.com/index.php/850- ... ce-manual/

Post by **rspi** » 11 Oct 2014, 17:36

I tried to post to this tread before and the website collapsed on me. My guess would have been a clogged catalyst converter, but since you found low fuel pressure, check that out further.

Post by **scot850** » 11 Oct 2014, 20:09

The fuel pressure should be 43psi as said, but there is also pressure drop rate and time if the the system is is in good shape. Don't know th3 specs but hopefully some who does will chime in, or check some old posts on fuel pressure issues

Change the fuel filter first before worrying about the fuel pump. Check the pressure again after changing the fuel filter. I think there is also a check valve in the system to help maintain pressure. This is the path I plan to follow also.

Hopefully this means you are getting some progress! Good luck.

Neil.