98 V70 AWD Slight Power Loss

Post by **rmmagow** » 06 Jun 2014, 09:28

My 219K car generally runs very well. Actually, for a while it ran super good, very slight pressure on the gas and a nice smooth delivery of power. Lately it has been feeling like there's a sort of flat spot in the engine, lack of smooth delivery of power. Not all the time though.
On the LPT engines, how much does the turbo control valve contribute to light pedal power? I.E. on slight pedal pressure does the TCV still control what's going on turbo-wise. Mileage is around 24 mpg, plugs are 50K old and Volvo. This morning it started running real good again for no particular reason I could find. The difference in power delivery is slight, mostly like the boost you feel when the car is running in damp, high humidity conditions.

Post by **jblackburn** » 06 Jun 2014, 09:41

TCV allows ECU to control the wastegate. It should command the wastegate to stay closed from roughly 2200 RPM on up until knock is encountered or until the torque target being commanded by the gas pedal is reached.

If you build up max. boost, then quickly let off the pedal entirely, do you hear a "PSH" from the turbo, or more of a fluttering sound?

Post by **rmmagow** » 06 Jun 2014, 10:04

I used to get a bad drop-off with high acceleration but that turned out to be a loose intercooler hose at the bottom on the intercooler. I'll have to get my wife to ride with me to listen for the blow-off noise, I can't really tell but then I can't hear too good anyway. It pulls very well and I can feel a pretty distinct difference between "S" and "E". I've been draining and filling the tranny too, have one more dump to go.

Post by **jblackburn** » 06 Jun 2014, 10:11

Is it by chance cooler/less humid today? Are you running 89 or 93 octane? A weather change would be more than enough to attribute to a slightly different response in acceleration - and if you're running 89 in hot weather, the car may be pulling power at a certain rev range/engine load as a result of knock.

I imagine the LPT's response is much different, but I could never stand Sport mode. It was great for aggressive driving on a nice mountain road, where you wanted it to drop 2 gears instantly when you come out of a corner and get back on the throttle, but in any other driving, I'd rather just drop one gear and let the turbo spool up and provide the torque to carry me away.

Post by **rmmagow** » 09 Jun 2014, 09:14

It gets more strange. Yeah, I know the P04xx codes for EVAP aren't supposed to affect performance but... My ongoing P0455 just up and stopped. I didn't actually do anything to fix it so I am guessing it is the purge valve sticking once in a while. After about 700 miles with "NO CODES" on the OBD reader all readiness indicators are NOT READY (sort of not worried about that yet) and no pending code at all. BUT, the car is now back to running really really good! Nice smooth power, good strong turbo feel and 24+ MPG and this is with the tranny in E not S. My guess is that the car just wants to have all systems working correctly and it will run as good as it can. I will either replace the purge valve or just let it run 'till August to finally get everything to go READY. Strange old beast. Gonna hit 220 next week.

Post by **jblackburn** » 09 Jun 2014, 09:24

Ah, but that makes sense. Fuel trim is disabled any time that the check engine light is lit or pending codes are stored.

Your car is now adjusting values away from defaults again.

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info