1998 XC70 poor mileage after ~stage 0

ilovemud · Post by **ilovemud** » 17 Nov 2014, 18:10

So I recently did most of the items that constitute a stage 0. My car had been throwing all kinds of codes, evap problems, misfire, etc. So I did the wires, plugs (Volvo), distributor, full pcv, oil change/filter, new injector seals and a new air filter. Everything is behaving correctly and the car is driving pretty well.

Since I fired things back up I have been getting pretty bad gas mileage and I did notice that the exhaust was a little sulfury. There are no codes.

Thanks for any help.

Post by **dosbricks** » 17 Nov 2014, 19:11

Welcome to the forum, mud

Since you did the PCV, check for a vacuum leak at the manifold or the vacuum lines in the general area. An air leak may be causing the ECM to richen the mixture.

ilovemud · Post by **ilovemud** » 17 Nov 2014, 19:22

Thanks, happy to be here. I am not new to Volvos but new to working on this one mostly myself. My wife said I needed a hobby and I suggested that I could work on (my) car when I told her the dealer was going to want over 1000 to fix the ABS unit. I bet the PCV fix would be up there as well. The fact that it started up and drives well earned me a lot of capital. Eventually I may even be able to convince her that I can do the brakes, too. My work involves a lot of plumbing high pressure gases and high vacuum systems so I figured I could handle a Volvo. What a bowl of spaghetti that thing is...geez. I am still learning what all of the tubes are. There is a series of tubes with what looks like little check valves and filters...should I change those too?

I should probably go in and check the tightness of the various vacuum lines after they have warmed up. I also did not clean the PTC and after looking at some of the older posts here it is clear I need to do that as well.

Post by **Ozark Lee** » 17 Nov 2014, 21:33

After big changes in the system it will take a bit of time for the ECU to reset the adaptives. You can hasten that process by removing a battery cable for a few minutes (You will need your radio code). Wiping the memory in the ECU will reset all of the starting trim levels to their center range and it will learn from there which is often quicker than having it re-learn from a pre tune-up point to a post tune-up point. During the learning period (several hundred miles - a couple of tanks of gas) the mileage will typically be terrible.

...Lee

ilovemud · Post by **ilovemud** » 18 Nov 2014, 14:58

Thanks Lee, I could not find anything that was loose so I will stick with it and hope things work their way out. I did do a lot to the car.

Post by **rspi** » 18 Nov 2014, 17:45

Make sure you installed plugs for the turbo car and not the na car. Sometimes the dealers sell the na plugs because they are cheaper.

Also, how old is the thermostat? Is the car warming up good? I know temps there have plummeted so, that may be effecting your mileage a little. What kind of mileage are you getting?

ilovemud · Post by **ilovemud** » 18 Nov 2014, 18:41

I got the plugs from IPD so I hope they are right. I inputted my details for the car correctly and torqued them down correctly. I can probably look at my order and check the pn.

The car warms up fine and is solid. My ambient air temp reads really low. I replaced it when I did all of this other work but the temp was still about 20 F low. I replaced the sensor on the right side under the bumper. Then I discovered another one on the drivers side but I only had the one new sensor and could not find the other one...must have chucked it.

I am getting around 10-12 around town driving. I would expect a little better than that.

Also no evidence for leaking or gas smells.

Yep it is coooold here but at least I don't live in Buffalo or Watertown, they are getting destroyed with lake effect snows.