Can't figure out my lousy gas mileage!

Jack · Post by **Jack** » Tue Mar 21, 2006 12:58 pm

How many miles are on the engine rebuild? It might take 10-15K miles to completely break in the engine to the point where the MPG stabilizes. I've documented increasing MPG on our Volvo XC90 though to the 10-13k miles range. . . and no, the 2005 XC90 is not squirted!

jib

malloy1 · Post by **malloy1** » Tue Mar 21, 2006 1:21 pm

It was rebuilt 30-35K miles ago. For a Volvo engine, it's a freshly rebuilt engine.

I don't think the mileage issue is due to the engine being worn out. The engine has plenty of power, and doesn't use a drop of oil. But, I could do a compression check, or anything else anyone can think of?

Paul

malloy1 · Post by **malloy1** » Tue Mar 21, 2006 2:12 pm

therealpinto · Post by **therealpinto** » Tue Mar 21, 2006 10:59 pm

malloy1 wrote:i'm tempted to say that advancing more spark might be better...., but you dont control timing i understand.
-> Correct, MS is controlling fuel only. Timing is set to factory settings of 15* at idle, no vacuum.

May I chip in here? You say "no vacuum", do you mean there is a vacuum pot that's not connected, or a dizzy with no vacuum advance?

Generally I would suggest running vacuum advance, IME it helps midrange and cruise economy. Of course, the 240 ignition system may have it's own control box as well?

Another option is to let MS control spark as well, I think that's quite easy on the Volvos.

Regards

Gustaf

woh · Post by **woh** » Wed Mar 22, 2006 4:34 am

Timing is set to factory settings of 15* at idle, no vacuum

I think this is your problem. For good fuel economy, you need timing that is load sensitive (vacuum) not only rpm sensitive. At cruise the timing advance should be very high (~36Âº or more) This amount of advance is not tolerable at WOT which is what rpm only advance will be set to.

3liter914-6 · Post by **3liter914-6** » Wed Mar 22, 2006 7:09 am

therealpinto wrote:
May I chip in here? You say "no vacuum", do you mean there is a vacuum pot that's not connected, or a dizzy with no vacuum advance?f

On older distributor cars, base timing is checked and set with all vacuum advance/retard mechanisms disconnected so as not to interfere with the reading. This is what I think he's saying, not that he has or is running his dizzy purely mechanically.

That's not to say that the dizzy and timing isn't worth checking out.

3liter914-6 · Post by **3liter914-6** » Wed Mar 22, 2006 7:14 am

You might want to try talking to some of the guys on forums.turbobricks.com. They are quite a few running MS on volvos (although mostly boosted applications as the name suggests), some of their fueling and timing maps might be of help though, and there are a few NA guys MS'd there as well. Maybe even your engine (B21E?).

http://forums.turbobricks.com/forumdisplay.php?f=21

detcollector · Post by **detcollector** » Wed Mar 22, 2006 7:23 am

I haven't done any of this for over a year but:-
Looks like 2 problems to me.
We can question the wideband but i suggest you start by getting the temperatures right. Coolant at 203 looks like default for sensor failure. I'm not sure I believe your air temperature either. Both look flatlined.
The MS has to be able to move the fueling from the starting value to the switch point of the O2 sensor. Looks like your EGO correction is stuck at 100%. I can't remember what the code does and couldn't read your settings but make sure you have enought correction range and all the parameters actually turn the EGO correction on.

malloy1 · Post by **malloy1** » Wed Mar 22, 2006 8:12 am

On older distributor cars, base timing is checked and set with all vacuum advance/retard mechanisms disconnected so as not to interfere with the reading.
-> Correct, the vacuum line is disconnected when setting the timing, and reconnected. The vacuum does advance to ~ 35* at high rpm's

...i suggest you start by getting the temperatures right.
->I did check that the startup temperatures do match closely with the ambient temperatures (i.e. both sensors did read about 16*F this morning, and that closely matched the ambient temperature). They both do gradually increase over time. The AIT sensor is mounted about 6 inches from the throttle body, and I may have some heat soak going on.

Looks like your EGO correction is stuck at 100%.
->I have the EGO correction set at +/-10%, and it does fluctuate around 100%.

I did find that the LC-1 wasn't set to instantaneous, it was set to something like 1/12th sec, but I did set it back to instantaneous.

BTW-The EGO is set to 16 ignition events per step. So, it makes a correction every 4th revolution. I don't know if that is too slow, but any faster, the EGO correction is very erratic.

Paul

LT401Vette · Post by **LT401Vette** » Wed Mar 22, 2006 8:35 am

Define high RPM's?

Stock, most EFI setups are running over 40* timing at cruising speed/load. I'm with the others, I bet you have a few mpg just by getting vacuum advance back on it or letting MS run the timing.