Vacuum relative to economy?

[Andrew162]

Just thought I'd throw an idea out to see if what I'm seeing makes any sense...

Since I re-routed the vacuum lines to the way they're supposed to be working, I've found that the fuel economy seems to have picked up a bit... nothing surprisingly obvious like 400km per tank, but certainly marginally better than what I was getting.

The vacuum lines are the only things I've modified between tanks, so I want to know if it's possible that the vacuum system could possibly enhance fuel economy.


If not, then I'll go back to the wacky-weed.

[mrshin]

Hmmm... your car has a MAP sensor and maybe something else was tee'd into the sensor vacuum hose before, that was letting in a bit of air and upsetting the signal??

[Rattlehead]

I was getting good fuel economy when my vacuum hose wasn't connected to my fuel reg...or it may have been the other way around.

[Ta2272]

sounds strange has anything canged on the dial of the vacum gauge?

Jaosn

[TRAV-KE55]

It is possible, the vac lines go to sensors and swithches that control valve for various operations, perhaps the egr system was running all the time, or map sensor was getting an interuppted signal, etc etc.
An increase in economy generally means an increase in effecientcy, so you should see a little increase in vac on you boost gauge at cruise. It would only be marginal thoughand it would have to be back to back test done on same flat road, same gear, same speed yada yada yada same wind etc to really see the diffirence, otherwise the increase in fuel economy is about as good as a way of telling as any.
Trav

[Andrew162]

Thanks for all the replies guys. A bit of an old topic now, but I thought I'd revive it with some more news about what's happening.

Took it for a cruise up the North Coast over the New Year period and it got almost 500km to the tank. VERY surprising for a bizarre car like mine... I also found out that this hiccup in acceleration is vacuum-related as well. When it happens, the throttle is pushed down a bit, and the acceleration picks up then dies just as quickly... like there's a blockage in a vacuum line somewhere... however, when you release the throttle, it picks up again and eventually goes back to idle. When cruising, sometimes this happens and goes away just as quickly, but other times, it makes the car die while in motion.

I found the only thing that temporarily rectifies this problem is to disconnect the vacuum line from the TB to the MAP sensor while the car is running at idle, until the car dies because no vacuum signal is getting to the MAP anymore. Reconnect the vacuum line, start it again, and it's like it never had a problem. It revs and operates fine until the next time it feels like stuffing up again.

The circumstances for this to happen are completely random... from highway cruising to stop-start traffic, hot outside air, cold outside air, just after warm-up, when the engine's hot, etc. Anything. I was hoping someone could shed some light on this kind of incident.

[mic*]

Your MAP sensor is buggered. Standard management?

[Mr DOHC]

i remember that my mate got 5L/100k in his astra when cruising when re removed his vac advance

[Mr DOHC]

pointless, but still useful

[oldcorollas]

When it happens, the throttle is pushed down a bit, and the acceleration picks up then dies just as quickly... like there's a blockage in a vacuum line somewhere... however, when you release the throttle, it picks up again and eventually goes back to idle.

so it's runnign lean (better economy) and when you push throttle, it puts in a small amount of extra fuel for accel enrich, so it revs up, but then accel enrich stops and the revs die down again as soon as it is lean?
like you could have experience on a carby car with the old accel pump squirting in fuel

[Andrew162]

Yeah I guess that's kind of like it, but instead it's vacuum-related, not fuel-related. The last time I saw something like this happen was in my dad's old 89 TN Magna and we had a full charcoal canister, which was affecting the vacuum system.

This problem with my ride appears to be completely random though, and since I brought it back from it's trip up the north coast, it hasn't done it for a while. Just too weird...

[Andrew162]

Your MAP sensor is buggered. Standard management?

The MAP is faulty, I know this for a fact. If you move it about with the engine running, sometimes it just cuts out the engine. Faulty wire or some shit.... I've fixed it as much as I can so it doesn't move and the connectors insode are making proper contact. But I know that it's too hard to get a replacement from Toyota and costs way too much. May as well get an A'PEXi AVCR instead with it's own MAP onboard.

I'm running an A'PEXi ST205/SW20 ECU (programmable controller included).

[oldcorollas]

how different is the MAP sensor to other cars ones?
how different is it to some other options.. like the motorola ones... might look a littl ebodge, but if you can find ut the range of voltage/pressure, and find if it is absolute or relative pressure... a replacement could be found i'm almost sure...
www.digikey.com has a good range of them...

[mic*]

...and if you know that its rooted, id be trying to replace it before spending too much more time and energy looking for another problem.

If your MAP sensor was intermittently working then playing up (could be thremal expansion, humidity, how rough the road is), that would explain all the problematic symptoms you have for my liking.

[Joshstix]

If you have access to the datalogit setup for the Power FC you can replace the map sensor with anything you want and then recallibrate the curve in the computer for the new sensor.