vacuum reference on regulator

[67ragtp]

Jody,

The vacuum port Im using is the big one at the bottom of the throttle plate. Its got a small piece of hose then a vacuum "Y" fitting is connected to it, one side goes right to the MAP sensor and the other goes up to the regulator.

If it were a fuel filter limiting the pressure it would still be low when I disconnected the vacuum line from the regulator- is that right?

The under hood temp was very high, could very high fuel temps cause this?

Could I run the car with out the vacuum reference, it was tuned this way, would the idle A/F be richer with the small additional pressure running with out the vacuum line?

Thanks Rich

[camcojb]

Originally Posted by 67ragtp

Jody,

The vacuum port Im using is the big one at the bottom of the throttle plate. Its got a small piece of hose then a vacuum "Y" fitting is connected to it, one side goes right to the MAP sensor and the other goes up to the regulator.

If it were a fuel filter limiting the pressure it would still be low when I disconnected the vacuum line from the regulator- is that right?

The under hood temp was very high, could very high fuel temps cause this?

Could I run the car with out the vacuum reference, it was tuned this way, would the idle A/F be richer with the small additional pressure running with out the vacuum line?

Thanks Rich

when the fuel temp gets high enough the pump starts to cavitate and fuel pressure drops, until it won't run at all if it escalates enough. You'd know in advance if you pay attention as the pump gets louder.

If the car was tuned without it you would have thrown the idle and cruise tuning off some by adding it, unless you re-tuned for the reference line. The line would have dropped pressure in those situations.

You might try no line and see how the fuel pressure works out when the fuel temps get high. If it has the same issues (which I think it might) then you need to do something to control fuel temps.

Jody

[67ragtp]

Jody,

The car was tuned with the vacuum reference line connected, I will try it with out the line and see how it reacts.

Thanks for your help- really appreciate it- Rich

[camcojb]

Originally Posted by 67ragtp

Jody,

The car was tuned with the vacuum reference line connected, I will try it with out the line and see how it reacts.

Thanks for your help- really appreciate it- Rich

should be rich at idle and cruise without it. I read your last post as it was tuned without it, not with it.

Jody

[67ragtp]

still has me stumped, the A/F at idle goes from 14.0 down to 13.7 at idle with the vacuum hose plugged and removed from the regulator. I waited until it was dead cold and it still seems to drop to 35 psi when I hit the throttle and it takes its time to return to about 40. Both filters are clear.

This may sound nuts, but is it possible for a new engine after about 750 miles to actually improve its vacuum response at the manifold? This thing seems like its pulling more vacuum now, even my old data logs show a lower KPA value at idle. When we did the tune on the engine it had maybe 10 miles on the engine.

I pulled the hose, plugged the line and have a solid 44psi always, as soon as I can get out I will se how it runs. Is it prefered to run a vacuum reference?

Thanks Rich

[camcojb]

Originally Posted by 67ragtp

still has me stumped, the A/F at idle goes from 14.0 down to 13.7 at idle with the vacuum hose plugged and removed from the regulator. I waited until it was dead cold and it still seems to drop to 35 psi when I hit the throttle and it takes its time to return to about 40. Both filters are clear.

This may sound nuts, but is it possible for a new engine after about 750 miles to actually improve its vacuum response at the manifold? This thing seems like its pulling more vacuum now, even my old data logs show a lower KPA value at idle. When we did the tune on the engine it had maybe 10 miles on the engine.

I pulled the hose, plugged the line and have a solid 44psi always, as soon as I can get out I will se how it runs. Is it prefered to run a vacuum reference?

Thanks Rich

most prefer to run it but I've never had a problem without on a naturally aspirated setup. If your tune is made to have it I'd run it.

It could be that you're making more vacuum. If the tune improves, more timing at idle, as the engine breaks in, etc. it can and will improve. Put a gauge on it and see. I just don't remember any regulators that change the psi more than 3-5 psi. Plus, it should go up under load, not down.

What size return line on the regulator, and what pump are you running? What filter are you running before the pump?

Jody

[67ragtp]

The small piece feeding the pump is #10 into a 100micron/10 micron out and #10 all the way to the "Y" under the hood then #6 coming out of the "Y" feeding the rails and # 6 going into the regulator. The return coming out of the regulator is #6 for 30 inches(just behind the upper control arm) then increases to #8 braided line all the way back to the tank. A-1000 pump.