nogoslo

Does anyone have an idea why my boost gauge started functioning in the negative number range?

While driving around 70 mph on a highway, I started hearing air leaking sounds. At that moment I lost most of my boost and the boost gauge started functioning abnormally. I found a clip that wasn’t tightened down enough on the y pipe and replaced it. Now, I’ve got normal boost back, but the gauge shows boost activity in the negative 20 to positive 10 range. It used to rest at 0 and go into the positive numbers on the right half of the gauge. Now it rests around –22, gets up to 0 at about 3000 rpms, then hits around 10 at full boost. (I can’t push it to max because I’m still breaking in a rebuilt engine). It’s as if the number range showing boost has stretched backward.

I’m just wondering if I should replace the gauge, or if it might be an indication of something else. It’s a ’93, sequential.

Thanks for reading/responding.

Railgun

You mean that you weren't reading vac before?

Mahjik

iTrader: (1)

Most boost gauges have a pressure and vacuum reading. The vacuum reading will appear to be negative, but it's a positive number. While cruising, you should see anywhere from 17-22 inHg on the vacuum side. As you begin to boost, the gauge should move out of vacuum toward 0 and then begin building positive boost on the pressure side of the gauge.

http://www.scuderiaciriani.com/rx7/boost_test.html

nogoslo

Thanks for the info. I'll read the scuderiaciriani page in more detail later. Something must be out of whack since the page says, "10 psi at 3000 rpm (mine is at 0 then).
No- I never had the needle moving on the left (vacuum) side of the gauge. I didn't know it was supposed to. The air leakage problem somehow made it start working! Should the needle rest at -20 when the car is not running and when idling, as mine now is?

neofreak

-20 is good vaccuum. Boost per RPM varies depending on how much throttle you give the car.

Mahjik

iTrader: (1)

This depends on load on the engine. If you go WOT (Wide Open Throttle = pedal to the floor) in 3rd gear, you have 0 boost at 3000 rpms?

nogoslo

In 3rd gear, I have about 10 boost at 3000 rpm.

RX7Wishing

Edit: i had nothing nice to say. so im editing it out for sake of argument.