cblake3

iTrader: (2)

I did a search and didin't find an answer in the 30 posts I looked through.
What kind of vacuum should I be seeing at idle on a series 4 TII. I am showing 12 psi.
That seems lower than I remember.
I am trying to track down a problem with Rexy.
Every time I apply the brakes, the idle drops. If I pump the brakes at idle I can actually kill the car. The problem gets much worse with the headlights on.
I am not sure if it is a vac leak, problem with the BAC/TPS, or electrical.
Any ideas??

DaleClark

iTrader: (55)

You may have a problem with your brake booster or the brake booster's check valve. Try capping off the vacuum to the brake booster and see how the engine runs. If it does the same thing, it's an electrical problem.

12 inches of vacuum is pretty low. A good motor should pull at least 15 inches of vacuum. A tight motor is about 17-20 inches.

Also, double check your vacuum line from the gauge to the engine - if you have that cheesy nylon vacuum line that comes with the Autometer gauges, they're prone to small leaks that can affect the reading.

Dale

hugues

12 inches of vacuum is pretty low but that doesn't mean you should not have a decent idle

This is a BAC problem in my opinion.

The BAC should pump up the idle whenever anything electrical is put on your engine.

Check the BAC:
have your car idle
unplug the BAC, rpm should drop (should be an even bigger drop if electricals are on)
If nothing happens, bad BAC or bad ECU to BAC connection
If rpm drops, your BAC system is ok
[note: if ur idle rpm is set high, like 1100 rpm, you may not see this drop...I am assuming your idle is at 750 rpm,
if not, then it s a different can of worms]

What you can also do to check if ECU is sending proper signal to the BAC is monitor voltage at BAC connector. At idle, when you put on something electrical, the voltage (dc) should drop a little (like going from 10V to 9.5 when turning on the candles). If you see this, the ECU to BAC is working correctly.

What happens is that when you turn on the lights or apply brakes, the alt is harder to turn and thus the rpm drops while the throttle plates are at same position, the ecu then tells the BAC to give more air by pulsing more.

Now,
you could have 2 other problems combined with this:

1) TPS misadjusted
2) bad charging system (bad battery and/or bad alt)

The above is best to my knowledge, blah blah.

Hugues -