Hi,

I've asked about, when I pump the brake at idle, the AFR will become 14.7. Normally, its 12.5 at idle.

So I checked with the AFR monitor with re-route the ground and battery wires directly to the battery. It still shows 12.5 at idle, 14.7 when pump the brake.

I suspect the brake booster or hoses have leak. So which hoses near the brake booster normally have leakage?

 

I bet you have a bad check valve...

 

Which check valves in the system?

 

Brake booster check valve - it's inline in the hose to the brake booster. It's to prevent boost from going to the booster.

Because you can change the AFR when you pump the brakes, I think you're adding air to the intake via the booster.

It also occurred to me that you could have a tear in the brake booster diaphragm... When you step on the brakes, that tear opens up and allows extra air to get sucked into the intake (which would give you the lean condition). Changing a brake booster is no small job...

 

Got it! So I going to order one, since this is cheap part and give a try! Thx!

 

It has nothing to do with the check valve.

When you pump the brakes, you allow the volume of air in the brake booster, to enter the intake tract behind the throttle body.

That's why the AFR changes and leans out.

It happens on all the cars.


TonyG

 

Thx Tony. Well, I un-screw the AFM bypass valve trying to lean out the AFR to 14.7 at idle, the screw can't losen further and the AFR stay at 13.2 only. Also, I can hear a bit backfire when off throttle in low RPM.

So now how do I adjust the AFR at idle is, I screw the AFM bypass valve then pump the brake to see whether it reach approx 14.7. It's back to 12.5 when stop pumping. So the backfire in low PRM has gone.

Here is what I get from few adjustments.

Adjustment 1.)
-13.2 (From the highest thread on the AFM bypass valve, No brake pumping)
-15.6 (That cause the backfire at low RPM, Brake Pumping)
Adjustment 2.)
-12.5 (screw 4 turns,No brake pumping)
-15 (Brake Pumping)
Adjustment 3.)
-12.5 (screw 2 more turns,No brake pumping)
-14.9 (Brake Pumping)
Adjustment 4.)
-12.5 (2 more turns,No brake pumping)
-14.7 (Brake Pumping)

The only result is either 12.5 or 13.2 at idle, so strange T___T