Ok, so I was driving in Chicago and got to a stop light. I wanted to test the brakes so I was pumping them fast and my ari/fuel drops to 17.9 - and beyond. The engine sputters. WTH! This is probably the first car I have ever seen this on.

 

My guess is that the engine was more than likely going into dfco (decel fuel cut off) if you were in gear coasting at the time. That is again of course just a guess without more info to go on.

 

No idea about your problem, besides something being wrong with the brake booster vacuum line. On a separate note I dissected a Cyclone 4300 engine for an engineering class, ever since then I've wanted one! Good luck with your purchase

 

THanks, I'm heading toward the vac line. I was going to bleed the brakes just to make sure that I didn't have extra air in the lines so it wasnt pulling VAC when pumping.

 

I notice a change in air/fuel and fuel trims when quickly applying the brakes or pumping them as well.

It's normal. They are vacuum assisted so you are changing the airflow through the intake manifold which in turn changes the fueling as well. It takes a split second for the computer to catch the change and adjust accordingly - That's during normal brake application.

Keep pumping the brakes and it will keep changing the air/fuel ratio. The computer has to keep adjusting the fueling to compensate for the change in air.

 

Do you still have the vacuum tank hooked up? I deleted mine a while ago.

 

Yes.

But that vacuum tank has nothing to do with it. The HUGE diaphram in the brake booster itself is causing the fluctuation in the intake manifold which skews the readings. It's perfectly normal and the car goes back to normal as soon as you stop pumping the brakes.

Even coming to a stop at a light, the initial application of the brakes will cause a quick fluctuation in the a/f ratio & fuel trims but will return to normal even while holding the brake pedal while stopped.

 

yeah my car does this too lol