4AF Brake Booster problems

[corolladiy]

I have a 1988 Corolla with the 4AF engine. Everytime I am driving with some enthusiasim, I'll downshift and press on the brakes and I can hear a constant backfire through the exaust which confuses me since the timing is 20 degrees retarded.
Also, when I am idling, and pump the brake pedal my engine starts to stutter and the idle becomes extrememly choppy.
I think it's a vacuum problem but I dont knwo where I should start....

[freakinbox]

vacuum problems are FUN to find... just start looking. Found the problem on mine is a plastic spliter that screws into the intake just before cylinder 1's intake runner.... so it's sucking in tonns of air that isn't supposed to be there.

Could also be a carb issue...

Or maybe it's time to replace the plugs and the cap and wires...

The timing should be at the 10 degree mark on the plastic timing cover no?

[corolladiy]

I'll most def check that out and maybe advance my timing just a tad like you suggested to see if that helps. I already replaced the plugs, wires and cap just a couple thousand miles ago and since its backfiring, im assuming that something is catching on fire in the cylinders! just not at the right time!

Thanks a lot!

[corolladiy]

I thought having the timing at 20 degrees was best for fuel economy because more fuel is burned up?

[Ghostyman]

You can try using carb cleaner to check for vacuum leaks. Spray it around and when it gets sucked in, the engine RPM should increase. I've never done it myself but other people swear by it.

[Flashmn]

I'll downshift and press on the brakes and I can hear a constant backfire through the exaust which confuses me since the timing is 20 degrees retarded.

Well your engine shouldnt even be that retarded to begin with.... maybe you should recheck the amount of timing, I think you've made a mistake here.

[freakinbox]

At the age of our cars, replacing them one by one is a good idea, hell you could do it outside the local parts store lol

[Donald]

Have you actually seen an improvement in fuel economy with the timing retarded?

Are you experiencing backfire (through the carb) or after fire (in the exhaust pipe)?

[Flashmn]

Timing being that retarded I think its about impossible. It should be ADVANCED about 10degrees without vacuum advance IIRC. So we're talking 30degrees off in the wrong direction. Thats why I think theres a mistake here.

[freakinbox]

the car would run like garbage.

Only time I've heard of someone intentionally retarding the timing on the 4af was they took it to a guy in the gta, he did a few things to it that the guy could remember. Such as disconnect the EGR valve, couple other things he couldn't remember. In the end the guy also retarded the timing and the car could only run on Premium. Was an ae92 sedan, the guy was having flash backs looking at my motor lol.

[Donald]

Originally Posted by freakinbox

the car would run like garbage.

That is my belief also. That is why I ask if he actually has seen any benefit.

I know people who have done things like that, on someone elses advice, and never took a baseline or made an effort to verify any gain or loss.


Back to the original question corolladiy.
I think there might be a leak in the brake booster, as you seem to alresdy suspect. In addition to your timing being out.

[Flashmn]

Might not, if its actually running wiht the timing like that then it might be just that. I wouldnt judge the brake booster yet. Sort one thing at a time

[Donald]

Originally Posted by Flashmn

Might not, if its actually running wiht the timing like that then it might be just that. I wouldnt judge the brake booster yet. Sort one thing at a time

I agree.
Fix the thing that you know for sure is wrong first. The timing.

[corolladiy]

ALRIGHTY! wow that was a lot of responses! Thanks all!

In the coming week I am goign to

Redo the timing, change the oil, plugs, wires and cap, rebuild the carb...

AND I had recently replaced the wheel cylinders in the car because they were both frozen out and dragging the brakes to the smoking point in oly a few blocks...once I did that and bled the whole system with no air in it, my parking brake became extremely loose but backing up a lot hasn't even helped that out.. I'm going to check today wether I shold just replace the like because it's probably original (like half the stuff in the car lol) I think it's the cable though because only the handle is half up (and still not dragging) do I get decent braking.

[Donald]

Originally Posted by corolladiy

AND I had recently replaced the wheel cylinders in the car because they were both frozen out and dragging the brakes to the smoking point in oly a few blocks...once I did that and bled the whole system with no air in it, my parking brake became extremely loose but backing up a lot hasn't even helped that out.. I'm going to check today wether I shold just replace the like because it's probably original (like half the stuff in the car lol) I think it's the cable though because only the handle is half up (and still not dragging) do I get decent braking.

If everything is nice and loose (not gummed uo or corroded) you should be able to get your hand brake to self adjust by rolling backward slowly, and pulling the hand brake up rapidly and repeatedly. It will probably take up to 30 pulls on the hand brake depending on how much it needs adjusting.

The other way is to block the front wheels, jack a rear wheel up, let off the hand brake, stick a screwdriver into the adjuster hole in the backing plate, and while you turn the wheel by hand turn the adjuster star wheel to tighten up the slack in the brake shoes.
Tighten the adjuster until you just barely feel or hear the brake shoes dragging in the drum.
Press the brake pedal a couple of times, then go back and check the adjuster again while turning the wheel.
That will adjust up your rear brakes and your hand brake.