car was running fine, then i switched back to an auto tranny. now it seems like i have absolutly no vacuum below 1200rpms. i havent had time to put the gauges back in the a-piller so im not sure what it is yet.


what would make me lose vacuum? i've never had problems with losing brakes at idle, but i can hardly stop when the car is at low rpms.

what should i check first?

 

How does the rest of the car act? I doubt it's a case of no vacuum. Rather, I would suspect it would be a vacuum leak, if anything. As long as the pistons are moving up and down, manifold vacuum will be created, unless you have some stuck valves or something, which I doubt.

Basically, are the brakes the only thing effected? Vacuum to the booster would be the strongest at lower rpm's, when the throttle is more and more closed. Sounds like you have a mushy pedal. hav eyou tried bleeding the brakes to make sure you don't have air in the system?

 

see i thought i had a soft brake pedal at first to when i first backed the car out of the garage, but then i figured that it only happens at low speeds then i almost ruled that out. it almost seems like the vacuum advance dist. isnt working right.

i will try to run some tests tonight, and see what it actually is doing. the brakes and dist. are the only vacuum assisted accesories on my car. im thinking that i have a vacuum leak some place

 

If there was a vacuum leak, the engine would run rough. If it doesn't run rough, i doubt you have a vacuum leak. Vacuum can't leak out. It can only draw extra air in. That unmetered air throws off the balance set by the ECM, assuming EFI.

So, if the car is running ok, then unmetered air isn't getting in, in turn, I doubt you have a leak. Perhaps a bad MC or brake lines.

 

well i got the interior put together and took the car for a drive. i have a maximum of 4 inches of vacuum. wtf? i used to have 14. its a steady 4", but i can hardly stop the car with that. also at the same time, when i get on throttle more then normal the engine goes extremly lean (pegs the a/f gauge). that means that there isnt enough vacuum to advance the distributor right?

can anyone shed some light on this for me? what can i look for. the car runs awesome at idle, doesnt surge or anything, but just doesnt have the power that it used to off idle. could i have a stuck valve?....but then wouldnt the vacuum flutter back and forth?

 

Sounds to me like your timing is WAY retarded.

Just try advancing it and see what happens. Screw what the mark says; the engine doesn't look at the mark, read the number, and decide how to run accordingly. It will run its best at whatever timing it runs best at, regardless of what the "mark" reads. Just give the engine what it wants, and don't bother with what the "mark" says, or what you think the "number" "should" or "shouldn't" be.

A/F going lean has nothing directly to do with distributor advance. And besides, when you "get on teh throttle", any and all vacuum advance should disappear anyway, so it's not an issue.

I seriously doubt that a vacuum leak is the problem to your symptoms; unless it's really really MASSIVE, like the PCV fitting not hooked up or something drastic like that. And also remember, when your vacuum is low (throttles wide open at low RPM) the vacuum will be low no matter what, and when the vacuum is low, a vacuum leak has virtually no effect, because little or no air will be getting sucked in through it (there being no suction). Therefore, a vacuum leak will have NO EFFECT on WOT performance, even though it will HUGELY affect idle and cruise, when vacuum is high.

I'm assuming of course that you have a distributor with mechanical and vacuum advance in it, and that you've already tuned its centrifugal (RPM based) advance for best engine performance.

 

did you pull the dist when you swapped trannys? Sounds like your timing is way off....

edit RB beat me to it with a much better post. Ignore me.

 

i will play with the timing when i get home from work tonight

it only has 4" of vacuum at idle even(why i cant hold the car with the brakes hardly) do you think i can make up for the lost 10" of vacuum with just timing? i have a msd billet dist. that i played with springs until the car "felt" the best. is that the right way to adjust centrifugal advance? but that was back when i still had the 5 speed tranny though.....