ok... i know i posted this in one of my other threads, but i just took it for another spin and its getting worse. any kind of bump i go over slowly the rpms drop to near 0 at the peak of the bump and then shoot back up again. this seems to be a new problem that ive never had before. i dont understand why it doesnt stall, but it seems like it should. i have a more minor form of this at idle randomly where the rpm's drop down by about 100 or so at a 700rpm idle when im at stop lights and have been driveing around for a while, but at speed bumps its alot more server. what could cause this?

 

A loose ground wire at the back of the engine...

 

i checked it after reading this and its on there pretty solid. i even checked all the ground connections with a multimeter and its all good......

 

loose fuel pick-up in the tank?

 

Can you hear the engine Dieing or do you just see it on the tach? You could have a loose connection at the Tach..

 

You may want to check for a loose part in the distributor. I had the same problem and, as I recall, it was a loose screw.

 

those are some good suggestions, if it was the fuel pump, that wouldnt surprise me..... its about the only thing i havent replaced.
yeah, i can actualy hear the engine dieing, i swear it actualy stops for half a second, it goes dead quiet and then roars back to life again. i just installed a new vacume advance canister in my distributor a few days ago and i made sure all the bolts were tight, but i will pull off the cap and check again tonight anyway. at wot its fine though, the car runs very very nice, the only time i ever have problems with this car is at idle. and now, over speed bumps is there any way to tell if my fuel pump is gona crap out soon?

 

are you sure you have your vaccuum line hooked to the carb in the right port? One has vacuum all the time , the other, only when accelerating...

 

i have one vacume line going from the timed vacume port to the vacuume advance canister, and one going from the full vacuume port to my heater control "tube".

 

do you have a PVC setup?

 

pvc? do you mean pcv? as in positive crankcase valve? if so, yes i do have a pcv valve hooked up. if not, i have no idea what a pvc is

 

LOL..PVC>>PCV LOL now thats a bunch of letters... Sorry man , just trying to narrow things down a little.

 

where is your pcv connected to(hose)?

 

i have it going from the drivers side valve cover, to the big port on the front of my edelbrock carb. its right between the timed vacume port and the full vacume port.

 

also, i have a breather on the passangerside valve cover

 

Seems all that is in order.....you have a strange situation here...Sorry I cant be of more help. I'm sure someone else will jump in here. Good Luck

 

thanks anyway, for the replys

 

Not sure what cam you have but here is another Idea.....
Long Duration Camshaft
If the engine has a fairly radical camshaft it may require an excessive amount of throttle opening for idle and/or have low idle vacuum levels. Either condition can lead to poor levels of adjustability and erratic idles.


Another fix for the above condition is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.

Measure the manifold vacuum at idle. If it is below 7" Hg, there is a good chance that the Metering Rods are in the up (rich) position. When combined with a high idle air rate this can cause the Nozzles to discharge fuel at idle. Use a weaker Step-Up Spring (see section on Step-Up calibration) to keep the Rods down at idle. With some cams, a stiffer spring (pink or silver) is necessary. Experimentation is the best way to determine which is best for your application.
The problem sure sounds like a fuel/vacuum problem...I would for sure check the fuel pressure..at least...just a thought

 

WOW...I never thought this was happening to anyone but me!

I have the same carb #1406 electric choke.

I replaced the fuel pump to electric...messed with all of the electrical system..yada yada yada....

I think I just figured it out today and it turns out I had the choke positive lead going to the battery and not an ignition source. So this meant my choke never worked really. I am not sure if you have the electric choke or not, or how you wired it, but this could be your problem. I am not sure if this was my problem either but you should check it out. I also hear that it could be caused by flodding due to the bump causing fuel slosh. The remedy for this is to lower the floats. I looked in the manual and it doesn't look that easy, instead it looks pretty easy to screw up. I am gonna wait and install some new metering rods in the carb soon and I will attempt to lower the floats a bit then.

Good luck with it...if you solve it please let me know what the prob. was!

 

yeah i was afraid i would have to screw around with the rods and jets. i havent quite figured out how to do that yet i am pretty new to carbs. i have my choke wired up to my primary fan power source wich is on when i turn the key (through a relay). and i have the ground connected to one of the choke screws. i have also heard about the float being the cause of this problem, but usualy in older cars. it does kind of sound like its flooding when i go over the speed bumps and i figure my dieseling problem probly prevents it from stalling

 

hey 330hp_91RS, did you convert from TPI to carb?

 

Hey!!! are you running any type of fuel pressure regulator? the FP in the FI cars is too high with the stock pump...your carb wants 5-7psi

 

If the same problem happens on hard braking or hard cornering, then the problem is fuel slosh and you can easily fix it by lowering the fuel level in the bowls by adjusting the floats.... maybe 1/8" lower at the full setting.

 

It doesn't really do it on corners or hard braking that much, but if I am at a stop light, and just pump the brake pedal couple of times really fast....the rpm's soot up about 500 rpm more than the regular idle. Fuel pressure is set at 5 psi= Holley red pump and 3 port reg. It seems to be the worst when the car is hot, really hot like when the fan is coming on and off. I re-routed the fuel lines so that the fuel will not boil also. It used to do it on bumps All the TIME before I tuned it with my A/F gauge, now it only does it once in a while.


Quote:
Psyte: hey 330hp_91RS, did you convert from TPI to carb?

No, Quadrajet L69 to carb. This is my 84' we are taking about. all mods are in sig.

 

change in RPM when hitting the brake pedal could be a couple of things.
one is a damaged brake booster
another is fuel slosh.

You have two symptoms that point to fuel slosh.