Tehsocks

Hey guys, ive been trying to figure out how to fix this problem but I just dont know whats left.

Basically if the car is fully warmed up and good to go. If i floor it from a stop i will get to about 45-50mph and it will STOP ACCELERATING, make and just STAY at the rpm its doing. If i have a rolling start (20mph ish) and i floor it i can usually make it to about 65-70mph.

I have tried 2 different quadrajet carbs, I have put a new cat on there, Completely new exhaust, Plugs, wires, fuel and air filters, open element air cleaner, cap and rotor, got the timing adjusted right, and a new fuel pump. NOTHING seems to even help this or make it worse. These things have made the car run nicer and faster even, but it will STILL just STOP ACCELERATING?

I always thought it was the carb, so after getting a carb off of an 84 firebird that was good to go (owner upgraded to an edelbrock) the problem STILL EXISTS!

It feels like its running out of fuel in the bowl, but it cant be, the fuel pump flows plenty enough.... Anyone have any idea's?

The car is an 85 Z28 with an LG4 (NON COMPUTER CONTROLLED)

Thanks

camarito

is the throttle cable opening the carb to full throttle?
Some times the pedal goes to the floor and the carb still not fully open

Tehsocks

Yeah, ive checked that. And this is also a very ovbious and obnoxious thing.

Just imagine flooring your car, you feel the pull then it stops accelerating suddenly. unless you let off for a couple seconds then try again.

camarito

strange did you check how the timing advances with the rpm? it could be a distributor problem

Tehsocks

Yes timing does advance with RPM. i thought it might be centrifigul weight related too. but it has no issues through all the rpm's of 1st gear. Its a load issue, its worse on hills. but timing is ok as far as i can tell.

Damon

Sounds to me like either the fuel system isn't keeping up (fuel pump, clogged filter) or the converter is plugged up.

Does it go like a bat-outta-heck and then just "hit al wall" (usually indicated a fuel delivery deficiency) or does it just not have much to give from the instant you put the pedal down (usually indicating an exhaust restriction or severely retarded timing).

Also, does it surge, hesitate or "pop" when you encounter the problem?

Tehsocks

When i first step on it, it bogs for a second(what i understand to be normal for a quadrajet) then goes like a bat outta hell till about 45-50mph, then it just falls flat on its face and just stays doing whatever speed it stopped at, and if you keep it floored for long enough it starts slowing down...

unless you let off for a couple seconds, then give it more gas. Its not RPM related, its engine LOAD related. Hills make this problem even worse.

But ive gone through 5 fuel filters, a fuel pump and a carb. I remember reading in my GM service manual that there was a fuel flow test to see if the fuel system was delivering enough fuel. Bascially put the fuel line in a clear bottle and measure it, and it made almost half a liter of fuel with 4 engine rotations, (which was plenty ovbiously lol)

Im thinking maybe its vacuum advance related. But why would it work for so long then STOP not work at all....

AnotherfastIROC

Is you motor Computer controlled or mechanical carb and Dizzy?

Damon

Did you change out the fliter in the nose of the carb? They get dirty from the INSIDE so you can't tell if they're plugged up just lookng at the outside.

THat is almost certainly a fuel-related problem.

Pat1990GTA

A good thing to do is a fuel volume check. Basically you just take the line off the front of the carb and use a beaker to see how much fuel comes out after cranking a certain amount of time. I cant recall the specs so you will have to look them up. Also look for air bubbles (aeration) in the beaker when the fuel is coming out

Could is also be a ignition coil breaking down when is has to work to hard?

acliad

iTrader: (1)

Someone will have to confirm this, but I believe there is a sock filter on the sending unit in the fuel tank. I had a similar thing happening on mine, and what I did was take the fuel cap off and blew air, in intervals, through the fuel delivery line. Obviously the right way to do it would be to drop the tank, take out the sending unit, and clean or replace the sock filter.

Mine hasn't done it since, but I haven't drove it very much either so I'm still waiting to see if it's going to do it again.

Tehsocks

I have tried a fuel volume test and I had more than enough. Also I don't think it could be the coil because I can hold steady 4000rpm in park for as long as I want

And its mechanical. No computer

acliad

iTrader: (1)

Same thing with mine, the lack of fuel wouldn't show up until I put a load on it. Have you tried doing the fuel volume test after the problem occurs?

If we assume it is fuel related, the problem should be before the carb (assuming at least one you tried was good). There would have to be some sort of restriction in the line. That leaves bad fuel pump, some sort of line restriction, or plugged fuel filter. Can you blow through the fuel line?

I had a clear in-line fuel filter and I could tell the difference between before it started to run out of fuel and after. If I just let it rev in park it wouldn't run out, but after I put a load on it the filter was empty.

88camaroscv6

iTrader: (1)

if your fuel tank is rusty it could be clogging the in-tank fuel pump sock

redneckjoe

just a few shots in the dark,... pinched fuel line? choke issues? verify initial and total timing,... vaccuum leaks? i agree that it kinda sounds like a fuel problem. your bog can probably be cured with an accelerator pump arm adjustment and a secondary spring adjustment. you could put some fresh plugs in it and run it hard down the road til it messes up,...shut it off and do a quick plug reading. might give you some info?

91CamaroRS/SS

Heres another shot in the dark. When I had the 3.1 in and lets say I was getting on the highway from a stoplight, it would run like the v6 should up till about 45-50, but it was in 3rd gear and had a hard time going to overdrive untill you let off the gas a little, pull some more, then go into OD. If you dont give it WOT does it climb all the way through the gears with no hesitation?

Tehsocks

Almost, Its all dependant on load, Accelerating at half throttle up a hill, it will cut out if i need to go fast enough and the hill is steep enough. WOT just makes the problem easy to explain and easy to test.

And how would i measure fuel flow at load? Like i said i have to be doing like a good 45mph before it will do this, that might be tricky. and i imagine after the problem occurs fuel volume would be fine. If i let off the gas for about 3 seconds, shes good to go again.

Ill double check the timing today and let you guys know where shes at.

Apeiron

You don't have to measure it at load, fuel flow is independent of load.

Ajaxzem

iTrader: (1)

I had the same exact problem with my car when i first got it. It drove me crazy. Mine ended up being the little filter in the neck of the carb where the fuel line connects. I know you said you had tried switching carbs so that kinda rules that out, but i would double check just in case. You can have all the fuel delivery in the world to the carb but if its clogged right there it won't matter if its 100psi or 1. I took my filter out and ran one inline between the pump and the carb for a day. At that time the hesitation stopped and it would pull to any speed easily. I pulled the filter off after that first day and blew it out. I couldn't believe the stuff that came out. I did this for a few days until the filter no longer collected debris. Not i check or replace the filter monthly.

84_Cruiser

The same exact thing happens to me. I have a bone stock, unrestored 84 Caprice with a 305 and an electronically metered quadrajet. At WOT it will rev up to 3500 or 4000 depending on which gear im in and then it will stop accelerating. I found that if I feather it a little there is a "sweet spot" where the engine pulls really hard just before my foot is all the way on the floor. Once I feather it then it will shift into the next gear and keep accelerating. As far as I can tell its just a quirk that the quadrajet has.

Instead of taking your foot completely off the throttle and then mashing it again, when it stops pull your foot back just a little bit, also, if you have your foot a little bit off the floor the whole time the engine will probably accelerate faster through the whole RPM range. Works on my car.

JLCustomizing

I'm having the same problem. I just had my quadrajet rebuilt with cliffs kit, replaced the fuel pump, fuel filter, and have new fuel lines under the hood. It flies up to 45mph then just hits a brick wall. Its a mechanical carb and dizzy as well. Fixes??

pvr007

iTrader: (1)

same problem... =[

zombienerd

I'd take a look at the Catalytic Converter... Although if that was the issue, I'd think you'd have the problem @ High RPM even in 1st and 2nd gear as well...

Being that you're only experiencing this issue in top gear, could it be a Torque converter lockup failure? Very odd issue indeed.

yoshirocks702

i'm having this problem as well on my 84 l69 ccc carb 5 spd. My carb is spotless inside, and it has a new pump, I wonder if this problem has to do with vapour lock or fuel boiling as it only happens when the engine is hot. As well as gm having multiple TSB's on the issue...

84_Cruiser

I have straight pipes and it does it in all gears if i put my foot all the way down. actually since i straight piped it i noticed that when this problem is happening the engine is misfiring as well

AKATDOG

iTrader: (1)

Anyone figure this out yet? I have the same problem but my car is non CC and 700r4 trans, I thought it was vapour lock also so I insulated the fuel lines but no difference....

pvr007

iTrader: (1)

i fixed my problem... bad timing

AKATDOG

iTrader: (1)

Was the timing too advanced or retarded?

pvr007

iTrader: (1)

Too advanced

Tehsocks

Sorry, i forgot about this topic...

I fixed my issue too, i had the EGR valve hooked upto the wrong vacuum port. I still have a bog when i floor it, but i can hold WOT till i run out of gas!

ACLerok

iTrader: (1)

I have an 84 H/O 305 that would seriously bog down at 40 in every gear. I replaced the cap, rotor, spark plugs, wires, and fuel pump, and even timed it to find out that the distributor was not vacuum advanced. Once I replaced the distributor the car stopped having issues.