77 Caprice losing power Help???????????????

Question

I have a 77 Caprice 305 motor a couple of week ago i was coming home from work the car hit 40mph and just started losing power i eased off the accelerator for a few seconds then hit it again. It catches power then starts bucking) (Again it starts dying down. I changed fuel pump, carb rebuild, changed spark plugs, changed fuel filter in carb (dropped fuel tank & cleaned out)I replaced rubber fuel lines that connect to steel lines still does same thing always around 40mph im lost please help???????????????

No cat running straight pipe from manifold to muffler

If it's the timing chain will it be making noise because this is a off and on thing sometimes it does fine then sometimes it dose'nt when the car is in park it runs fine.

Answer 1

have you check the catalitic converter ?? a pluged catalitic converter expesially the long flat rectangular ones always plug up....

Id start there - remove the exhaust pipe before the catalitic converter and see if that helps - dont worry about the noise just drive it see if that helps.

Good Luck

Answer 2

If it were timing it would be a constant problem because the timing would be out at any engine speed. It sounds to me you either put the wrong plugs in, didn't gap them correctly, or they are fouled already from running to rich or oil burning. Also, if you purchased cheap 7mm wires they could ultimately do the same thing. Make sure you have the right plugs. I occassionaly use AC Delco but prefer the Bosch Platinum 4. My truck has the 350 and seems to run the best on the Bosch. I've had problems with AC Delco's before. All the rest like Champion, Autolite, etc just don't make the cut for my plug of choice. I've been fixing chevy's for 35 years! When you tune a chevy use the high intensity cap- not the cheap aluminum contact one! Change the rotor, plugs , wires, air filter, fuel filter, PVC, adjust the carb and timing, check and replace worn vacuum lines etc. One other problem could be an electrical wire that feeds the distributor and runs back by the fire wall. It can be a typical chevy problem too.

Answer 3

two different things that I know of can cause that. 1st if the distributor has a vacuum hose attached to it, temporarily remove and plug the hose then drive your car around. Did that fix the problem? If so the pickup coil inside of the distributor is failing, Replace the Pickup coil or replace the whole distributor with a rebuilt unit if you do not know how to dissassembly the distributor to replace the pickup coil.
2nd the purge solenoid valve attached to the carburator bowl vent has failed and fails to vent properly. Unplug the bowl vent hose attached to the carburator. Is there raw fuel inside of the hose? Next look inside the purge vent valve is the fuel in it? Check all vacuum hoses to the vent valve and replace as needed and replace the purge vent valve. Also check the charcoal canister for raw fuel, a bad purge vent valve will riun the charcoal canister and load it up with raw fuel whick means that will also need replacement along with any fuel saturate hoses to and from the purge valve to the canister.
Drive vehicle temporarily with the purge vent valve diss connected. Did that fix your problem? then the Purge vent valve is the cause.

Answer 4

Wow timing is a good answer I would first make sure theres not a in line fuel filter along the frame rail trace the fuel line all the way from tank to carb. Then I would have to say timing. Check you timing with a light make sure its not jumping around. Hope this helps .

Answer 5

I like Erasmu BD answer but try this, when its dark out side,with helper, hood open, wheels chocked, brake on, left foot on the regular brake pedal and in drive, apply slight load on the gas pedal and see if helper sees any sparks (light) showing from the spark plugs, ignition wires, and or the distributor cap area. A simple test, but it works. At worst, cam shaft or timing chain.

Answer 6

i would say timing chain, good indicator is if the more you step on the gas, the more it backfires/pops then eases up when you let off. good way to see if the chain is loose is to remove the distributor cap and take a large socket and breaker bar, put it on the big bolt that holds the crankshaft pulley on, then rock the crankshaft back and forth. if you can turn the crank back and forth more than 15-20 degrees without the rotor moving, the chain is way loose and probably has jumped timing

Answer 7

Check for a clogged muffler. Place a vacuum gauge on a vacuum port and bring the motor up to a steady 2500 rpm. If the gauge drops after you hold it steady, thats your problem.

Answer 8

check the vac line that goes on the distributer for the vac advance,one of those lines may have come off, be lose or cracked.make sure they are all on the carb and manifold too.if thats not it id check the rotor and distributor cap. maybe the plug wires see if they arent touching something. check the timming

Answer 9

i own a repair shop,,and the 305 engine is good to wear timing chains and gears out in them,,when they do they don't have no power at all,they,ll barely run,and if it is the chain it may completely jump timing on you all together ,i have had them jump timing while i was looking at the engine and it idling..it makes a big mess to if it jumps or breaks,you have to clean the whole bottom end of the engine out on it,,Chevy's are well known for timing chains,,check it or have it checked,and see if that isn't it,,good luck with it,i hope this helps

Answer 10

What about the torque converter? Does the motor make unusual noise or is it just revving? I would check the tranny.