Misfire on acceleration 85 cutlass 305 4brl HEI

[stevo88]

id take a video for you guys to hear it but no matter what camera i use the microphone gets overloaded, its pretty damn loud lol. i might have to get a condenser mic

 

[79elky454ss]

Start with the ground. It may not be the problem, but make certain the frame is grounded to the body and the engine. Many electrical problems can result from poor grounds. It is a good baseline to start from. I have seen an engine which would torque itself during acceleration and stretch the ground cable resulting in all sorts of issues.

 

[azmalibuwagon]

check the spark plug wires and make sure they are separated so your not getting cross fire induction, also look in the cap for for any indication of the spark jumping around in there.

x2 - Arcing can sure cause missing under load, and can be tough to find. Could be wires, coil, disty cap, pretty much anywhere along the electrical system. Take a look under the hood when it's good and dark, you might be able to see it arcing or a glow.

 

[stevo88]

ah! i found the issue guys! there is a little connector infront of the carb on the passenger side i believe it is a DTVS valve (correct me if im wrong), it has 3 vacuum lines going to it, EGR, Trans and Spark Advance for distributor. that little thing is cracked just a tiny bit and as i rev the motor it leaks air. That must be the issue because without a spark advance it will misfire. so basically i have no initial to total timing curve anymore it tries to accelerate from idle spark timing so therefore it bogs down but eventually when the rpm picks up, i assume the distributor advances the spark just through centrifugal force alone, i am surprised it even accelerates!

 

[stevo88]

correction, the valve on the passenger side which is broken does not connect to the distributor, the valve on the driver side does (which doesnt appear to be broken)

but according to the diagrams ive looked at, the passenger side valve should be operating the spark advance, they look like similar valves but they both plug into the carb at different points. the broken valve has a line that runs toward the back of the engine and can reach the dist but it has a screw in it to plug it off (that is how the car came)

can someone get me an accurate vacuum diagram of an 85 cutlass with a chevy 305 4 barrel? the ones ive been looking at are from pickup trucks which appear to have all the same components as my car but i just want to be sure

also, can having one broken valve affect the other valve aswell?

 

[stevo88]

ok so the spark advance doesnt really affect anything, i just pulled out the timing light and it was set at 0 deg at idle and about 18 deg at around 4000rpm, i advanced them to 12 deg idle and 32 deg at 4000, that seems to have the best results, i cannot believe how big of a difference that made, not only does the car haul like a truck at lower rpm, when i punch it, it really effin goes! it even chirps 2nd! now i can finally enjoy my new ride!