440 6-Pack misfire... Driving me crazy!

[440-6pack]

Hi everyone,

Still a rookie at forums and need your help. So I have a 1971 440 6-pack. Non matching numbers. It has a 1967 440 HP non 6 pack block. Everything was running 100% up until suddenly after a burn out. It has rough idle and upon hard acceleration the car surges off and on like it is starving for fuel or someone is turning the key off and on real quick. There is sometimes a popping sound or a combustion puff sound that is not igniting. I have brand new reproduction wiring harnesses front to back including a new fuses block and custom ordered for electronic ignition set up, all new reproduction gauges. I have a new flame thrower coil, and one at a time I changed out the distributor, then ignition box, voltage regulator, alternator and ballast resistor. Still same problems. Spark plug wires were doubled checked for correct firing order and replaced, pick up gap was set to .008, timing set to 12*@900rpm and 36*@3000rpm. I changed the valley pan thinking there was a vacuum leak and rebuilt all three carbs. No change. I changed timing chain and gears. No change. Fuel pressure 5psi. Compression test reads 155-165psi, leak down test 15-17% leakage. Need your help please...I’m at a loss and frustrated!

 

[440-6pack]

Oh... and port vacuum is 20” at idle, 24” on deceleration, 3” on acceleration. The needle never jumps at idle or cruising.

 

[ph23vo]

connect a hot wire from battery to coil or resistor...this by passes all wiring but the engine.. weird for sure..

 

[Cudakiller70]

When you replaced your timing chain did you check your rocker arms for punch through and/or bent pushrods?
Your new flame thrower coil is a replacement for the old coil?
Rotor and cap changed also?
Running a test wire to coil is a good idea to try and test.

 

[Cudakiller70]

Fuel psi stays steady at all rpms? Did you get new gas shortly before? ECU and engine block to frame grounded well?

 

[440-6pack]

Hi Everyone,

I can’t thank you all enough for you feedback.

- Yes, I have ran a hot wire to the coil directly from the battery.
- I have cleaned all grounds and even added a ground strap between block and firewall. I even ran a ground wire from ground strap to ECU.
- I have replaced the cap and rotor twice. Yes, flame thrower was to replace old coil, I have even bought a stock coil since.
- Fuel pressure stays fairly steady with rpm increase.

Thank you

 

[AUSTA]

Silly question you have changed the plugs right
Mine does that if i foul a plug under heavy acceleration the plug sort of fires intermittently causing the engine to go stop like a rev limiter

 

[halifaxhop]

Is it a stock mopar points system still or did you go electric and if so what type.

 

[440-6pack]

Great question, I changed them 3 times over 100 miles of driving. All gapped at .040. Champion plugs.

In response to an earlier reply, when I had the valley pan off I looked at the pushrods, none visually seem to be bent.See attached picture.

 

[AUSTA]

have you tried removing the leads 1 at a time to isolate the miss if your compression is even you would think that lifters are ok
You could try placing a spare plug on each lead 1 at a time to check spark or placing a timing on each lead and check at idle for a steady flash
If that is ok it could be 1 carby not performing correctly

 

[brian6pac]

Did you use a paper gasket with the valley pan ? You should always use a paper composite gasket with aluminum intakes.
Take a long piece of vacuum hose and put one end in your ear and go all around the intake and carbs and see if you hear a vacuum leak.

 

[440-6pack]

Hey guys,

I’ve tried removing the leads one by one and the engine runs worse and no noticeable change on either cylinder at idle. I’ll try my timing light on all, great idea.

I used gaskets and silicone on the intake. I also tried propane to look for leaks. No luck...

 

[AUSTA]

Hey guys,

I’ve tried removing the leads one by one and the engine runs worse and no noticeable change on either cylinder at idle. I’ll try my timing light on all, great idea.

I used gaskets and silicone on the intake. I also tried propane to look for leaks. No luck...

If the manifold leaks at the bottom it would normally suck in oil & smoke
It seems something was damaged by the high RPM burnout maybe sticky or collapsed lifter or sticky valve
the surging is strange.
The puffing sounds like it is firing with a valve slightly open.

 

[wedg2go]

Steady needle on the vac test (assuming it has a factory - or close to - grind on the cam)?

 

[Rich G.]

Did it backfire and blow the power valve in the carb?

 

[440-6pack]

Hey Rich, I changed the power valve when I rebuild the carbs. It has a 10.5. This was done post the burn out.

 

[brian6pac]

I think you have a bent exhaust valve, Doing a high RPM burnout might have floated a valve and it hit the piston ? Have you run a compression test yet.

 

[440-6pack]

Hi Brian,

I feel like it is valve related...Compression test reads 155-165psi, leak down test 15-17% leakage.

I have done some research and apparently valves and lifters can stick. If I can’t find the solution soon, my next step is pulling the heads off.

 

[440-6pack]

Oh... and I now hear a boiling sound coming from the engine after it is warmed up and I shut the engine down. I don’t remember hearing this before.

 

[AUSTA]

Head gasket ??