460 Missing

Hey guys. I am new here but have been here many times researching my build. I've got a 460 in my Bronco that will not rev over 4500 RPM. It starts to miss about 3500 and gets really bad at 4500. This is just sitting in my driveway taking the Rpm's up slowly. At 4500 I am giving it more throttle but it wont rev past 4500 and has even died a time or two. I have tried 3 distributors, 2 coils and 2 sets of wires. I have checked rotor phasing and cap and rotor are new. I currently have a msd distributor and msd 6AL. I have tried different rev limiter pills and tried it without any at all. My timing is at 14 initial and 35 total in by 3000. My fuel system is a 110 gph mechanical pump with stock 3/8 lines and the filter was perfectly clean. I watched the float levels when I was revving it and they didn't move at all so I don't think its running out of fuel. Mechanically it has 115-125 lbs pressure in the cylinders. The heads I bought complete but had to have the valves reground because they weren't sealing. I am not sure what valvesprings are on it but they are duals installed at 2.05 height. They are listed as 100-135 seat and 250-300 open pressure. Sorry for the long winded post. I have been messing with this for months now and have probably forgotten something. I will take any suggestion and pretty much try anything at this point. The motor is a 460 bored .030 over. I have KB D-cups set at zero deck and compression is about 8.6:1. The crank and rods are stock. The heads are ported D3ves with 2.19 int. and 1.72 ex. valves. The cam is a comp hydraulic X4 262H-11 installed at 107 degree centerline. The timing chain is an early model. I actually took the front cover off and re-verified everything was correct and it was. The intake is a non-CJ stealth and a 750 quick-fuel vacuum secondary. Thanks again.

Only issue is that it will not rev past 4500 in park? Any other missing or anything before 4500? What happens driving when you hit 4500 in gear?

What carb are you running?

I will say freewheeling on your driveway may not be the best choice for your front pump, but define the the miss ...constant, erratic, backfire etc.

The miss is constant. While driving it sputters around 4000 then backfires so i let off. Carb is Quickfuel VS 750.

Plugs?

Broken valve spring?

The plugs are Motorcraft ASF42C gapped at .045. I have tried .035 gap as well and autolite 25's. No broken valve springs but I am going to take one to the machinist and have him check the lbs@ installed height just to see where I am at. Also while I am thinking about it I have the lifter preload set at zero lash plus half turn. I have tried quarter turn as well and one full turn all the same results.

BillM70 wrote:The plugs are Motorcraft ASF42C gapped at .045. I have tried .035 gap as well and autolite 25's. No broken valve springs but I am going to take one to the machinist and have him check the lbs@ installed height just to see where I am at. Also while I am thinking about it I have the lifter preload set at zero lash plus half turn. I have tried quarter turn as well and one full turn all the same results.

How do your plugs look?

The plugs are kind of a grey-ish color. There were 3 that were more on the white side with hardly any color. I do have an lm-1 A/F ratio gauge and have jetted the carb up a little but it wasn't making much difference so I left that alone for now.

Carb float level too low or stuck and one bowl not filling.  Its leaning out of fuel when the engine is in the upper RPM range.

Have you swapped the MSD box for another one?

jbozzelle wrote:Have you swapped the MSD box for another one?

There's your problem I've seen it twice before.

Dave De wrote:

jbozzelle wrote:Have you swapped the MSD box for another one?

There's your problem I've seen it twice before.

Just had a 7AL3 fixed that was doing something similar...

I have disconnected the 6AL and the problem actually seems a little worse. I have an msd ready to run distributor but it was used so not sure how good it is. I also have a performance distributors duraspark distributor and dyna mod control module but it was used as well. The other was a stock remanned distributor from auto-zone. Is it possible the module in the msd is bad? Is there a way to test it? I am thinking it is time for a different distributor. What is a good one to get?

Nothing wrong with a Duraspark.

Hyd flat tappet spring set up at 2.050

I would suggest pulling one spring and testing the pressures.

Why is it set up at that install height?

I bought the heads complete so i am not sure why the install height is what it is. I had the springs checked but forgot the retainer but he checked them anyways and got 85lbs at 2.05. he said that would probably be 95lbs or so with the retainer. The recommended spring from comp was the 926-16 which is a single spring rated at 105lbs @1.800. Now for the ignition I am currently running the duraspark set-up. It works fine but still wont allow me to rev. I think it ran a little better with the msd set-up. It seemed like it would pull a little more rpm before it started popping. It always fires right up and idles well though.

You have checked the valve springs as you mentioned, have you checked the pushrods for length and straightness as a bent or incorrect pushrod(s) will cause the described issues. A vacuum leak is also a consideration check carefully, also look at the wires on 7/8 and make sure they are separated as they are consecutive cylinders, you can run the car in the dark and look for crossfire issues. Finally do you have a gauge in the fuel line after the pump that you can check the pressure under acceleration.

I had a similar issue in a cleveland and it was a wiped cam.

This is my second cam and I took all the recommended break-in precautions. I measured for pushrod length and ordered the trickflow 8.75 length. I had the heads off a little while ago and i checked the cam and it looked ok from what i could see. All the lifters came out nice and easy. (last time my cam was wiped the lifter was mushroomed and stuck in the bore). I eyeballed the pushrods but didnt actually check them for straightness because i didn't think i had a reason to. My #7and 8 wires run in a loom side by side so i will separate those. I have run it at night and didnt see anything but tonight is rainy so maybe i will look again. I have checked for vacuum leaks but didn't find anything. I do have a fuel pressure gauge i can hook up. I tested it once but forgot results. I think it was7psi at idle and 4 or 5psi at wot. I can check it again. Now as for the timing I have started at 8 and went all the way to 24 initial. I have also locked out the msd mechanical advance and started the motor then set it at 36 degrees timing and it was the same. I used a piston stop tool to verify my tdc mark was correct on the pulley. Thanks for all the input.