This engine is driving me crazy!!

[rebelrouser]

I will ask for some advice, mild 454 chevy tunnel ram two AFB style carbs. Been sitting for a few years it is in a jet boat, owner fires it up and it has a miss, check it and the cam has two flat lobes, hydraulic flat tappet. Tear it apart clean and hone it, rings, bearings, grind the valves. Checked springs and they are good enough for a hydraulic roller 140 on the seat around 325 open. Order a Comp cam CBXM 284HR-12 hydraulic roller. About the same size cam that was in it before. .547 lift and 230/236 @.050 duration. 112 center, I put it in at 110. Fire it up on the dyno and it sounds like a John Deere B tractor, barely able to keep it running working the throttle. Exhaust temps on the dyno only cylinders 2 and 7 making any heat, rest are around 250 degrees. So I check everything I can think of, 150lbs compression all cylinders, 5% to 8% leak. I loosened the lifters to zero lash just to make sure they were not holding open a valve. I have a new MSD digital 6 and matching coil on my dyno, did a scope pattern on the ignition, and the pickup in the distributor looks OK. So, I think did I somehow install the timing gear wrong? Nope pulled the front cover and verified it is correct. Pulled the tops off the carbs they look just fine as well. The other weird thing is that at idle the O2's are reading very lean, So I grit my teeth and give it some more rpm slow, It cracks and pops a little and then the exhaust temps all go super hot 1,6000 degrees and I shut it down. The O2's did start to go rich as the temp built. So I am thinking it has to be the way the cam is ground? I call comp thinking that maybe by mistake they sent me a reverse rotation camshaft since it is sold as a marine cam, he says all reverse rotation cams are special grind only. I pull the covers and it looks like number cylinder 8 is opening the intake at close to the right time compared to number 1. So I am just lost. I am going to pull off the dyno and try another camshaft, any other thoughts????

[Schurkey]

Misfire will read "lean" on an O2 sensor. There's no point to paying attention to the O2 sensor if the engine doesn't run on all cylinders that the sensor is sampling.

Fouled plugs?

Heaps of unburned fuel in the exhaust system, that finally lit-off when the RPM increased?

Scope pattern shows problems with the second cylinder from the right.

[1972ho]

Are you running the digital 6al if so did you put the dip switch on the right engine cylinder selection remember that one has 6 options.

[rebelrouser]

New plugs and yes Digital box is set correctly, just had a big block mopar on it last week and ignition all worked fine. I realize O2's will read lean under missfire but 17 to 1 at idle? two pumps of the throttle and it fires right off cold. Carbs are right took apart and checked them. No raw fuel on the plugs either when I leaked and checked the compression.

[af2]

Turn the thing the clock wise direction and see...

Could be a a swap cam 4/7

[PRH]

I’d put a single carb intake on it with a “known good” carb before I pulled the cam out.

Did you check the duration @.006 on the cam?

[af2]

I’d put a single carb intake on it with a “known good” carb before I pulled the cam out.

There is 2......
Don't have to pull the cam to verify.

[PRH]

“Single carb intake” + “ known good carb”

In reference to his comment:

I am going to pull off the dyno and try another camshaft, any other thoughts????

[af2]

“Single carb intake” + “ known good carb”

In reference to his comment:

I am going to pull off the dyno and try another camshaft, any other thoughts????

I understand and like you I want to verify a problem before I go south.. That cam does not come up and wandering if it is a 4/7 swap??? Easy to check.

[PRH]

The cam is part number 11-451-8....... not shown as a 4/7 swap.

I had a Lunati stocker cam that the base circle on the intake lobes didn’t get done correctly when they went from roughing to finishing..........which added a bunch of duration at .006 to those lobes........which prompted my question about whether he checked that or not.

I’ve seen enough camshaft “oddities” thru the years that I’ve learned to check them out pretty carefully during installation.

[Walter R. Malik]

This is simple to check ... be sure the wires are attached to the cap utilizing the correct rotation in the correct firing order.

[mag2555]

I have not read thru all of this, but would that Cam happen to be ground with a 4 and 7 swap?

[Schurkey]

Exhaust temps on the dyno only cylinders 2 and 7 making any heat, rest are around 250 degrees.

Could be a a swap cam 4/7

I have not read thru all of this, but would that Cam happen to be ground with a 4 and 7 swap?

I don't know how a 4/7 cam swap would allow #7 to be one of the GOOD cylinders, unless the plug wires aren't installed properly.

did a scope pattern on the ignition,

Scope pattern shows problems with the second cylinder from the right.

No explanation for the bum 'scope pattern? Second from right is terrible, some of the others are somewhat questionable but not as bad.

[Racer97]

You could try removing the spark plugs and replace them with cork's spin the engine over by hand. Check the rotor position when the cork pops out.

[learner1]

Can't tell you why you're missing cylinders on the scope pattern but the high firing line is indicating several possibilities. One would be a high resistance, in this case since it's affecting all cylinders possibly a bad coil wire or an issue with the contact in the cap. Another is a large gap, for ex, the incorrect length of rotor which would give you a large gap between the rotor tip and the cap. It also could be caused by a lean mixture or perhaps a combination of these things. The spark line also indicates a lean mixture.