Help!! Engine Miss

[junior barns]

Originally Posted by mtkawboy

Ive had a broken valve spring cause a similar problem

This is what I would check

[Tony Curcio]

I've been watching this for a while, scratchin my head. Here's my guess:

Water in the fuel would start and idle fine, and it would struggle to rev up. I see you drained the fuel and replaced it in October 2011, but does the fuel cell have foam in it? If so, moisture could be retained in there, which would blend with new fuel instantly.

You mentioned that you " ..pulled the plugs a number of times and I don't see anything that screams out as being an offending cylinder". Does this mean you tried pulling the plug wires off at the cap one at a time, with the engine running, to listen for one that doesn't cause the engine to drop off?

[Ben Kallies]

Tony,

I'm running the factory gas tank, and had it drained well. I was even able to get a rag in there and soak up any residual, and peek in with a flashlight to double check.

I haven't pulled the plug wires off one by one as you're suggesting. Thanks for your input.

I guess I'll be visually inspecting the valve springs soon. Thanks.

-Ben

[Adger Smith]

While you are on the fuel tank give the sock (fine wire, plastic in some, mesh) that is on the pickup tube some attention. Leave the gas cap off and go to your fuel line upstream from the tank pickup and blow(blast) compressed air, at least 150 lbs back through the fuel line. If the sock is varnished up or clogged it will usually dislodge whatever is there or blow the sock off. That just eliminates a restriction in the fuel system. Be sure to not have your fuel pump in line or the cap on the tank when applying the air pressure. Another way to give the pick up attention is by removing the tank and remove the fuel line/sender access and remove the pickup screen.

[P Bailey]

Originally Posted by Ben Kallies

Joe,

The battery is in the factory location behind the driver's seat ('71 Corvette), and the negative cable goes through the floor and grounds directly to the frame. I've got an additional ground wire from the cylinder head to the front of the frame.

I haven't performed any mechanical tests yet. I've had the valve covers off, and reset the valves, but it's worth a second look.

-Ben

Ben,You might want to check the ground at the frame. We have had problems with the connector on the end of the cable inside the rubber cover.Good Luck with your problem. Phil

[Tony Curcio]

It sounds like you've isolated everything external to the engine- after 67 posts it's hard to take it all in.

As you said, the valve train is your next suspect. You've had the valve covers off- did you run the engine while they were off? This is a quick way to see if a lobe is flattened, a pushrod bent, a stud pulled out of its threads, or a broken valve spring. You'd probably be able to spot these things even if you just cranked it with the covers off. Any of these will make a popping sound in a consistent rhythm.

An overtight valve just sounds like crap, hard to describe, but a valve is not closing, so it's just weak and shakey.

One more thing I remember chasing long ago- a head gasket that is blown between two cylinders. Spits out the exhaust and intake of the two affected cylinders.

All of the above have a distinctive sound. If it was possible to post an audio file, many here would probably recognize it.

Hope you solve it soon, and hope you'll post it when you do.

[Ben Kallies]

Adger,

I can see the fuel sender and sock very easily looking through the filler neck. I didn't blow it out, but it looks very clean. I'll consider this.

Tony,

I was just talking with my dad about mocking up a set of see-through valve covers to watch the valve train. I couldn't run the engine with the valve covers off - I'm too much of a neat freak. I spun it with the covers off, and didn't see anything, but again, it's worth a second look.

I'm running MLS head gaskets, so I'd be really surprised (and disappointed) to find something wrong with them. I leave it open as a possibility though.

I will certainly post whenever I find the source of my frustration. If I have any money left, I may even throw a party.

-Ben

[Bill Grubbs]

Ben,
Back a number of years ago I had a similar problem where the motor on Brenda's car would skip (miss) when I would set the timing, or accelerate at a normal (non-dragstrip pace). However, the car would go like a scalded dog down the track. I was pulling my hair out over this. Then at a Nat Event, I asked Mike Walter to come take a look/listen. After 30 seconds he said there is no problem...its a race carb...set up to run at idle, OR wide open throttle, and nowhere in between. He further explained the secondaries are set up with such a light tip in for reaction off the line, so they flutter on slow acceleration.

Not saying...just relaying something to think about.

Bill

[Jim Hanig]

Ben several years ago i had a 396 that had almost the same problem. It was a ground i checked everything like you have . I found it when i pulled on each ground,one of them pulled apart. Just another thought. Jim

[Herbie Null]

I fought the same problem for six months engine would miss around 3 grand are under a load. I changed out every thing over 3 thousands dollars in parts, the only thing that was not changed out by me was that stupid disconect switch at the back. I orderd a 175 amp switch and problem was solved. Switch was corroded inside and not supplying enough amps to the msd.