Help!! Engine Miss

[Ben Kallies]

Unfortunately, there is no short version of this story, so here goes: I pulled the engine out of my stocker in '08 for a rebuild. Performed the rebuild, had it on the dyno, ran great. Installed the engine in the car, and now it has a bad miss. The engine fires right up, and is very responsive when I blip the throttle, but it had a hard time holding 3,000 rpm when setting the timing. I took it on the road, and it was breaking up so bad that it wouldn't even hit 3,000 rpm under load. You can also feel it breaking up when you increase the RPM slowly with the car in nuetral.

I'm running the same distributor, cap, rotor, wires, and plugs that I used on the dyno. I figured it had to be something internal to the car, so I did all of the following, one at a time, with no change:

swapped in a new coil
swapped in a new MSD box (6AL)
swapped in a new MSD to distributor connector
swapped in a new distributor cap and wires
disconnected the MSD 2-step
disconnected the green wire from the tachometer to the MSD
disconnected the alternator
checked for loose wires to battery, starter, MSD, etc.

The only change that I made to the car itself while the engine was out was to install new switches for the fuel pump, water pump, and electric fan, etc. I used most of the existing wiring and just changed out the switches, with the exception of adding a terminal block for ground wires, as my old switches did not require a ground wire.

I'm totally perplexed at this point, and would appreciate any ideas on where to go from here. Thank you.

Ben Kallies 3869
B/S '71 Corvette 454/365

[Alan Roehrich]

Ben,
The new switches and new wiring are the first place I'd look.

[Daran Summerton]

Chuck a hei in her with a hot wire right to the pos post. Process of elimination - timing marks jumping around can be electrical or mechanical.

[Greg Hill]

Could be that old quadrajet deciding to take a dump.

[Alan Roehrich]

How long between when the engine was on the dyno and running well, and when it was put in the car and fired up?

Did you flush all of the old fuel and crap out of the fuel system on the car before you hooked it back up to the carburetor?

[Ben Kallies]

Alan,

The engine was on the dyno in late December 2010. I didn't do anything with the fuel system since 2008. Just 10 gallons of fresh race gas, and probably about 2 gallons of 2008 gas. I guess if I had a fuel issue, I'd expect to have issues with staring as well, and that's not the case - It fires right up. Do you disagree?
I've looked over the new switch wiring, and I don't see anything that stands out.

Greg,

The Carb was rebuilt in 2008 and ran great on the dyno. I'd be very surprised to find something wrong with it.

Thanks for brainstorming with me. Keep 'em coming.

-Ben

[krugracing12]

A while back I had an interference issue in a dragster with the green/violet wires to the distributor. It would ghost fire and break up. We moved the wires outside the frame away from everything else, it ran fine. We replaced the green/violet wires with a shielded cable and it was fine.

[MEXJOE]

How about the neutral safety switch?

[69Cobra]

Do like Alan said and eliminate everything and use jumper wires straight to the battery. I would bet that your issue is somewhere with the new ground wires for the switches either at the switch or at the terminal block. Hope you find it soon.

[Ben Kallies]

Hans - When the problem started, I was using my old battery. I replaced it last month with a brand new one.

Larry - Good thoughts. I wouldn't have considered that. If I can pinpoint the problem to the wiring, I plan to just replace it all.

Alan - I'm leaning towards doing what your saying. If I can find one, I may just wire in an HEI as someone had previously suggested, and eliminate the ignition system this way.

Bob - At this point, I'm pretty confident that it's not the carb or fuel system. Fuel pressure is steady as a rock, and the plugs definitely do no show a lean condition. I'm actually seeing some unburned fuel, pointing me towards the ignition system.

TWRS2006 - The distributor was just out, and looks great. I tried another distributor this past weekend, and the problem persists. The distributor connector from the MSD is the same one that I used before with no problems, so I know that the wires aren't crossed.

Thank you again to everyone for your responses. You're ideas keep me thinking and I find them very encouraging. We'll get this figured out eventually.

-Ben