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Old 09-09-2011, 05:17 PM   #1
Ben Kallies
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Default Help!! Engine Miss

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.

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Old 09-09-2011, 05:31 PM   #2
Alan Roehrich
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Default Re: Help!! Engine Miss

Ben,
The new switches and new wiring are the first place I'd look.
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Old 09-09-2011, 05:41 PM   #3
Daran Summerton
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Default Re: Help!! Engine Miss

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.
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Old 09-09-2011, 06:58 PM   #4
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Default Re: Help!! Engine Miss

Could be that old quadrajet deciding to take a dump.
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Old 09-09-2011, 07:00 PM   #5
Alan Roehrich
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Default Re: Help!! Engine Miss

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?
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Old 09-09-2011, 07:36 PM   #6
Ben Kallies
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Default Re: Help!! Engine Miss

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
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Old 09-09-2011, 08:04 PM   #7
krugracing12
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Default Re: Help!! Engine Miss

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.
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Old 09-09-2011, 09:44 PM   #8
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Default Re: Help!! Engine Miss

Check to see if the polarity of the wires to the distributor have been crossed. Will limit RPM.
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Old 09-10-2011, 07:22 AM   #9
Ben Kallies
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Default Re: Help!! Engine Miss

Krugracing12 - I had previously heard of others having the same interference proble,, so when I installed the new MSD, I ran the coil wires outside the car, direct to the coil to eliminate the possibility of the interference problem that you're speaking of. Thanks for your 2 cents.

-Ben
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Old 09-10-2011, 07:25 AM   #10
Ben Kallies
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Default Re: Help!! Engine Miss

Voltdr - The MSD distributor connector is notched so that it can only be installed one way, eliminating the possibility of a polarity issue. Thanks.

-Ben
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