47stude

I cannot get my ls1 to run right at any cost. Initially I thought it was carburetion and jetting. After I could not get it to run right I took it to a guy that is an expert on carbs, jetting etc. He ran four different carburetors on it and definitely got it running better than I did. He had the best luck with a with a 850 double pumper Holly, but he says the hesitation and misfires is a timing issue, not a carb issue. He claims it sporadically misfires. He said on one occasion at idle he got more than 20° of timing jump on one coil. Sometimes it runs rough at cruising speeds, sometimes at Idle. I have checked everything I can think of, ground, sensors, wiring, spark plugs, spark plug gaps, fuel pressure you name it. The only conclusion I can come to is a bad eldelbrock MSD control modulator. Naturally I contacted Edelbrock and MSD they both claim there can not be anything wrong with the box because if there were it would not run at all. Can anybody think of something I'm missing I should note I am at 4800 feet in altitude I have tried all the pills. it doesn't want to run at all on 1,2, or 3 and 4,5, and 6 pills it doesn't seem to make any difference.
Specs: 47 studebaker pickup. New ls1 crate motor, Edelbrock RPM performer Dual plane manifold with edelbrock control box. Edelbrock 2216 big cam, Harlem sharp roller rockers, Holly 770 Street avenger vac secondaries. (10" of vac at idle) 700r4 with 3500 stall.
The problem seems to be worse after 2 or 3 short 1/2 mile testing runs and the motor gets warm. The first run after warm-up it runs pretty good, especially with 850 double pumper. Any ideas or help would be appreciated I know I can buy the MSD box and try and program it but I hate to throw out 350 bucks if I don't have to. the Edelbrock control box is brand-new. Thanks

R. Finkle

based on your troubleshooting, I'd go back to the beginning. Sounds like you've covered your bases, but that's usually when there is an easy fix.

Check all your grounds. Hell, add another one. That's a known issue with these engines.

If your fuel is good and your carb is good, stop looking at any type of fuel/air problem. See if anybody will let you borrow another msd box, or get another one and try it out. If its the same, send it back for a refund, then you'll know it isn't the box.

Last would be the harness. You'll need to shoot wires until you find your culprit, and unfortunately you might not find it if it is an intermittent problem like you say.

Good luck to you sir.

47stude

Thanks for the reply, I went ahead and ordered a new MSD box.
Does anyone out there have a similar set up as mine at a similar elevation to mind being 4800 feet? if so what pill are you running? The tech advisor at MSD told me 1,2, or 3 should work the best at my altitude but my truck doesn't even want to run on those.
Thanks

chickenbalLS

had the same issue turned out to be a coil pak going bad, misfires started at wot, every once in a while slowly got worse.

47stude

The thought definitely crossed my mind but people have told me coils either work or they don't. Others have said to put a voltmeter on each coil at Idle & make sure there is 12 V. How did you determine which coil was going bad? Voyage under 12v?
Thanks

Horsepwraddict

iTrader: (12)

I fought a similar problem with my old carbed 5.3. I had a couple problems but one of them was the tach. I had an Autometer monster tach and it was creating RF signals and messing with the box. I unplugged it and the problem went away. An old racing friend told me he had seen it before.