breaking up at 5000rpm

Gary Stubbs · #1 (**permalink**) 02-02-2005, 04:48 AM

Help!
302,30lb injectors,gt40 heads and vortec supercharger V-2s.
Under full throttle at approx 5000rpm starts to break up and nose over on power. Changed cap and rotor and seemed to help a little. Plugs look ok for burn. Not up to speed on v-2s tech
Appreciate any input

Ron61 · #2 (**permalink**) 02-02-2005, 05:25 AM

Gary,

Wish I could be of more help but fuel injection is not something that I know a lot about. However the breaking up and losing power would sound almost as if you may not be getting the amount of fuel that you need at that RPM. Also if you have a weak ignition spark it could be to weak under power to ignite the fuel completely at that point. The guy's with fuel injection can tell you what fuel pressures to check for and what else to check. Also could timing be an issue?

Ron

SCOBRAC · #3 (**permalink**) 02-02-2005, 09:19 AM

What's your fuel pressure? You recalibrate the computer and replaced the fuel pump to feed the larger injectors right??

Gary Stubbs · #4 (**permalink**) 02-02-2005, 06:16 PM

Thks for responding

Fuel pressure and timing makes sense. Will try to find out from local club on pressure. Timing is 1 1/2 per pound i believe. I am smelling gas for the first time also.

Tommy · #5 (**permalink**) 02-02-2005, 07:13 PM

I don't know squat about superchargers or fuel injection, but I have had several cars suffer the same symptoms over the years . In each case it was weak spark. The last time was a set of bad spark plug wires.

Tim Brewer · #6 (**permalink**) 02-02-2005, 07:29 PM

Just checking, but do you have a rev limiter hooked up? If so, is it a 5000 one? I'm sure you would have checked, but that's the kind of thing I would probably missed looking for something more serious. Good luck,
Tim

HighPlainsDrifter · #7 (**permalink**) 02-02-2005, 07:42 PM

Gary,
The extra cylinder pressure of the blower will snuff out the spark even with a MSD. The KEY here is to reduce spark plug gap to .030 .
Sounds simple but it's true, had the same trouble on my '87 5L coupe that I put a turbo on.
Perry.

Wade Chamberlain · #8 (**permalink**) 02-03-2005, 04:12 AM

get it on a chassis dyno asap. If you're running an FMU, I'd bet you have WAAAYYYYYY too much fuel up top. I had the same problem w/ 30# injectors and FMU. It completely went away when I switched to 42's and scrapped the FMU.

BTW, if you ARE running an FMU, has it been recalibrated for the 30# injectors (different disk...about $35 from vortech).

I agree w/ the lower plug gap. I wouldn't go quite that far though. I've had good experience w/ .040" using a Crane Hi6TRC ignition, and about .035 w/ stock ignition.

coyled · #9 (**permalink**) 02-03-2005, 06:37 AM

Its the gap, go down to .035. I had the exact same thing when adding a supercharger years ago. Scott

Gary Stubbs · #10 (**permalink**) 03-04-2005, 05:11 AM

Thxs for all the suggestions for a fix. This is what it took to correct. Route vent line to manifold of supercharger instead of dumping into the air, unplug line under manifold and connect to pcv valve, connect vacum lines correctly, set proper timing, balance 30lb injectors, replace paper header gasket(paper and glued????), header bolts replaced with proper length so they would not bottom out and so the o2 sensors would read correctly, computer chip to help run supercharger with the rest of engine, reinstall original air meter(better than previous install by other repair shop), new plugs again and replace valve spring and keepers(for trucks??) that were at 50% of what suppose to be. Icould compress the springs by hand!!.
Needless to say not a happy camper with just buying and 4,000 later.

Pulls strong to 6500 and have to get use to a smooth engine and alot more horsepower. yea