My friend has a 1997 LT1 Firebird that stumbles and stutters above 5000 rpm. It will pull hard, then stutter like it is hitting a wall. Sometimes it pulls through and shifts, sometimes it doesn't. The problem is more obvious in third gear, and especially after the car has warmed up. Here are the mods:

Lt4 hotcam kit w/ springs
1.6 rr's
3" hooker exhaust
hooker LT headers
cold air intake
ed wright tune
LT4 KM
160 degree stat

The problem has been there since day one of the swap (LT1 into a V6 car). The motor was opened up and inspected, and a bad optispark was replaced with a brand new one from Dal. Here is what we have replaced since:

30# fuel injectors
255 l/hr fuel pump
msd coil
NGK plugs
msd wires
optispark harness
engine wiring harness
MAF

We also tried readjusting the valves twice and tried 100 octane unleaded to make sure it wasn't a knock sensor issue.

After looking at the dyno graphs, I don't believe it is a fuel issue. What else could the problem be?

Here are the dyno charts:
http://www.ctbasses.com/misc/run02.jpg Ed Wright baseline
http://www.ctbasses.com/misc/run03.jpg Speed inc tune
http://www.ctbasses.com/misc/run04.jpg Speed inc tune, more fuel
http://www.ctbasses.com/misc/run05.jpg Speed inc tune, less fuel up top

We are running in circles and getting nowhere. MSD cap/rotor is on order, and I would prefer not to replace the whole optispark unless absolutely necessary. I am also going to check the vacuum on the optispark and check the grounds in the engine compartment. I also ordered another set of wires and plugs to be sure, but I am not sure what else to do.

Please help,
Thank you,
-Aaron

 

For ***** and giggles, try an OBDI PCM. Replace the knock sensor with one for an OBDI computer.

 

i have a 94 trans am and i was gona post this exact thread...i have the same modifications only i have the complete lt4 conversion and just over 5000 it starts to break up and sputter...this is killin me cause when i use the nitrous it still doin it and its very annoying..whats your fuel pressure at? try adjusting it higher

 

Plugs, wires, coil. Cured my 6000 RPM stutter!

Ken

 

This definately sounds like an ignition problem. Never rule the opti out, even if its brand new. How old is your opti? Did dal give you a receipt? When i bought mine from calvin at van devere, he put a receipt in the box, so i could get warranty at any local dealer. I think it has a 1 year warranty on it ( maybe 3 ) Id take it back to a local dealer and get a new one if you can.

 

MIne did that too and it turned out to be a bad coil and valve float. You have a new coil and springs so I'm at a loss here.

 

Coil is brand new, plugs and wires are on the way. I will try a OBDI PCM and knock sensor if I have to, but that will be a last resort. As for the Optispark, it has probably been 4 years since I bought it, so I will just have to buy a new one from Jason Cromer.

-Aaron

 

ttt

-aaron

 

With the car running, start jiggling all the connectors an wires. Do this on the coil first then the other connectors.

Sounds to me like an electrical problem and a bad connection somewhere.

 

My car was doing the same and I had a bad opti that was brand new. If your going to do a cap and rotor I would go ahead and do the opti. I hope everything works out.

 

Why last? It's the easiest to do of all the probable scenarios mentioned thus far.

 

Getting my hands on both and having the PCM tuned for the mods I have would be the problem.

-Aaron

 

Yeah, I don't know about anyone else but my LT1 Edit copy is locked to my PCM's VIN. Would be costly to purchase a new copy of it. Also, I was reading up on the LT1 Edit mailing list and knock sensors are not interchangeable so I *think* the sensor has to match the PCM (different ones for OBD1 and OBD2). *********UPDATE********** on my high RPM miss: blackdogz brings up a good point about bad electrical connections. I figured out mine was due to the individual coils vibrating loose (Delteq) and losing their connections. She spins to 6000+ now.

 

i had the same problem on my 383 once i took it above 6grand and after replacing the opti, wires, coil, and plugs i tryed an msd 6al and bam it was gone. Hasnt missed once since the install. I was reading in a magizine that by design an opti looses power in anything over 4300 rpms, hence the msd box.