Yeah I know. Heres the story. I built a tuned port LT1 for my '86 using an LT1 longblock and an accel conversion intake base with SLP runners. I have the motor running, all the wiring sorted out, but it doesnt want to idle long and it stalls when dropped into gear. Runs fine otherwise, other than being a little on the sluggish side compared to a factory tuned port but it's not bad. I marked the damper and made a timing pointer, but I need a way to time it, since I am still running the opti for the CPS.

In other words I have an opti for the sensor only and Im using a distributor for spark distribution (bad cap, didnt have a plug, etc...) but the computer keeps trying to adjust the timing at idle. I know tuned ports have a timing connector but I doubt the LT1 has one, never have heard of it since the opti is non adjustable. Im trying to get the tuning issues worked out but I really need to get it timed better before I can adjust idle and fuel pressure. During cranking it cranks and stops then starts again like it's far out of time. Any suggestions?

 

Hmm, did you install the cam straight up or did you degree it in?. The 305 isnt a big cam and should run fine with the stock tuning. It may run a little rich requiring you to lean it out a little but it should run pretty decent. Im not sure what year your opti is but if you have the 93-94 non vented you could have it installed a tooth or so off.

 

Which PCM are you running?

 

OBD1 conversion, '97 harness. Everything wired in and everything hooked up and working on the engine. Tach is still not up though but all sensors are functional. Still trying to sort that one out.

cam installed straight up, it has a vented opti. I already pulled it once... had a bad cap but the cam sensor is still good. Spark in, no spark out...

runs ok but it's taking alot of IAC and TB to keep it at idle. Near idle it runs for awhile then stumbles and eventually dies unless I give it a snap of the throttle. Hard to start, has the crank/lug/crank deal going on and it hiccups from the intake during cranking. Other than that it runs like a champ. I think the corvette converter is trying to pull the engine down at idle lower than it's willing to go, stalling it when it's put into gear.

 

Any tuning software?

 

Madz28 tune by Ion for the cam and intake, and an autoXray scan tool. No software so I cant adjust anything stored in the PCM.

 

Yep, the opti is non-adjustable. You'll have to pull timing through the PCM.

Have you tried retarding the distributor?

 

I've tried both, but I have nothing to use as a reference other than cyl #1's terminal facing it's cylinder. timing jumps around too much to establish a 'base' idle, cant disable the spark advance anyway. The PCM is asking for between 15 and 35 degrees so it's obvious it's comfused. Probably explains the idle.

 

Also, I usually add closed TPS timing with a cammed engine. I wonder if just raising the idle rpm would help, or raising the idle rpm in gear table.

 

Yeah, probably confused using the opti and distributor.

 

it will idle stable at 1200. Thats to high for a cc305. Under that it becomes unstable after awhile.

I figure I could pull the cap and set it back to cyl 1 TDC on the compression stroke, take note of the rotor position and put the cap #1 terminal as close as possible, but I dont imagine I will get within more than 5 degrees. Since the timing is set through the PCM I doubt it would matter much as long as the coil fires while the rotor is close enough to the correct terminal in the cap...

 

Got an idea. Since I established TDC cyl 1 on the CS Im going to use that as a reference, then mark the damper further up and try to match the PCM's spark advance with the timing light reading. Plus the base timing. Im assuming it's 6... I'll have to check. Might be hard to find since it's an LT1 though...

 

That seems to have worked. Its asking for 26 degrees advance and its idling steady at 1000... doesnt drop off when put into gear. I'm gonna go drive it real quick and see if that did it

 

What distributor are you using? Where does the white wire from pin B5 of the LT1 PCM attach to? If you don't have the white wire connected to the IC Module, I don't see how the PCM can affect the timing.

 

Im using a standard external coil HEI TPI distributor for spark distro and using the LT1 opti for its cam sensor. I can always try to disconnect that wire, might put me closer to the base timing. I was thinking of setting it at 8 but figured I should stay at 6. Right now I just have it 'close', it ran fairly good yesterday. Idle was a little unstable but it ran and didnt die off in gear. Significant improvement. Still needs a new starter, fuel pump (doesnt hold pressure) and a brake booster (leaks, it's capped off)