From my other thread ya'll know I just installed an LT4 with a hotcam in my 1995 Vette. Opti, wires, plugs, w/p, injectors are all new. Mail order tune done by pcm4less.

It has a hard time starting, stumbles, stalls, etc. By keeping my foot on the gas I can keep it runnning. Once it goes into closed loop it smooths right out, idles right at 900rpm in neutral and about 700-750 in gear.

So what can cause it to run so lousy in open loop and then smooth right out in closed loop?

Only code is an H43 Knock sensor.

A crap tune.

If you are running the LT4's OBDII knock sensors you will have to switch back to the OBDI sensors from your 95. The OBDII knock sensors are not compatible with your OBDI PCM.

need to get it tuned for that cam

Mike, that is true. But would knock sensors affect it when is open loop?

Bogus, same kind of question. If the tune was bad then why does it run good in closed loop?

I did a tune for a guy that was running the wrong knock sensors, it ran fairly well but was pulling 12* of timing at idle.

It is possible that the tune/file was corrupt when flashed into your PCM, I had that happen once. Can you flash your own PCM? If so, flash the stock tune back in and see if it will idle.

Part of my checklist was to swap the knock sensors from the old LT1 to the 'new' LT4. When they would not come out of the old LT1 I bought one new one and left the one that was in the LT4 block in there. So now I have a new LT1 sensor and an old LT4 sensor. Guess I better get that sensor changed out first and see if it makes a difference.

Quote:

If they didn't modify the base tables, weird things can happen.

Quote:

I checked my Chevy Fuel Injection bible (by probst) and he says that the knock sensors are not used in open loop. Having said that, lets fix the obvious things first and change out that knock sensor.

On the tune, if the base tables are out then things will always improve when it goes into closed loop. I've been chasing the opposite situation this last couple of weeks where it runs great in open loop but like crap in closed loop - mine is an issue with the large cam messing up the O2 sensor readings. My point is we should scan the car to see what's going on in open loop and closed loop (Also see your PM's)

An LT4 with a Hot Cam should run OK with the stock tune. It may have a hard time idling with the A4's low idle rpm, but there is not extensive tuning that needs to be done to get it to run.

You mention new injectors, are they Bosch III's?

You could also try resetting the PCM by disconnecting the negative cable, sometimes this will help clear things for a new tune.

Yes, the injectors are BoschIIIs from FIC. He said I needed 32lb injectors and I went by what he said. Hope they aren't the problem. I did take the battery cable off and put it back on with no change.

I'm running the Bosch III 32's in my 94 and they definately respond to tuning differently than the stock injectors. I had a difficult time dialing mine in. Using what I would use on the stock injectors the Bosch III's would be so rich at start at times I would have to hold the gas pedal to the floor to shut the injectors off, then it would run dangerously lean at cruise.

If you are going to run the Bosch III's I would highly recommend buying some datalogging software before you put too many miles on the car.