Some serious tuning problems.

[ablackFormula]

Hey guys, I'm hoping I can get some insight as to what to do here, I'm at a complete loss:

I just installed a FAST unit in a 95 Formula (Firebird) with a stock LT1 engine (normally aspirated.) I did some datalogging with the stock computer in place and found that the car idles with an average pulsewidth of 2 milliseconds.

After installing the FAST unit, the car idles with a pulsewidth greater than 5, close to 6, milliseconds (but idles smoothly). The car constantly blows out black smoke and idle, during driving, deceleration, all the time. Idling in a still spot will leave stains on the ground it's so bad. I pulled a plug and it's black as can be.

I tried adjusting the a/f ratio and ve tables, and got the pulsewidth down to 2 seconds, but now the engine hunts horribly and I can't seem to adjust for it in the IAC tables (and the throttle blade screw has already been opened a good amount to get the IAC counts down to around 10 when the pulsewidths were at 5.) RPMs vary from 4 to 500 all the way up to 1000. Pulsewidths go from low 2's to 11's in milliseconds.

Timing at idle is set to 20 degrees. If anyone has any ideas please share, and if you'd like to see some files I have calibration files and a datalog of the engine hunting.

The electrode on the spark plug does look a little worn, but the gap isn't off by more than .003". I'm not ruling out physical problems with the engine, but it just seems odd that something would go wrong from changing nothing but the computer.

 

[Ricky Trussell]

Send your .gct to me and a log if you have one. I will look at it for you. I have a N/A engine also. My set up was real close to yours before a changed cam.

You need to verify your set up parameters and timing to make everything is set right.

 

[bobc455]

If I saw the car, a couple things I would check:

- All the operating parameters (injector size, etc.) as well as double-check the fuel pressure
- Make sure indicated timing = actual timing (with a timing light)
- I would check out AE vs. MAP- you might have so much AE vs. MAP. On an NA car, I zero out the AE vs. MAP and only use AE vs. TPS (and increase the AE vs. TPS accordingly)
- Zero out the timing trim
- Set target A/F to 13.7:1 for starters (I would go leaner later once things smooth out)
- Finagle the VE table to get the correct actual A/F
- If that all doesn't work, I might try reducing the P and D IAC parameters (although if you have the IAC position at 10, those shouldn't matter too much)
- Play with the timing (up and down) to see if that makes a difference, but 20 isn't too bad (if this is the parameter that makes the difference, I would try raising the timing to 30 or so)

Do you have a bank-to-bank? Remember a system that fires twice per revolution would have a different PW than an engine that only fires the injectors once per rev...

Of course I'm no expert- I've definately gone away from cars very exasperated (right tyrefryer?)...

-Bob C.

 

[berrelauto]

Did you give your dealer your info so he could give you a good start up program? If not we could tune it. We are about 2 hours south on the Turnpike.

 

[tyerfryer]

Thats right Bob! but i commend you for trying. You did get it running better than me though.