Stubborn Gen 4 Firebird

[rick@ahp]

Built a sweet 2002 Firebird with PRC heads, FAST intake and fairly strong cam. Dyno tuning went well and this baby cranks out about 525 HP. Driveability in closed loop was pretty decent even though owner couldn't afford a new torque converter so normal big cam, small converter issues. Two lingering problems:

1. Really ragged, surging cold start idle. Tried all the normal stuff with spark & fuel but couldn't get it to settle down. Noticed that it started up reasonably well but after less than a minute it went into this big surge. Often stalled several times. Had to just sit there and wait till it warmed up enough to settle down and drive away. Figured out that the surging started when it went into closed loop and the O2s just weren't ready. Increased the closed loop delay long enough for it to warm up sufficiently and problem went away.

2. Problem we're still having is sort of a throttle hang-up. Take your foot off the gas at 50-60 mph and it just keeps going like it's on cruise control. RPM very slowly decays but can go a mile or more down the road before it really starts to slow down. Occasionally see the same thing in neutral when you give the throttle a blip and kick it up to 2000-2500 rpm. Just sits there for 30 seconds or more before it starts to come down and often hangs up around 1300 or so without returning to normal idle. No mechanical issues that we've found.

Most of our work is with the Gen 5 so not a lot of experience with these older cars. Any thoughts or help? Tune file attached.

[SultanHassanMasTuning]

data log would help alot

[schpenxel]

Log needed

[rick@ahp]

I'll get a fresh one today and post.

[GHuggins]

Something to try - Base running airflow. Try subtracting 2 or 3... Then I don't know, it might work great in this case, but I might recommend looking over those timing tables again? Then if it's really got a "big" cam you might be able to clean up the cold start surging with injection timing and flat lined ect table?

[rick@ahp]

Sorry for the delay in getting the log. Weather and holidays got in the way. Log file attached.

Starts with a cold start. You'll notice closed loop doesn't kick in until ECT hits 130. Idles a little ragged but doesn't surge the way it did. You'll see where I kick it into gear at 1:22 (REV) and 1:35 (DRV). Big RPM drop but catches.

Takes a little while to get out on the road and at 6:00 I'm up to speed. At 6:06 I lift throttle and let her coast. Slightly uphill road. You can see how RPM and speed slowly decays and at 20 seconds I'm just down to 1500 RPM and 40 mph.

Thoughts?

Drive_1_010516_crz1.hpl

And thanks for the suggestion, GHuggins. Haven't had a chance to try it yet.

[rick@ahp]

Log needed

Log posted above. Any thoughts?

[schpenxel]

Sorry, thought I was in the gen 4 section when I said that. If it were a gen 4 I would lower the minimum airflow in the idle settings. I'm not sure what the equivalent is on gen 3's though.

[mowton]

Idle Air Flow is Base Running Air Flow or BRAF (RAF for short). As a Drive by Cable you will have an Idle Air Control (IAC) which will need to be set first. There is a setscrew to adjust the closed throttle blade position. To make the adjustments easy, remove the setscrew from the bottom of the TB and reinsert from the top. The goal here is to adjust the set screw so the the IAC step count is like 30-50 (TPS (V) < .9v) at operating temp. You will log IAC Pos, Desire IAC and TPS (V) for this step. May take several iterations. Once complete, remove the IAC and TPS connectors and turn on the key on (no start) for 20-30 seconds. Turn the key off, replace the 2 connectors and start car. Verify settings are as they were. Should be good to go as far as initial setup. Now you need to log Idle Desired Air and tune the RAF table. Perform RussK config which is a cold to hot idle scan collecting Idle Desired Air which is the RAF value with Adaptive Idle correction values derived from LTIT and STIT, will need to log these as well. Setup a histogram copying the BRAF table ald log Desired Idle Air. Copy the resultant cold to hot data to the RAF table...google for the exact approach. As you have an IAC you will have to tweak the idle tuning using the idle effective area table. It converts internally generated mm2 effective area to IAC stepper motor counts. during RUSS K san, Log Idle Desired air, Dynamic air and IAC pos PIDS. If Dynamic is > Desired then lower the step count in the table, if Dynamic is < Desired than increase the step count. To quote an old Forum senior member....wash, rinse and repeat.

Ed M

[MMGT1]

Pay special attention to mowton's suggestion on setting up your throttle blade. DO NOT EXCEED .9v, this is very important. I, with scanner running, set screw to open 2% then reset and test, I will go 2% for a second go if it's still out. Then just one more % on top of the two you may have done. If you hit .9v, return blade to origional position(write down and keep the v reading before moving set-screw)and now your drilling your blade to get idle. If you end up in this position, make sure you look up how the blade is drilled properly and not end up overshooting your goal. I have never had to do this, but I have read and seen a few that have when a cam is big enough. Just don't start with a drill, not to be done unless you have too... capish?

[rick@ahp]

Awesome feedback. Thanks. I'll let you know how it goes later this week.