All:

My car has had a cold start issue from day 1. I swapped from a FAST 102 TB to a NW 102 to get the better IAC port, played with the startup fueling tables, etc. Nothing has worked.

Do you think it's an airflow problem with the IAC or just fueling being off at startup and throwing the A/F? I know they are related so I may be chasing my proverbial tail for a while, but this is what typically happens, and I don't know if this is even worth logging - it might just be a listen to see what the motor is doing. But when it seemed to be "lean," it would just hit bap-bap-bap for 5-10 secs and not fire on the initial start. Then I'd wait a few seconds and try again and on the third hit or so it would fire. But it would fire, climb to 500 rpm, sound terrible, and then die. Rinse repeat. Usually on the third or fourth false start it would climb up over 1000 and nearly catch. Then I knew, it was go time on the next start. And it would fire and catch. The issue is, that's a lot of stress on the motor and battery to have 5-6 false starts before it catches. I assume that's a lean condition and over time it builds up enough fueling in the chamber to actually "light off."

I added some fuel in the cranking tables... and I added too much. It would fire on the first hit of the starter and immediately die. I leaned out the tables (still richer than stock for First Pulse) but it still doesn't want to light off correctly. My wideband doesn't really seem to pick up much from lighting off for a second and dying, so I can't really see what the a/f is at the point of startup.

It starts up warm usually first or second try with no issue. And the car runs fabulously. Also IAC counts are typically in the high 40s or low 50s hot at idle. The throttle blade is open .63V I believe.

Any ideas? Drill out the IAC port? Drill a hole in the blade? Add more fuel? Set it on fire?

What?!

Here is my combo btw and the tune. No logs since it would just show it not starting. But I can take some tomorrow once it's cold again.

My combo is as follows:
02 Trans Am
EPS 234/242 111+3 Cam
TEA Stage 2 LS6 Heads 62cc
FAST 102 Manifold and NW 102 TB
TSP 100mm MAF with the LS3 Cartridge (disabled - only using the IAT)
Kooks 1-7/8" LT Headers and 3" True Duals
TR6 Plugs
Bosch EV14 52lbs Injectors with data from FICAttachment 49701
Racetronix Pump & new WIX Fuel Filter
FLT Level 6 4L60E
CircleD 2E 4200 Stall Converter
BeCool Aluminum Radiator with 160 T-Stat
New Delphi MAP relocated to front of FAST
New IAC Motor

 

Have you followed the HPT Idle tuning procedure?
http://www.hptuners.com/forum/showth...8w-pictures%29

A critical part is logging the desired base idle airflow as the engine warms up and putting those values into the idle airflow table. Your Idle airflow table seems much too high, your 68F value is almost double mine.

For comparison, you are running between 8 and 14 degrees more advance at idle than I am, e.g. in the 0.32 g/cyl range. IIRC too much advance can make an engine hard to start.

Note: I am just learning how to interpret other people's tunes, so take this as a novice's feedback, which might be all wrong.

 

Yeah, my idle airflow is what it is. I've logged it probably 200 times. It's within .5g now no matter the ambient temp.

As far as the advance goes, it's what the car wants. Big cams like mine love a lot of idle timing. It provides the lowest kPa reading. And my car idles in the 800-1200 cells - additional timing in the other cells acts as a sort of "buffer" if the RPM drops too much. It idles fine. Even with A/C on. In a parking lot with brakes on, ac on, and power steering going, it doesn't die. My A/F there is very lean and it doesn't bounce around.

The only issue I have is the hard starts when cold.

 

I don't know if this will help but I had a Camaro with odd cold start problems. What I finally did was try to start it and when it stopped I pulled the plugs to see what was on them. I had oil getting on mine and the plugs would foul, engine would shut off. I repaired the valve guides and the weird starting stopped.

There are a few other things you could check like cold cranking compression, spark and fuel delivery while cold cranking.

 

Did it run fine otherwise?

 

It's weird. Once it seems to get enough fuel in there to light off it runs fine.

I plan to drive it to get it on the dyno either next week or the week after - that'll let me know if there are any weird problems going on when I see the dyno chart.

 

Once it was warmed up it ran perfect. But cold it was miserable. I'll tell ya another weirdo cold start problem I had with a carbed engine below freezing it would start and run fow a few mins then die. Checked everything you could think of. Nothing found Until I pulled the intake off, condensation from the cold exhaust was getting pushed back into the carb through a burned out choke feed tube<I about lost my mind finding that one.

 

I hope you are using the newer style starter with the 2 equal length bolts. If not I wouldn't start it again until you change it out, If the old style uneven bolt style nose fails it will damage the block.

The newer style is much stronger.

 

Yeah, I have a newer LS3 type starter.

 

Can you confirm that you have full fuel pressure while starting?

Your Idle airflow value of 22.98 at 68F has got be wrong. I have a value of 13.3 in my 419 stroker with a 239/251 cam. The too-high value does not enrichen the starting mixture, it just confuses the IAC; heck it might even lean out the start by letting too much air in through the IAC. Sorry, I have forgotten where/how to set the fuel enrichment during start.

 

There are a few things that catch my eye right away. Remember there are very very tables that you can change that just effect that one table, it usually affects several other tables. Your timing is too high at idle for the mods you listed. With the timing being to high you have had to change other tables to make up for it starting a snowball effect. Once the trends starts you'll just keep fighting little issues (cold start, for example) because every time you change another table more it causes another to be off.
Just lowering the timing will not fix it though because other tables are off because of the timing. The cranking VE is another table that looks way off, I never had to adjust one that much for a car with similar mods to yours. Alot of times if your IAC is range, timing and fuel are right they will start with the stock cranking VE. My 13.5:1 427 still had the stock cranking VE values in it actually.

 

I changed it to be more in line with the actual VE table (which shows the counts falling off a cliff below 1600 in order to achieve a lean idle). But that didn't change anything. In fact, I could go all the way back to my tune in October and all the things I've changed and nothing has done anything to fix the cold start issue. Even swapping TBs for one with a lot more IAC flow (NW vs FAST) didn't do anything to help the issue.

Maybe I just need to hog out the IAC port or gasp, drill a hole in the blade?

The spark table I got from Ed Hutchings. It drives very well and has little to no bucking under light load at low RPMs (which is pretty remarkable). But, are you saying my idle tables have too much timing? I've had them at 24 all the way up to 32 with no difference in cold start quality. All I know is that it idles rock solid with a/c, power brakes, and power steering and does low speed stuff in parking lots without any trouble now with all the added timing (which is why the timing is where it's at - to give me enough torque to run those things with little vacuum).

Here is my last log.

 

Confirm that your TPS when closed is between .25 and .45V, and of course reads 0%.
Hate to see you drilling holes.

Other than upsetting the TPS values a bit, it seems that giving a bit of throttle during the start would be similar to drilling the blade.

 

My voltage is .63V and reads 0%. You can go up higher than that and still read 0% TPS.

What's weird is, if I press the pedal, it dies out instantly. So I've always thought it was way too lean - not in need of more airfow. The fact that it wants so much when cold is also weird. But I'll never see the 68 degree cell until Dec. So it's a moot cell for me.

 

So far in ten years I have never drilled a throttle body so I dont think thats the issue. Its just a quick fix vs correcting the actual issue IMO. Im not arguing if it drives good or not, it can drive just as good with less timing also. Its just not a simple one table fix though.
Whats lean idle as you were referring to?
Whats your IACon cold start going to?

 

Once it actually lights off, it's around 180-210 cold on cold start. It just pegs 310 on the series of bad cold starts as the IAC never moves. It doesn't have a chance to before the car sputters out.

Lean idle is switching my narrowbands as close to 0 mV as I can get them and having it actually sit steady at idle and not hunt. I did it more by sound to start with to find the lean stumble/chop sound. Then I started dialing in with the VE table by looking at my O2s. Wideband reads like 15.2:1, but with the overlap, that's not a very sound number.

And I don't want to drill a hole. If that was the issue, it'd not idle and certainly not idle with my hot counts around 50 if my TPS is still at 0%.

Like I said, it seems like it needs more fuel than it's getting and once it finally gets enough it lights off. I may have to check the rail pressure, but it's weird it'd have issues only on cold start with fuel pressure. I guess anything is possible.

 

One other thing: when the motor is not fully warmed up (say below 180), loads still manage to kill it. Like backing out of the drive way, applying the brake, and turning the wheel. When hot, that's not an issue.

Also, if I give it gas when it's in the "warm up" phase, it'll usually die out. I've added fuel in the Open Loop F/A table trying to get it to behave, but it doesn't. I've even put that at 1.00 across the board and neither seemed to work. But at 180+ on the temp, all the issues go away. Same thing for the A/C. Kick the a/c compressor on during warm up and it'll die out. Any kind of load while the motor is cold will kill it.

Is that in anyway related to the cold start issue? Any suggestions there?

 

All of them are related IMO. Like I said earlier when one table is off it starts a snowball effect and makes other tables have to try to make up for it making you have to enter data that isnt correct to compensate.

 

Some guidance I got on the HPTuners forum is my EOIT is off. In fact, it follows the stock cam graph when it should be something like 6.5 for the new normal across the board to adjust for my cam's overlap. And it shouldn't change based on temp. That's perhaps why it does better as it warms up. I'm about to go try and see what it does.

I've returned a lot of the other tables like the startup airflow and startup fueling tables to near stock. I don't need all of them to be that different for my setup. But as you said, it was a recursive snowball effect.

 

That didn't do anything. If anything it was actually harder to start. Here is the current tune. Several logs. First is just trying to start it. Next is me opening the throttle blade to .73V (which resulted in a 1500 RPM idle), then .67V hot idle with hot counts in the 20s for IAC vs the .69V with 50 hot counts IAC. I also have one where I turned the A/C on (just charged it up, so wanted to see what it did - bogged the motor but with no adaptive airflow it worked).

I'm beginning to think the throttle body may be the issue. I swapped to NW becasue the FAST has almost no bypass air with the IAC port whereas the NW is considerably larger. But I'm wondering if I don't need more bypass air in the IAC port. There's a balance that adjusting the blade perhaps can't hit. It idles fine in gear at .69V (but P/N idle is higher than commanded - leading me to believe there is more air bypassing the blade than needed). .67V idles closer to commanded for P/N but gear IAC counts go into the 20s to maintain the same idle. If the IAC port were larger then .67 or possibly less work work?

I had a FAST on there before and it idled at the same counts at .47V and seemed to allow more bypass air around the blade than the NW. The issue was the IAC port was smaller and didn't look as easy to "open up." But I think at this point, I may open them both up and see which one does better. I thought the cold start issues were related to the FAST's IAC but the NW didn't fix it. If anything, the FAST actually drove better...

Also, my lean idle seems to have enriched by delaying the EOIT. I'm seeing my O2s reading in the 80-90s vs 0-40 before... so do I need to lean it out a little more now that more fuel is actually making it into the combustion chamber?

Finally, I returned most of the airflow and fueling tables to something close to stock to adjust some of the variability out of it. I also enriched the Cranking F/A Multi tables by 5% to see if that would help... nope.