Cold Start Issues Still

[JakeFusion]

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.

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

[GHuggins]

Without tune, can't really comment and I don't remember exactly which table it is, but I do remember it's under idle airflow and addresses the lack of fuel during starting. Exactly what you are experiencing. I'll try to get my notes out and get back to you if someone else doesn't. Sorry couldn't be of more help right now.

[JasonS5555]

Hey Jake,

I'm running out the door so only time for a few thoughts.

1. You've moved your injector "normal" table to move EOIT for your cam and larger injectors. With the cam you have, I would change the cold ECT values to match the warm values. There is no point in having EOIT really early like the stock tables when your cam has significant overlap.

2. You may want to move the EOIT even farther so that SOIT is after your exh valve is closed.

3. Change the startup airflow friction values back to stock. I'm not sure why those were changed but they look like big changes. (not 100% sure on this one, it just caught my eye).

Your idle airflow tables don't look that far off, nor do your cranking vs primary ve tables.

I'll look some more this weekend.

Jason

[JakeFusion]

That's be great if you could find it and let me know. I've adjusted the pulse tables under fueling. I've also messed with cranking VE to no avail.

And thanks, Jason. I'll take a look at those. I messed with the startup airflow friction tables early on trying to chase this down. Never moved them back to stock or near stock.

[JasonS5555]

I think the table in question is idle-airflow-startup airflow initial.

That helps the PCM know how much air is entering initially. The values in your table are much bigger than what I've seen in other tunes. You may want to look at those numbers as well.

Jason

[JakeFusion]

Yeah, those numbers were large. I moved them back to stock and then added 1g a sec across the table as I've seen folks talk about adding a little there to help with hard starts. I think I started down that path and kept adding airflow.

EOIT is probably a little conservative for the cam, but it's close. I think when I calculated it ended up being 6.29 vs the 6.25 I have in there, so I don't know how much of a difference it would be.

And lastly, on your statement, "With the cam you have, I would change the cold ECT values to match the warm values." Where are you referring to this?

Thanks!

[GHuggins]

Sorry, I was thinking of cranking fuel tables... Under fuel - cranking fuel - mulitiplier tables 1 & 2. They use your airflow tables to adjust for amount of fuel needed to start the motor. Visit tune repository, look at 2002 corvette with 5.7 fuel multiplier tables. You can see they're a little richer than yours. You can start by just copying these over to your tune and seeing if they make any difference. General rule of thumb is to multiply them by 1.02 to 1.05 at a time until you have a good easy start. Me personally... I would follow what Jason said. Fix your airflow tables, change your injector values for your cam, recheck what you've got, then tune the cranking fuel and open loop tables. But that's me....

Hope this all helps.

[GHuggins]

Yeah, those numbers were large. I moved them back to stock and then added 1g a sec across the table as I've seen folks talk about adding a little there to help with hard starts. I think I started down that path and kept adding airflow.

EOIT is probably a little conservative for the cam, but it's close. I think when I calculated it ended up being 6.29 vs the 6.25 I have in there, so I don't know how much of a difference it would be.

And lastly, on your statement, "With the cam you have, I would change the cold ECT values to match the warm values." Where are you referring to this?

Thanks!

Read Jason's post - Tip in Bog, O2's read lean, lots of fuel added by pcm. Think its all explained in there. He got his almost down to a science on the injector end of things.

[JakeFusion]

Okay, I set the Idle Startup Airflow initial back to stock and added 1g/sec to it and reset the Idle Startup Friction Airflow to stock.

I also put the stock tables back in for Crank Fuel Mult Table 1 and 2 and multiplied by 1.05 across the board. I also returned the Pulse tables to stock as I've rarely ever seen then played with even on more radical setups.

As far as EOIT goes, how much further out should I push it? Right now, it drives around well. The issue is just the cold startup.

[JakeFusion]

Btw, here is a log I did that shows the no start condition. I stopped logging and it fired on the next one only to eventually die. Then it fired and held idle no problem.

This is typical.

[GHuggins]

Did you try the vette cranking fuel/air multiplier tables 1 & 2? Then also recommend reading Jasons problem that he got sorted out listed above.

[JakeFusion]

No, haven't tried yet. It's midnight and my car is loud enough to wake the dead.

[JasonS5555]

I only learned from the guys who first sorted the inj timing in this post:

http://www.hptuners.com/forum/showth...ereencing-what

They deserve the real credit.

Jake what I was saying is that the stock inj timing is based on NO overlap. I haven't looked at the exact numbers but just based on the duration and close lobe sep of your cam, I'm betting your 13+ deg of overlap. So the stock strategy of spraying the fuel on the back of the closed intake valve just doesn't work because when the intake valve opens for you, the exh valve is still really open and a ton of the fuel just goes right out the exh.

So for guys with big(er) cams it is often better to worry about starting inj after the exh valve is basically closed (I've used the 0.06" lift number). My car, granted its an LT1, showed drastic improvement in idle, off idle, and low RPM behavior after I changed to this strategy.

In addition, the stock normal table has the EOIT really early in the cold ECT cells because with NO overlap, they were dumping the fuel in early to give it more time to atomize. So again with a lot of overlap, this won't work for you and the cold ECT cells in the normal table should be the same as the warm cells. That way at cold start your not dumping a bunch of fuel out the exh valve during overlap.

I'm running boundary 7.3 and all the cells in the normal table at 5.7. My cam is smaller than yours with more lobe sep. So try those values as a start since you'll most likely have to go farther, but you'll need to look at the EOIT spreadsheet and your inj pulsewidth (once its idleing).

Just as an example with inj pulse width set to 3ms SOIT is:

Your inj timing warm: 350 deg
Your inj timing cold: 77 deg
My inj timing: 370 deg

Does that help clarify what I was saying about the cold inj timing? It may be a part of what's causing cold start issues and then the car runs OK once you get out of those cold inj timing cells.

HTH,
Jason

[JasonS5555]

Just had a look at your log file. The IAC counts are pegged at the max value of 310. What are they at warm idle?

Jason

[JakeFusion]

Warm idle is 45-55 IAC counts. Here is a log I took the other day. Hot idle is at Frame 5970 and onward. For some reason, I do get a higher idle in park vs gear with the commanded RPM at 950 in either, so that's weird. But at 950 in drive you can see the counts in the 45-55 range.

I have my EOIT moved back per Soundengineer's spreadsheet. I think it came out to 6.29, so I backed it off to 6.25 for whatever reason. My lobes are very fast seat to seat, so the .006 numbers are fairly small in comparison to the .050 duration numbers. The overlap at .050 is 16 degrees.

[JakeFusion]

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? I know when it's cold, the A/F is richer, but the car simply does not seem to like being cold.

[JasonS5555]

This all sounds like the cold EOIT is WAY too early. Run the numbers using the cold number vs the warmed up number. You'll see that all 16 deg of overlap are being used to pump fuel out the exh instead of into the cyl. So yes, I think this is a big part of why it doesn't like being cold. Set the "normal" table to a constant value. It should not vary for a big cam.

If you have 16 deg of overlap at .050, then yeah your EOIT is still too early. It is certainly with the exh valve still open so you're pumping fuel out the exh. How did you settle on the 6.29 number? With as much overlap as you have you certainly want the START of injection (SOIT) to be after the exh valve is closed. I'm certain that is not the case with it starting at 350 deg.

Jason

[JasonS5555]

Looking at your cam your exh valve doesn't pass at 0.050 until 367 deg, so even if 0.050 to seat is fast, like an LSL or LXL, you'll still have significant exh interaction for another 20 deg passed that. So I would look at putting the SOIT around say 390 which would use a normal value of 6.70 if you leave the boundary at 6.5.

This should help low RPM driveability and if you make all the cells in the normal table 6.70 you should have much better cold start as well.

Oh, and looking at your IAC, it drops away from 310 pretty quickly. So you may be OK if you fix the inj timing

Jason

[JakeFusion]

I can open the blade a little more to bring the IAC counts down. I'll adjust the EOIT to 6.7... you say across the board at all ECTs?

The lobes are EPS on Intake and Exhaust... so the .006 numbers are 283 and 291. So a little faster than the LXL or LSL.

Does surpassing the boundary make any difference? But I could definitely see what you're saying. If I'm at 6.25 @ 154+ and that's when it starts to act right, then I could see the issue. Will this change the VE table at all? And now that I think about it, I don't know why I had the EOIT different at different ECTs. That makes no sense. The overlap isn't variable with temp.

Btw, this is the worksheet I used.

[JasonS5555]

I looked at the IAC and it drops away from 310 almost imediatly after it starts running. You may be OK there if you get the fuel inj timing worked out.

Yes, 6.7 across the board. No variation. The stock normal table has the EOIT really early in the cold ECT cells because with NO overlap, they were dumping the fuel in early to give it more time to atomize. So again with a lot of overlap, this won't work for you.

HTH,
Jason