Help with warm start please

[Michael_D]

I'm trying to get the tune dialed well enough to venture outside the garage to take some logs and start working the MAF in forced open loop, but at this point, I don't dare to do that, as the engine does not want to start after it is up to temp (starts great when cold though). I was able to keep it from stalling, which was progress. And yes, I am very new to this wonderful world of tuning via laptop. - This is my first go at it actually.

If I could indulge your generosity and patience, I'd be most grateful for some input / help. I have been studying till my head hurts and can navigate HPT well enough now, I believe. (finally figured out how to get the histograms to work, which now I feel foolish for asking earlier).

08 Z06 - ported heads, cam has 18 deg overlap (235/255 113 646/670)

I have been playing with start up air flow (raised it in increments up to 40%), and wasn't making much progress, so copied the start up air from an LPE 660 tune in the repository to see if that might help, as the cam / heads are similar to what I have, but it did not. I suspect I need to work base idle timing a bit now after comparing a few different tunes to what I have now. I am starting out with a base tune that not stock as I bought the car with mild cam installed.

I also suspect I have a miss. I installed new plugs (TR6 @ .038") and new wires (MSD). The wires seam to be locked well, but I'm terribly impressed with them....

[Michael_D]

26 views and not one bit of advice....Not quite as good as the last question I asked on this board with 130 views and no advice.... What, does my breath stink? Or do I need to figure out what the secret handshake is?

[vette_c6]

your car is not on open lope
its working on Close lop
i wouldnt Trust the Wideband on idle on Cammed Zo6
i would tune the idle in STFT and LTFT
your base running airflow is a high ,,
but if your car like that ,, its not wrong

you dont need to be scared of the Power enrichment
command it in what you want and fix the maf after you are done

below 3000 RPM you car is working on VE
you have to choices ,, use bluecats to work your hidden Ve
or use pure maf by lowering the dynamic airflow

good luck

[Michael_D]

Thanks for looking.

I am only trying to get the car to start right now, when up to temp. It should be in open loop, up to 130 deg ECT, no?

I had planned to tune the MAF LO Freq after I am confident it will start when up to temp. After I get the MAF reasonably close, then I will work the VE. Then work idle.

But, right now my problem is getting the damn thing to start when it is up to temp. I'm not sure where to start. Changing start up air flow did not help. I've changed timing 8 deg up/down from where it is now and that did not help.

I have also moved PE up from 0 - 1000 rpm quite a bit, but that didn't help either.

[PGA2B]

You realize it is a holiday weekend, right?? I wouldn't get to upset about the lack of responses. Most regulars are not even on the boards this weekend.

I am working on the same issue with my car. My car is mostly stock with the only changes being an aftermarket air intake, exhaust, and upgraded injectors. I am working with my startup airflow table and so far with increasing it my car is starting fine cold and hot. Not saying that will help you but you might try it.

[Michael_D]

Start up air flow was the first thing I tried. I have moved it up 40% from where it was, but it flared too much at the 40% increase. I moved it down 25% from that amount. Seams to like this amount when cold.

I was considering lowering cranking PE about 10%, as the overlap has lowered lower rpm VE, but after reviewing several tunes, cranking PE does not appear to be moved from stock very often. And I don't want to just start changing things that I do not have a complete understanding of what they do, and why.

[PGA2B]

You should only change the area that you are having trouble with. I adjusted everything above 111* in mine and am testing it. I first tried changing cranking fuel and it seemed to work also. It was suggested to me to leave the fuel alone and change airflow so I am testing that now.

[Michael_D]

Cranking fuel? Where's that?

[PGA2B]

In my tune it is under Engine> Fuel > Cranking Fuel

[edcmat-l1]

How far off is the MAF table? Have you dialed that in yet? If your fueling is off bad at idle, it's not going to want to start up cleanly. Get the engine warm, dial in the MAF and/or VE so your fuel trims aren't way off, then see how it starts up warm.

[Michael_D]

I have FA muti stage 1 vs time under cranking fuel. I'm somewhat at a loss to exactly what that function does.

MAF is not terribly bad, but feel free to veiw the log file I posted to make your own judgment.

I think MAF is reasonably close. STFT puts the error into a +/- swing of +5 / -5 at idle. I know I need to work it more (as well as virtual VE), but as I have said, I really don't want to wander off down the road, in traffic, knowing that it will not start if I happen to stall it. I'd have to sit there for about ten minutes before it would start.

[PGA2B]

I have FA muti stage 1 vs time under cranking fuel.

That's the one, but try adding some to your start up airflow in the hotter areas so you don't screw up your cold start. That seems to have fixed my issue.

[Michael_D]

Thanks, but I already tried that. I gave in and ordered the beginner's at home course from the tuning school. I'm getting directions before I get too lost this time.....

[vette_c6]

after you read your book
and you feel conf with the book

Visit Bob
the book writer, u will learn alot

[z0sleeper]

my o7 does the same thing bro. I'm starting to miss f-bodies
Oh well cant win them all!!

[PGA2B]

I was finally able to fix mine by adding 20% to my start up airflow and taking 10% away from my start up fueling above 111* ECT on airflow and 104* on the fuel table.

[bruckdeschel]

Mine did the same when I swapped an LS3 stroker in place of my LS2 in my V. I ended up having to increase the startup timing from the stock numbers. I believe they were either 0 or negative and I ended up somewhere around 8-10 degrees.

[DSteck]

Dialing in fuel always comes first. Just remember that.

[Chevy406]

I'll try removing some fuel during cranking and also check out the startup ignition advance on the 1966 LS376/480 Corvette that I am working on. Thanks for the good ideas in this thread. I believe Ed and DSteck also nailed it as my tune still is pulling fuel. Surely the combination of these ideas will help with the only remaining problem being the hot start needs a little throttle pedal to bring the engine to life.

[Michael_D]

I replaced the tune and log attached to my initial post.

I'm still fighting this hot start issue. I have quite literally tried moving start air upwards in 10% increments to max of 32 g/sec. I've tried moving cranking fuel both down and up. I can only make marginal improvements. Double cranking air and lowering cranking fuel 10% is about the best combination, but it's still not right. Something else is going on. The engine will start almost immediately, but nose dives, then it tries to catch itself. Sometimes it will, sometimes it will not. I've also tried increasing start up overspeed and underspeed time. Again, small help, but not right.

I have been told two completely different things that happen if you have to depress the throttle, 1) it needs more fuel 2) it needs more air. Which one is of those stories is true?? I'm not seeing the TPS do anything when I depress the throttle, so I'm betting on #1... Frame 10,500 is when I started the engine and depressed the throttle.

If I hit the start button, and depress the throttle just a wee bit after it initially fires up, it will roll nicely into a idle. It will also start just fine if I depress the throttle during crank/start.

I took a few logs of this, and the only thing I can see, is the injector pulse halves itself about .5 seconds after it fires and it is pulling timing. If you look at the log, you can see this at frame 10,403. I'm assuming that flare control is pulling timing?? Not sure why it will pull so much timing if the engine is not up to idle speed. Could that be what I'm fighting??

Since I first posted this question, I have calibrated both VVE and MAF, spent way too much time dicking with timing (but it's close), WOT cal, min air flow, and idle. This damn start up is about all that's left until I can get the car to the dyno.