Hot starting issues after sitting a few minutes 2006 GTO e40 ecm

[pferris]

I have been having an issue with hot starts that I cannot for the life of me resolve.

The car has afr 220 heads, a torquer v2 cam, stock ls2 intake headers and ls3 injectors.

It starts well cold and starts just fine hot if you turn it off and then start it right back up. But after sitting for at least a few minutes or an hour while still hot/warm it will not start without cranking forever. Hot quick restart it will crank for just over a second before firing up. But after sitting I will have to crank it 3 or 4 times before it does eventually fire. I do have log files and a tune I can attach. It looks to be lean while cranking, atleast initally but does richen up after some cranking, not sure if that is just the sensor being after the header while cranking at lower rpm. Ive added alot of fuel in the tune without seeing that initial cranking richen.


I have added startup airflow, lowered and raised cranking VE, added to the lower row on my main VE table, changes cranking spark some, and played around with the Cranking FA multistage table. I am not really sure what else to try, once it is running it idles well, and drives overall good. Some bucking at slow speeds, but otherwise AFR's are pretty close. Looking for any advice, I am lost on this one!

[SiriusC1024]

Quick thing to try is to bias more toward ECT than IAT. Airflow>General>Cylinder Charge Temperature.

As far as the bucking, a lot of that is because of the mismatch between idle spark and main spark.

[verlon]

You are catching vapor lock.

Your Pontiac doesn't like vanilla ice-cream

[pferris]

Quick thing to try is to bias more toward ECT than IAT. Airflow>General>Cylinder Charge Temperature.

As far as the bucking, a lot of that is because of the mismatch between idle spark and main spark.

Thank you! I haven't really gotten to fixing the bucking, but I bet that is it.

You are catching vapor lock.


Your Pontiac doesn't like vanilla ice-cream

I am really leaning towards vapor lock, seems to have the symptom just not really sure why it would have it. I'll take a look at all the lines and see if any are close to the headers or exhaust

[pferris]

for the bucking: Should I make the base idle spark and the coastdown spark the same as the base high octane table?


I did kinda start over from scratch for the idle/startup tuning. I attached my latest log of a hot start after sitting, and the current tune. It is better, but it still struggles.

[SiriusC1024]

Was thinking more like this:

[pferris]

Was thinking more like this:

Thank you again, I will give that a shot and report back.

I did also try the charge temp bias change yesterday, and it didn't seem to have made a difference. I was inching up the startup airflow table after replacing it with the stock one, I think i was up 1.5 or 2g/s for the first couple of seconds at the warmer temps.

[pferris]

I think I need to put the idle spark back close to stock, because it didn't seem to be happy cold with this table. But it also didn't fix the bucking issues, as spark was still oscillating at very low throttle at low rpms. I'm guessing it is the idle overspeed control cutting spark, but I don't want to eliminate that, not sure the best way to resolve.

Ive been trying more cutting startup fuel by lowering the cranking VE table, and adding air by the startup airflow table, but still having it start fine hot right after shutting down, and not after sitting for 10 minutes or an hour.

[Alvin]

I think the first thing you should do is make sure it builds and holds 58 psi of fuel pressure while cranking. If it doesn't it will have a hard start.

[pferris]

I think the first thing you should do is make sure it builds and holds 58 psi of fuel pressure while cranking. If it doesn't it will have a hard start.

I did verify fuel pressure a couple days ago, was thinking the same thing.

[Pekka_Perkeles]

Was thinking more like this:

I personally would not put advance similar on main tables and idle tables. It just takes ignition-based idle control away and makes engine sluggish when getting car rolling from the standing start.

If I recall right, a stock LS7 has 40 degrees of advance at those areas on high octane table. If you take it, say, 20 degrees the seven liter wonder is like tiny 2 litre engine.

Just my 2 cents.

[Pekka_Perkeles]

I think I need to put the idle spark back close to stock, because it didn't seem to be happy cold with this table. But it also didn't fix the bucking issues..

I agree.

[pferris]

I personally would not put advance similar on main tables and idle tables. It just takes ignition-based idle control away and makes engine sluggish when getting car rolling from the standing start.

If I recall right, a stock LS7 has 40 degrees of advance at those areas on high octane table. If you take it, say, 20 degrees the seven liter wonder is like tiny 2 litre engine.

Just my 2 cents.

Yeah, it seemed like cold it had too much timing and was not having it. Switched the base table back, and it seemed happier idling. Left the coast down the copied main spark table, and it hangs revs for sure while coasting down. It will hang at 1200rpm or so until I come to a stop and then it will drop to 800.

Even with both changed, it seems to be using the idle overspeed timing cut at very low throttle and still has the bucking. Is there a way to change the parameters at which the computer determines it is at idle and not throttle? I can't seem to find anything

[morepowerjoe]

First off you have a lot a things done that need to be undone. The first thing I would do is get your base running airflow correct. Your currently running lower then your stock settings. I would start out with stock and add 10% to start and go from there.

[Alvin]

I did verify fuel pressure a couple days ago, was thinking the same thing.

Have you already tried adding to the start up airflow tables? If the car is not starting I usually move it by 15% at least.

[pferris]

First off you have a lot a things done that need to be undone. The first thing I would do is get your base running airflow correct. Your currently running lower then your stock settings. I would start out with stock and add 10% to start and go from there.

I did have the base airflow table higher, then lowered it after making changes to the idle spark table because it was idling higher after. It is all at or above the stock numbers, just not by that much.

Have you already tried adding to the start up airflow tables? If the car is not starting I usually move it by 15% at least.

I have added to startup airflow before, but I also changed other startup parameters quite a bit. Now it seems to start hot if i crank it for a little while feathering the gas. I'll keep adding a bit more and see how it goes.

[Alvin]

Keep the tuning simple and if you don't get a good effect modifying a table or do not understand it completely go back to stock.

The main airflow stuff is where the majority of the work is done.