Trouble with "warm" starts

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06-12-2022
kyotey1693

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Trouble with "warm" starts

The car will cold and hot start just fine. It seems I have trouble once it has sat for somewhere in the range of 20 minutes to 2 hours. Somewhere in the 140-160 ECT range. I've added and removed a lot of airflow in small increments over time with very little, if any success. Since it's such a small window of problem it's hard to catch. It will usually start with maybe 20-30% throttle which is why I thought it needed more air or fuel but neither seem to help.

I considered the issue might be leaky injectors but these are brand new FIC's so I don't think that's the issue. I've played with cranking spark, cranking VE, and the FA tables as well but still no noticeable improvement.

The car is 99 WS6, 5.7, 799 heads, LS6 intake, 92mm TB, 227/234 .600/.600 111LSA cam, long tubes etc. The MAF and VE are tuned. MAF disabled below 1200 rpm.

On a side note, I've got BR7 plugs for some nitrous. I feel like they cost me a little bit in driveability issues over what a set of TR6's would do. Any thoughts on that? Think they would help with the start up?

Here's the tune and a couple logs. Each with varying amounts of air but no substantial change in the start.

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06-13-2022
smokeshow

Open loop fueling is gutted at 140 and up...put it back.
06-13-2022
kingtal0n

Theres a map which related IACV position to IAT... In my car the IAT would heat soak and this closed off the IACV causing shit warm starts after 20min-2hour windows.

Just make the entire IACV vs IAT map a nice solid number like 12g/sec or something across the board. When the engine fires it will rise sharply then settle back down. You can gradually reduce the number if you don't want it to start so suddenly.
06-13-2022
kyotey1693

Thanks smokeshow. So, you're thinking it's a lean fuel issue causing the poor starts? I always have the wideband going before I start it but it's still hard to get a good read on AFR during startups. I'll definitely try your suggestion.

King - can you tell me exactly which table you're referring to? Sounds like you're talking about Park Position Airflow? If so, my understanding on it is that it's just the starting location for the IAC when the key is on but actual IAC position is controlled by BRAF, Startup, and Friction Airflow numbers combined?
06-13-2022
kingtal0n

Theres two tables, park is one of them. There is another one. I dont have the software on my computer here. Just look for IAT vs IACV position in g/sec (airflow when set to g/sec)

Does park say that? I can't remember what park units are. For some reason I don't think its park though. But you could try both?
06-13-2022
kevin87turbot

1 Attachment(s)

The startup airflow table has been zero'd in most of the active range. This is likely your problem. It needs to be closer to stock. I typically adjust it a little higher than stock for an application like yours. What is your IAC position at a warm idle? Does it start up if you lightly crack the throttle? Some aftermarket TB's have very small IAC passages and you have to make a few tweaks to compensate.
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06-13-2022
smokeshow

Startup airflow won't cause a no-fire like that. There's enough air in the manifold at 0 rpm to get the engine started. If it flares and dies or struggles on the run-up, that's something start-up airflow can help.

Remember... opening the throttle or IAC with the engine at or near 0 RPM doesn't change airflow at all. You can't control cranking airflow because the throttle is not capable of actually throttling the engine. Focus on the fuel and spark... primarily fuel.
06-13-2022
kyotey1693

Thanks guys. I appreciate the tips.

Kevin - I run about 40-50 counts on IAC warm idle. I previously had a cheap tb with a small IAC opening, it also leaked through the shaft seals. So, I'm running a Nick Williams now and it seemed to clear up a lot of issues. For the longest time I couldn't understand the difference between Friction Airflow and Initial Airflow until someone explained that they are in addition to whatever you have in the BRAF table. So, to keep mine simple I just zero'd the Startup Initial and focused my changes on the Friction table. It seemed simpler and less redundant to me. I'm still kinda green on some of this stuff. So if my logic is wrong, y'all feel free to educate me.

Smokeshow - I'll play with the fueling over the next few days. I think you're right that it is a fuel problem because I have added and removed air with no change. I just assumed it was too much fuel or maybe a wet combustion chamber from the overlap of the cam at idle and it just hadn't had enough time for evaporation in the 2 hour window. I was thinking I might need to lower the cranking fuel but I'll leave it and try putting back the open loop fuel. Any suggestions what I should focus on for spark? It's stock cranking spark for now.

King - the way I understand Park Position Airflow is that it commands where the IAC is when the key is off. Once the key is on it uses added the BRAF, Startup Initial, and Friction to set the IAC position. The only other IAC table that I'm aware of is the IAC steps table and I've got it pretty well dialed in based on chopperdoc's method. Maybe when you get to you computer you can point me to which table you're talking about.
06-13-2022
kevin87turbot

You can typically just try cracking the throttle a bit during cranking and quickly determine if the additional airflow helps the engine to start. If it doesn't help, then it's not an airflow issue, it's a fuel issue.
06-13-2022
smokeshow

Quote:

Originally Posted by kevin87turbot

You can typically just try cracking the throttle a bit during cranking and quickly determine if the additional airflow helps the engine to start. If it doesn't help, then it's not an airflow issue, it's a fuel issue.

That's another tricky counterintuitive one... Cracking the throttle yourself during cranking is still almost exclusively a change in fueling. Because of how fast airflow can change during a start relative to engine speed, injection scheduling is particularly sensitive. When the engine speed is 180rpm at crank, what the throttle is doing has more affect on future airflow rather than present airflow. If you tip into the throttle during startup, the ECM will anticipate more airflow during the next few engine cycles and add extra fuel to prevent a lean condition. This surge of fuel often helps a struggling engine to start where it otherwise wouldn't. So it seems like the throttle is helping with airflow...but it's still the fuel that is making the difference. Pretty common misconception actually.
06-14-2022
kyotey1693

Quote:

Originally Posted by smokeshow

That's another tricky counterintuitive one... Cracking the throttle yourself during cranking is still almost exclusively a change in fueling. Because of how fast airflow can change during a start relative to engine speed, injection scheduling is particularly sensitive. When the engine speed is 180rpm at crank, what the throttle is doing has more affect on future airflow rather than present airflow. If you tip into the throttle during startup, the ECM will anticipate more airflow during the next few engine cycles and add extra fuel to prevent a lean condition. This surge of fuel often helps a struggling engine to start where it otherwise wouldn't. So it seems like the throttle is helping with airflow...but it's still the fuel that is making the difference. Pretty common misconception actually.

That's essentially what happens in my case. I always wondered if it was the extra fuel or the air making it start. Makes sense the way you explained it.
06-14-2022
kevin87turbot

Quote:

Originally Posted by smokeshow

That's another tricky counterintuitive one... Cracking the throttle yourself during cranking is still almost exclusively a change in fueling. Because of how fast airflow can change during a start relative to engine speed, injection scheduling is particularly sensitive. When the engine speed is 180rpm at crank, what the throttle is doing has more affect on future airflow rather than present airflow. If you tip into the throttle during startup, the ECM will anticipate more airflow during the next few engine cycles and add extra fuel to prevent a lean condition. This surge of fuel often helps a struggling engine to start where it otherwise wouldn't. So it seems like the throttle is helping with airflow...but it's still the fuel that is making the difference. Pretty common misconception actually.

That's good information. Thanks for sharing.
I get to tune a lot of aftermarket stuff at my shop as well. I've noticed that typically, the FAST and Holley stuff simply ignore the TPS position during cranking (assuming that it's steady state.) unless you're in Crank/Flood mode. I always thought that the OE stuff functioned the same.
06-14-2022
kingtal0n

The TPS% Has no reflection on cranking fuel that I can see. Not in OEM ecu tables available to us. Aftermarket, sure, but we set those tables ourselves cranking pulse vs TPS%.
Doesn't your Holley have a Cranking pulse vs TPS% Table? Last one I did, I saw that. I always setup for less fuel as the throttle is cranking open to gradually work towards clear flood.

If its true that when we open the throttle the ECU isn't able to adjust fueling based on TPS, then the ECU has no way of knowing or understanding the amount of air going into the engine is changing other than the BARO and MAP based stuff. So if the map changes, then sure fuel can change. But not solely based on TPS%. I think if you open the throttle you remove some restriction allowing more airflow at the same MAP condition, so, same fuel, more air. That fires a flooded engine up more quickly. In 99% of cases where adding throttle position allows an engine to start more easily, the answer is to reduce cranking fuel. Not add. It works the same as with a carb'd engine. Nothing is counter intuitive here.
06-14-2022
smokeshow

Quote:

Originally Posted by kingtal0n

The TPS% Has no reflection on cranking fuel that I can see. Not in OEM ecu tables available to us. Aftermarket, sure, but we set those tables ourselves cranking pulse vs TPS%.
Doesn't your Holley have a Cranking pulse vs TPS% Table? Last one I did, I saw that. I always setup for less fuel as the throttle is cranking open to gradually work towards clear flood.

If its true that when we open the throttle the ECU isn't able to adjust fueling based on TPS, then the ECU has no way of knowing or understanding the amount of air going into the engine is changing other than the BARO and MAP based stuff. So if the map changes, then sure fuel can change. But not solely based on TPS%. I think if you open the throttle you remove some restriction allowing more airflow at the same MAP condition, so, same fuel, more air. That fires a flooded engine up more quickly. In 99% of cases where adding throttle position allows an engine to start more easily, the answer is to reduce cranking fuel. Not add. It works the same as with a carb'd engine. Nothing is counter intuitive here.

Its like you think I just make this stuff up lol. Here's the description and patent reference. Feel free to stop polluting the forum with trash information.

Quote:

Originally Posted by GM Patent # US20060243039A1

The crank-to-run GPO prediction also includes 1st, 2nd and 3rd step ahead GPO predictions and measurement update. As explained in further detail below, there is a transitional period during which the crank GPO prediction and the crank-to-run GPO prediction function concurrently. Once wholly in the crank-to-run mode, the crank-to-run GPO prediction is used alone. The crank-to-run GPO prediction is used to predict GPO for those cylinders that will ingest their air charge during operation in the crank-to-run mode.

The GPO predictor module 500 generates GPOk+1|k, GPOk+2|k and GPOk+3|k based on PBARO, MAP, TPS, RPM, TOIL, SOC, GPC and IAT. The particular prediction model or models used depend on the current event number and the engine mode (e.g., misfire and poor-start) and include crank GPO prediction, crank-to-run GPO prediction and run GPO prediction, misfire GPO prediction and poor-start GPO prediction.

https://i.ibb.co/PQsjz0d/US200602430...102-D00004.png

https://i.ibb.co/VL6pYKw/US200602430...102-D00005.png
06-15-2022
kingtal0n

From the patent

Quote:

The fuel control system includes a first module that determines a plurality of step-ahead cylinder air masses (GPOs) for a cylinder based on a plurality of GPO prediction models

Quote:

It is assumed that the most accurate way to estimate the true GPO is using bottom dead center (BDC) MAP data. Due to hardware constraints, the closest MAP measurement is sampled at a specified cylinder event

GPO calculation prediction doesn't care about TPS for cranking fuel. I will provide supporting details next,

Quote:

GPOk is calculated based on the following equation:
GPOk=αCRK-VEVECRKMAPk/IATk (5)
where VECRK is the volumetric efficiency at the cranking speed, which is calculated from the geometry of the piston and cylinder head using a known compression ratio, αCRK-VE is a scaling coefficient used to match the units of VECRK and MAPk/IATk.

AlphaCrank based on VE which is predicted via MAP and IAT of k, where k denotes the step ahead function of k,i.e. k+1 is the next predicted step, k+2 is two steps ahead, k+3 is three steps ahead, etc...

Here is the quote,

Quote:

The crank GPO prediction consists of 1st, 2nd and 3rd step ahead GPO predictions, with a measurement update. The crank GPO prediction is used during operation in the crank mode. The following equations are associated with the crank GPO prediction:

Equations

Quote:

GPOk+3|k=αCRKGPOk+2|k+(1−αCRK)GPOk+1|k (1)
GPOk+2|k=αCRKGPOk+1|k+(1−αCRK)GPOk|k (2)
GPOk+1|k=αCRKGPOk|k+(1−αCRK)GPOk−1|k (3)
GPOk|k=GPOk|k−1+KG(GPOk−GPOk|k−1) (4)
Equation 1 is the 3rd step ahead prediction, Equation 2 is the 2nd step ahead prediction, Equation 3 is the 1st step ahead prediction and Equation 4 is a measurement update. αCRK is a single fixed number for all engine start conditions and KG denotes a steady-state Kalman filter gain. Because the crank GPO predictor only runs for a short period of time (e.g., only the first three engine events for the exemplary I-4 engine), αCRK is tuned manually.

Alpha CRK tuned manually and GPOk prediction is

Quote:

GPOk=αCRK-VEVECRKMAPk/IATk

i.e. VE based on MAP/IAT plus some manually calculated coefficient.

Equation 9 is interesting, 'measurement update' lets look at that

Quote:

Equation 9 is the measurement update.

Quote:

In the Equation 9, GPOk is calculated based on the following equation:
GPOk=αRUN-VEVERUN(MAPk,RPMk)MAPk/IATk (21)
where VERUN(.) is the volumetric efficiency at the normal or run operating condition and is determined based on MAP and RPM, and αRUN-VE is a scaling coefficient used to match the units of VERUN(.) and MAPk/IATk.

Nice, MAP and IAT again. Nothing about TPS.

I'd keep going but oh no its a text wall! Yeah the whole @#)(@# damn document is a huge text wall- but it doesn't bother me.
text walls are my friend. And I am a mathemetician.. mathematishin? mathatisin. I like math, bring it on.

bottom line: During cranking if you open the throttle the MAP won't change and so no extra fuel will go in, according to the published document.

Reduced friction at the throttle valve will increase airflow throughput to the engine, allowing the engine to clear flood more easily as the throttle gets wider, meaning you can start a flooding engine more easily by opening the throttle some with the same fuel input. Which is how all engines should work. Imagine if opening the throttle caused more fuel to go inside... You would ALWAYS flood the engine worse and worse the more you opened it!!! Oh my what a disaster it would never start. You could clear flood and it would just re-flood over and over no matter what. Clear flood which is the final stage of opening the throttle is the most airflow with no fuel, final position. It is NOT counter intuitive to us people. It is extremely simple and works just like with a carb, except for the clear flood part. Like all engines. Nothing to see here, it wasn't smoke it was just water vapour, clouding your windows.

BTW Please bring up cranking to run next so I can post some equations and look more deeply at the math. I dare you. Cranking to run is used after the engine already fires- of no interest to us unless the engine fires and then dies. In which case, bring it on.
06-15-2022
kingtal0n

this is the patent
https://patents.google.com/patent/US20060243039

This is what a spline function is
https://dmpeli.math.mcmaster.ca/Matl...ecture2-3.html

It works like a zener diode, with a maximum linear position and trailing edges on either side.

Meaning there is a range where the fuel coefficients peak and hold, they do not wander within that range, the equation locks them to a specific number like a flat line.

If he was actually an engineer he would have read the paper but instead just blindly posted it hoping I wouldn't be able to read it. LOL big mistake buddy. Call me more names.

What an @$$
06-15-2022
smokeshow

Quote:

Originally Posted by kingtal0n

Equation 9 is interesting, 'measurement update' lets look at that

Nice, MAP and IAT again. Nothing about TPS.

That's measurement. Not prediction. You can stop any time...
06-15-2022
kyotey1693

You guys are way over my head on logic and function but I can tell you that putting the OL fuel back in has seemed to resolve this issue. Thus, more fuel helped. Thanks smokeshow, I appreciate the quick fix and education.

And just a simple observation if the above debate continues- when I had the no start issue and would give it about 20-30% throttle to get it to start, I could see the injector duty cycle increase. Which I assume was causing more fuel delivery based on the change in TPS, since the MAP and IAT didn't change.
06-15-2022
smokeshow

Quote:

Originally Posted by kyotey1693

You guys are way over my head on logic and function but I can tell you that putting the OL fuel back in has seemed to resolve this issue. Thus, more fuel helped. Thanks smokeshow, I appreciate the quick fix and education.

And just a simple observation if the above debate continues- when I had the no start issue and would give it about 20-30% throttle to get it to start, I could see the injector duty cycle increase. Which I assume was causing more fuel delivery based on the change in TPS, since the MAP and IAT didn't change.

No problem. And yep, that's what the algo is designed to do. Long as you're not a guy who likes to cherry pick around the stuff you disagree with in the patent docs :crazy: Lol crazy thread.
06-16-2022
kevin87turbot

Quote:

Originally Posted by kyotey1693

You guys are way over my head on logic and function but I can tell you that putting the OL fuel back in has seemed to resolve this issue. Thus, more fuel helped. Thanks smokeshow, I appreciate the quick fix and education.

And just a simple observation if the above debate continues- when I had the no start issue and would give it about 20-30% throttle to get it to start, I could see the injector duty cycle increase. Which I assume was causing more fuel delivery based on the change in TPS, since the MAP and IAT didn't change.

Thanks for the update. Smokeshow nailed the solution again...and we all learned something new. Good job!