Fix idle AFR after car warms up Supercharged Corvette

[ranger10251950]

I am trying to get a custom built supercharged Corvette to idle correctly. Custom cam and supercharger. I've got the car to idle fairly smooth on startup with a richer AFR but after the car is sitting for awhile at idle something is readjusting my AFR to almost lean. Being in the car it seems to idle best at 11.5 - 13.0 AFR and would like to get tune to keep it in this area. When it readjust it is 14.8-16 AFR and obviously runs like crap. I'm puzzled as to which tables or adjustments are causing this.... Can anyone help point me in the right direction?

8th z06 run after WB install.hpl

brandon z06 ver 3 VE tune 5.hpt

[5FDP]

I think another part of your problem is that you are allowing the timing to change way too much and that is gets too high.

Pull the idle timing way back down to around 18-20 degrees and set the over/underspeed spark correction to about 6 to 8 degrees +/-.

[ranger10251950]

I think another part of your problem is that you are allowing the timing to change way too much and that is gets too high.

Pull the idle timing way back down to around 18-20 degrees and set the over/underspeed spark correction to about 6 to 8 degrees +/-.

Thanks for the advice, I went in and adjusted timing. After reading some on AFR and Idle, I also went in and adjusted "EQ ratio" under open loop to command around 13 AFR around idle kPa.

I captured both the new tune and log below, it did run better. AFR only got up to high 13's after warming up (previous run they crept up to high 15's). Not sure if I adjusted the timing enough, it still seemed to jump around.


9th z06 run after WB install.hpl

brandon z06 ver 3 VE tune 6.hpt

[5FDP]

Is this vehicle going to be open loop only with no o2 sensors??

The short term trims in closed loop would help keep it at the commanded stoich value if you choose to do that. Of course you can't modify the open loop table like you did you want to run o2 sensors.

How big is this camshaft?

What injectors are you running?

What fuel pressure are you running and what are the injectors rated for?

Like you can't run 80psi if they rate the injectors at 58psi type of thing. They won't work correctly if you did.

[kingtal0n]

1. you need the idle and cruise a/f ratio to be 14.4 to 14.9 or the plugs with carbon up and foul over time, and black sooty carbon will coat everything

2. The a/f may be drifting due to IAT heat soak. Verify by watching IAT sensor as it heats up.

In gen3 you can't do anything about IAT heat soak in the computer. The only way I was able to fix is by installing a variable resistor to the IAT sensor. Add approx 1000Ohms variable resistor and adjust as necessary in real time.

[ranger10251950]

- LS9 cam
- Larger Injectors MOSTPLUS M02A80, 80 lb, 835cc, 12 Ohms High Impedance (rated 830cc/min at 43.5 PSI)
- Fuel pressure set to 48 PSI or close to.

I just put in a new set of NGK TR6 V-Power 4177 spark plugs, gaped to 0.033 the other day. Most of the old plugs looked OK, gaps were all over the place. I went ahead and did a compression test on all Cylinders to make sure everything is healthy (155 across the board). Went ahead and installed my EGT gauge to grab baseline numbers.

I played with a few more idle tunes making a few notes and car just runs better with a rich idle and like crap leaner I made it... right in the 11's seem be sweet spot.

Loaded up the tune attached below and took it out for a few pulls to see how it was doing, notes below:

75 degrees weather, 8/21, new plugs with smaller gap
- EGT 700 at idle
- EGT 1280 at WOT
- 4000 rpm starts building boost (5 psi)
- max 12 psi at 6500rpm
- 57.5% injector duty cycle at WOT (goal to stay below 80%) - think I have some room to turn up the boost, how much?
- Car runs noticeably smoother at idle with rich 11 AFR
- Car feels strong at WOT no missing or issues.

12th z06 run after WB install new plugs.hpl

brandon z06 ver 3 VE tune 9.hpt


Not sure where to go from here, I know its not recommended to run rich idle but this car doesn't like that normal stoich area.. WOT it ran good and AFR looks good, I know most folks recommend richer 11.5 AFR for boosted LS motor, not sure if it is worth making it a little richer from 12.1 area it is running at.. Open to some suggestions on making this tune better

[5FDP]

Never heard of those injectors before, did they come with good data?

If they didn't, I wouldn't trust any fueling with them.

[blindsquirrel]

https://www.google.com/search?tbs=li...OSTPLUS+M02A80

Seems legit to me!

[kingtal0n]

Something is wrong if it won't idle well at 14.5 to 15:1 air fuel ratio. Either the injectors aren't able to open properly at low pulse widths, or some of them are clogged, something like that.

I'd figure out the idle before doing much more with the wot stuff. because wot A/F ratio just like idle is averaged across all cylinders, so if you have a couple clogged injectors and see 11:1 you are really seeing some cylinders at 10:1 and some at 12 or 13:1

could also be the wideband is simply WRONG. Which if true is another serious issue.

Finally, even if it idles well at 11:1 due to fickle injector behavior, you can't leave it like that because it will foul the plugs and soon the car will develop a misfire and everything will be coated in carbon...sticky diamond like coating which will further impede your engine's progress. It sticks to valves and makes them difficult to close. it sticks to piston surface and raises compression ratio and creates an uneven surface with potential for hot spots. It gets down into the cylinder-ring recess and prevents the ring from being able to move over time which creates issues with the cylinder wall finish, causes blow-by to develope, uneven bore wear, its just serious bad business.

proceed with caution

[ranger10251950]

Wideband is good and trusted, used it to tune my turbo car to perfect. You guys might be on to something with these injectors.... I found an interesting read

https://ls1tech.com/forums/pcm-diagn...ch-idle-2.html

Don't think they are dirty but might be wrong for this setup after reading this article. Injectors are big cost to throw a new set on to troubleshoot this but it might be my issue. Guys at Texas Speed have noted tuners facing similar issues with injector brands they don't sell.

Any ideas on how to confirm it is the injectors without just replacing them? Big question after if I do have to replace them what should narrow my choice down too... I would like to turn up the boost, not as easy to test and try as with a turbo setup. How much can these aluminum blocks take safely? I've been away from LS motors for awhile but last I remember was around 12 psi.. granted I've got the pistons etc.. to handle probably 20-25 psi with appropriate fuel.

Some options I found below:
https://www.texas-speed.com/p-3976-f...injectors.aspx
https://www.texas-speed.com/p-3974-f...-set-of-8.aspx
https://www.texas-speed.com/p-3973-f...-set-of-8.aspx
https://www.texas-speed.com/p-3983-f...-set-of-8.aspx

[Davem3261]

I have had good results with fuel injector clinic. If you turn on closed loop, check and see if your stft is more that 2% from bank to bank. If so it might be those injectors

[kingtal0n]

Most injectors start to have a panic attack at duty cycles below 2ms (including the 1ms of delay built into the delay map). So, around 1ms of "on time" plus 1ms of delay.

They may refuse to open or sporadically open at those low pulse widths.

This is what separates a high quality injector from a typical shit injector, how low the pulse can still provide consistent fueling.

In a normal stand alone what I do is reduce the injector on-time in real time while the engine is running, at some point it will start to lean misfire and cause trouble, thats your 'minimum pulse'. This minimum is also based on fuel pressure, manifold pressure, and voltage. For example a higher voltage, a lower fuel pressure, and more manifold vacuum may help the injectors open much easier at low pulse widths and help the car idle and get the fuel it needs but not too much. So you might try those things first, and also consider raising the idle speed.

In hPtuners without real time the only way I can think of to easily test your minimum pulse is to use the scanner and gradually remove fuel while watching display pulse width, and then remember to add in the delay pulse from your voltage/pressure/offset table.

[aaronc7]

I'm running Deka 60s, and anything less than 1.4ms you can see they dont actually open. Doing VE/MAF tuning, I disable DFCO, and under engine braking I can see whenever commanded pw is less than 1.4....it goes super lean, like sensor limit 29:1 lean. I did this running open loop, but shouldnt really matter. I just looked thru the scanner/log manually.

Knowing that my no shit min pw is about 1.4ms, and that @ 14V, my voltage offset table is around 0.7ms, I set my "min pw" tables to 0.7. So now the sum of those is 1.4, and my pcm final commanded pw will never be less than 1.4. If my voltage is around 13.5, I think the voltage table is slightly higher, so maybe 1.45ms or whatever minimum. I figure for 99 percent of driving conditions this should work well. I'm very slightly rich on engine decel at 1.4ms, but when I'm all done I will re-enable DFCO anyways so won't really matter. I idle around 2ms.