Help with off idle stumble

[GHuggins]

Are you sure the injectors and rails are clean? Not to mention the lines to them? This could simply be a supply issue, but usually you see that with rpms on top of off idle. You could even have rusted up intake valves not seating. That's the whole reason I mentioned mechanical issues to begin with because what you're experiencing is often enough associated with compression, valve seal and general base fueling issues. Especially if it had that kind of damage in the fuel system already. Injectors can look clean but still not flow correctly. They could even be sticking a little.

[Loose_Screws]

Are you sure the injectors and rails are clean? Not to mention the lines to them? This could simply be a supply issue, but usually you see that with rpms on top of off idle. You could even have rusted up intake valves not seating. That's the whole reason I mentioned mechanical issues to begin with because what you're experiencing is often enough associated with compression, valve seal and general base fueling issues. Especially if it had that kind of damage in the fuel system already. Injectors can look clean but still not flow correctly. They could even be sticking a little.

I pulled the rail and injectors and inspected them. The rail was clean, no trash/rust/anything found. I also backflushed the injectors with cleaner while using an benchtop injector driver. The engine runs very, very smooth...no issues at any RPM other than the tip in point (log shows lean). I just don't feel like it is a mechanical issue due to how well everything is performing outside of the tip in stumble.

Also, the tip in stumble only occurs from a stop and when using very light to light throttle. If I am a little more aggressive with the throttle, there's no stumble...I just need to make sure the car is pointed in a safe direction.

[Loose_Screws]

I just pulled the injector data spreadsheet blindsquirrel posted (v2.1) and it appears my injector data does NOT match. I'm comparing now and will try to summarize what is different, have you guys review before I make changes.

[GHuggins]

Well, I mean if it didn't do it before and nothing was changed with the build, then it would have to be a mechanical associated item. I guess it could be idling at a different airflow requirement now and thinking it's still supposed to be in idle mode while you're cracking the throttle. If that were the case you can lower the effective area in the idle airflow section down to something like .5 smaller than it is and see if it has any affect. That is your percent max and percent max brake settings. I'm still coming back to a mechanical fuel problem. You might even want to dump in a large dose of lubricant like marvel or lucas and run it through the tank just to see if the problem starts to subside. If it does then look into injectors some more. I assume the tank was thoroughly cleaned by hand?

Hopefully if the injector data is wrong, that's all it is, but I would still run some cleaner/lube...

[Loose_Screws]

Well, I mean if it didn't do it before and nothing was changed with the build, then it would have to be a mechanical associated item. I guess it could be idling at a different airflow requirement now and thinking it's still supposed to be in idle mode while you're cracking the throttle. If that were the case you can lower the effective area in the idle airflow section down to something like .5 smaller than it is and see if it has any affect. That is your percent max and percent max brake settings. I'm still coming back to a mechanical fuel problem. You might even want to dump in a large dose of lubricant like marvel or lucas and run it through the tank just to see if the problem starts to subside. If it does then look into injectors some more. I assume the tank was thoroughly cleaned by hand?

Hopefully if the injector data is wrong, that's all it is, but I would still run some cleaner/lube...

The fuel tank was dropped from the car and flushed. Cleaned best I could with a home garage setup. I will try some fuel injector cleaner, see if it helps any. Unfortunately the car doesn't get driven as a daily...just on weekends and occasionally to work, so it will take me a while to put enough miles on it to see a difference.

I'm reading through the effective area in idle airflow. And I'm wondering if idle mode can be logged, see if it is switching in and out.

[Loose_Screws]

Another though...would the brake switch on/off affect anything related to idle? I'll add channel to log to monitor brake switch input.

[GHuggins]

The fuel tank was dropped from the car and flushed. Cleaned best I could with a home garage setup. I will try some fuel injector cleaner, see if it helps any. Unfortunately the car doesn't get driven as a daily...just on weekends and occasionally to work, so it will take me a while to put enough miles on it to see a difference.

I'm reading through the effective area in idle airflow. And I'm wondering if idle mode can be logged, see if it is switching in and out.

It can be. It's called throttle mode or something like that. I would dump quite a hefty dose of marvel in it if correcting the injector data and reworking your VE and MAF tables don't solve it. Might even want to do that while your re-tuning it.

Brake switch would only cause issues if it's torque management, which you should see through some tm pids.

[edcmat-l1]

Cool lookin wagon.

Has a data log of the event been posted? Time stamp?

[edcmat-l1]

I'm not understanding why we don't start with the obvious first? VVE is still not straightened out and it's in speed density. No wonder it has a tip in stumble.

I went back and read your initial post. At the time stamp you noted, the injectors are fluctuating pretty badly. Looks just like there is an off idle jump or step in the airflow model. The injector action indicates that.

Dial in the VVE and your stumble will probably go away.

PS it'll always stink of raw fuel bad because you have no cats. Even delaying the injection timing won't get rid of all the smell.

[Loose_Screws]

Cool lookin wagon.

Has a data log of the event been posted? Time stamp?

Attached is a quick log with the stumble. Occurs anytime you lightly press the throttle pedal at base idle. You can see the RPMs oscillate in the log as well as the WB/02.

[Loose_Screws]

I'm not understanding why we don't start with the obvious first? VVE is still not straightened out and it's in speed density. No wonder it has a tip in stumble.

I went back and read your initial post. At the time stamp you noted, the injectors are fluctuating pretty badly. Looks just like there is an off idle jump or step in the airflow model. The injector action indicates that.

Dial in the VVE and your stumble will probably go away.

PS it'll always stink of raw fuel bad because you have no cats. Even delaying the injection timing won't get rid of all the smell.

Can you help me understand what parameters need changing to change it from SD to MAF in my tune?

I'm reviewing (confirming) the injector profile, will make those changes before I start adjusting the VVE. Going to be a slow process as I am drinking from a fire hose on how to tune still. All I have tuned before has been SD and was on far simpler systems (Megasquirt and Holley Sniper).

I'm thinking the fuel smell is actually unburnt fuel when it goes lean. Hoping a better tune will result in a little better exhaust aroma!

[edcmat-l1]

I'm thinking the fuel smell is actually unburnt fuel when it goes lean. Hoping a better tune will result in a little better exhaust aroma!

The fuel smell is from a cam with overlap. If you take the cats off a bone stock LS car it'll stink pretty good. Put a cam in with some overlap and it really stinks up the joint. You understand what overlap is, yes?

To put it back in MAF mode you'd set the MAF fail Hz back to what it was from GM. Something like 13500 or 14500. But that doesn't mean that will fix it. No telling if the maf is dialed in. My point was, your tuner went to the trouble to purposely put it in speed density but then failed to dial in the VVE table. Makes no sense. That's the kind of stuff that makes me say find another tuner.