1988 TC Surging Idle With AC On

[wickettoby1]

I'm trying to sort out a couple issues on a buddies 88 TC. The car is fully built (MS ECU, FMIC, 60 Lb inj, 60mm turbo, dp, ect...) but has a few drivability issues that I'm trying to

resolve. The first issue is an erratic idle with the AC on. In the ECU i have the AC idle up feature turned on but nothing has been wired into one of the ECU's accessory inputs so i'm

not sure if the ECU knows that the AC is on or not. This is not a new issue, it has been a problem since the car was built a few years ago. Any help or suggestions would be greatly

appreciated. Attached is the current tune and a data log showing the idle surge.

[Stinger]

If there is nothing wired into the ECU yet then it doesn't know the a/c is turned on. It just sees load increase. If you don't plan to wire it in then you need to enable and configure idle advance so it can feed in timing when load increases and isn't so reliant on the IAC.

[wickettoby1]

I don't have an issue adding an input from the AC clutch if that's the better way to go vs just using the idle advance option. If using the idle advance how many deg of timing
do you suggest to add?

[Stinger]

Either option works fine. The idle advance option works for all external loads (alternator, fan, a/c, stereo, lights, etc.) while idle up is only for a/c. You can run both idle advance and a/c idle up if you want as well.

The idea is you retard timing at idle under "normal" conditions from where you are now down to 18 deg or so and then feed in timing the farther from the idle target it is.

[wickettoby1]

Here is an updated log and tune file. The surge with the AC on is better but still not great. If i pull too much timing from the base map the engine doesnt seem to like it. I experimented with less base and more adaptive timing and it just wasn't happy. I'm still considering adding an input from the AC system but dont know if the effort will gain me anything?

[Stinger]

The whole idea of less idle timing is that it doesn't "like it" as much as it likes more timing. This is what allows the idle advance with increased load to work. As it gets more load, it gets more timing which it "likes" which helps it maintain idle speed. This is how all of our PiMPx base tunes are configured. With that said, it takes some tinkering to get it dialed in (when you're not provided with "dialed in" settings in a base tune), and to get the IAC PID settings dialed in.

With less timing, you should set the idle screw so the idle PWM is about 25% at your target idle speed without the a/c on. This way you're not relying on the IAC for most of the idle air. Be sure to recalibrate the TPS afterwards.

It looks like you misunderstood what RPM Delta means in the idle adaptive advance timing table. It's how far it is away from target (+ or - target). You've got it configured as if it's RPM (800, 850, 900, etc.). If you look at the default table values, you'll see it goes from -250 rpm to +250 rpm. This is more like what your values should be. It should swing from around +3 or 4 deg to -3 or 4 deg within that RPM delta. With the way it's currently configured, it's always stuck at one value since idle is always less than 800 rpm away from target.

[wickettoby1]

Can you provide a little more detail in regards to the last two paragraphs in your previous post? 

It sounds like i need to turn in the curb idle screw on the TB but how do I know how far i need to go? You say go to 25% of the PWM at target idle with the AC off. 

I will take a look at the adaptive timing in the base tune to get a better understanding of how it works and how it should be configured. 

Thank you for the help so far, I really appreciate it.

Justin

[Stinger]

You look at the pwm idle duty percentage while it's running and see that it's in like the 40% range or something and then you turn the throttle screw and it will adjust the pwm idle percentage down to maintain idle speed and once it reaches 25% or so you know you went far enough. Then you recalibrate the TPS.

[wickettoby1]

What should the minimum duty for PID % be set to? Whatever I set that to is what the Idle PWM % reads.

[Stinger]

Min should be the minimum PWM that changes idle speed when you test different PWM values.

[wickettoby1]

Hey guys here is an update and a few more questions. So i've got the idle surge issue pretty well solved but there is another issue that still remains. When driving down the road with the AC on when you come to a stoplight or a stop sign and engage the clutch the engine will sometimes stall. Attached is a log and my tune showing this. I still haven't wired an input (from the AC clutch) in to the MS to tell it that the AC is on, I was hoping that i could resolve these issues without having to do that. My other observation is the engine seems to be running quite rich which I havent experienced in the past. Also it seems to run even richer if i turn the "use AFR target setting" on. I will add a second log to show the richness of the AFR while driving. Its like the wideband is not sure what's going on. As always any help would be greatly appreciated. Justin

[Stinger]

I would never give it 15% authority for EGO control. In the case of a wideband sensor failure, you're allowing it to pull 15% fuel which will cause catastrophic engine failure. I'd lower that to something more like 5% or less.

With that said, it does seem like something "wonky" is going on with EGO control as it seems to be feeding in more fuel when it's already richer than target and it's also not following the "step size" when it goes from 85-100% but it is stepping as it goes back towards 85%. I'd be tempted to disable EGO control and see how much better it is, and give it some more tuning time without EGO enabled.

I wouldn't worry about AC on behavior until AFR is corrected.

[wickettoby1]

Update. I went ahead and lowered the EGO authority to 5% like suggested. I also disabled the EGO control and went for a drive. Looking at the drive log something still doesn't seem right with the fueling. Even at a steady cruise when it should be 13.5 to 14.5 AFR its down in the 12.0 range or lower. And also if you look at the AFR while cruising it seems very jerky not fluid (on/off vs constantly micro changing). This car was dyno tuned and very few changes have been made to the timing, fuel or AFR maps since the dyno tuning. Any new ideas are good ideas and as always thanks for the help. If you look at the end of the log that is a long 4th gear pull. In the middle of it i see the TPS signal dip, not sure if i let off or if im dealing with a sensor issue. Also you can see that the AFR is 1 point richer than the AFR map is requesting (not sure if this is valis with the EGO disabled)  and its dead smooth. 

Attachments:

CurrentTune.msq (107.8 KB)

Drive EGO Control Off.mlg (516.77 KB)

[wickettoby1]

Heres another couple of logs showing the idle contol with the EGO enabled and not enabled.

Attachments:

Idling AC and HLs On EGO Disabled.mlg (186.78 KB)

Idling AC and HLs On EGO Enabled.mlg (70.73 KB)

CurrentTune.msq (107.8 KB)

[wickettoby1]

So after a lot of learning and experimenting and adjusting and firmware updating I've managed to get the idle control working very well. Somewhere along the way I developed a lean condition that I cant seem to wrap my head around. At about 123 seconds into the log I made a 3rd gear pull where you can see the inconsistency of the actual AFR vs the commanded AFR. As the boost ramps up you can see how lean it goes. If I attempt the same thing in 4th gear it still goes lean but not a bad because the boost doesn't come on as quickly. Only minor changes to the fuel VE table have occurred since the car was on the chassis dyno a couple years ago so I'm leaning away from the VE table being the issue. I can only assume that a change I inadvertently made to the AE must have had a negative impact when under heavy acceleration and boost. I've tried increasing the TPSDOT parameters but nothing I've changed seems to have helped. I haven't ruled out an issue with the fuel pump but I don't currently have a way to monitor fuel pressure while on the road. Attached is a log and the current tune, I'd love to hear your thoughts on what might be the culprit.

Attachments:

Drive With 4K Issue 10-7-23.mlg (811.84 KB)

CurrentTune.msq (120.6 KB)