What, if any, changes to my tune should I expect when changing to a larger throttle body?

I'm running the EBL Flash (not P4) on my 89 IROC with the stock TB on my 414ci motor up to now. Datalogs show 6-8kpa vac at WOT 5k+ so Ive purchased a Summit 58mm TB to install this weekend. One thing I'm not quite clear about is how the idle is set, or reset on the EBL system. Other than getting the idle set, it doesn't seem there would be a lot of changes to make. The only thing that comes to mind is possibly lowering my PE engage TPS setting since the larger TB would reach any given load at a lower TPS position. There could be changes to the AE tables since the TPS for a given condition would also be lower and the TPS change for load changes may be lower as well. I read some TB swap test on other motors where they said some changes to MAP tables were necessary but I can't really imagine why. It seems that a given MAP would result in the same airflow regardless of the TB opening in degrees, although it would be at a lower TPS.

Which brings up the question, how does TPS comes into play in a steady state condition with EBL system?

Any thoughts or shared experience would be appreciated.

 

When I switched to the larger throttle body a few weeks ago when I upped the turbo size, I only adjusted the IAC - Init Position vs Baro. The VE Learning will tune your kpa areas for you after that, so no need to worry about that part. I only look at Acceleration Enrichment when the datalogs show that the fueling is playing catchup with the O2 correction, so you won't really know until you stomp on it, then just add in increments until satisfied if need be. Not sure what your asking in relation with the TPS% and steady state condition...

 

To sync up the ECM and IAC, start the engine and let it run for a moment. Blip the throttle (just a little), then when the engine RPM settles down key-off. After 4 seconds the IAC and ECM will be in sync.

Give it a good ten seconds and you can restart the engine.

The TPS adjustment isn't critical, anything between .4 volts and .7 volts works.

On a warm engine, in P/N, and no other loads, the IAC should be around 25 steps (use WUD to observe). Can adjust the idle stop screw to achieve this.

RBob.

 

Thanks Bob and SL. I haven't been using VE learn here lately because since it turned colder the learn feature seems to wander up and down quite a lot. One trip it wants to add fuel, the next it takes it right back out. Then the "odd areas" where it only occasionally adjusts get real weird. I believe the root cause is in my IAT adjustments and I've been working on that too. In the mean time I have just been datalogging and manually making adjustments. I'm also learning in the process the AFR the motor "likes" at certain conditions so I'm going back and making adjustments to the OL vs AFR table. So far I have had the most success in Open loop and that's what I'm running now. I know I went a bit off topic but I think it all relates.

As far as the "TPS in steady state" question I was wondering if the TPS data is used somehow in a steady state operating condition. For example, when running a MAF system, it used the TPS, RPM and MAF data to calculate a "Load" value that was somewhat similar to MAP value. If no other values changed except for the TPS reading, it would affect the LV8 data. I just didn't know if the EBL's speed density system places any value on the TPS data while in a steady operating condition. Maybe I'm thinking too much. I can pretty much understand how the larger throttle body could affect systems like AE, DE and so forth since they make adjustment based off of the differential TPS data over a given amount of time. A smaller movement of the throttle blades will have a greater affect than before so AE may need some additional enrichment. Am I getting warm here?

 

To make sure I understand. My IAC is currently around 50-65 when the engine is warm, and TPS voltage is .5. So I should raise the base idle at the TB screw until I achieve 25 steps? I know it's mute now since I'm about to change the TB anyway but I didn't realize the base opening was off that far. Then after the TB idle screw is set to achieve IAC around 25 steps, go back and make sure the TPS voltage is .4-.7, correct?

 

With the exception of entering and staying in PE mode, steady state on the TPS does nothing. For engine control it is only used for transitions.

The MAF set ups are the same way, load (LV8) is calculated from RPM & airflow (plus a scalar).

You are on the right track regarding AE and opening of the throttle.

This is correct. Note that while opening the throttle via the idle stop screw the ECM can drop out of idle mode. The WUD will show this. Can either open the throttle before starting the engine and go the other way.

Or key-off for 10 seconds and restart the engine. Will need to let it sit and idle for a minute before continuing.

RBob.

 

Thanks Bob. I had "assumed" the tps was in play on my MAF system cause when I was adjusting my TPS I thought I noticed the LV8 change. But anyway, thanks for the lesson and procedure for EBL idle.
I'm installing my larger TB today and will need that info soon. Funny, on a modified setup there's always some things that keep it from being a bolt on. Been working on it most of the day.

 

Hey Bob I noticed my bin has a table for IAC Minimum idle steps. It shows 41-46 at normal temp. Does this (or any other) table need to be changed for the "25 steps" IAC?

 

That table usually doesn't need to be changed. It is used during warm up to prevent a high idle when coming to a stop. Say you start the engine cold and it is idling at 1000 RPM with 110 IAC steps.

Drive away and the engine is warming up, drive for say 10 minutes without having to stop. If the ECM retained the 110 IAC steps for the proper idle, the engine would now be at a high RPM until the ECM steps the IAC down.

The IAC Minimum Idle table values are used during this warm up period. Instead of retaining the 110 IAC steps, the ECM uses the values from that table. So when you finally come to a stop the IAC is already stepped down.

If the values in the table are too low the idle RPM can dip then recover. If the values are too high the idle RPM will be high until the ECM brings it down.

Once up to temperature the ECM learns and saves the proper IAC steps for idle and the Minimum Idle table is no longer used.

RBob.

 

It is likely that the ECM thought that the MAF was bad. In this case the airflow value is generated from the TPS and RPM values (N-Alpha mode).

RBob.

 

Thank you for the explanations. I am doing my best to research these issues myself but it sure helps to have your input. The throttle body is installed and other than some ae changes seems to be doing well. It isn't a dramatic change but does seem to be better. Especially at wot midrange.
Another unrelated issue i am experiencing is this. I got my fuel pretty good when the temps were very cold 30-40f. It's warmed up a bit to the 50s and now it's lean when warm. In the morning when it's still fairly cold iat around 10c it's rich - as the day warms up iat 30c it gets leaner. Is the ct/iat table the only way to adjust for this? It seems that when I biad toward the coolant temp (raise table value at x gr/sec) it gets leaner. But as temps continue to rise it doesn't stay consistent. I'm not sure I'm describing it perfectly but I can get it right for a given temp then it changes as temperature changes. Also my coolant temp stays cooler (80c) when it's cold out but runs at 85-90c when warmer out. I suspect this may be a part of my problem. Last, does the ol/afr mult vs ct table work off of the ct or the I/c blended value?

 

> does the ol/afr mult vs ct table work off of the ct or the I/c blended value?

CTS only.

> Is the ct/iat table the only way to adjust for this?

Yes. For the changing AFR cold/warm, go more toward the CTS. That will lean it out, adjust the VE to compensate. This will cause the IAT to have less effect on the injector PW.

RBob.

 

When adjusting the iat/ct blend should I adjust each gm/sec point by point and change the slope or grab the entire line and adjust the whole table up out down and keep the slope consistent?