IAC steps very high.

[willn]

Alright, so I have been doing a bunch of reading and most people are saying, even with a cammed engine I should have about 50-60 steps on the IAC at idle.

I am seeing about 120-150 steps. If I force anything less with DVT, the engine immediately dies. What could cause this? I know I have a larger cam, but I have seen guys with larger or equal cams to me and they aren't this high on IAC steps.

Cam is Comp 230/238 .600 .603 @ 114.

Any ideas from latest logs?

17523

17524

[nm2769]

What intake and throttle body are you running?

[willn]

Stock truck intake and stock 78mm TB.

[minytrker]

You'll have to adjust the TB open some more in order to lower the IAC steps.

[willn]

I am in a 2000 Silverado. It doesn't really have a TB adjustment. It is a DBW.

[picnic_george]

If it's DBW there is no IAC hence no IAC steps to count.


I don't think 2000 silverados came DBW????

[Taz]

Some pre-2003 Trucks were DBW. If it is a 2000 model, then it probably uses OS12205612.

Take a look at the idle airflow values - generally these need to be increased slightly with a larger (non-OEM) camshaft. Start with B4307 and B4308 - then look at the corrections parameters if you are still having issues.

[willn]

Sorry guys, it is DBC. My bad. I have got the idle airflow values to where it idles perfectly driving and cruising, but I am still at 150+ on steps.

Here is latest log and tune.

17549

17548

[johnv]

If it drives and idles fine, leave it alone.
If not crack the throttle stop open until counts are down around 30-50, be careful not to go too far or TPS volts may go out of range, (you may have to do a TPS reset) .
Then log and adjust Running airflow again.

[nm2769]

I agree if it runs and drives fine. Leave it alone. Don't get to caught up in the counts.

[willn]

It does run pretty well right now, but the shift feel very lazy and also anytime above about 10MPH, it still will basically drive itself. When I slow down to about 5-6MPH, it will act normal. I felt like it could be something with my torque converter. Is that possible?

I am attaching a log for the transmission run.

17550

[nm2769]

Have you read this tutorial https://forum.efilive.com/showthread.php?4661-Idle-Tuning-Helpful-Info-Inside ? Sounds like normal idle tuning issues after a cam install. I have had good results following these tips.

[willn]

Yes, I have been through that guide with a fine tooth comb and have done everything in it. The desired table is dialed in perfectly now based on logging DYNAIR vs. ECT in gear and in park. This does bring up another question though. To do the desired airflow based on Shawn's guide at https://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks in SD, I would use DYNAIR instead of MAF, right?

What about cruising? Would I need to take it out of follower or cracker even more than in the tutorial. The only reason I didn't think it was that was because I am at 0% throttle and just letting it cruise, so neither of them should come into play.

[willn]

So I thought about an idea, but not sure if I am on the right track here. What if I write a calculated PID that did the following:

"{GM.DYNAIR} - ({GM.IAC_SUM_DMA}+{GM.IAC_TC_DMA}+{GM.IAC_TF_DMA})"

My thought process on this would be that I can tell at "idle" conditions how far off of desired I am with the cracker and follower modifying my total.

Any feedback?

[statesman]

Take some air out of your cracker table.

[willn]

statesman, that's what I was going to try next, thanks man. Curious though. Do I even need any additional airflow from cracker if I have the follower? Could I just zero out cracker?

[statesman]

Follower is additional air "on-throttle". Cracker is additional air "off-throttle".

You can zero out your cracker table completely, but when you lift off the throttle your deceleration will be more pronounced without the additional air... particularly at higher RPMs. Some people don't mind the harder deceleration and set it this way. Personally, I'd just adjust it down enough to get rid of the cruise-control effect.

[willn]

OK, so I tried to 0 out the cracker table and it didn't work, i.e. the table didn't even program! I read it back after programming and it didn't change, so I filled it with 0.01 and it took.

Sad to say, I still have slight cruise control effect. Could it have anything to do with spark and/or torque converter? I have a 2800 stall and I am running about 24-26* of timing at that cruise RPM.

[statesman]

Zero out {B4338} and see if that changes anything.

[willn]

I had issues with stalling when turning to far to one side before. Would this bring that back, or do you think the trims will be able to compensate?

Also, did you see in my logs how much the STITs were bouncing around? Is that normal?

[statesman]

I had issues with stalling when turning to far to one side before. Would this bring that back, or do you think the trims will be able to compensate?


It probably will bring that back. If you've got stalling issues, then you need to add air to the Desired Airflow table.



Also, did you see in my logs how much the STITs were bouncing around? Is that normal?

No, I wasn't looking for that... I was looking for what's causing your cruise control issue.

[willn]

I did the RAFIG and RAFPN both using DYNAIR (since I am SD) and they are both dialed perfectly with this method, so I will zero that table and give it a shot. The trims bouncing so much is causing a slight surging problem. I can feel it and everytime I feel it I can see the trims changing.

So you don't think timing or torque converter would have any effect on cruise control feeling?

[statesman]

RAFIG/RAFPN is not a perfect method... it can give wrong values, particularly with cammed engines.

[willn]

Yeah, I was following Shawn's post where he used the MAF(or in my case the DYNAIR) vs. ECT instead of the trims to dial it in. I thought that method was much closer. It runs well, just the cruise issue and slight surge.

So you saying even Shawn's method can give wrong values too? I read that using the trims would give too low of values.