7427 hunting/surging idle

[1BadAction]

I'm about to pull my hair out here, 7060 idled fine, no hunting for an idle, same RPMs and nothing mechanically changed. Swapped to the 7427 and I can't get it to stop oscillating. I have made a few changes and its better, but still not gone in park/neutral. Is there a way to slow the IAC?

I've attached my tune...

[dave w]

Maybe you can post a data log? Maybe the idle is going into Async?

Please include the .adx file used with the .xdl file.:thumbsup:

dave w

[brian617]

I'm about to pull my hair out here, 7060 idled fine, no hunting for an idle, same RPMs and nothing mechanically changed. Swapped to the 7427 and I can't get it to stop oscillating. I have made a few changes and its better, but still not gone in park/neutral. Is there a way to slow the IAC?

I've attached my tune...

Let me know when you fix yours. Haven't figured out how to calm mine down yet either. :mad1:

[1BadAction]

Idle portion is at the end of the first log, and the second log is a little bit of me idling through a parking lot, foot off the gas... with a surge... :nono:

[dave w]

I only had a few minutes during my lunch break to crunch / combine both data logs. I used an Excel spreadsheet to crunch the data logs. The attached screen shots are a summary view.

Two things:
I did not see Async active at idle.
I did not see AE active at idle.

I find it interesting there are knock counts in the idle RPM / Kpa.

dave w

[1BadAction]

I find it interesting there are knock counts in the idle RPM / Kpa.

dave w
Comp link bar roller lifters, they're noisy. From the logs I have done looking at knock counts to fine tune my spark, it doesn't seem to effect anything above idle very much.

I understand it is slightly lean in the other light load areas, that's why the first datalog was long, I'm going back to adjust the VE tables this evening.

When I first got it warmed up with all the IAC tables stock, it would oscillate bad enough to hit AE. I almost eliminated the spark compensation and it is much better. The second bin is better than the first one I posted, that bin is the one that both of those datalogs are from. I seem to be going in the right direction, just wish there was a way to slow down that IAC response time slightly.

[Roadknee]

Have you changed any of the fuel trim parameters? The O2 switching points look lean and the fuel trim parameters look pretty aggressive for a non-stock engine IMO. These can contribute to surging at idle and low throttle settings.

[1BadAction]

The idle 02 switching points are there because anything more is extremely rich at that "low" idle speed. Even with the stock fuel trim settings, it would surge as it does now. They were the exact same on the 7060 and it was rock solid, in open or closed loop idle (stock was open loop idle, so thats what I used after I messed around with CL idle).

What other fuel trims are you asking about besides that?

[ony]

maybe the 427 is retarding the timming at idle then going back to normal?

[dave w]

Maybe the attached BHDC.bin will help? I used the BHDC.bin as a starter .bin file for 1987 1 Ton Pickup (454 / TH400) '7427 computer conversion. Maybe the BHDC.bin will have IAC, O2, and Idle parameters that will help?

dave w

[Roadknee]

The idle 02 switching points are there because anything more is extremely rich at that "low" idle speed. Even with the stock fuel trim settings, it would surge as it does now. They were the exact same on the 7060 and it was rock solid, in open or closed loop idle (stock was open loop idle, so thats what I used after I messed around with CL idle).

What other fuel trims are you asking about besides that?

I was looking primarily at proportional counts vs slow 02 error and slow 02 filter coefficient vs airflow. I only have experience with $OD tuning small blocks and the stock parameters are much lower than those in your tune. (Note that these numbers in your tune are the same as those posted in Dave's Bin) I had to reduce them quite a bit along with some other changes to get rid of surge is a 5.7 with a pretty good cam.

I looked at your log some more and you're getting surge from IAC that appears unrelated to O2 swings. Perhaps your cause is something different than fuel trim.

[dave w]

I compared .bin files (BHDC vs. BHDH-Suburban), there are over 2000 differences. I noticed many of the IAC and Idle tables are very different. The BHDC.bin file is a manual transmission .bin file, which works good for the 1987 454 / TH400 pickup I upgraded to a '7427 computer. I don't fully understand why there are so many IAC and Idle table differences, auto vs. manual transmission. I did not have any idle issues with the 1987 454 / TH400 '7427 upgrade. Sometimes "ZERO's" in a parameter table(s) is a good thing?

dave w

http://i239.photobucket.com/albums/ff290/buildabot2002/BHDCCompare.jpg (http://s239.photobucket.com/user/buildabot2002/media/BHDCCompare.jpg.html)

[1BadAction]

My truck is a 4l80E not a 400, so I can't just use your bin as a test. However, IAC tables should have little or no change in a 400 vs an 80E, so I'm going to look at these IAC tables and figure out how to attack it so I know which change made the difference in idle. It will probably involve idling in my driveway half the night with the emulator making one change at a time. LOL.

I think it's worth noting that a bunch of those 2000 changes are in the force motor and spark tables. ;)

[billygraves]

My truck is a 4l80E not a 400, so I can't just use your bin as a test. However, IAC tables should have little or no change in a 400 vs an 80E, so I'm going to look at these IAC tables and figure out how to attack it so I know which change made the difference in idle. It will probably involve idling in my driveway half the night with the emulator making one change at a time. LOL.

I think it's worth noting that a bunch of those 2000 changes are in the force motor and spark tables. ;)

My two cents.
If you can't get a handle on this, it could be what we found with the 4L80-E. The line pressure is a bit to high at idle. This causes the converter clutch to drag slightly. As this occurs, it will drag a bit more and bring the idle down. as the Idle goes down, the IAC backs out and Idle Spark adds to catch the downward spd. As the RPM rises, the items return to recover and go over. This cycle continues. As the cycle continues, we found the FM was turning off from calibrations in the VCM. This was set at 450 RPM where base idle was 600 @ the time. As the cycle continues, the cl still drags and when the FM turns off, the pressure rises hi and the cl drags more. Some stall and others continue.
I found a trans company has this Pres REg vavle to stop this. I called and talked to them. Don't buy it. The testing was on one vehicle and one test. IT was an invalid test and he claims this fixes it. It could IF he builds up the land to divert less oil volume to the cooler. Less oil to the cooler? This upsets the balance inside the converter and provides less to the gear lube. If he cut the land down to add cooler volume, it starves the other part of the volume for Clutch oil when needed under stress and hi temps. Use this at your own risk - I wouldn't.

What stopped these cases was to reduce the steady state line pressure at LOW Throttles like 0% and only. If you hang a line pres guage you can see this. Pryor years were released for correct this with a cal to flash or mem-cal.

I am VERY interested in what corrects this. I have a $6E or a 165 ECM running my BBC and I have NO IAC at start up. I use the small block Throttle body with wiring verified several times with a Fluke 87 DVOM and Fluke 77 DVOM. Several years of manuals have been checked. If I use the Tech-1 and command the Mode 4 RPM or IAC the system responds and takes off idling hi. Cold I get no RPM gain and you can't hear the IAC opening. I use the Bosch MAF. I have 6 ECMs and mem-cals. I have used a stock Memcal with a loaded cal in the PROM. COld or hot the idle is 675 or so commanded and actual. Idle tables and the same in P/N or D. I have no P/N sw. I have tried the signal grd or open and caled as Auto and Manual. But what gets me is the Tech-1 will activate the IAC and run the engine RPM hi and low. You can hear the IAC open as I use a K/N air filter for now.
So I too need help and am interested in this for myself.

[brian617]

I too suspected the IAC because I could see the IAC moving back and forth with the rpm, however I unplugged it and the idle continued to rise and fall. I guess the IAC was just following the engine speed change. Then I thought it could be the o2 sensor driving the idle back and forth so I unplugged it (open loop) and still no change. I've played with the o2 mean values, VE table and still :mad1: I even have the idle over/under speed spark corrections values cut in half from factory BIN.

[1BadAction]

I even have the idle over/under speed spark corrections values cut in half from factory BIN.
I cut the multiplier to .06 overspeed and .125 underspeed... which for the most part eliminated the spark compensation. That helped the surge quite a bit, but didn't eliminate it.

[96lt4c4]

I cut the multiplier to .06 overspeed and .125 underspeed... which for the most part eliminated the spark compensation. That helped the surge quite a bit, but didn't eliminate it. I am on my phone so can't look at you bin, what is your base timing? Timing is used to control idle more than IAC. Timing reacts faster. I would look more into a timing issue. Raise the timing at idle till you get the lowest KPA value you can, then back it off about 4 degrees. That should be you idle timing.

[96lt4c4]

Did you ever figure this out? Just looked at your bin, and your timing tables are pretty crazy looking. Your open and close throttle tables should match, at least in the areas around idle. You had 3 degrees difference. That could cause the idle to start to swing.

Try this bin.

[1BadAction]

Yes, it's fixed. I'll post up the changes when I get a chance on a PC. I'm on my phone in South Louisiana right now, and heading on to Florida in it tomorrow.

[96lt4c4]

Yes, it's fixed. I'll post up the changes when I get a chance on a PC. I'm on my phone in South Louisiana right now, and heading on to Florida in it tomorrow.

Nice, wish I was heading south myself.

[1BadAction]

Kind of forgot about this thread, but it was brought up again... So, after a bit of looking through other bins IAC logic in both OEs and ODs, I opened up my BHDH ($0E) tune, and a rock stock BJYM ($0D) tune in a second instance of tunerpro (with the correct XDFs, of course), then copied the BJYM IAC tables over to my BHDH tune, one by one. The SBC IAC tables are much less aggressive than the BBC tables are. The only other change I made besides this was to further lower the IAC flow VS IAC steps table, so (for example) 10% flow would be 13 steps instead of 21. On first start once it was up to temperature, it was NOT hunting, but idling a hair low. After about 10 miles driving around town with a few starts and stops, the ECM learned where it needed to be and it has been rock solid from then on, roughly 3000 miles and a bunch of starts and stops, from 15 degrees to 80+ ambient temps. I am extremely pleased with it.

[1BadAction]

I changed it the 9th but that was only to make a slight cold start and open loop fuel adjustment. The idle logic has been the same since I left Dallas on the 21st of December.

[brian617]

The SBC IAC tables are much less aggressive than the BBC tables are.

I wonder if it was a result of the change between the early and late style IAC passages on the BBC TBIs? I'm guessing the IAC logic in the 7060 was a lot less complicated?

I did some crazy work to my idle spark table and it seemed to help in my situation. Really cleaned up my cold starts. I'll post my .BIN when I get to my TP PC.

[1BadAction]

I wonder if it was a result of the change between the early and late style IAC passages on the BBC TBIs? I'm guessing the IAC logic in the 7060 was a lot less complicated?

I did some crazy work to my idle spark table and it seemed to help in my situation. Really cleaned up my cold starts. I'll post my .BIN when I get to my TP PC.
Possible, and the 7060 was much less complicated. It also had bad windup on a free-rev, where the 7427 IAC controls it very tightly.

Didn't need to do much of anything wild, just bumped the choke a hair richer. Now that I have the idle and VE nailed, it had a little bit of a cold start lean "dip" in the teens and 20s.