Idle issues and lean surging on decel at highway spees

[95GMC]

Having a couple issues on my tune which are kind of frustrating and I can't seem to fix. First issue is that in closed loop idle the engine is running lean and surging. I can see the factory narrow band o2 reading extremely low which agrees with my wideband which has read up to 16.5 or so when the worst surging happens, however, the integrator and block learn are both indicating rich? Doesn't make much sense to me.


I've tried more fuel and less fuel, neither helped. Tried more timing and less timing, neither helped. Is there something I can do to get the integrator and block learn to agree with the actual mixture? I also seem to be having this same issue in the low kpa range when coasting at highway speeds, the faster I'm going the worse the lean/lean surge gets. I thought maybe exhaust leak introducing extra air so I used the powersmoker smoke machine at work (goes to around 30 psi) and there are no leaks. Just to be 100% sure I ran it in open loop and had the same issue.


The rest of the tuning has went pretty decent and I'm fairly happy with everything else, if I can get these 2 things squared away I'll be ready to do some WOT tuning. I attached a log as well as the bin, xdf, and adx I'm using below and am running a 7427 ecm with $0D mask. I would really appreciate some advice on this, I've been pulling my hair out on this one.


One last thing I will note is for whatever reason my AEM wideband displays a slightly different reading than what tunerpro reads when using the linear egr trick to display afr with the supplied formula, so if you don't use my adx file the afr reading displayed will likely be off. Still not really sure why that is but with my adx they match up fine so I haven't invested much time into looking into it. Idle issue is near end of log, several decel issues in log but good one at 215 seconds run time, thanks again for any help/pointers.

[tayto]

what has been done to the engine? cam, etc. sounds like you are running lean if it's surging. WOT tuning is usually the first thing to tackle once it's ”safe” mixture wise

[95GMC]

It's a 355 running 9.5:1 compression with a stock lt4 cam. Has a factory 5.7 tbi unit bored out to 50mm and horns shaved off with new factory spec 5.7 injectors with fuel pressure bumped up to 18psi and 30 psi big block fuel pump in the tank. Edelbrock performer intake with summit vortec heads and shorty headers, I think that's pretty much it. I definitely need to get to the WOT tuning for sure

[tayto]

How does it run in open Loop? You can try disabling closed loop until you get ve map sorted. On near stock stuff not really needed but you are modified.

[tayto]

Here's a good thread to read: https://www.thirdgen.org/forums/tbi/...ing-async.html

There's even some sample bins you can look at!

[95GMC]

It definitely idles a lot better in open loop. I've only actually driven it in open loop once and it ran ok but I was mostly just trying to see if it would help with lean surge on decel at highway speeds. I found out something interesting today, I figured if the truck was actually able to idle right in open loop maybe I could just run open loop at idle so I did some research and found "stay in open loop idle temp threshold" in my bin and change it to max temp but the thing still goes into closed loop somehow??? Thanks for the thread link I'll definitely check it out

[ralmo94]

It definitely idles a lot better in open loop. I've only actually driven it in open loop once and it ran ok but I was mostly just trying to see if it would help with lean surge on decel at highway speeds. I found out something interesting today, I figured if the truck was actually able to idle right in open loop maybe I could just run open loop at idle so I did some research and found "stay in open loop idle temp threshold" in my bin and change it to max temp but the thing still goes into closed loop somehow??? Thanks for the thread link I'll definitely check it out

If I remember correctly, there might be a flag for open loop idle. You could also change maximum and minimum IDLE BLM and INT to 128

[95GMC]

Finally got the open loop idle to work by using one of the bin files from the thread tayto linked and doing the exact same thing I already tried with raising the temp qualifier... I guess somehow the bin I was using was corrupted or something? At any rate I transferred all my VE tables etc. over to that bin and I have a decent idle for now. Before I did this I tried several things and still couldn't get the closed loop idle working well, I'm not sure what's going on it's a very mild engine in comparison to some I've seen on here and other forums that idled well in closed loop. I also drove the truck again and still have the lean surge only on decel from say 30mph and above that gets worse with more speed. I guess for now I'll just drive it and do some of the WOT tuning. I guess I could always cheat and enable the DFCO earlier so it can't physically run lean since it's not technically running but I really want to fix this the right way, whatever that entails.

[ralmo94]

Finally got the open loop idle to work by using one of the bin files from the thread tayto linked and doing the exact same thing I already tried with raising the temp qualifier... I guess somehow the bin I was using was corrupted or something? At any rate I transferred all my VE tables etc. over to that bin and I have a decent idle for now. Before I did this I tried several things and still couldn't get the closed loop idle working well, I'm not sure what's going on it's a very mild engine in comparison to some I've seen on here and other forums that idled well in closed loop. I also drove the truck again and still have the lean surge only on decel from say 30mph and above that gets worse with more speed. I guess for now I'll just drive it and do some of the WOT tuning. I guess I could always cheat and enable the DFCO earlier so it can't physically run lean since it's not technically running but I really want to fix this the right way, whatever that entails.

You might think about switching to a 4 wire o2 from like a 98 or something, and run the signal ground right to the pcm wire that grounds on the engine, and not ground that on the engine, to make sure you are getting accurate signals. Otherwise the signal ground is on the exhaust pipe.

[95GMC]

That's a great idea and heck for the price I'll definitely give it a shot

[ralmo94]

Make sure you DON'T connect signal ground to heater ground

[95GMC]

Oh yeah for sure definitely don't want to try to pull 5+ amps through the signal ground haha I imagine that'd fry the driver in the ecm pretty quickly

[tayto]

disable DFCO and see if the lean surge goes away. it is one of those things you should enable AFTER you get your VE table dialed in. Since you are running headers,.you will probably have to mess with proportional gains. A 3 or 4 wire is a good idea for headers IMO.

[ralmo94]

disable DFCO and see if the lean surge goes away. it is one of those things you should enable AFTER you get your VE table dialed in. Since you are running headers,.you will probably have to mess with proportional gains. A 3 or 4 wire is a good idea for headers IMO.

There may also be a Decel ENLEANMENT

[95GMC]

My truck does have a factory 3 wire o2 but I'm going to do the 4 wire swap anyways, I like the idea for sure. I have dfco disabled when this happens but I'll make sure to disable decel enleanment before I take it out again.