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2G idle surge/stumble on snap throttle/cruise&boost fine to 150mph

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smbgsx

Proven Member
225
42
Apr 15, 2017
Richfield, Minnesota
1995 gsx
fp2 cams
6-bolt magnus bottom end (compression test yesterday: All cylinders = 95psi first crank, 168-175psi after 5 cranks. throttle 100% open.)
fp3052 turbo (garret gt3076 with different hotside)
external wg with dump pipe
coil on plug conversion (no ignition box)
front mount
id1700's
3" catless
ecm v3 with SD setup.
e85 tuned
cant find any vacuum leaks.
I don't have a boost leak tester, but I cannot visually find any boost leaks. all clamps tight and couplers intact.
fluids look appropriate (no coolant in oil etc...)
I do have a exhaust leak in my header around my egt gauge bung, im not sure how to fix it at this point. I've tried sealing it like 3 times. that lasts about 3 weeks.
I unplugged coils one at a time they all contribute evenly.
I disabled injectors one at a time they all contribute evenly.
I don't have an oscilloscope. I wish I could see what my ckp and cas were doing, see what my coils were doing. but I cannot.
I recently did timing belt with mistu pulleys and tensioner, gates racing belt. all the timing marks appear to line up although I feel like the idle got weak after the timing belt. but it ws starting to develop cold start issues and wouldn't hold idle as well as it once did shortly prior to the belt R&R. so I not sure if they're related or not.
noticed my throttle cable has a strand that is broken and un wound slightly, don't know if that would effect anything.


My issue is a weak idle and stalling at times when coming off throttle to idle. it is less prone to stalling after warming past 122-degrees or so, but its still weak and fluctuates.
It seems like sometimes it idles at the correct target rpm, but its just not strong there. if I snap the throttle there is a bog down to near 400 rpm and then bounces around. If I open the throttle really quick I can get it to stall. If I ease the throttle and get past around 1500 rpm I can pretty much do whatever. It does idle around 800 when warm which is not its target.
The car cruises fine and still rips hard. it does have a small intermittent miss at idle but it always has. my wideband recently took a shit so all I have is a narrowband gauge. it is a brand new sensor and it tells me im idling rich of stoich at all times. fuel base pressure is set to about 43 and is running around 37-38 with the vacuum line hooked up. my boost gauge says im idling at 15 in/hg, which I feel is lower than it used to be. I used to be around 17-18. but my idle was higher then too. my ecu target idle has always been 1100, but I was typically really around 1300. I just did my timing belt and im not sure if this issue was related. cold start is way better since the timing belt, but my idle stability has gotten worse. but it was deteriorating already before I did the timing belt and many mornings it wouldn't want to move until I got some heat in it and then ripped it hard one time. then it would drive normal. Now its starts better, but the stumble on wot from low rpm never really goes away. just to see what happened I advanced both cams 4 degrees and ran it. no change. I retarded both cams 4 degrees and no change. I did notice that my intake cam didn't want to move on its own like my exhaust cam does after loosening the cam gear set bolts. I looked under my valve cover after doing my belt and didn't see anything of note. so I don't know maybe my cam was just in a spot where the springs didn't want to rotate it?
I do have logs, don't know if it will help. One is all idle and throttle manipulation. the other is my start-up and drive to work. I hit 150mph in that log at some point. please don't judge me LOL.

any help or direction would be appreciated.
 

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Add some base tip in to give the injectors a bigger squirt when you stab the throttle. Shud help the bog, thats what it is for.
 
thanks I'll try it out, where should I adjust. there are settings for 0 to 8. I ask because I really have no reference as to what those numbers mean LOL. I have a good concept of tuning theory, just very little practice. the tip in adjust is basically transient enrichment, I know in other software you will have adjustments for attack (commanded increase) and sustain (duration). for ecmlink should I think of the vertical axis as attack and the horizontal axis as sustain?
 
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the leak at the egt bung or any exhaust leak can cause the intermittent miss at idle.

if your running e85 how can you tune the fuel without a wideband. If your using the narrowband, which is calibrated for gas (14.7:1) your fuct cause stoich on e85 is (9.765:1)
 
Smbgsx, I just play with the tip in. Add more at the initial slope and make a nice curve and see how she acts. I play with this stuff just to see what it does. Can always chg it back. :thumb:
 
dusty I tuned on a dyno, and stoich for e85 is 9.87 btw, usually rounded up to 9.9.
my wideband shit out like a month ago because I used to run c16 leaded race fuel. The best we are going to get at the pump by federal law is e83 anyway. they don't mix true e85 at the pump anywhere. even the flex fuel function in aem infinity has stoich for e85 set for 10:1 I believe.
I tried turning off closed loop so the ecm would ignore the o2 sensor once, just o see if the miss went away, and so my fuel trims didn't keep pulling richer and richer in an attempt to make up for an indicated lean mix that really isn't there. it made no difference honestly that I could see.
I have the car on the lift right now and didn't have a chance to get to it today, I will play with it tomorrow and see how it goes. I hope it is just an issue related to tau and upping the accel enrichment fixes it.
but what about my weak idle? Im going to lock the PCM in base timing and use a timing light to verify my base is on point tomorrow. I have heard if I have a failing IAC that unplugging it should let the idle come up to the target base idle setting and that would give me an indication of where to look next. maybe do some pinpoint tests with a DMM on the IAC and TPS sensor? is there anything else I can check? it surges like crazy after a minute or two of idling and eventually dies. Maybe I have 2 issues, one being my accel enrichment (I did put in a higher flowing filter and fix a leaking exhaust manifold gasket after the car was tuned. im guessing this really helped VE because its been a little off ever since those upgrades).
thanks for all the help.
 
also why am I always running in the 900mv range on my o2 sensor? that's pretty rich, and it doesn't cycle at all. should I increase some of the numbers in my ve table at idle? like I had mentioned I did fix a pretty severe exhaust manifold gasket leak and added a much larger air filter after tuning on the dyno. I know factory calibrations target 450mv at idle and cruise and cycle rich to lean rich to lean. normally up to about 800mv then back down to 350. a nice sine wave that is steady.
 
You would want to decrease the areas in your ve table where your rich, not increase it. Your o2 sensor is measuring Lambda so it doesnt matter really that its setup for gasoline, the trick is that it is DISPLAYING the stoich for gasoline, the Lambda for gasoline and E85 and basically any other fuel is the same, ergo its a chemical reaction measurement, we want a Lambda of one for most all motor fuels, in the case of gasoline that is a chemical afr of 14.7 to 1 in the case of E85 it is a chemical afr of around 9.7 to one or so, a Lambda of one means that all of the fuel has combined with the available oxygen, its that simple so 14.7 to one and E85 at 9.7 to one are both Lambda one, therefore if your stock o2 output is showing proper afr for gasoline its proper afr for E85 being displayed, that being said the narrowband is just that, a narrow reading of afr, not desirable for tuning at all but good enough for cruising around or idle where you would only need a Lambda of one.

Performance cams and E85 is pretty much asking for idle problems, the E85 especially when cold does not atomize as well as gasoline and needs fine tuning to make up for this, and the cams because of the trade off of max power vs driveability due to cam overlap, they need an isc that can move faster and flow more than our stock unit was ever designed to be able to do, alot of owners bandaid fix this with a higher base idle to get past the poor idle area where the cam causes pumping loses in the engine (inefficient area in the cam design) and just depend on the isc to try to keep it in that area.
 
Gotta agree with Motomattx, DECREASE your number in the idle cells to lean it out. This should start the O2 sensor cycling. When you get to the right point, the sensor will tell the ECU that it sees a rich condition so the ECU should cut fuel and the sensor will then see it go lean and the ECU should pick it up and then add fuel. Its a normal cycling event if it is working correctly. It is a good sensor, right?
 
I was going to type what you said about o2 sensors using 14.7 as the multiplier as I am aware of how they work. but I was too lazy LOL. the sensor is brand new and a bosch, so im guessing its working properly.
I tried playing with the throttle tip in today. it may have helped a little, not much though. ill play with the ve table tomorrow if I get a chance. my car used to idle solid after it was tuned on the dyno. why would it run worse for no apparent reason? its been progressive over the last few months. all ive changed was a going from one cast header to another and replacing the defective gasket. I did put new gaskets in my exhaust system too
I appreciate the feedback on decreasing the ve table, I was thinking of it backwards, I had in my mind that the changes I made would increase ve, (and they may have), but the table was wrong to begin with since it was calibrated with the leaks (and false readings that came with them).
but... if im spiking lean on tip in and I lower the ve table portion at idle wont it make that problem worse?
In case it makes a difference, the problem is near non existent if the engine is under load. even letting out the clutch at a stoplight I don't really notice it. its basically only if I snap the throttle in neutral I get that momentary bog. driving home tonight I didn't even notice it.
thank you all for the continued input.
 
Richening the VE table wont cover the "hole" you create when you stab the throttle all of a sudden. Thats the tip in's job like an accelerator pump on a carb just to put it in a different perspective.
 
If it didn't help, then put it back to the stock settings, or close. I thought it would help more than you noticed. Still trying to think of what is happening when you stab the gas. It shouldn't stumble....
 
yea I don't know, I made small adjustments at first trying to keep a slope, then after 3 times of not seeing any difference and having to turn the car on and off each time to update it I just maxed everything. if it made any difference it was slight to near unnoticeable. I unplugged my IAC to see if I could notice a change and I'm not really sure. Idle seems the same plugged in or not. I drove it home from work unplugged and if I hadn't have done it myself I wouldn't even be able to tell something was unplugged.
 
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