Is the FPR vacuum port connected to full time vacuum? Has the internal FPR removed and a block off plate in place? Was the modified BIN flashed in? There should be very little difference in the VE values between the non-VRFPR and the VRFPR.

RBob.

 

That may be expected. Lets say 35 MAP 65 VAC the BPC has increased quite a bit with a drop in fuel pressure. If you look at the WU you may see a big change in PW of injectors. Each VEL should be better. What is the BLM showing in CL at idle?

 

I found my problem I modified the VE table too much trying to compensate for the changes in BPC and FP I copied my ole VE table in and it was much better within 10% thanks tho ... And my blm is locked for wideband O2 learn

 

Ok ... When my engine is cold it fires right up no problem but after it gets good and hot if u try to turn it off them right back on it don't wanna crank it acts like it's not getting enough fuel or something like if it was carbureted it acts like u need to flash the throttle a couple times to get it to crank ??? But if u let it cool off for 10-15 min it fires right up ? Thanks ! Ima post a couple screen shots if y'all can make out anything tht needs adjusted please inform me of what I need to do thanks again !


Sorry I couldn't post the whole data log ... My internet at the house is down right now so I have no way to do so .. This is the only way I could figure out how to post some of it I tried to get different map loads and TPS percentages so someone might be able to find what they need to help me get a tune nailed down ... I still haven't really been able to get a good full day of VE learns in yet due to weather ... It should be back up to around 60 all next week with no rain so I hope to get the tune dialed in within the next week so I can actually hammer down on this thing n see what it will do ... It's mostly way too rich right now so the power is way down with the AFR :-/

 

I am experiencing an intermittent misfire that I can't figure out. A little about my set-up:
350 vortec, mpfi edelbrock 3500 intake with the edelbrock (pico) 35lb injectors, 255l fuel pump, EBL flash, mild roller cam, Vortech S trim supercharger installed ain a 93 k2500 with an NV4500 tranny.

It feels very much like an ignition misfire, and generally happens when the vehicle is warm at low rpm <1800 and high load >60kpa. It has never misfired during idle, on occasion it misfires at higher RPM and higher load, but generally doesn't misfire at high rpm low load. All exhaust primarys are the same temperature.

I have exhanged every ignition component several times, and still have the issue present. I have exchanged the following components with known working parts:

Plug wires, coil, distributor and module, ESC, leads from dizzy to coil. All new engine grounds, no voltage drop at ECM grounds from battery. New fuel pump and fuel filter. New fuel injectors.

I have ran various types of spark plugs and gaps. Currently am running R44LTS gapped at .45, in the past ran 41-933 at .60. Plugs look good when changed and no signs of carbon tracing, all cylinders appear to be evenly fueled.

Compression is 135-145 @ 8700 ft altitude. Leakdown test shows good results with all cylinders < 12%. Fuel pressure is steady at 43PSI all the time.

I have thoroughly inspected the wiring of the injectors. With the current set-up I have 15.5 +/- .1 ohms resistance at each injector, and when measured at the ecm 3.9 ohms for each bank. All resistance testing performed cold. I performed a variety of other tests and don't believe that I have a poor connection, or a short to ground.

At this point I have no clue how to procede. There is no indication of any issues in the logs. The only thing that I can think of doing is spending some money on a scope and scoping out all of the critical signals: Injector driver, MAP, TPS, Tach, etc in case the ECM is unable to catch an intermittent signal issue.

Please let me know if there is anything that I am missing here. At this point I feel that the only thing that can be the problem is the ECM, as I think I have exhausted all other possibilities.

 

Also this is how my low speed is shaping out ...
Any suggestions? idk y the 2000rpm 20 kpa cell keeps pulling down like that? I've pulled it back up twice now





High speed has only been learned in the lower rpm area mabey up to 2600 and a few cells here n there up to mabey 3600 .. Whenever I get a high rpm cell to hit I always smooth the surrounding area to that learned cell

 

some questions/comments to some older posts:

There's a BIN in the EBL files that has a inj comp table for bigger injectors at higher fuel pressure, you might wanna check that one out just for reference.
also i'd think that there wouldn't be any difference for compensation between the different size # injectors, but not sure.

you have talked quite a bit about resolution of this table, while i don't think anyone else is really concerned with it. i recently had problems with injector offsets and i learned how critical they are. but if you look at accels table, the resolution of the EBL sure is good enough - everything between the data points you enter in the bin will be interpolated!?
imho you're still looking at some other problems. you said you run into issues with the fan or other electric acc kicking on. does your voltage actually drop then? it might be still a problem of your IAC or other idle issue?


Bob, are you talking about INJ - Small PW Correction - PORT Only?
I still don't get what this table is about.. if you could shed some light on this please? thanks!

i use this program for interpolating, or more correctly, "sampling" the data from the graph in the accel data at the correct sample points (the voltage breakpoints in the EBL table) - http://www.frantz.fi/software/g3data.php
that's a good point btw on the n-heptane, haven't taken that into consideration, thanks. on the p/n, well i think most parts are made by someone else anyways

 

does it windmill when it's hot, like, crank cleanly without firing, crank with some intermitting firing, or...? does it start up when you give it some throttle? you could try to spray it with some carb cleaner or "starting spray", if the calibration doesn't have enough fuel for hot start then it would start that way.
also not sure if you're aware of this, if you depress the throttle over a specific amount it will go to "flood clear mode" and not inject anything (or only very little?).

I was gonna suggest experimenting with plug gaps since you have tried about everything else, but seems that is not it. thought it might be possible the spark is blown out.. you mentioned load > 60 kPa, so that's still under atmospheric (off-boost), right?

 

I was gonna suggest experimenting with plug gaps since you have tried about everything else, but seems that is not it. thought it might be possible the spark is blown out.. you mentioned load > 60 kPa, so that's still under atmospheric (off-boost), right?[/quote]

It does feel very similar to spark plug blow out. I feel that I have exhausted everything ignition related, but may have to re try switching out wires 1 at a time, even though they all ohmed out good. I am running Accel 9000 wires, have tried both a stock distributor, a MSD billet dizzy. 2 MSD coils and the stock coil. As well as various working Caps and Rotors that I had around

The vehicle ran great for a long time, and then it seemed to start doing this after I got gas one day. I changed out the fuel filter and the fuel pump but still experienced issues. I wonder if it is an intermittent fuel injector issue. I may try to exchange the injectors with some Bosch injectors that I have, that didn't all flow evenly and are probably due for service but may help with diag.

It also seems like it will run good for the first couple hundred miles with fresh plugs, but then the mis will develop again. However, it is so intermittant that I am having any troubles correlating it to anything. I have my wbo2 on 1 bank and my nb on the other. When I experience the mis I sometimes see 1 bank go slightly lean. It doesn't appear that it is limited to 1 cylinder.

I have exchanged so many parts and played with the tune at this time, and it almost always feels like I solved the problem, but then it just randomly comes back.

 

No it acts like it's flooding mabey ... Like it will crank and barely chug chug chug at like 400 rpm and never gain any rpm ad eventually die or just keep chugging at 400rpm for 30 sec or so

 

if it was me, i would do it like this:
a) check if engine is actually flooded by cranking in flood clear mode for like 10 seconds and see if the rpms or sound/characteristics of the cranking engine changes
b) if it does, and you're not getting an occasional firing, you might have too much fuel (IOW it's flooding)
c) if it doesn't, you have too less fuel or a spark issue. you can try to diagnose too less fuel by using starter spray as mentioned.
that's my 2c

 

Low and high speed VE tables ... And here a
Couple dump old pics



















Any suggestions Based on these pictures ? Thanks for any help !!!

 

We'll I may have found the smoking gun. Sprayed the plug wires tonight and noticed some arcing, primarily wire to wire but some wire to ground. These are accel 9000 about 6 weeks old, my previous set of these wires were great but this set failed in less than 1000 miles, and I wouldn't notice a misfire with new plugs. I did notice that the new accel 9000 wires have black boots and the old had silver, this may be indicative of changing manufacturing from Mexico to China. Anyone know who still makes good plug wires these days?

 

For me I used MSD 8.5mm on my Xfire for years, and do same on my LT-5 now

 

+1 on MSDs, or from what i hear Taylor (?) are also supposed to be good, otherwise maybe DUI if you go with their coil and distri (might be overkill?). anyways glad you got it figured out before messing with scope and such. I myself am not a too big fan of the Accel stuff tbh. If there's anything to their stuff it's only that it's yellow and that's about it lol.

1991sleeper you should try to get your internet fixed, we can work way better with you if you can supply the current bin you're working on and some dumps/logs. plus photographs of screenshots are just devil's work in my book heh

for me personally nothing at all to comment on the shots you posted, low VE 20-96 seems kinda odd tho unless you're using a stump puller engine that's kinda all done at 4krpm.
what problems are you looking at? not sure what to look for... we need more input.

also have you tried my suggestion for working around the hot restart issue?

 

Had some more time to work on it. New injectors in with known constants.
Got it running pretty good however.....
BLMs 128 +/- 2.
Stoich is 14.7 or 450mv on the narrowband-correct?
O2 window terms are adjusted to 450mv mnR/L with rich/lean +50 and -50.
With the wideband TT1 set at 14.7 for stoich the afr would show 13.8 to 14.2-since we run 10% around here and stoich for 10% is 14.1 so I figured I had it.
BUT then on the TT1 I changed it to 14.1 stoich and the wideband was then reading low 13s and the lambda corresponding.
I have to pass smog here in Kalifornia......so really need it 14.7 or actual 14.1 for our 10%.
Do I need to skew the O2 window terms lean to obtain leaner for what I need?
If the narrowband goes for stoich I just don't understand why the wideband wouldn't match the narrowband.
And I still can't wrap my pea brain around changing stoich on the TT1 to 14.1 made it show so much richer......what's my real afr????!!!! Arrrrggggghhhh-now I have to laugh at myself!

 

13.8 suggests you are running rich. Wb's are typically dead on.

Yup you are rich.

is the NB cycling over 450? cross counts occuring?... Or steady 450?

In the analysis do you see millivolts constantly changing?

During steady cruise not lean cruise I see in CL my WB A/F cycling back forth back forth over stoich

 

Yes I got the hot restart thing fixed ... Now I'm just trying to get it tuned for best performance drivability is pretty good most of the time I just feel like there's ALOT of performance left in the tune ... And about the stump pulling thing with this cam I should be shifting at 6000 rpm ... And everytime I start to get VE close I run into VE overflow ... So I uped the FP from 22 to 27 PSI @WOT and left the BPC alone .... I'm running the 3006 bin SA tables and really haven't changed much from the stock bin except the obvious stuff AE, PG, SA, BPC

 

Hey Nate, not sure on how much power you were planning on this build but it usually goes a long way to up the FP enough so you don't run into the VE overflowing and having to redo your tables There's this EBL Utility that comes with the EBL to give you an idea for that, I take it you got your BPC calculated from there anyways(?) but just sayin.. I might have missed it but did you list any build details yet?
Sounds like you're on the right track in general tho; by the way what was the remedy for your hot restart issue?

 

How can I post a copy of my bin and a dump log ? I'm not real good with computers :-/ ... This laptops only use in life is tuning my car

Oh and another thin that I think may be affecting my tune is after I installed the under drive pulley set while driving my IGN voltage is only about 13.5-13.8 and pump voltage is around 13.7-13.9 at idle it's down to 12.5 12.6

 

Yes u can check out the full build on my thread titled " LO3 Rebuild (HP estimates) ... And from what everyone has said this combo shouldn't make more than 330 hp which is where I started my FP and BPC and now I'm up to 27psi w 68# injectors which is "supposed" to b good for 370
Here's a link to my build thread my combo changed along the way so I'm not using swirl ports like the first page of thread indicates I'm using trick flow 175's thanks for all the help man !

https://www.thirdgen.org/forums/tbi/....html?styleid=

 

i see, reason i'm asking is i was wondering how you were gonna pull off 6krpm shifts with swirl ports ("L03 rebuild") but as you said plans changed and you moved to the trick flow 175s which doesnt sound like a bad combo at all. anyways, 27 psi and 68 lbs injectors is huge fuel already in my book.. what ranges were you getting the VE overflows at anyways?
and one more just to clarify because of this line:
you would typically set "static" or "base" fuel pressure at atmospheric pressure (read: with the vac line [of the FPR] disconnected).. should be close to whatever it reads at WOT tho (well, depending on the intake manifold and stuff, but just sayin). also, BPC should be adjusted to what you get out of mentioned EBL Utility for starters. and you also should change your injector offsets since you bumped up the FP quite an amount, but not sure if you already messed with that.

 

Yes I set my FP with vacuum line unplugged at 22psi to start with and ran into VE overflow @ 1400RPM 90KPA ... So I unplugged the vacuum line and bumped it up to 27psi and hooked vacuum back up and it sets at about 20PSi at idle (700RPm 17in. HG) .... And the intake is a summit brand dual plane 1500-6000 RPm advertised , with a small section of the divider removed ( 1" down 2.5" long) and port matched to the heads ..... And I have not messed with inj offsets or anything like that and wouldn't really know what to do with them And that 27psi is measured at the inlet to the throttle body with an autometer in car electric gauge Where the dot on VE table is was VE overflow and even after 27psi it's still at 91.5 VE @ 1400 rpm ? I still got 4500 RPM to go and only 10% VE headroom ... Just doesn't seem right then the VE drops back off from 1400 To like 2200rpm then start goin back up ??? Makes no sense to me... Last VE learn which resulted in these VE tables

 

Yes the narrowband does cycle back and forth and the wide band reflects that also-I was giving avg numbers on wb.
Guess I'll try adjusting the O2 window terms to try leaning it out.
Anyone "dampen" the wideband to get a steadier readout from closed loop?

 

Well I hooked up my FP gauge to the Ebl on a adc channel today and unhooked the vacuum reference again and my fuel pressure is actually @ 30 psi under WOT or high kpa conditions ! WTF ! Why is my VE so high at low rpm !!!! I know this thing ain't gonna make 400hp !!! Even tho that would b awesome for a 305 lol

 

i'm not quite sure what you're trying to achieve (WB reading jumping too much?) but you can do that by going to File->Preferences->ADC Channels in the WUD, then selecting a higher filter value for the WB channel. i usually use about 10% for the ZT2 but have never messed with it so far.

that's crazy, in my book there's no way you could run out of fuel at that little engine speed with that combo.. cause high MAP would dictate you're actually getting the static fuel pressure (22 psi) so that's some massive fuel there. that might be something with the injector offsets imho, since you stated VE would drop off again till 2krpm, that's strange.. see the injector needs a longer time to open and close since the added pressure acts agains the pintle, make sense to you? so that needs to be changed for higher pressure.. do or search first it's been done a few times in this thread, but i guess we could work it out too, otherwise.
also -- how did you actually do the VE learn? i see you do have a T5 so that makes things easier (you can hold it at a given operating point better than with an AT) but still, how did you learn that 1400rpm high MAP VE point in? steep hill grade, high gear?

and just to make sure, you're running the VRFPR off manifold vacuum (behind the TB), not ported vacuum (before the TB), right?

at the inlet to the throttle body, hmmm... someone needs to confirm this for me but i *think* you need to measure the pressure in the return line on the TBI?
dug up an old link for my "reference install" of an external FPR for TBI:
FSC Full Size Chevy External Aeromotive AFPR he's running the FPR and the gauge off the return line..!

btw you can upload a .bin or any other file (note: size restrictions apply) with the "Manage Attachments" button in the "additional options" tab under the post, if you hit "Go Advanced" first....

haven't messed with the ADC channels or fuel pressure transducers myself but need to check if the range of the sender is maybe only 0.5-4.5V instead of the whole 0-5V range or similar, you could get an error in the reading there. just sayin to check before being dead sure on the readings in the WUD, as they differ from the sender manufacturer's gauge.

 

i know i should just edit my previous post but think it would get too crammed.

injector offsets: just looked at you pics Nate and it looks like you have what is called the "bathtub curve", where at one side you get high VE at low rpm, then it goes lower at mid rpm and then rises again with higher rpm. as said do a search here and also refer to this here: http://dynamicefi.com/Tune_Intro2.php "Injector Compensation"

measuring fuel pressure: i was wrong. the "rail pressure" (pressure reaching the injectors) is of course only apparent before the FPR, which in this FSC guy's situation is at the fuel pressure regulator interior, BEFORE the external FPR's return line port which is at the _bottom_ on the aeromotive reg (you can see the braided hose going behind the engine = return line).
well anyways, you have to measure it in the feed line, before the FPR.
might wanna give some details on your FPR installation anyways.

 

Yes the FP gauge is .5-4.5v 0-30psi gauge ... And I'm reading 29-30 psi on the Wud and the gauge .... 20 psi at idle .... The return line on the regulator is hooked up to the return line on the frame rail ... Everything else is hooked up to the inlet/outlets So the preassure should be static or equal on other 3 lines ? Transducer on back of TBI on feed line An yea I think I used a steep grade and a high gear to get that learn about 60% throttle .... And I also use the e brake during learns sometimes too .... E brake helps slow the rpm rise a lot !

Do I increase the inj correction offset or multiplier ? Or both ?

 

Shouldn't plumb the FPR/TBI like that. You are dead-heading the TBI off the FPR, which causes any vapors to go out the injectors.

Need to feed fuel directly to the TBI unit. Then the return port on the TBI unit (pass side) goes to the FPR (a side port). This way the system is recirculating through the TBI unit.

The return off the bottom of the FPR is fine, no need to change it.

Can put the gauge port either on the feed such it is now. Or more it to one of the side ports on the FPR. On the FPR is probably better as it is post the fuel usage point.

RBob.

 

pic one looks good provided the braided line is going straight to the frame feed line (well see below, seems it doesnt ), and black line going to some pressure measurement (transducer).

other pics, wow that's quite some plumbing there. on the aeromotive, bottom line = return line of regulator hooked to frame rail return line - okay. but eeeeh, the frame feed line is on your fpr as well? did you feed it to the center distribution port and then make it run to the braided feed line on the TB, and plugged the return port on the TB? interesting setup. never saw it done that way, but that doesn't mean it doesn't work that way.. just sayin.
the braided line on the black top hat of the AFPR is vacuum - where did you hook it up? needs manifold vac (from after the TB) as mentioned.
just doublechecking everything here.

on the injector offsets.. check out the dynamicefi link i posted and search around this thread here.. and/or read this here and onwards: https://www.thirdgen.org/forums/diy-...ml#post5287957

edit: ok just saw rbobs post, seems there's something fishy with the afpr plumbing indeed. you might also wanna check out the FullSizeChevy link i posted earlier, as said i think it's a good reference on how to do it.

 

Need to feed fuel directly to the TBI unit. Then the return port on the TBI unit (pass side) goes to the FPR (a side port). This way the system is recirculating through the TBI unit.

That's exactly how it is ?? ... The side ports of the regulator one goes to TBI feed one goes to TBI return and one comes from fuel pump feed .. The bottom goes to tank return

 

Ok the fuel comes off the frame rail from feed line into a side port on regulator then comes out of another side port into the throttle body then comes out of the throttle body back to another side port on the regulator and out the bottom of the regulator back to the frame rail return line ??? I don't see the problem ? An the vacuum hose goes to manifold vacuum on the TBI unit .. The far left port on front of throttle body ...



Edit: update ! I copied over the inj correction offsets from the 113' head bin with 22psi and my VE tables look much better after the first learn .. I think they may need slightly increased more seeing as I'm way over 22psi .. But it definitely helped get the VE away from overflow ! Should I copy over the multiplier table also ?

 

See attached picture. Need to change it as such:

Disconnect the two lines that are circled in red.

Connect the two lines together via an AN-to-AN coupler.

Use two AN caps and cap off the now open ports/fittings on the FPR.

RBob.

 

Ah ok I see what ur saying .. Thanks for the help

 

Well I did as u suggested with the FPR and actually had to back off the regulator about one full turn to get the same preassure I was reading (27psi)

 

This sounds like a throttle stomp, AE issue?

You can also see false overflow (demand) if delivery does not match commanded values, pump consistency is vital.

 

My MSD 8.5's came with defective assembly and turned to complete crap within 3 years.

I don't care for Taylor's boot design, but their wire has a long history of top quality.

This time the beast just got Summit's 8.5 stuff, they can't be any worse than the MSD were.

Someday, I will build a set of Taylor's with boots I like...

 

Actually this was cruising with very slow throttle increase up a hill and using the ebrake to increase load and was the third time I got VE overflow in that area and I have increased fuel pressure 3 times

 

I also am using summit brand 8.5's ... My experience with any MSD stuff has not been good so far no complaints here with ANY summit brand stuff even tho I prolly wouldn't use summit brand on any critical internal engine components :-o except rocker arms which I have

 

I see, then PE/time might be helpful.

I had top end problems, 'till I got real serious like these SX pumps (bought out by Edelbrock) http://sxperformance.com/Fuel_Pumps.htm , about pump supply.

Aeromotive also sells the SX pumps with their name on it. I'm not suggesting you need that much pump. http://www.diyautotune.com/catalog/a...ump-p-528.html
But.
When high PW condition's o2 readings don't respond to the changes you make, it's a good indication actual delivery is not what you are asking it for, and I found that to be the case in my situation.

I had a problem with the summit brand big-slot, stepped, pushrod guideplates in my mildly (.575") cammed rat, so I just enlarged the stockers for the win. It has been said they sell Asian copies of some parts.

 

I dont believe AE will affect the VE Learns. I believe RBob has that disallowed in his software. Exhaust leak will however in a big way but that would be globally I would think. Maybe more so at lower RPM's.....

I have never achieved Learn at 90 MAP. Not many mountains near me. Maybe i tow my ski boat with my Vette?

 

It will require less VE when need is satisfied with AE.
But
I try hard to keep the demand covered as much as possible with VE, keeping the supplements moderate as I can. This overall may not be the best mileage strategy, I've not yet tried to lipstick my pig.

Anyway I got sidetracked, to get it to stop overflowing the BPC needs changed to center the table on the graph.

 

Anyway I got sidetracked, to get it to stop overflowing the BPC needs changed to center the table on the graph.

What exactly do u mean by this ?

 

I think it's maybe best that RBob explains this 'cause I will might did say it backward lol, (edited to correct) too many egg-noggs tonight, burp.

BPC= 1461.5*(volume/flow rate)

Raising the BPC will require smaller values in the VE table for the same fuel and vice-versa. In this fashion you can move your whole table up and down on the graph.

That should be right, RBob will fix me if not.

 

Rbob-I need some help again.....
Wideband shows .94 to .95 lambda closed loop.(10% ethanol fuel/same with TT1 set at 14.1 or 14.7 lambda) AFR 13.6/13.2 Avg.
I need to lean it out for smog-trying for 14.7.
I adjusted the O2 window terms all the way down to mean 300/rich 350/lean 250.
When I switch to that bin it will initially lean out, then blms adjust up to 140s and the afr/lambda go right back where they were.
I thought that by adjusting the O2 window terms it would hold it leaner or richer in closed loop????
Is there another table along with O2 window terms that has to be adjusted to let it hold it?
Thanks, Pete.

 

Some questions on AE:
1) why is there this <TPS% Double MAP Threshold? maybe for big-cam engines, to avoid going into AE for oscillating MAP at idle?
2) I saw this earlier post quoted above, where there was a >TPS% Double MAP AE threshold.. just wondering what that is/was used for and why this parameter disappeared.
3) some more for the understanding in regards to mentioned post:

"Even though there is a lot of dTPS PW, the filters are higher for a shorter duration" - this is due to the intake path to the valves being shorter, so TPS-triggered changes in airflow reach the chambers faster?

if you could outline some more as to why the other parameters were changed the way it was done would be helpful input for me haven't had to mess with AE too much or let's just say i haven't bothered enough so far
thanks!

edit: questions are in regard to an MPFI engine

 

There is another set of values for when in idle:

O2 - Idle O2 Window Terms

RBob.

 

Yes I also set those at mean 300, rich 350 and lean at 250. I made big changes because I wasn't seeing any difference.
Again it just adjusts the blm to bring it back to where it was.
What can I do to keep it where I want it????

 

It will prevent MAP AE when the throttle isn't open much, as the manifold vacuum will be higher. This negates the need for the total volume of AE.

It does help with a lumpy idle too. It allows for a lower threshold for MAP AE for a quicker response.

The actual parameter was: "AE - >TPS% double MAP AE"

Which meant that once the TPS was open far enough the ECM would double the volume of MAP AE. This made it easy to flood the engine, literally bog it down with too much fuel.

It was best to eliminate that parameter and code then to retain it.

The idea was to get enough fuel into the intake in as short a period of time as possible (high dTPS PW values). Then let that excess fuel which is wetting the interior of the intake to be pulled off over time.

On a wet flow TBI set up the intake manifold acts like a capacitor, damping the flow of AE fuel to the cylinders. More so as this car runs a colder then stock intake system.

If this car had the stock GM intake with all of the preheat, this technique would likely result in a rich bog at the onset of AE.

MPFI engines require different AE then a TBI set up. Many stock GM MPFI MaskId's don't even have MAP AE, just TPS AE. And that capacitor effect I mentioned with TBI, it is not present.

This makes it tricky to get just the right volume of AE. Easy to be too much or too little. What I tend to do is to use too little at lower TPS openings. Let the INT rise to cover for the small lack of some AE.

At medium TPS openings bump up the AE so that the INT doesn't move, or very little movement.

RBob.

 

Then something else is going on. It may be that the O2 sensor temperature is varying with the different AFR. Check the O2 sensor swing via a data log.

One other thing, running stoich isn't the best for emissions. Running a bit richer then stoich is best, more so at idle.

RBob.