Randomly going rich, then lean

StockishS197

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As the title states, battling an odd and random issue. Randomly and only when the car is at a hot idle, AFR swings rich (.80 or less lambda) for about 10 seconds, drifts very lean (1.4 lambda), runs rough, recovers and begins idling normally again. Car has the FRPP Mani, FRPP 24lb injectors, FRPP Hot Rod cams, catted X.

Logs show STFTs and LTFTs are completely normal sitting at 1, +/- 2-3%, however 02 voltage will linearly increase, then linearly decrease at the same rate (log almost looks like a pyramid on the logs) on both banks and stop switching during that 10-20 seconds. New 02s and the issue still persists. New SP547Xs and still happening.

Logging the MAF it also looks normal....just not sure what would drive O2 voltage up in a perfectly flat pattern on both banks. Car runs and drives great otherwise and it only happens at idle. For some reason my head keeps pointing to the MAF. It also randomly started on known good tunes, including Lito's prior tune so I don't think its a tune issue either.

Went around doing jiggle tests on any vacuum line, electrical connection etc and no luck.

Any ideas?

ETA: The only code I have gotten during this time is a bank 2 O2 slow to heat (replaced the sensor after that) and the occasional P0430, though it's not consistent there either.
 
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StockishS197

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Both Litos tune and my tune did it. Only trouble code was the P0430 - no codes for lean or MAF issues.

I went ahead and replaced the MAF and may have been the fix. Haven’t had the issue arise and random idle dip seems improved as well.

Also adding, don’t use cheap parts store MAF unless it’s the Hitchati (OEM Ford MAF supplier) or FoMoCo. The aftermarket MAF I tried initially showed a 10% difference in LTFTs over the Hitachi/Ford. Element was also a different design too.
 

AdamBorz

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what do the narrow band 02 volts show? Do they rapidly change during this event? The issue my car is having, the narrow band volts drop to 0
 

StockishS197

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I actually figured this out - it was a tune issue. The manifold volume scalar was set too low for my cams (reversion makes effective volume larger) + FRPP intake manifold (physically larger than the stock plenum). Was causing transient fuel issues during idle. I had my intake manifold volume scalar set to the physical volume of the FRPP Mani (11.45L vs stock at 10.9L), but wasn’t enough to compensate, so I increased it another ~10% to account for the cams.

But to answer your question above, O2 voltage would go very high linearly up to .8+ during the rich swing and the log basically looked like a pyramid on both banks over about 10 seconds, then go down at the same rate to effectively zero voltage when it went super lean, then recovered.

O2 voltage switching is expected and normal CL operation…when it stopped switching during closed loop, there is typically a problem.
 

AdamBorz

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I actually figured this out - it was a tune issue. The manifold volume scalar was set too low for my cams (reversion makes effective volume larger) + FRPP intake manifold (physically larger than the stock plenum). Was causing transient fuel issues during idle. I had my intake manifold volume scalar set to the physical volume of the FRPP Mani (11.45L vs stock at 10.9L), but wasn’t enough to compensate, so I increased it another ~10% to account for the cams.

But to answer your question above, O2 voltage would go very high linearly up to .8+ during the rich swing and the log basically looked like a pyramid on both banks over about 10 seconds, then go down at the same rate to effectively zero voltage when it went super lean, then recovered.

O2 voltage switching is expected and normal CL operation…when it stopped switching during closed loop, there is typically a problem.
That manifold volume scaler is interesting. The tune my car came with had it set to 6 (supercharged, cammed, ported heads etc). Lito changed it way higher
 

StockishS197

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Are you having the issue with the Lito tune or not since he changed it?

Your O2 volts will get close to 0V when oscillating, especially with high overlap cams...but it should switch back and forth and not stay close to 0V.
 

AdamBorz

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Since the Lito tune… I just think the DFCO is too extreme… but the narrow bands are going to 0, but the wideband is showing super rich which is opposite. I have a new wide band to install my old old must be glitching
 

AdamBorz

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I feel your pain… my car keeps eating spark plugs. Lito just had me switch to 2 step colder NGK’s.

Gotta be lean but the wide band showing rich…. I gotta get the new one installed!
 

GlassTop09

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Well, the MV scalar didn’t end up solving my issue here so back to the drawing board.
If you're interested.............check out the following:

https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-6 starting from post #112........
thru to this: https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-8 thru to post #159

Kinda went down the road back then that you seem to be currently going down now............something to think about.........

Post #159 is my summary of all this testing, discovery & application\resolution. Within all this there exists 2 copies of Forscan IM Readiness Mode 6 Self-Check results while still running the Kooks Hi Flow cats using Big Daddies CEL Eliminators, 1 from the start while I still had a FRPP Intake Manifold installed......the 2nd is w\ the current 08 OEM IM w\ CMDP's installed back then replacing the FRPP IM........2 dyno sheets as well.......1 w\ the FRPP IM installed prior discovery of my issues & 2nd w\ the current 08 OEM IM installed overlaid over the FRPP IM curves.........all this went on w\ my car before I started doing my own tuning.

Hope this helps.......................
 

StockishS197

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If you're interested.............check out the following:

https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-6 starting from post #112........
thru to this: https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-8 thru to post #159

Kinda went down the road back then that you seem to be currently going down now............something to think about.........

Post #159 is my summary of all this testing, discovery & application\resolution. Within all this there exists 2 copies of Forscan IM Readiness Mode 6 Self-Check results while still running the Kooks Hi Flow cats using Big Daddies CEL Eliminators, 1 from the start while I still had a FRPP Intake Manifold installed......the 2nd is w\ the current 08 OEM IM w\ CMDP's installed back then replacing the FRPP IM........2 dyno sheets as well.......1 w\ the FRPP IM installed prior discovery of my issues & 2nd w\ the current 08 OEM IM installed overlaid over the FRPP IM curves.........all this went on w\ my car before I started doing my own tuning.

Hope this helps.......................
My gut had a feeling this was EVAP related...so much so that I have started logging commanded purge to see if it correlated. It ONLY happens after spirited, hard runs when the car is hot and at idle and very intermittent and momentary.

Starting to see why Lito advised against the FRPP IM....more of a PITA to dialed in perfectly if you are as OCD as I am (and appears GlassTop is even higher level lol).
 
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StockishS197

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After a few logging sessions, EVAP is definitely consistently purging at idle. I haven’t been able to replicate the rich/lean oscillation while logging, but I wonder if it could be related to DFCO preventing purge on decel, vapors accumulating then a heavy purge when DFCO disables and returns to idle, causing a momentary heavy rich condition, followed by a momentary lean condition, then stabilizing?
 

StockishS197

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More testing here….on my tune, I increased min load to allow the EVAP purge test and the issue still occurs. When logging EVAP flow, the car mostly idles fine, even when purging. I also switched back again to Lito’s tune and it tries to do the same thing…but when logging, I noticed STFTs would almost always increase linearly when coasting, clutch in/neutral while moving up to 1.20+, which appears to be causing the rich condition, then lean oscillation….see screenshot attached. During coasting, clutch in the O2s are also showing pig rich (.9V+) and aren’t oscillating…but when at stopped idle, they start switching again as normal and issue subsides….

Because it’s happening over two completely separate tunes…different strategies even, with EVAP purge disabled at idle…I’m at a loss. Happening on both banks and via STFTs…which makes me think the PCM is doing something odd rather than a physical issue of the FRPP IM EVAP design itself.

Is it normal for STFTs to act that way when coasting and effectively load up fuel on tip in, return to idle?

Editing to add: during normal driving, STFTs are switching as normal and within a normal range: .95-1.05.

IMG_6994.jpeg
 
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AdamBorz

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In my tune, Lito has the EVAP purge testing turned off. I tried to turn it back on but don’t have access to it. I don’t have near the knowledge about this that you do, but definitely seems EVAP related.
 

GlassTop09

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Because it’s happening over two completely separate tunes…different strategies even, with EVAP purge disabled at idle…I’m at a loss. Happening on both banks and via STFTs…which makes me think the PCM is doing something odd rather than a physical issue of the FRPP IM EVAP design itself.
Hate to say this..........but sometimes you gotta just trust\accept the results. What's the common thing\denominator between the 2 tune cals exhibiting these issues........the FRIM, the EVAP system & the B1S1\B2S1 NB O2 sensor operations.........whether you like this or not.

Your issues are not showing to be tuning related, they're component related........the issue for you is accepting this & then start doing proper component checks & stop messing around in the tune cals trying to hopefully find some answer that in reality doesn't exist........then do the necessary work that is needed to be done to properly fix this......even if you don't want to.........or accept the issues & consequences from them as they are if you can't.

In the end.........it's your car & your money thus you can do whatever you choose to do...............or not do..............

The NB O2 sensors are exhibiting weird responses to normal ECU operations when going into a coasting pattern at speed (fueling going initially lean--1.05--initially off APP closing throttle when you took your foot off the APP--as it should do--the NB O2 sensor voltages should go close to\at 0v........then DFCO kicking in shortly afterwards (shutting fuel off completely while coasting thus engine is pumping air only during CL.....thus the NB O2 sensor voltages should stay at close to\at 0v the entire time that DFCO is active....) thus are IMHO suspect--they should not be drifting--showing voltage outputs increasing off 0v--at all & need to be tested to confirm their operational integrity then replaced if found to be out of bounds. The EVAP system needs to also be smoke tested for integrity, starting w\ the CPV (this valve needs to be physically tested to fully seat off & hold when at 0% command--best tested while unplugged to ensure full closure--just turning the EVAP system off in the tune cal doesn't prove anything concerning this valve's operations......) then the rest of the system then fix\repair any leaks that show up & check the FTP sensor for its operations at the same time. These EVAP systems are getting old thus should not be taken for granted that they're OK (not trust the ECU to show MIL's.........these can fail while the ECU shows they still can pass the .040" leak test.......been there, done that). Posted a video on my car showing me smoke testing the EVAP system on my car :https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-3 post #60.........the ECU showed this EVAP system had passed the IM Readiness EVAP .040" leak down test.........w\ a bad CVS (wouldn't completely seal off when activated thus can invalidate a pressure test & cracked flex hose--vacuum & pressure leak--between the EVAP canister & CPV thus can potentially throw off fueling to engine\prematurely fail catalyst IM Readiness CE Ratio testing thru erroneous B1S1\B2S1 B1S2\B2S2 NB O2 sensor feedback---which the FRIM can aggravate & make this worse due to its EVAP port design sending too much of this EVAP flow thru the B1 #1 & #2 intake runners vs the rest thus causing bank to bank fueling imbalances thru falsely avg B1 fueling across B1 cyls causing the rear #3 & #4 cyls to run excessively lean vs the #1 & #2 cyls w\ the same thing happening on B2, just not as severe......

When checking NB O2 sensors.........the NB sensor voltage output patterns along w\ the sensor heater amp outputs are the key in proper analysis......not the STFT's......as the voltages are generated from the sensors themselves, when proper heater temps are maintained to sensor elements, in reaction to the amount of free O2% in exhaust vs the outside air. The ECU is only interpreting the NB O2 sensor voltage patterns to then determine fueling correction to apply--STFT's.......so if garbage in will most certainly give garbage out. If you aren't already datalogging the running exhaust temps, IMHO you need to start doing so......especially when system is going thru DFCO to see if the exhaust temps are cooling down too much......this WILL start the NB O2 sensors to drift towards "rich" during DFCO thus you might need to increase B1S1\B2S1 heater duty cycle% to help keep the NB O2 sensor elements warm enough to maintain proper operations during DFCO.........that is, AFTER checking & proving proper base NB O2 sensor function\operations.

I know you know all this........but........can you also accept what all this is showing you.........? Changing all these settings in 2 different tune cals w\o resolution should have been a wakeup call..................IMHO, of course.

YMMV...................

Hope you find resolution to your issues.................
 

StockishS197

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Yeah, all makes sense. Going to dive deeper into the EVAP system. I dropped the EVAP canister a few months back due to filling issues, and all seemed normal. Perhaps the vent solenoid is sticking open during purge? Not really sure.

The NB O2s are both new NTK units and are working fine, the CVP is also a new unit...also manually validated it holding vacuum (20+ inhg) using a vacuum gauge so I don't think that is the culprit.

Really an intermittent issue as the car ran and drove great today...not a single issue and the O2s and STFTs correlated as expected on my tune, even with hard runs. Might just disable the purge test entirely in the tune to see if that might be some correlation. Perhaps the colder weather is also leading to less vapor accumulation in the tank, thus less purging.

The coasting commentary from my prior comment where the O2 voltage spiked to .9v was not during DFCO, but rather clutch in/neutral so the car was still running as normal. Gear in coasting during DFCO, O2 voltage goes to 0v on both banks, and STFTs go to commanded lambda (1.04).
 

StockishS197

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After some testing, a couple things that helped….I ended up setting the IVO Fuel Injector Timing to 331 crank degrees instead of the true 311 crank degrees of the Hot Rod cams. I think setting the IVO scalar in the tune to 311 was too early causing poor atomization/pooling in the port due to the Hot Rods reversion. 331 really stabilized AFRs and fuel trims while also shifting the timing slightly closer to the Hot Rods insanely early IVO events.

The other for the EVAP related items, I increased idle speed a bit to add some vacuum.
 

StockishS197

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Well, with the warmer weather the AFR swing seems to have returned. Unplugging the EVAP purge solenoid solves it so it’s definitely due to purge.

I ended up pulling the FRPP mani and looking at the EVAP design and GlassTop is spot on.

The factory IM has the EVAP purging just behind the throttle blades in the center (that’s why there is a center post between the blades) whereas the FRPP literally just dumps in the plenum on the driver side.

Seems like a rather large compromise if you want to retain the factory EVAP for emissions and there isn’t a great way around it.
 

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