AFR Goes Lean ..... Sometimes

[Dirty Howie]

I need some help.....

During the last ten days my car is running perfect AFR one day and the next it is extreamly lean. The tune is not being changed. I have a WB. When it is lean (over 14.0 it is pinging) so I believe the WB is accurate and something is allowing air in .... but not every day. I have cleaned the MAF and turned the airpump off. I also put the car in SD to confirm its not the MAF signal.


Would someone like to offer some possibilities and how to check for them.

Thanks,

DH

[redhardsupra]

1. if it's pinging, you might wanna back off and not see how many times it can do that, unless that new engine needs to be upgraded again
2. the usual: post logs of normal and abnormal, point us to some interesting frames

[Dirty Howie]

1. if it's pinging, you might wanna back off and not see how many times it can do that, unless that new engine needs to be upgraded again
2. the usual: post logs of normal and abnormal, point us to some interesting frames

Yes, I'm shutting down the soon as I hear ping ..... thats why I did some logs.

Here is the tune and a short log from yesterday where WOT tracked AFR nicely and then today when its way lean. The ambient temps were only 10* different.

DH

[Bill@HPTuners]

I wonder if its a possible issue with the maf, I setup a pretty simple histogram plotting injector pulse width avg. against the maf table & the 12/31 log is several % lower for no obvious reason.

[redhardsupra]

the fact that the whole lean vs normal occurs means it's a hardware base failure. so potential candidates are: MAF (it's too choppy for my taste anyway, but most of the descreened ones are), WB (but if it pings then it's probably actually quite lean, but it doesn't rule out that it's healthy, WB might be just kinda off, lost the ground connection or something), injectors (but why would they be right one day and off the other.

you seem to be less off on higher rpm than lower rpm, which means MAF is probably less wrong than the VE table. i'd also log MAF airflow and VE airflow and see how far they disagree.

the WB kinda follows AFRcommanded, jut not as closely as we'd like. that means the problem is across the board, not particular to the amount of airflow or pulsewidth, which might mean your battery is just weak. log battery voltage as well. the only time when your WB is closed to AFRcommanded is on decel after a WOT. does it mean something's clogged and it needs a vigorous 'blow through'? put some injector cleaner through it.

speaking of injectors, log for individual misfires, a faulty injector shows up easiest on these.

that's all i can think of right now, bring back some new logs and we'll see what else shows up.

[Dirty Howie]

I wonder if its a possible issue with the maf, I setup a pretty simple histogram plotting injector pulse width avg. against the maf table & the 12/31 log is several % lower for no obvious reason.

I ran in OLSD yesterday as well and got the same high AFR's

This would eliminate the MAF as the culprit wouldn't it????

Thanks,

DH

[Dirty Howie]

the fact that the whole lean vs normal occurs means it's a hardware base failure. so potential candidates are: MAF (it's too choppy for my taste anyway, but most of the descreened ones are), WB (but if it pings then it's probably actually quite lean, but it doesn't rule out that it's healthy, WB might be just kinda off, lost the ground connection or something), injectors (but why would they be right one day and off the other.

you seem to be less off on higher rpm than lower rpm, which means MAF is probably less wrong than the VE table. i'd also log MAF airflow and VE airflow and see how far they disagree.

the WB kinda follows AFRcommanded, jut not as closely as we'd like. that means the problem is across the board, not particular to the amount of airflow or pulsewidth, which might mean your battery is just weak. log battery voltage as well. the only time when your WB is closed to AFRcommanded is on decel after a WOT. does it mean something's clogged and it needs a vigorous 'blow through'? put some injector cleaner through it.

speaking of injectors, log for individual misfires, a faulty injector shows up easiest on these.

that's all i can think of right now, bring back some new logs and we'll see what else shows up.

I logged yesterday in SD and same lean condition.

Battery is new and starts easily

Whole engine is new.....bottom, heads, injectors, cam

MAF is old as is MAP and IAT

There was an issue with some wiring shorting causing ABS and TC failure. My WB wires might be involved too. But when AFR was at commanded no ping....and its been correct for a while now.

Going out to block the A.I.R inlet to rule out air getting by a bad check vlave and will get another log. Just don't want to go WOT till I'm sure my AFR is right.

Could a little leak in one of my PCV lines do this???

Thanks,

DH

[Dirty Howie]

Well I was hoping it was the AIR pump or check valve.....it still might be???

I blocked the AIR line and it didn't change anything.....still very lean everywhere.

So I hooked it back up and also reinabled the pump in the tune.

It doesn't seem as bad as yesterday now.

Here is what I observe:
1. now the AFR is good at idle in gear but is a little lean in park. (you can see this at the very end of the log.
2. seems like its taking longer to get the IAT down to ambient where it normally is
3. IDC is a little lower WOT at 88 .... usually 90
4. soon as you give it some throttle it goes lean

Any more HELP


DH

[WS6FirebirdTA00]

the odd part about this is the whole time you logged a month ago we never saw this. I know my WB would do screwy things when it was on its way out. Other than that, as long as the IAT is similar and MAP is normal, I am stumped (although it may be something simple we are overlooking ). If the IAT is heat soaked, it could cause it to go lean.

[redhardsupra]

it's not heatsoak, WB would not follow AFR on deceleration so well.

[WS6FirebirdTA00]

When my old WB got hot, it would act screwy. It was really easy to tell, but if you had another sensor laying around, I would give that a shot. MAF is not an issue since it happened in SD. IAT shouldn't be an issue, fueling didn't change much with a decent temperature swing. You MAP seems to be OK, it should be in a steady state of fueling for a given RPM vs MAP in the VE table.

[Dirty Howie]

the odd part about this is the whole time you logged a month ago we never saw this. I know my WB would do screwy things when it was on its way out. Other than that, as long as the IAT is similar and MAP is normal, I am stumped (although it may be something simple we are overlooking ). If the IAT is heat soaked, it could cause it to go lean.

Mike

I think the MAF/AFR was dialed in GREAT. And yes this never happened before. And then one day it was lean. I futzed around and then it was spot on again as shown in the good log. Then the very next day.....NOTHING CHANGING....not gas or ambient temps....boom....LEAN.

I rotated my MAF slightly so the wires to it and the IAT dont' rub against the hood head liner (doubt this is an issue...been like that forever). I doubt any of my PCV lines/fittings or catch cans are leaking....but I may remove them all and test.

I have noticed a small gas smell occasionally.

Someone else suggested fuel pump...is this possible???

Could one injector going bad (these are all new) do it ???? RedhardSupra suggested some test but I don't know how to set up the config


DH

[WS6FirebirdTA00]

Yeah, I was not thinking you still heard it ping, which would verify it is lean.

You can open the scanner, go to the VCM controls, and do a cyl balance test. This is one thing you can do to check injectors, but I doubt it will show anything because it is OK at idle it seems.

Do you have a fuel pressure gauge?

[Dirty Howie]

it's not heatsoak, WB would not follow AFR on deceleration so well.

So do you have some other ideas??

Something else to scan for???

thanks,

DH

[Dirty Howie]

Yeah, I was not thinking you still heard it ping, which would verify it is lean.

You can open the scanner, go to the VCM controls, and do a cyl balance test. This is one thing you can do to check injectors, but I doubt it will show anything because it is OK at idle it seems.

Do you have a fuel pressure gauge?

I will do cylinder balance at lunch.

No fuel pressure guage ........ so you think fuel pressure could cause this??

DH

[redhardsupra]

So do you have some other ideas??
Something else to scan for???

didn't i give you enough to try in post#5?

[WS6FirebirdTA00]

Not really sure what you told him in post 5 that he has not already checked or has proven to not to be an issue, just injectors are a WB connection, which I doubt the WB connections would cause the fueling to be somewhat steady at WOT, but lean, and showing ping.

[Dirty Howie]

Here is a long log to work this morning. Starts off way lean (19) at cold start. Settles down but still lean at idle. Very lean at cruise. Then at 32850 and 34650 near end of log there are a couple of short (not wanting to hear anymore ping) WOT burst where comanded AFR is followed. But another in that same are that is lean.

Also I did the cylinder balance. I assume this is done at idle. I did it 3 times and the results were within 1% of whats shown here.

COULD I have a WB wire/sensor that is loose/shorting causing this inconsistancy??

All I know for sure is that we had my AFR dialed in...working on street, canyons and the track just a couple of weeks ago!!!!!!

Any other ideas or tests ????

[Dirty Howie]

didn't i give you enough to try in post#5?

Sorry Marcin

I thought I was logging MAF and VE.

I think my VE is pretty decent......here is a log from the track on Dec.12

How do I log for individual misfires???


DH

[WS6FirebirdTA00]

go in to the scanner and insert them to the table. Just right click the table and insert, it is under engine diagnostics>misfire.