Need ideas on why I'm going LEAN

[Embalmer]

While cruising, usually at low RPM in 4th or 5th gear, my car will nose down a bit and my A/F will jump from 14.x to 18-21. This will usually only last a second or two, and a bit of throttle will make it go away. Obviously, this is telling me I have a vacuum leak and somehow unmetered air is getting in to the motor. Last night the motor died a few times after cruising when I took it our of gear and I let the motor idle while coming up to a stop.

I thought my issue was related to the UPR catch can I plumbed in a few months ago, that air might be getting into the motor through one of those hoses, but apparently it's not because I removed the hoses and returned to stock configuration. I also replaced the hose going from the passenger cam cover to the CAI I have, and used clamps to secure it. I checked all the other clamps around the TB, CAI, filter, and found non of them loose.

Am I overlooking something?

 

[SteveP]

Is it a regular A/F or a wideband? Also, get a fogger and thats the easiest way to find a vacuum leak.

 

[Embalmer]

Is it a regular A/F or a wideband? Also, get a fogger and thats the easiest way to find a vacuum leak.

It's an Innovate LC-1 wideband. Fogger?

 

[Wicked97]

some times we will spray carb clean or something like that around the vacuum hoses and if the motor revs up when you spray you know there is a leak.

you don't have to spray alot just a few quick squirts.

 

[Liftedbronco]

could even be something like a fuel pump issue. got a fuel pressure gauge? would be cool to see what thats doing while you get your hiccup.

 

[Embalmer]

could even be something like a fuel pump issue. got a fuel pressure gauge? would be cool to see what thats doing while you get your hiccup.

Isn't the fuel pump under more demand during a spirited run then at cruising? I never have these issues at WOT, or any more than slight throttle. I can make the issue happen if I lift off the pedal in 4th or 5th gear, where there is almost no demand for fuel.

 

[Liftedbronco]

yea i know what you mean...but im trying to lay out all the possabilities so u can go through it systematicly. This works better on pre-super high tech cars (fox bodies for example) but bear with me...

it could be a fuel issue or an air issue. cant be spark cuz that could only make you be rich if spark is failing.

fuel can only be the pump (or injector related) because ur symptoms dont make sense for a filter issue.

could be a TB issue. stepper motor screwing up, blade sticking...tps (do we have one? lol) going bad.

Definitley like the idea of looking for a vacuum leak, but unless youve messed around alot in there I wouldnt think that would be likley.

Check the wiring to the maf....make sure all the pcv hoses are ok and plugged in tight. definitley hit the obvious stuff first.

Lastly - how long has this been happening? No CEL?

 

[Embalmer]

yea i know what you mean...but im trying to lay out all the possabilities so u can go through it systematicly. This works better on pre-super high tech cars (fox bodies for example) but bear with me...

it could be a fuel issue or an air issue. cant be spark cuz that could only make you be rich if spark is failing.

fuel can only be the pump (or injector related) because ur symptoms dont make sense for a filter issue.

could be a TB issue. stepper motor screwing up, blade sticking...tps (do we have one? lol) going bad.

Definitley like the idea of looking for a vacuum leak, but unless youve messed around alot in there I wouldnt think that would be likley.

Check the wiring to the maf....make sure all the pcv hoses are ok and plugged in tight. definitley hit the obvious stuff first.

Lastly - how long has this been happening? No CEL?

It's been happening since around the time I put on the catch can. I just assumed one of the connections wasn't good and was letting air in under high vacuum, like when the throttle is closed and the engine is running. It's also hard to duplicate when I'm not driving the car, so diagnosing it is gonna be tough.

 

[leavnon3rd]

how about the tune? you sig says its a bren speed tune, im 1 for 2 with them, 06 gt tune was awsome, 08 gt has low rpm throttle issues bucks, noses over and sent it back to brenspeed for a retune/update i dont have a wideband on the car so i dont know if its a tps/tb issue or a lean condition.

what do you consider low rpm? i can make my issue happen in any gear between 1,000-1,400 rpm but with the load in 4th n 5th its more noticable.

and for a fogger most shops have a smoke machine they use to track evap leaks and ive used them on alot of euro cars that have sealed pcv systems, a slight valve cover leak can cause a lean condition! you could use it to spot any air leaks. The reason i dont think it is a vacuum leak or unmetered air is becuase it should act up pretty consistantly.

another option is to put a good scan tool, or a dash hawk/aeroforce in the car. and log or watch the MAF signal, MAf's are sensative to oiled air filters, a little residue on that cartridge type mass air can make it do all types of things. Although i havent heard anyone on hear from the reading ive done have an issue like that, i know alot of late GM stuff has.

 

[slow06stang]

Maybe an exhaust leak

 

[Meister]

Are you experiencing any missfires when this happens? A miss will show up as a lean AFR reading. Does it stumble or anything when this happen?

Paul

 

[Joser281]

This has happened to me twice a while ago when at idle my car died once and the second time after I let off at WOT. It turned out to be the MAF sensor was dirty and cleaned it with some electronics cleaner I got at Fry's. Since then it hasn't happened to me again. Not sure if that could be it since you said it is a vaccum leak but maybe a dirty MAF can make it seem like a vaccum leak, no?

 

[Embalmer]

Are you experiencing any missfires when this happens? A miss will show up as a lean AFR reading. Does it stumble or anything when this happen?

Paul

Why would a misfire show as lean? Wouldn't the unburned fuel cause a rich condition?

 

[Simon]

I would lean towards tuning. Seems to be the #1 answer for drivability type issues with aftermarket tunes.

 

[psfracer]

I ran into this problem a while back. The car would go way lean while cruising or when trying to slightly accelerate from a stop, I would blip the throttle (while cruising) and it would come back---the falling on its face while trying to accelerate was only during slight accel---aggressive and WOT acceleration it wouldn't do it. Also, the problem was not consistent either, many times the car would run fine, but once in a while it would do what you describe.

In any case at one point I thought it was a bad PCM---as it just started doing it out of the blue. I think that when I replaced the 02s the problem was corrected if I remember correctly.

I would start with vacuum leak, then check all fuel pump wiring. Datalog your fuel pressure while driving and see what it does when the A/F goes lean. Just a start.

 

[Embalmer]

Well, first thing I'm going to do is double check all my connections, then try a little propane when the car is running. Then, I will re load the tune (maybe trying the 87 instead of the 93) to see if that makes a difference. Then, I'll get the laptop out and datalog the issue. I'll report back my findings. Thanks, guys...

 

[kenneth]

My car was running a little lean at Idle and tip-in during regular driving.
Finally have some good weather, started off checking for vacuum leaks,using first smoke than starting fluid, everything checked out good.
Next squeezed my fat ass under the car and replaced the front 02 sensors, started the car, seems like the AFR richened up some, but still showing 15.0-15.5 at idle.

Today, under the car again fixed a small exhaust leak on the crossover pipe for the H-pipe, than went for a little ride.
AFR now at idle stays around 14.6-15.1.
WOT AFR starts at 11.0 and raises to 11.5 in upper RPM's

Not sure if the 02 sensors took some time to correct the AFR OR the exhaust leak even though it was really small and behind the sensors, But seems to be in a good reading now.

BTW I'm using the AFX wideband with NGK sensor (brand new)

 

[Embalmer]

I'm going to datalog tomorrow, I got my new Innovate OT-2 hooked up and connected to my iPad. What PID's should I datalog to try and track down this issue? I'm guessing it's a throttle, MAF, or fuel issue.

Basically what happens is in 4th or 5th gear, under very light throttle, my air fuel will fluctuate from lean to rich, like 11-12 rich to 19-22 lean very briefly, and the car will stumble, or nose down, but my application of throttle will end the episode. Also, when coasting in the aforementioned gears, I will get full lean (it is speed dependent, higher speeds make leaner readings) and the car will nosedive until I apply throttle.

 

[JeremyH]

All the rest aside, this really sounds like the fuel pump hesitation tsb.

 

[Embalmer]

Here's my setup using the Innovate LC-1 to measure air/fuel, integrated into the Innovate OT-2 wideband logger unit which my iPad can pick up and datalog using the free Logworks app. Now, I just have to figure out what all the channel names mean.

And a brief video of it up and running:
http://s77.photobucket.com/albums/j56/faxisis/Mustang GT/?action=view&current=P1000131.mp4

Tomorrow: Datalogging a run so I can show you guys what's happening.