Car randomly goes lean

[Kaotic_red]

Well after driving the car around it randomly goes lean. The front O2 spikes at .94v then falls flat on its face to .06v. This happens whether I am driving at partial throttle, steady cruise or WOT. The car has a AEM Uego with the Bosch O2 sensor, MAF-T Pro, with V2.5 link. This has had me boggled for about a week now and cannot come up with a solution. Any input would be greatly appreciated.

Thanks,
Sean

 

[gofer]

Sounds like your MAF, check the wiring and connector and if everything looks good see if a 2g buddy can't let you swap their MAF real quick and see if the problem continues. Depending on where you welded the bung in for your wideband o2 sensor you might also have an exhaust leak at the flex section.

 

[Kaotic_red]

The MAF has been changed out for a known good one. The car was previously running into a problem with the link and maf-t conflicting with each other but we resolved that issue. I'll have to take a look at the bung.

Thanks,
Sean

 

[gofer]

I guess you can eliminate the MAF being the problem then if you swapped it for a KNOWN good one and it still goes lean randomly. It wouldn't hurt to ohm out the wiring going to the connector at the MAF though, you might have a loose butt connector if you didn't solder everything.

If your wideband sensor is downstream from a flex section in your downpipe and the flex section has an exhaust leak you could also be seeing false readings on the wideband, as well as lean spikes.

 

[ramsack]

the narrowband o2 should bounce around up and down at partial throttle and idle. at WOT it should stay pegged at rich (higher voltage.) the sensor could be dying already, or an exhaust leak, or it's stuck in closed loop.

 

[Kaotic_red]

its a wideband Uego, We have already changed out the bosch o2 sensor once when it first started to happen. It cant be stuck in closed loop as it leans out at random times while driving it.

 

[Kaotic_red]

the Uego stays pretty steady jumping around at normal then out of no where it pegs out to 18+; then I turn off the car and turn it back on and it runs fine. It has yet to lean out on me at WOT, sometimes after i let off after a pull or while cruising at partial throttle. There is no way of provoking it; Just happens at random.

 

[gofer]

Does the car die or go lean on decel/idle or just while cruising? When you said spiking lean I thought or assumed I guess that it was a good AFR and then it would spike lean, then drop down to a safe AFR reading. I wouldn't suspect a faulty MAF or a exhaust leak at the flex section now that you've told us the above piece of information.
Check for vacuum leaks and if its going lean and dieing on decel/idle then you might have to adjust your idle air clamp settings in dsmlink.

 

[Kaotic_red]

well everything will be all and well then the car looses power(ie starts misfiring/bogs real bad) and when I look at my Uego it shows it jumping around 18. Now I know thats really bad for the car so I shut it off, let it sit for a minute, then turn it back on and everything works great again. My log will show that the cars O2 readings nearly flat line @ 318.

 

[Kaotic_red]

Here is the log

 

[gofer]

Ill check the log out when I get home... I had a similar problem and I found the connector at the back of my CAS was cracked and the connection was intermittent, it wasn't only at partial throttle though it would do it at WOT as well.

 

[Kaotic_red]

I havent had it happen to me at WOT(thank god). Leaning out that far at WOT would surely be destructive.

 

[mike96]

my car did something very similar to yours. i would be driving down the freeway with the cruse control set and all of a sudden it would lose power and starting spitting/misfiring, quick look at my WBo2 would show 18 - 19:1 AFR. only every time it did it to me the problem would continue until i did something to the car. not sure what exactly caused the problem but the most solid fix i did was re doing all of the electrical connectors. i replaced MAF's, coils, ECU's, power transistors, coolant temp sensors.... went from stock MAF to MAFT/3"GM, but the problem always came back... until i went through the wiring harness, never actually found one "bad wire" per-say, but replacing the couple of bad connectors and cleaning the rest of them seemed to help the most. not sure if the problem ever came back... that car got totaled and i haven’t finished building my replacement yet

 

[gofer]

If your running 1600cc injectors your global settings seem off no matter what type of fuel your using, E85 or gasoline. For E85 after doing the math I'm getting a global of -58% and for gasoline it should be -72%, in your log however it shows your running a global of -48%. You also need to set your MAFComp sliders because right now everything is ZERO'd and your running a 3" GM MAF...

Get the above settings changed to match your setup and see if your car still does it. The ECU only goes into open loop for a number of reasons, and none of them I see happening when it does it.

 

[ramsack]

if i'm not mistaken aren't the 1600cc injectors the ones with a dip in the middle of the graph as the ms pulses go up in time, so as ms grew it would start to rise, have a spiked dip, then rise back up. that spot would be where you are hitting lean. here's the graph of the 1600cc injectors to show what i'm talking about. look around 1.5 msec of the red graph line.

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[Kaotic_red]

If your running 1600cc injectors your global settings seem off no matter what type of fuel your using, E85 or gasoline. For E85 after doing the math I'm getting a global of -58% and for gasoline it should be -72%, in your log however it shows your running a global of -48%. You also need to set your MAFComp sliders because right now everything is ZERO'd and your running a 3" GM MAF...

Get the above settings changed to match your setup and see if your car still does it. The ECU only goes into open loop for a number of reasons, and none of them I see happening when it does it.

We did notice the MAF Comp yesterday and adjusted it. Ill have to look at the global and correct that.

Thanks,
Sean

 

[Kaotic_red]

if i'm not mistaken aren't the 1600cc injectors the ones with a dip in the middle of the graph as the ms pulses go up in time, so as ms grew it would start to rise, have a spiked dip, then rise back up. that spot would be where you are hitting lean. here's the graph of the 1600cc injectors to show what i'm talking about. look around 1.5 msec of the red graph line.

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but its not throttle dependent. that and it doesnt go away until I turn off the car.

 

[gofer]

I'm not sure how you tuned your MAFComp settings but if you've got a MAP sensor and a WB this is the way to get it perfect. GMAF Calibration How-To I &
GMAF Calibration How-To II After you get all this setup and your CombinedFT while the car is at idle/cruise is 0 (+/- 2) then we can figure out why its getting stuck in open loop.

 

[Kaotic_red]

Got it all taken care of. global is set so low becasue we set the base fuel pressure to 36psi. Fuel shouldnt be an issue with the PTE 1600cc injectors and twin Bosch 044's. The MAF Comp settings is what had to be played with. Everything is running as it should now. Thanks Gofer for all the help!

/Sean