Car drives lean under 4k

[Chicken Patty]

Hello

My car drives really lean before 4k, idles fine however. After about 4k goes to about 12.0 a/f ratio and drives fine. I am on stock injectors and fuel pressure is 42-43psi. Really have no idea. I tried different ECU's and MAF's. Any suggestions?



Fix: Replaced Upstream o2 sensor

 

[gringo72884]

First step should be a boost leak test. If its runnig lean through normal cruising I wouldn't worry about it too much as your ECU is in closed loop mode. BTW 12.0 AFR is a rich condition...not lean.

 

[Chicken Patty]

I forgot to mention that according to my logger the o2 voltage is not cycling, meaning it might be stuck in open loop?

I know 12 is rich, but under 4k rpm it is 16-17 Which is very lean then when it hits 4k rpm it goes richer and picks up fine. What can cause a car to be stuck in open loop if that was to be the case?

 

[XiKeiyaZI]

Just for starters I'd make sure that your TPS is adjusted correctly.

Next I'd make sure that the 02 housing is bolted down and getting a good seal. It's TECHNICALLY post turbo so you'd get the correct air/fuel ratio, but the leaking exhaust there would throw your 02 sensor out.

Go ahead and change your 02 sensor. Do a boost leak test for good measure. Also check your Coolant Temp Sensor and make sure that it's displaying the correct reading for the ECU. If the ECU doesn't see the correct voltage then it won't meet the standards to enter closed loop.

 

[Chicken Patty]

Just for starters I'd make sure that your TPS is adjusted correctly.

Next I'd make sure that the 02 housing is bolted down and getting a good seal. It's TECHNICALLY post turbo so you'd get the correct air/fuel ratio, but the leaking exhaust there would throw your 02 sensor out.

Go ahead and change your 02 sensor. Do a boost leak test for good measure. Also check your Coolant Temp Sensor and make sure that it's displaying the correct reading for the ECU. If the ECU doesn't see the correct voltage then it won't meet the standards to enter closed loop.

Here's what I'm noticing.

Seems like car is in closed loop although it's not cycling the voltage. At about 4k or so i'm a bit heavy on the gas to get up to speed and then all of the sudden the car dips richer and the car just goes! I think that's when it switches to open loop, correct?

Another thing, I went ahead and put back my thermostat and check the coolant temp sensor wiring and all seems fine.

Now my questions:

1 - What is the correct TPS voltage and how can I test for it, just a regular multimeter correct? I just keep seeing how people get different voltage readings and some say it's .55, some say it's .64v.

2 - bad o2 sensor can definitely cause this correct?

3 - What will a boost leak determine in this case?

 

[XiKeiyaZI]

Here's what I'm noticing.

Seems like car is in closed loop although it's not cycling the voltage. At about 4k or so i'm a bit heavy on the gas to get up to speed and then all of the sudden the car dips richer and the car just goes! I think that's when it switches to open loop, correct?

Another thing, I went ahead and put back my thermostat and check the coolant temp sensor wiring and all seems fine.

Now my questions:

1 - What is the correct TPS voltage and how can I test for it, just a regular multimeter correct? I just keep seeing how people get different voltage readings and some say it's .55, some say it's .64v.

2 - bad o2 sensor can definitely cause this correct?

3 - What will a boost leak determine in this case?

That is weird...

1 : The correct resistance is .064.
2 : Yes, a bad 02 sensor can cause a plethora of things to go bad, like what you're experiencing.
3 : If anything, a boost leak will determine if you have any leaks.

You want the car to stay in closed loop. When it's in open loop, it reads only from the maps saved in the ECU. When it's in closed loop, it adjusts your AFR's based on your 02 sensor.

 

[Chicken Patty]

Would you be able to link me to a guide on how to adjust the TPS properly? I just want to make sure I'm doing correctly.

Also, I can't get the logger to connect to my car with the EPROM, so I can't even see the TPS voltage or to see if anything funny would show. I tried changing the baudrate and all of that like it says on the DSM Chips website.

At this point I want to make sure my TPS is correct and that it is NOT the cause of this problem. If so then I'll proceed to buy the o2 sensor.

 

[gofer]

If your o2 isn't cycling (getting stuck) then your cars getting stuck in open loop like you said. I'm guessing that its stuck at a higher voltage (.5 to .9v) since its idling lean? Thats because the ECU sees that voltage and assumes its rich and its trying to lean things out.

Now your probably wondering, why in the hell does it start going rich after 4k and run fine? Thats because at that RPM (and under a load) your ECU doesn't care what your front o2 sensors doing. It uses the fuel/timing maps that are loaded onto it, when it does this its pulling a set AFR from the map and not watching the front o2.

The verdict, replace your front o2 sensor OR make sure the damn things plugged into the correct connector. I was helping a buddy for nearly 3 weeks over the phone because his car was going lean and his front o2 wasn't cycling, come to find out he had it plugged into his cruise control.

 

[Chicken Patty]

Thanks gofer, I'm going to do that today then, it's gotta be that. I'll keep you guys posted later today. I know it's plugged in correctly, already checked that. Thanks for looking dude, really appreciate it. I'll give you some yep later today when I get home, using tapatalk at the moment.

 

[XiKeiyaZI]

Damnit Gofer! You got to check the thread before I did! Haha.

But yeah, he's absolutely correct. I'm banking on a bad sensor. Make your basic checks and then change it. Should clear your issue right up.

 

[Chicken Patty]

Any suggestions on what o2 to get? Or should I only get a OEM Mitsubishi one?

 

[gofer]

Bosch, and dont get the universal one.

 

[Chicken Patty]

Bosch, and dont get the universal one.

Thanks bro, the near by Advance Auto Parts has the O.E. Bosch for $70. I'll go pick it up shortly.

 

[gofer]

Don't forget PB Blaster, gray anti seize, a breaker bar, and an o2 sensor socket if you don't already have all the stuff.

 

[Chicken Patty]

Don't forget PB Blaster, gray anti seize, a breaker bar, and an o2 sensor socket if you don't already have all the stuff.

I'll get that stuff at Autozone, don't got the breaker bar though

 

[gofer]

Have fun trying to get the old sensor out of there then, they sell them for $12 and mines more than paid for itself since I use it on everything I can.

 

[XiKeiyaZI]

My 02 sensor wasn't hard to get out at all. I had a large solid wrench, though. Most 02 sensors, specifically Bosch, come with the grey anti seize already in place.

 

[Chicken Patty]

Yeah, it wasn't hard at all, came right off! I had removed it before when I upgraded my o2 housing a while back.

Well the car drives a heck of a lot better than it did. I have to see how it does on cold starts. It was horrible, car had no fuel whatsoever! So I'll see how that goes tomorrow morning.

I still notice the car is a little flaky in it's driveability, but you have to keep in mind I am running a GM Maf, and the car has a couple of mods and has nothing to tune. I am currently on stock injectors, so don't go by my profile. I think the car just needs to be dialed in from here.

 

[Chicken Patty]

Well the completely lean condition on cold startups is gone! That's definitely a relief.

You guys think I should also replace the downstream o2 sensor as well?

 

[delta448]

Not unless you get the CEL on and the DTC code thrown for it on your logger or code reader.

The downstream O2 sensor is only there to make sure the catalytic converter is doing it's job. It's voltage signal is directly compared by the ECU against the front O2 sensor voltage to determine if the converter is functioning.

 

[Chicken Patty]

No CEL, so I'll leave it as is.

OK here's a update.

At first obviously the car was super great to me because I saw a huge improvement. Now that I'm getting used to it it still drives kinda crappy.

Before the car would just drive really lean, 16+ on the wideband up to about 4k RPM's. Now I don't see lean conditions at all, not on idle, not low or high RPM's. However, the car still feels like it's bogged down under 4k. most of the time feels like I need more gas to get it to accelerate, feels held back!

Sometimes it has like a little in and out feeling, like the car goes a bit then gets held back again, and so forth, not really bad but it's noticeable. Really don't know where to start here.

I have already tried the stock 2G Maf as opposed to the GM Maf, no difference. Any ideas/suggestions guys?

 

[delta448]

Any ideas/suggestions guys?

Try to get your logger going again ASAP, it will help immensely in diagnosing your problems.

Things you could look into:
Double check that your Eprom chip is for stock injectors.
Check the knock sensor for any leaking goo.
How fresh are your plugs, are they 6's gapped to 0.028"?
Check battery health, also remember to reset your ECU after installing the O2 sensor.
Replace the fuel filter if you haven't ever.
Check plug wires.
Remember, misfires will read as a lean condition on a wideband.


How's the car act when you first start it and let it idle?
Fire right up or crank for 5+ seconds?
Purr like a kitten at idle or cough and sputter?
Does idle quality change with engine temp?
Stab the throttle at idle in neutral, what happens?

 

[gofer]

The only way we can accurately diagnose whats going on is by you getting a logger and even then, unless your able to log your WB gauge, we've got to rely on what you tell us your AFR's are through the pull. I'm not saying your trying to mislead us but its not exactly easy to watch the road and stare at the WB during the entire RPM band...

I don't see any sort of logger setup in your mods list, what are you using or what do you plan on using?

 

[docb002000]

The verdict, replace your front o2 sensor OR make sure the damn things plugged into the correct connector. I was helping a buddy for nearly 3 weeks over the phone because his car was going lean and his front o2 wasn't cycling, come to find out he had it plugged into his cruise control.

too funny thanks

 

[Chicken Patty]

@gofer

I have EVOSCAN, but does not connect with the EPROM ECU, did fine with my non EPROM ECU.

Before I switched the o2 the car was driving in lean conditions which it is not doing anymore, coldstarts before were horrible, now it's fine. The car now just feels boggy, like it's held back but when this happens my wideband is reading normal cruising readings, about 14.5.

I'll try my best to log it, you think the TPS might be needing adjustment? Perhaps I should also try a boost leak test?