# Code 43, I'm running lean (thirsty Sentra)



## Sprout98 (Jan 3, 2008)

Hello,

So, my Sentra's been anemic for a little while. I replaced both O2 sensors, no luck. Just replaced the fuel filter, no luck. I keep pulling the code 43. How do I adjust my air/fuel mix on a '98 Sentra w/ 2.0L? I read another post that basically said "by turning the adjustment screw." Really? Where is it? A diagram or picture for the 2.0 would be beautiful. Or, if there's a better (or another) way to adjust this mixture, I'm all ears. I don't doubt the accuracy of this code; I just need the right way to remedy it. It's not drastically off, just a little lean. Thanks for helping out!


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## Jopet (Aug 10, 2009)

Try MAF (intake fileter) sensor. have the same problem since I bought my 95 sentra. Got to trimming my K&N filter this weekend to make sure the sensor was completely in the filter and sensing the air that's coming in. If you have the stock filter, you might just need to change it or clean it. Make sure you clean the sensor as well.


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## mattdc_07 (Aug 3, 2008)

If you are only runing lean and thats all, with no other problems, an easy and quick way to fix this on the 2.0 engine would be to take the vacum hose off the fuel pressure reg and this will up the press just a little, enough to make it run a little rich, and be sure to cap the ends with something as well


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## Sprout98 (Jan 3, 2008)

Jopet said:


> Try MAF (intake fileter) sensor. have the same problem since I bought my 95 sentra. Got to trimming my K&N filter this weekend to make sure the sensor was completely in the filter and sensing the air that's coming in. If you have the stock filter, you might just need to change it or clean it. Make sure you clean the sensor as well.


Hi Jopet,

Thanks for your reply. My air filter is new. If I understand right, cleaning the MAF sensor is just wiping it down with some carb cleaner. Could a little film on the MAF really cause me to run lean?


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## Sprout98 (Jan 3, 2008)

mattdc_07 said:


> If you are only runing lean and thats all, with no other problems, an easy and quick way to fix this on the 2.0 engine would be to take the vacum hose off the fuel pressure reg and this will up the press just a little, enough to make it run a little rich, and be sure to cap the ends with something as well


Hi Mattdc 07,

I hear you on this suggestion, but I'm not sure it's the right long term solution. I'm getting ready to face maybe the 3 most-feared words in the English language "California Smog Test." They do a visual inspection and I can picture them seeing my vacuum hose with a golf tee plugging it, asking WTF.


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## Jopet (Aug 10, 2009)

Yup. That sensor is very sensitive. Im from the older type of engines. Carburators, ingnition coils, contact points, condenser and all that kind of stuff. Im just a beginner DYI when it comes to fuel injected machines. My research came up with the idea or the MAF sensor and it cured my problem. In the olden times you can pump your accelerator and squeeze more gas into the engine. Nowadays (as my experience) that does not do anything. The fuel input is restricted (like its blocked) when there is not enough air coming in. The increase of gasoline in the cylinders is based on the air that comes in. The front and rear sensor adjust this further to make sure that your emission is within limits.


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## jdg (Aug 27, 2009)

Sprout98 said:


> How do I adjust my air/fuel mix on a '98 Sentra w/ 2.0L? I read another post that basically said "by turning the adjustment screw."


You don't adjust the A/F mixture on almost anything post-95. The computer does the adjusting. The only way you can adjust the A/F ratio is by reprogramming the ECU. The screw you're talking about is probably the minimum idle air screw (not sure, I don't have a 2.0L).

As far as cleaning your MAF sensor...Carb cleaner? That's a sure way to ruin the MAF. Use a Q-tip dabbed with rubbing alcohol and lightly swipe the thin elements inside of the screen.

Plugging the Fuel pressure regulator vacuum line? I don't think so much. That's a good way to get an extra 3-4psi of fuel pressure at idle and totally screw up the injector pulse widths and basically make the engine not run worth crap. The regulator is there to keep a relatively constant pressure differential between the fuel injector tip and the intake manifold pressure. However, briefly plugging the vacuum line or taking it off the regulator (and blocking the leaking air from the line) while the engine is idling will tell you if the regulator is even working at all since the engine will either idle way up or stumble and then return to normal when you plug it back in. A better way is to put a pressure gauge on the fuel rails and see what it reads.


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## Sprout98 (Jan 3, 2008)

Maybe I need a redirect: can anyone confirm if code 43 on a '98 Sentra SE is "running lean", or is it "throttle position sensor circuit open"? I don't want to chase my tail trying to solve the wrong problem. How would the car act if the throttle position sensor circuit was open? IanH, you out there?:waving:


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## jdg (Aug 27, 2009)

Sprout98 said:


> Maybe I need a redirect: can anyone confirm if code 43 on a '98 Sentra SE is "running lean", or is it "throttle position sensor circuit open"? I don't want to chase my tail trying to solve the wrong problem. How would the car act if the throttle position sensor circuit was open? IanH, you out there?:waving:


I've got an open TPS on my list. If the TPS was open, it wouldn't be able to detect if you foot was off the gas (idling) and might not know to kick in the IAC valve and steady out the idle. It also wouldn't know when you foot was into it and kick the car into 'WOT' mode, open loop/power mode, so you might feel a bit weak on the top end (although the computer has other methods of figuring out when your foot's on the floor, low MAP, high RPMs, etc).
Take it down to the local 'Autozone'. If you've got a real code 43, the DTC for the check engine light will probably be a P0120.


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## Sprout98 (Jan 3, 2008)

Hey JD,

I didn't make it to Autozone on account of the holiday, but the ECU is def. throwing a code 43. Here's the two main symptoms of my car running like poop: 1) when in reverse, backing in slowly, the idle jumps around the worst (just short of bucking) 2) driving steep canyons. Sentra used to roar thru at 70+ no problem, I had the gas pegged to the floor yesterday, only doing 25mph. I had to turn around. Embarrassing. It was still running smooth, just amazingly anemic. Not getting enough gas? I cleaned the MAF like we talked about but it didn't help. I don't have a fuel pressure gauge and am not really sure how to use it anyhow. Ideas? Getting ready to give up and take it to the mechanic, but boy do I hate that!


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## jdg (Aug 27, 2009)

Sprout98 said:


> I didn't make it to Autozone on account of the holiday, but the ECU is def. throwing a code 43


Well make sure that ECU code 43 is the same OBD DTC code P0120.



> It was still running smooth, just amazingly anemic. Not getting enough gas?


And if the TPS is no good, the computer will never know when you have your foot in it, and therefore won't change the A/F ratio to WOT because it doesn't know your foot is at WOT, and therefore won't get enough gas at the top end. Oh it'll get 'enough'...enough to keep the EPA clowns and the catalytic converter happy, but not enough to keep you happy. Get a book (Haynes manual, Chilton manual, go to the library if you don't want to buy it, whatever, there is a Sentra FSM floating around somewhere on the net, I'll bet you can find it with a simple Google search), check the TPS, check the wiring, or just replace the TPS for grins.
Or..since we've been talking about the TPS, you could just disconnect it and see if it runs the same...


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## Exalta (Jan 21, 2003)

does it smell like gas outside the car?have you checked if there's a kink or pinched fuel line? even a small pinhole in the fuel line will lower the fuel pressure...

and how's the fuel pump by the way?


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## Sprout98 (Jan 3, 2008)

Hey Exalta,

I will try to look at the fuel line today. It definitely doesn't smell like gas. I think the fuel pump is OK, but I don't know what the correct fuel pressure for this car should be. I'm still pretty sure I'm running lean. I went to Autozone today and was informed that they don't do the OBD scans there anymore (for California, that is) :lame: I'm taking it to the mechanic Thursday; this blows  and I'm not getting anywhere


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## jdg (Aug 27, 2009)

Sprout98 said:


> Hey Exalta,
> I will try to look at the fuel line today. It definitely doesn't smell like gas. I think the fuel pump is OK, but I don't know what the correct fuel pressure for this car should be. I'm still pretty sure I'm running lean. I went to Autozone today and was informed that they don't do the OBD scans there anymore (for California, that is) :lame: I'm taking it to the mechanic Thursday; this blows  and I'm not getting anywhere


You're running around in circles, trying to circumvent the original problem in the hopes that you'll find something drastically wrong with the vehicle when the only problem here is the Code 43 for the bad TPS which you haven't addressed yet by looking around for a bad MAF, bad O2 sensors, cracks in fuel lines, bad fuel pumps, and whatever else...EXCEPT for the only thing you haven't checked up on yet!!!

A bad TPS will cause the ECU to NOT see that the throttle position is towards the wide-open throttle position. When you hit roughly 70% throttle, the ECU switches from closed-loop mode (maintaining a stoichiometric air/fuel ratio) to open-loop mode, where it feeds the engine a power mixture of fuel, much richer than stoich, roughly 12.5:1. If the computer doesn't know your foot is on the floor, it'll never switch over to the power mix, therefore your engine will seem just plain sloppy.
Same thing at idle. The ECU feeds the engine just a bit more fuel than stoich at idle because engines idle better that way, not much, but just a hair. That alone would account for the jacked up idle. Also, since the ECU doesn't know your foot is off the gas, it doesn't know to try to maintain X rpms by using the IAC valve and your engine will attempt to run at 'minimum-air' rpm which is set by the adjustment screw mentioned in the first few posts. And that's not the normal idle rpm. It's actually far below normal idle rpm.
So...jist of the story -> Replace the TPS. Or continue to waste your time... You could be fixed up tomorrow or next year chasing your tail. Your choice...


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## Sprout98 (Jan 3, 2008)

Replaced TPS, it didn't do crap. Car still runs like junk.:balls:


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## Jopet (Aug 10, 2009)

Sprout98 said:


> Replaced TPS, it didn't do crap. Car still runs like junk.:balls:


Yesterday I think I got everything that should have fixed my own performance problems. I worked on draining ang filling the coolant, pumping more air in the tires (5lbs off on all 4 because of the colder weather?), checked my cat which was just replaced a week ago btw made the car feel a lot lighter to drive. And about 3 weeks ago replace my maf, iacv (w/ add on diode) and air temp sensor as per nissan advice. runs greatest so far since I bought it. Im still measuring the mpg's if its up to expetation. I also change my oil regularly and had my tranny drained twice to make sure I got all the old fluid out of there. 

found this vide on youtube:





it seems to be a good way of checking the cat. I never tried to do it since my cat was rattling like crazy. 

Im sure you can find more how to's in this forum. I hope this help


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## Sprout98 (Jan 3, 2008)

So the closure on this issue is that the FIRST TPS I used was an aftermarket part, and it turned out to be no good. That might have been my fault because I didn't install it properly. I pulled that one out and replaced it with a genuine Nissan TPS. The car runs great now, and it is shocking what a difference this makes. I literally went from the engine not being able to climb above 2200 rpms & 20 mph on hills to flying up them at 80 + mph if I choose. Don't know if jdgrotte will see this post, but this guy knows his sh*t, and was right about this all along. Got to give props where they're due:waving:


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