I just got back from Sleeper Motorsports and I only got half a run done on the dyno because of very high air fuel ratio. The a/f was at 15 @ 3,000 rpm and it went off the scale (over 19) @ 4,500 rpm. The mechanic shut it down at 5,200 because he didn't want to risk damaging the engine. My mods are Injen intake, Stillen Ypipe, and Cattman Catback exhaust. What could be the cause of the problem? The mechanic said maybe I should get an AFC or fuel regulators. I went to the parts department at Superior Nissan in Puente Hills right after to see if I could pick up a MAF sensor and the dude at the counter said there is a TSB out for Air Flow Sensor so I'm going to take the car in to the service department on Monday. Anyway, what else could be messed up if it is not the MAF? Thanks in advance!!

Here's the dyno sheet

 

bad O2 sensors? A bad MAF would most likely cause you to run rich, but maybe not. Also, you may want to check your fuel pressure or try cleaing the fuel injectors... it could be a fuel delivery problem as well

 

BTW, that dyno looks waaay off. You are losing major power somewhere.

 

Thanks for the response. But at WOT the ECU doesn't take readings from the O2 sensors. Also, the dyno was way low because he shut it off at 5200 rpm. But it can definitely be a fuel delivery problem and the dyno guy said I should get an adjustable FPR and S-AFC...

 

Even though he shut down the dyno early, the numbers still look too low. You should not need the FPR of AFC if you are NA at all. I think you have a fuel problem somewhere. Don't rule out the O2 sensors either...

 

You're right! I dug up my old dyno sheet when the car was stock and I got 166hp at 5200 RPM. Damn this sucks....

 

have you noticed a performance hit in every day driving? I think you would notice a loss like that. I was thinking that you may need new ignition coils as well... there is a TSB on those. That could also contribute to the power loss. Have you heard any noticeable pinging or detonation? You may want to pull the plugs and check those since you may have been running lean for some time...

 

I knew the car wasn't running right. One day, there's a **** load of power and another day the car doesn't want to move. I did have the ignition coils replaced because I had detonation before. That was 2 yrs ago, and I still get detonation sometimes during light acceleration and almost always when going up hill. I also changed the spark plugs 2 yrs ago along with the ignition coils. But looking at the plugs back then, I could tell it was running lean. So, like you've said... I've been running lean for a while. But I had no idea it was this bad because I dynoed the car at R&D back in 2000 before the ignition coil TSB and they didn't have the A/F ratio readings on the dyno sheet. But I still managed 181hp stock back then. I'm not looking forward to dealing with those idiots at the service department... Took a lot of effort (5 visits) just to get them to change the ignition coils even when I had the TSB in hand. Ended up taking a technican on a test drive to show him the pinging. And then there was the brake warping TSB... Just hate those bastards....

 

I'm new to nissan, but have a ton of experience with a turbo car. With my talon, if you start getting that lean, the ping sensor starts to hit 30+ and timing gets yanked. I would assume at your AF ratio there is a ping issue and timing is being pulled? THere are some cheap OBDII logger out there that can measure that.

It still doesn't get to the bottom of the lean out condition but explains the HP loss. I wonder what your knock counts are and where timing is at?...

I think it all points to an overall fuel issue. The ECU would be open loop at WOT and pulsing the injectors to preset tables, if the fuel pressure isn't there that would explain the lean condition.

Personally, the first thing I would check is FP. Could be something as dumb as a fuel filter or possibly a failing fuel pump.

It doesn't sound like enough mods to need an AFC but I'm speaking from experience with a different car. Wouldn't you need bigger injectos or a lot more FP to use an AFC?

Aren't most ECUs programmed to cut fuel if the MAF exceeds a certain preset value (to avoid lean out)? If the MAF were an issue I would think the ECU would cut fuel just as a safety issue if AF went beyond stoich.

It all seems to point to a fuel control issue.

Like I said, most of my experience right now is with a different car so this may not be applicable, just trying to throw some thoughts out there.

 

I think that is because at WOT the ECUis in open loop. When The ECU is in Open loop it doesn't get feedback from the O2 sensors. Someone correct me if I am wrong.

 

Very informative post Nissan is known to have very sensitive knock sensors... The Sentra guys are basically disengaging the KS by taking it off the engine block, grounding the sensor and zip tying the sensor to the firewall.... Desensitising the KS recommended by JWT if they take out the balance shaft. So, I've been thinking maybe the extra vibrations and noises from the y-pipe and exhaust is causing the KS into thinking it is detonation and retarding the timing. So that can definitely account for the HP loss... But plenty of others have these mods and doesn't have the same problems.

The mechanic that dynoed my car today didn't think it could be the MAF. But I think it is because when the car goes into open loop mode, it goes to a fuel map and doesn't take readings from the O2 sensors... So the only thing the ECU is reading is from the MAF. Is this correct?

As far as fuel pressure goes, the mechanic said I should maybe change the fuel filter but then I know the damn thing is in the fuel tank... So I'll only do that as a last resort. If it comes down to it, I'll get myself the Walbro 255hp pump also

Thanks for the help guys!

 

Yes, in open loop the ECU uses only the signal from the MAF which is plugged into a fuel map table to calculate the pulse width of the fuel injectors.

Personally, I think your best bet is to data log the ECU and see what's up. WIth OBDii I don't think you can log knock counts, but if you see timing getting yankaed that's more than likely the culprit (knock). You should also be able to see the MAF signal output with an OBDii logger as well.

 

Very good response.

My guess is also a loss of fuel pressure due to a weak fuel pump or a clogged fuel filter.

 

If you don't mind a little bit of a drive (30-45 min), Connell Nissan in Costa Mesa is really good with the TSB issues. You should definitely talk to Mark Nutter, service advisor. He is really on top of things and has no problems validating the TSB work. Just keep in mind that he also asks about aftermarket performance mods so if you have any that might affect that part concerning the TSB or issue you are dealing with take it off and put the stock back on.

Hope you get your car worked out. Something is definitely wrong...160 something HP? Damn...

 

Thanks for the tip! I'm going to take the car to my dealer tomorrow first and if they are their usual self, I'll take the car to Connell Nissan I can't wait to hear their excuses... Probably going to say the dyno was inaccurate.

I took my mom's new car to the service department last week because the transmission was shifting rough and the transmission was way over filled. I don't think they even looked at the car, they said they couldn't find anything wrong with it. I asked if they checked the transmission fluid and it was obvious by the look on his face that they didn't.. He said "ahhh...it is a little high, but the engine is warm and so it is normal". I was like.. wotever sh1thead... I checked the fluid when the engine was cold. This is Superior Nissan in Puente Hills BTW... Just wait till I get my hands on one of those surveys Nissan send out after you visit the service department... I'm gonna rip them a new one.

 

That the Air/Fuel Mixture Ratio Self-Learning Control will judge a too lean condition as a malfunction and light up the MIL.

Possible Cause:
-Intake air leaks
-Heated oxygen sensor 1(front)
-Injectors
-Exhaust gas leaks
-Incorrect fuel pressure
-Lack of fuel
-Mass air flow sensor

So, if you didn't have a MIL, I'd guess your A/F reading was wrong.

 

Ya.... That's what the service manager at Superior Nissan said also. He said at that high of a reading, I should have heard a lot of pinging which I did not... Oh well... the car still runs like **** regardless... And I'm still looking at some very low numbers from the dyno. The car seems to run much smoother with the stock intake as compared to the Injen... There's some hesitation in the powerband.

 

That graph looks a lot like my dyno back when when I was na and auto with all bolt ons.. I was running extremly rich and got the same #'s.. An AFC solved that.. Oh yeah SC too

 

Take it to any mechanic and have him slap a fuel pressure gauge on there=$30. You should idle at 37-39 and immediately jump to 43-45 at WOT.

This can help you determine if you have a fuel delivery problem or not, or vacuum pressure problem.

Also, you can watch the gauge, while someone revs it in "Park", and see if the gauge is jumping around, which would suggest a clog in the system, or leak in the vacuum lines.