Hey,

If I floor the accel. in let's say 3rd gear, the rpms will climb fast but I won't feel the pull as much as I would if I start backing off the throttle. It feels like the car is chocking somewhere when I go WOT. There's no hesitation or anything though. This doesn't happen all the time though. Other times the car pull really strong. Maybe it's the MAFs. A few times the RPM jumped to 2k and stay there until would turn the car off and on a couple of times.

Thanks.

 

Change your fuel filter.

 

When was the last time you did any type of maintenance on your car, and what did you do?

 

i've noticed the same thing on my moms VQ auto. its definately alot slower at WOT, but if i back off to say 90% (VERY rough estimate) its slightly faster. doesnt the TPS send a WOT signal to the ECU and in doing so, the ECU dumps more fuel than necessary?

 

All the maintenance was done recently. I have a feeling it's due to either the TPS or the MAFS.

Thanks.

 

If your knock sensor is blown, it will dump your timing back, but the threshold is about 30% throttle or so from my OBD-II scanner, not 90%. I think 90% and above is when the ECU will jump over to open loop mode and run really rich (normal). It will also go to a different ignition timing map also. So it seems like something is happening on the closed loop to open-loop switchover.

If you've done all the maintenance including fuel-filter and you don't have a knock sensor ghost code (will not light the SES light) then I have no idea.

 

Definately not the knock sensor, cause I have all the torque down low but the high end is suffering sometimes. Might be that the front coils are going little by little. If already had to change the rears some time ago.

Later

 

my car feels the same way at wot slightly slower than at 75%-90%

 

Elaborate, IM not too sure what the 30% / 90% meant... I have a blown KS and its giving poor acceleration/gas mileage. What else should I expect?

 

my car is like that too.. partial throttle is faster than WOT...

and i have done FF, Spark Plugs, Oil in the past 2 months.. my CEL is always on so i guess my Knock Sensor might be gone

 

I doubt the car actually puts down more power at 80% throttle than WOT. There just isnt as much of a difference in acceleration between 80 and 100% as there is between, say, 40 - 80%.

It's like saying that a Y-pipe cuts low end power. It doesnt, but the high end gain is much more noticeable.

It's all mental:

 

I wish it was all mental, but unfortunately I can actually feel the difference when it happens.

Later.

 

Now that I think about this, my previous 2000 Altima did the same. I could be just a nissan thing if you know what I mean. Maybe the way the ECU is programed.

 

It's mental until you get dyno plots comparing 80% throttle to WOT. Butt-dyno is meaningless.

 

i dont know if you guys are stock or what, but IMHO the ECU senses WOT and dumps more than needed fuel, so it runs rich. i think this condition is helped if you're not stock..i dont relaly know about all the wiring and how the ECU works so this is purely my theory.
one question though:
when i floor my moms VQ, there is black smoke coming from the exhaust..there isnt alot but its more than none..if i back off the throttle it goes away, so i KNOW its running rich i'm just wondering if thats the cause of the WOT slowness.

 

I wish it was mental.. i actually used a stop watch for an 80 - 110 punch in 4th Gear on partial and on WOT..

and partial was quicker

 

Sprint,

Did you ever find the problem? This happend on the night I went to the track too! It was running beautifully that morning though I'm thinking it's the MAFs or the TPS along with O2 sensors. Those are the only three that control a/f delivery. But I'm not about to spend all that cash on finding the fix.

Later.

 

nope.. never made any attempt to fix it.. just dealt with it. i was hoping you would fix it first and let me know

 

the ECU ignores O2 and knock sensor readings at WOT, IIRC. i wonder why it runs rich at WOT if its still reading from the MAFS....

 

It does not ignore the KS at WOT. Just the O2s.

It may run rich because the map is just set rich. Generally speaking, richer is safer.

 

There's also the phenomenon called "cylinder soaking" that could be what you are feeling. From a dead stop, if you floor it suddenly, the engine can bog due to the immediate richness. Then it recovers from this shock of extra fuel and operates correctly. If you go to about 80-90% throttle, then WOT from a stop, the car will respond quicker. Crown Vics ('95-'99s) did this, and we were taught about it in a tactical driving course. I haven't really noticed it in my Maxima, but I haven't tried to notice it. This doesn't affect people brake torquing because the rpm's are already up.
This may be what you guys are feeling. Then again, it may not be.

Dave

 

when i say WOT feels slower, i mean from a roll...i know say 50% throttle, easing on as you get going is good from a standstill..at least in my moms auto. a WOT condition from a roll causes a downshift (violent if between 55 and 65) so the sudden richness problem shouldnt be an issue in that situation.
that cylinder soaking issue is especially present in VG autos..thats just my personal experiance/observation.

 

Hope you guys find the problem. I'm out of this conversation because I'm selling the max for a Mazdaspeed Protege

 

http://forums.maxima.org/showthread.php?t=233739

 

How does cylinder soaking happen? When you go WOT, the ECU doesnt just dump more fuel.

It will not dump more fuel until it sees more air. The instant the throttle opens, there isn't more air flowing yet...so no more fuel.

Sounds like something that may have effected older cars, but not newer ones.

Dont take this the wrong way, but I dont care what they told you in tact. driving class. I want to know exactly how and why this cylinder soaking might happen.

 

Last I heard, Mazdaspeed Protoges were having ECU lag/surge issues, so that might not solve your problems either. Mazda might finally have it fixed by now though, but you might want to check on the Mazda forums.

 

Like I said, I don't know if this affects the Maximas or not because I haven't tried to notice it. It definitely affects Crown Vics (which most police departments use) atleast up through '99s.

Let me try to find my NAPD Tactical Driving book from a few years ago. It should have the cause of cylinder soaking. But my basic understanding of it is the sudden increased air/fuel at WOT isn't initially burned efficiently (can explain the sudden black smoke from exhaust when first punched that doesn't continue while still at WOT). I'll look it up and get back to you on it.

Dave

 

I think this would happen quickly enough that you might not be able to tell the difference. As soon as you crack the throttle, the cylinders are taking in more air, and the flow rate through the MAF increases.

I think there might be some truth to what Dave was saying. From my OBD-II scanning logs, if you go to 80-90% throttle right off the line the ECU still stays in closed-loop operation. The mixture is leaner (more power) and the timing is much more advanced (more power). If you crack the throttle that last 10% (more power), now you're in open loop mode running much richer (less power but safer) and less timing (less power but safer).

Scenario A: 80-90% throttle, closed loop 14.7:1 mixture, 20 degrees timing.
Scenario B: 100% throttle, open loop 10-11:1 mixture, 10 degrees timing.

It's very well possible that off the line or at lower revs when you're launching, "A" would be more powerful than "B". As the revs ramp up at WOT, the timing curve will ramp up as well and get to about 25 degrees by the time you reach redline. At that point, 25 degrees of advance and 100% throttle in open-loop would probably beat out 80-90% throttle and 20 degrees of advance in closed-loop, but


You guys that think you're having a problem. Y'all need to get OBD-II scanners and do some data logging. That will help tremendously in figuring out what the hell is going on.

 

Probably because when you punch it and the ECU goes to open-loop operation the timing is pulled way back and there isn't enough timing advance to burn the mixture as well, especially when it's now way rich.

 

Anyways, I've noticed that the engine seems a little less responsive at WOT than at 80-90%, and I think the OBD-II logs show why. But I've taken the engine up to pretty much redline at 80-90% throttle, and it is DEFINITELY quicker at WOT. So as mzmtg mentioned, it could also be a psychological issue.

The engine is much more responsive to small throttle input changes in closed-loop when the mixture is leaner and the timing is more advanced. This is dulled out when you're very rich in open-loop with less timing, but there is still more power. Unless there is something wrong.

Since the ECU doesn't monitor the MAF or O2s during open-loop at WOT (I don't think it does), if you had something obstructing your intake path that would make the mixture even richer and less responsive. Check air filter? Got some crud in your intake tube? If you're at higher mileage, you'd definitely want to check your throttle body also and maybe do a throttle body cleaning. There could be all sorts of junk and crud in there contributing to the problem that you wouldn't notice in closed-loop because the ECU is adjusting for that.

 

no.. you smart fcks just need to tell us how and what to fix

 

Yeah I've read up on mazdaspeed protege alot. Mazda is almost out with a fix so I'm not stressed about it. Boost baby!

 

I already mentioned what you might look at.

 

This is one of those threads that makes all the sense in the world. What about us 95'ers that are running on OBDI?

Great link stevey.

 

You said you knew your knock sensor was blown, so all you have to do is replace it. Or as a temporary measure, disconnect the ks-subharnass and put a 470k resistor across the ECU end of the harnass temporarily.

 

time, sounds like a filter issue

 

Replacing is going to be my only option as I live in south florida where its almost always 80+ degrees and I like to hear my intake I learned a lot though. Good work

 

do u have a write up on how to do that ? and how do u know exactly when the ks is bad and what would a resistor do for it

 

Motorvate.ca

 

I think it's possible, if the fuel system is clogged/dirty or otherwise not pumping fuel quite as much as it should, that the Closed-Loop fuel trim ends up richer than open-loop (i.e. at open-loop, the mixture is too lean due to a fault in the fuel system, thus in Closed-Loop it compensates by using positive fuel trim values)... thus flooring it would run LEAN, not RICH, and backing off would put it back into positive fuel trim (Open Loop = fuel mixture computed from MAFS/ECT/IAT/etc, then in Closed Loop it uses Fuel trim values which define a percentage + or - open loop's mixture)
An OBD-II sensor scan tool might shed some light into that scenario, if it exists...