Do any of you guys have the same feel? My Q now has 140 on her, and it seems the throttle is much more responsive, the tranny shifts snappier and better, and just get a sense of more power when the motor is not fully warmed up.

Of course, this is not the time to be beating on the motor, but sometimes I can't resist since it feels so much quicker when cold. Does anyone else have this problem?

It's not as if the car is slow when warm...but it just feels generally sloppier. I have an o2 sensor that is bad that I need to replace though, maybe this has some bearing on it...

Each 11F change in air temperature changes air density by 1%.The ecu expects coolant to be 174F-194F above that it assumes summer conditions and begins to decrease ignition advance by 1 degree per 5F to reduce possibility of spark knock.

Not unusal to see a cumlative loss of 5>10% from all factors whenever the outside air temp goes above 80F.

The KS system is so effective and silent that it hears and deals with spark knock long before the driver is aware further decreasing power.

There are basically 3 types of operation in fuel injection.

Open loop and Closed loop.

Fuel injection is a feedback system, that is, it reacts to current conditions, load, and temp. When first started it is in Open loop. It is running on predefined values in the ECU. Only after the engine has reached a predifined temp will it go out and start reading the different sensors. Now it is making choices based on the input it gathers. This is called closed loop.

The other mode is seldomly used, its called get home mode. This is used if one of the sensors has failed and will use a value stored in ram to replace the missing data. If you have a bad O2 sensor, it is using this value.

Now these values are only to keep the engine running well enough to get home and allow repair. A properly working O2 sensor is needed to get the best performance. The value used when first starting up is different than the get home mode, it is based on mapping reflecting the warming up of the engine and that's why it runs ok while cold. It tends to be on the rich side, like a choke on a carb. Engines like rich alot more than lean.

I hope this helps. Get the sensor changed and you should be in Fat City.

Jonsey...........

During WOT or more than 30% acceleration O2 sensor are ignored.

You know, one can learn something every day. I wasn't aware of the operational limits of the O2 sensor. Is this a Nissan thing or do all cars follow this limitation?

This is why I like this forum, its not often you have members like Q45Tech and their skill set to help you with a problem.

Now as to the original question, I think Q45Tech would agree with me when I say that before any further diagnosis can procede you need to replace all bad parts with known good parts. I say known good, because a new part can be as defective as a used one.

Again, as a new member, I am thankful to all the members and their help. I belong to other forums related to my motorcycles, but by far this one has impressed me the most.

Jonsey....

jonseyq45 wrote:...before any further diagnosis can procede you need to replace all bad parts with known good parts. I say known good, because a new part can be as defective as a used one.

A founding precept of this Forum that many new members don't understand until several used parts have failed.

That is the best explanation of that i have EVER read.

Thank you both.

Even the lamest, carbureted engine will produce more power on a cold day than a warm one due to the differing air density. Ask anyone who ever flew a light plane on a hot day, and the same plane on a cold one.

All,

Maybe I am missing something. I reread the original post and the way I understand it, he is describing a cold engine transitioning to a fully warmed up one.

I don't think he was refering to ambient air temp. As to air condition,there is alot of different variables to take in consideration.

Altitude and temperature will affect the oxygen content of the air. This will in turn affect the mixture balance (lean\Rich) of the engine.

Humidity also affects how it runs, very much like water injection, which is used to lesson the tendency of pre-ignition (knock).

This will increase knock suppression which will then keep the knock sensor out the equation allowing advanced ignition timing which in turn make the engine more responsive.

As you can see it all connected, this leads to that and that leads to this and so on and so on.......

As oldmako brought up, pilots of small planes and old snowmobilers know all about altitude, temperature and mixture control.

Jonsey

“First lesson about Race_a car driving” he said ripping the rearview mirror off the windshield, “Once_a behind you, not_a matter”

Movie: Gumball Rally

Whoops. When I read the title, it seemed to mean outside ambient temperature, but a closer reading shows that the thrust of his question seems to be engine temp. RTFQ eh?

I maintain a very light foot (max 2000 rpm) until my engine coolant reaches at least one quarter throw so I have no idea about superior perf when cold. I always assumed that a FI engine sensed ambient temps immediately and adjusted FF to optimum, given the conditions. Sounds like there is quite a bit more to it. It's all PFM!

oldmako wrote:Even the lamest, carbureted engine will produce more power on a cold day than a warm one due to the differing air density.

With carburation. it is all abouit jetting to air density. Why all cars are fuel injected now to meet ideal fuel air ratios acroos all seasons, temperatures, and barometric pressures.

As far as an engine not upt to operationg temperature being more powerful, I just don't think so. Even if it were, it soon wouldn't be. Notice that no pilots take off before engines are up to operating temperature.

maxnix wrote:
As far as an engine not upt to operationg temperature being more powerful, I just don't think so.

Actually that's one of the tricks companies use to make their product look better. They dyno the stock setup when it's hot and then then their product on a cold engine and that's where a majority of the power comes from. It's only a few hp and it's only from the engine not being heat soaked.

As for the injection there are only 2 types on the Q. Simultaneous and sequential. During startup and failsafe the ecu faults to simultaneous. WOT and heavy loads and a few other dillemas it uses sequential in open loop. Any other time it's running it's closed loop sequential using all sensors.
Modified by T45 at 11:45 AM 3/13/2008

jonseyq45 wrote:There are basically 3 types of operation in fuel injection.

Open loop and Closed loop.

Fuel injection is a feedback system, that is, it reacts to current conditions, load, and temp. When first started it is in Open loop. It is running on predefined values in the ECU. Only after the engine has reached a predifined temp will it go out and start reading the different sensors. Now it is making choices based on the input it gathers. This is called closed loop.

The other mode is seldomly used, its called get home mode. This is used if one of the sensors has failed and will use a value stored in ram to replace the missing data. If you have a bad O2 sensor, it is using this value.

Now these values are only to keep the engine running well enough to get home and allow repair. A properly working O2 sensor is needed to get the best performance. The value used when first starting up is different than the get home mode, it is based on mapping reflecting the warming up of the engine and that's why it runs ok while cold. It tends to be on the rich side, like a choke on a carb. Engines like rich alot more than lean.

I hope this helps. Get the sensor changed and you should be in Fat City.

Jonsey, thanks for that great explanation.

Yes, I'm referring to performance as the MOTOR warms up, not ambient temperature. What I'm experiencing is definitely NOT a result of air density...I appreciate the great info above.

I have replaced 2 o2 sensors already. Unfortunately doing so didn't fix this issue, which existed before my third indicated fault. MAN, that sensor is not fun to change in driveway...drivers side post-cat sensor.

I'll get this sensor in before weekend and see how she feels. "Get Home" mode reminds me of a Chrysler LHS I had, which frequently after countless repairs would resort to "limp" mode, which was pretty limp.

Damn, you guys are good..................

This has been a good discussion so far. I think we all are learning some great information so far. I one of those guys that has to know all he can about every little thing. Just ask me about toilets......... just kidding.......... ok...ok.... if it makes a noise jiggle the handle...........ok ok enough.......

T45 added some great information.. I would like to expand on it without being preachie or big headed.

As he said fuel injection comes 2 basic flavors, I am referring to port type of injection not the throttle body type.

The first is called simultaneously ( I used spell check). This means all the injectors are firing all the time regardless of the piston position(compression or exhaust). So their firing all together, kinda like the grand finale at the 4th. All for one, one for all.

The second type is sequential (thank you spell check). The best way to describe is that it is like a ignition distributor for fuel. This is the kinder gentler injection. They are like those two chimpmunks on the Bugs Bunny show, no no after you....no no, so kindley, after you. They only fire when they are on the intake stroke, timed just like the spark plugs. This is by far the more efficient system. I t also allows a more precise control of the timing of the injectors.

I hope I don't come across as big headed, I just love this stuff. I used to have a T-shirt when I was younger that said " I eat, breathe, ride, live, love, and ride motorcycles. I feel that way about the cars I own also.

New dosen't impress me. Good solid engineering does. I have always wanted a Q45. Now I have one (see dumb luck post) to go with my 91 Maxima SE.

Your probably tired of me now, so off I go...........

Jonsey

"Don't forget....Where ever you go.........There U R ..."

Modified by jonseyq45 at 7:39 PM 3/12/2008

Modified by jonseyq45 at 10:47 PM 3/12/2008
Modified by jonseyq45 at 8:24 AM 3/13/2008

maxnix wrote: Notice that no pilots take off before engines are up to operating temperature.

Except for many of those who rent (and therefore pay by the minute). Their goal is to get going after all. Fortunately air cooled engines are wonderfully tolerant and designed to withstand sudden, and significant temperature excursions, as well as sloppy and careless technique.

Additionally, the fuel mixture is infinitely adjustable from the cockpit, as jetting cannot compensate for changes in altitude and density altitude that a plane experiences. Just splittin' hairs and no longer partially germane to this thread, but I still maintain that cold (denser) air produces more HP than warm. One reason why the bubbas all love it when it's cold on qualifying day.

4 sure good buddy.............

Cold = more Oxygen= more power

The Q doesn't use simultaneous at WOT, no need as there is still plenty of time to flow fuel................maximum injection time used is 11* milliseconds on 370cc injectors as the time between repeat events is 16 milliseconds at 120 rps or 7200 rpms. Duty cycle is 62.5%

* this is at 4,000 rpm, it declines as rpm rises due to VE losses to about 10 millisecs at redline

Q45tech wrote:The Q doesn't use simultaneous at WOT

I didn't recall that ever being asserted before, so thanks for the clarification. I remember the old Rochester fuel injection used on SBC. Sprayed continuously into the plenum. So kluge.

I think he was referring to my post. I accidentally put simultaneous twice instead of sequential. I fixed it.

paranoidjack wrote:Do any of you guys have the same feel? My Q now has 140 on her, and it seems the throttle is much more responsive, the tranny shifts snappier and better, and just get a sense of more power when the motor is not fully warmed up.

Of course, this is not the time to be beating on the motor, but sometimes I can't resist since it feels so much quicker when cold. Does anyone else have this problem?

It's not as if the car is slow when warm...but it just feels generally sloppier. I have an o2 sensor that is bad that I need to replace though, maybe this has some bearing on it...

OMFG. I asked the same question MONTHS ago and all I got was nonsense.

I don't even have to be tough on the motor, it does it by itself. The suspension seems nicer and lessens the road noise, the tranny shifts like brand new, the throttle is ultra responsive. I wiggle my toes and the car is flying. It feels like it just wants more.

At warmer temps, i get the same issue. Yesterday at 59 degrees, the car was great, but later on, it was a little sluggish. I get what you mean about sloppy. The acceleration just isn't there from the beginning as opposed to when it's operating well.

Haitian_King wrote:
OMFG. I asked the same question MONTHS ago and all I got was nonsense.

I don't even have to be tough on the motor, it does it by itself. The suspension seems nicer and lessens the road noise, the tranny shifts like brand new, the throttle is ultra responsive. I wiggle my toes and the car is flying. It feels like it just wants more.

At warmer temps, i get the same issue. Yesterday at 59 degrees, the car was great, but later on, it was a little sluggish. I get what you mean about sloppy. The acceleration just isn't there from the beginning as opposed to when it's operating well.

Again, I'm not talking about ambient temperature. I feel no difference in the suspension. I am speaking solely about throttle response, and yes, the tranny does seem a bit "snappier." Normal for many cars when cold...I'm referring more to the acuteness of the power response.

paranoidjack wrote:
Again, I'm not talking about ambient temperature. I feel no difference in the suspension. I am speaking solely about throttle response, and yes, the tranny does seem a bit "snappier." Normal for many cars when cold...I'm referring more to the acuteness of the power response.

Well, I do notice the change in suspension, but then again, I have a G50.

But yes, throttle response and the way the pedal feels changes (at least to me) in colder weather. Usually below 40.

The increased throttle response tempts me to really cut loose, but better judgement prevails and I don't run the cold engine as hard as I crave to on those nights.

Haitian_King wrote:
Well, I do notice the change in suspension, but then again, I have a G50.

But yes, throttle response and the way the pedal feels changes (at least to me) in colder weather. Usually below 40.

The increased throttle response tempts me to really cut loose, but better judgement prevails and I don't run the cold engine as hard as I crave to on those nights.

Again Haitian...I think you're referring to colder weather, I'm referring to colder oil! But I'm glad we're in agreeance, if only at least partially.

Nobody's asked so I will, have you modified your intake system? For a while I had a cone filter directly attached to the MAF and there was a very noticeable change in performance within the first 15-20 minutes of driving after the engine bay was warmed up.

Even with the stock system the engine and intake plumbing will get heat soaked after a while and increase intake temps which will decrease performance some.

qsiguy wrote:Nobody's asked so I will, have you modified your intake system? For a while I had a cone filter directly attached to the MAF and there was a very noticeable change in performance within the first 15-20 minutes of driving after the engine bay was warmed up.

Even with the stock system the engine and intake plumbing will get heat soaked after a while and increase intake temps which will decrease performance some.

Thanks, no. I've married myself to rehabbing this whole car with OEM parts, from OEM shocks/brakes to small missing screws I find here and there.

I will refrain from further comments until I change my o2 sensor, because that may be playing a large part here. From the above explanations, my bad o2 sensor would have zero bearing during warmup, so I think this explains it. I'll report back.

paranoidjack wrote:
Again Haitian...I think you're referring to colder weather, I'm referring to colder oil! But I'm glad we're in agreeance, if only at least partially.

Well, cold weather is the only sort I've been getting until recently. (62 today)

Cold oil itself? Like in moderate temperatures? I don't think I've noticed too much difference. In fact, I think I'm guilty of driving harder in warmer temps because I had felt that the oil wouldn't need as much time to warm up. Probably a bad idea.

paranoidjack wrote:Do any of you guys have the same feel? My Q now has 140 on her, and it seems the throttle is much more responsive, the tranny shifts snappier and better, and just get a sense of more power when the motor is not fully warmed up.

Of course, this is not the time to be beating on the motor, but sometimes I can't resist since it feels so much quicker when cold. Does anyone else have this problem?

It's not as if the car is slow when warm...but it just feels generally sloppier. I have an o2 sensor that is bad that I need to replace though, maybe this has some bearing on it...

LOL, I have an i30 and understand what you mean. Forget the outside temp, when I start the engine and the and the engine itself is cold, it drives great. It's not so fast after warming up.

I had an Escort Zx2 in the past and some people on a forum were putting a potentiometer on the air and coolant sensors to fool the car into thinking that it is still cold when the knobs were turned. This really worked but the side effects were, if you forgot to turn these knobs off, you can overheat your car.

This made the car run either more lean or rich while advancing the timing so the engine could "heat up" quicker. The engine did run different as I did it but take everything else with two grains of salt.