Cruise VS Throttle MPG increase. Calibration needed?

[jjcuff1]

Well I have a 07 M35 with just custom cat back, 20" Lexani, Dk Blue, Auto.

I have been average around 18MPG around town for the past year of ownership. I knew this going into the M35 and I am happy with the performance etc. But I still have been watching the gas mileage. Typically the Computer tracks veyr accurately to the real world #. I am getting around 280-305 Miles on a full tank around 16-17.5 gallon fillups so I am in the 17.5-18 range and maybe 19-20 on highway if I am doing 100+mile trips at hiway speed.

Well recently I have noticed a slight studder at warm up in the throttle. Not a miss. I had car serviced 2x since then and all is good and gas mileage consistent and no CEL. It goes away after warmup 99% of time but noticable on colder mornings especially after a little rain. It reminds me of the old 300Z start up loop for the TPS. It locked out the OD on the auto until the transmission warmed up.

Well the symptom is like the Drive By Wire throttle gap. When crusing at 2000-2500RPM range at steady speed the throttle feels like it loses gas then rengages. Sort like a surge but the RPM stays steady, I can step on it and it runs fine and takes off or if I feather throttle it disappears. Anyone see this?

Well I noticed on my last road trip and I checked the Fuel Gauge screen realtime and I noticed same effect on the higway around 70mph the car as hard to hold at fixed speed. On the fuel gauge holding the pedal fixed the Realtime MPG gauge would go to 30 like i got off the pedal then I have to give it more gas to get the car engaged again and hold speed.

Mind you this is all at like 1-4mph range nothing dramatic but noticable little surge to m35 owner like us all probably. So as experiment I tried the same thing with Cruise control on. Here are DRAMATIC results

1: before cruise I was racking in at probably 18-20mog trip to hilton head all at 65-75mph range no traffic. I typically do the trip at 360miles and get about 310miles if I push it to empty so not bad.

2: I reset the trip[ meter and did the cruise test at same speeds and no traffic and the sruge disappeared. The car stayed locked in at the fixed speed and the realtime gas gauge was not fluctuating at all!! Halfway there I was already at 220miles on half tank of gas!!!

3: I also realized unlike other cars I had that the gas pedal didnt move with the cruise so I assume the Cruise control monitors the VSS and PC and just controls the fuel under the hood at the TPS not via an actuator at the pedal? is this true?

4: If this is it is good because I probably found out that the gas pedal is maybe out of calibration or bad sensor that might improve my gas mileage?

5: Also will the UpRev chip allow tuning access to the pedal input voltage so I can change the twitchy throttle input and smooth out holding steady speed and therefore my city gas MPG when I am not on cruise?

End of story I realize that my cruise control with same driving habits as my foot on smoooth road in FL, I went from an average of 290-300Miles per tank to 440Miles per tank!!!!! I drove to Hilton Head on LESS THEN 1 tank of gas where I normally do it on 1.2 tanks or more. I made it there, 375miles with still 2.5 gallons in the tank and averaging 27mpg at the end!!! I never could have held this with just pedal input.

I understand the computer is better BUT not 33% improved gas mileage!!!

so anyone see this behavour?
Anyone have to calibrate or replace gas pedal/TPS
Anyone see improvements using UpRev for this throttle input/stability?

Thanks
Jim

[rxmclaren7]

i drive on average 2000+ miles a month, i have he M35X, andi am averaging 20.4 mpg combined city and highway driving.m if all i did was highway i would average 24+. the only difference is that i did not use my cruse for all of my trips. i can usually drive down and back to pick up my daughter which is about 370 miles and still have about (according to the trip computer anyway) 60 miles or so left in the tank. all this with sometimes spirited driving.

[jjcuff1]

Yes So I am seeing the same thing using Cruise. What I am surprised is why my throttle is sticking so bad and causing much less gas mileage at same driving habits. Hence I have some problem that is not engine related (miss fire etc) since it works in cruise not in manual

[myother45isalesbaer]

Jim,

I have an older 2004 M45. Mine closely mimics everything you have posted. In my opinion, your car is behaving normally. Around town if I don't really lay into the pedal I get about 18-19 mpg. I have a tendency to not look at the computer generated mpg numbers and use it more as amusement. If in doubt I check my mpg the old fashion way. Surprisingly the computer generated mpg is darn close to my manual checks. When I can get on cruise and stay there for a few hundred miles my mpg has gone as high as 24 to 25. I was also shocked at such an increase. I attributed it to a few things. The cruise can hold a much steadier speed than using the pedal. On downhills it cuts back and on uphills, when needed it does give a little surge. Not a full blown kick in the pants kind of surge but I can feel it kick in. The other thing I noticed and checked is that if you are changing altitude from your starting point to your ending one on a long trip the mpg's tends to go up. If you are going from a lower altitude it tends to go down. Its just a matter if overall are you going downhill or uphill.

In my opinion, your car seems to behaving normally. Other posters may disagree, but personally I would not put much thought into re-calibration unless something else is going on you think is more serious. Just my opinion as an owner and not a tech.

[jjcuff1]

Thanks yes I think it is behaving normal MPG but I have noticed (and forgot to mention) that I had occasional CEL pop on then off after a few restarts over the past few months. And I grabbed a EVAP code but has since cleared and intermittent so it is not reappearing. But reading about the code it appears the EVAP valve might be faulty. It is meant to open on open throttle position. Well if it is stuck open and I am part or almost full closed throttle like say at steady speed light throttle position at cruise and that baby is stuck open. Wouldn't I go lean enough to feel a small surge/stumble?

[myother45isalesbaer]

Jim,

You got me with some of the tech questions. I am not qualified to answer those. But over the years I have learned how internal combustion engines work. What the electronics or computers are doing I have to bail on those questions. However, for what ever reason, if you are dumping too much fuel into any motor, it can stumble, even loose power and will generate large quanities of black smoke. It could be running too rich. Running too lean will generate excessive heat which your temp quage should pick up. The best way I know to determine if its running lean or rich is to pull a few plugs and look at their color. Get a chart and compare the color of the end tips to the chart. I am old school and basically don't know stink about all the electronics in the new cars. I can rebuild a desktop or a laptop, but the stuff they are putting cars today to electronically manage their perfomance I am lost in the woods on what is going on.

Sorry......I just don't have the tech skills to give you a better answer. Hopefully someone on this site does.

[jjcuff1]

I understand your old school approach. I am too! It does not appear to be runnign rich/lean I had those problems too in past this is random event outside mechanical realm it feels electrical or some solenoid or sensor is tripping on/off or stuck or failing and causing weird stumble at low/part throttle cruise. Probably always there but since at wide throttle the leak is small enough tha t the a/f doesnt mater and car drives fine.

I will still have the plugs checked. I think this month since 60k on car now, I will do the brakes/disc and I already have the SS brake lines ready to install and I will change the fuel filter, flush the fuel line, check the plugs wires and injectors, if look dirty have them system flushed worse case clean injectors with off shelf injector service but do not think it needs it and then check the o2 maybe just replace them to be safe and I like to do an UpRev

[myother45isalesbaer]

My good friend,

Let us all know what the final solution was to your issues. Wish I could be more help, although I understand in general what the electronics are trying to do I honestly don't have a clue as to how to analyze and fix them.

Best of luck to you.

[jjcuff1]

Thanks I will take to shop to double check the emissions and possibly APP or TPS sensors and just monitor. The rest of car seems great except for that annoying squeak over passenger rear shocks. I ll get that looked at as well.

With just cat back anyone here do UpRev? does it really help seat of pants and gas mileage with econ/performance tunes.

Also, I have done the mod thing on almost all my cars. And This one has performance and sound and comfort and hate to just bolt on minimal gains and spend$$$ for CAI, additional exhaust stuff. So with Just Uprev and Catback is anything else worth the upgrade and the money for real hp gains? I think the CAI and spacers will sound better but not worth the $$ on this type of car and cat back sounds good already for few more ponies.

What about art pipes or xyz or HFC?

Or on ICE: anyone upgrade there 07 nav screen with video inout for ipod/airplay controls? Or replace all together with aftermarket and retain control of nav/phone etc features of dash/wheel?

[EniGmA1987]

I understand the computer is better BUT not 33% improved gas mileage!!!

Cruise control is not even close to better for me. I see an average of 15% mpg decrease using cruise. If I drive myself I can keep it far more steady and my best was driving 24 miles on the freeway (from work to home), along hill areas and flat places and I averaged 31.3 mpg doing 65-70 mph. Driving long distance I can average 27 mpg(computer says) on a complete trip with freeway only. The farthest I have ever gone on a tank between fill ups (filled 19~ gallons this time) was 430 miles. Using cruise I have never averaged above 22 mpg on all highway miles.

Sounds like something is definitely wrong with your car.

[The00Dustin]

Does the pedal feel like it sticks, or is it just the behavior of the car? If it is just the behavior of the car, I think you should search the forums for the throttle positions relearning procedure (I'm not sure all of those words are right for such a search). You can try that and see if it helps, if it doesn't, then maybe that's normal.

Beyond that, I know that it's very difficult to make a slow and smooth takeout until you spend a lot of time training the car (transmission?), and then as soon as you drive hard, it's like you have to start over on the training. Without feeling what your car is doing, I can't really be certain you're experiencing the behavior I refer to.

Regarding your concerns on the pedal not moving with cruise on, I find this annoying, because it makes it much more difficult to keep cruise smooth when you are coming up on a steep incline or ICC detects something in front of you that you don't need to slow down for. However, I believe it is normal and the commonly used term for it is "drive by wire". The pedal is actually only connected to a sensor, and not the actual fuel stuff. I believe in the 2003-04 they had a hybrid system that had a sensor and a physical connection, but I probably read that on this forum.

Regarding your concerns about running lean/rich, I don't know if this is true or not, but lots of articles about fuel mileage say that modern cars with computers don't get better (or worse) mileage with a clean air filter because the computer adjust the mixture ratio based on the amount of air available. As such, a dirty air filter would cause less power instead of lower fuel mileage (because it would adjust instead of running rich). If that is true, I wouldn't expect you to be running lean, either, regardless of what might cause that (at least not unless what would cause that was negatively affecting cruise control as well).

[jjcuff1]

No the pedal is not sticking. Yes it could be related to the learn in. Some mornings I start the car it gets going quick or sometimes I forget to start, ACC mode first then on/off again quick it could be related for random things like that. Isnt the learn procedure just on for 5 sec, off for 10sec on again off again and thats it?

Ok Thanks for confirming my cruise/pedal annoyance. I agree.

I also agree the car has a heavy tip in on the throttle like a big hump (voltage curve) at 0-2000 rpm you have to get on it to take off like a surge then lay off to cruise into the 2500-3000rpm throttle hole of the DBW. Or you can baby it from 0-2000rpm but it doesnt seem to accelerate at all like 0-30mph would take 1 min if I just gave part throttle
So I agree with you here as well.

As for the A/F yes the car does map within its limits to compensate for variations. If all the sensors are working! :-) The MAF will compenate with more/less fuel if say there is a vac before the MAF but after the MAF it is the o2 sensor then it becomes a do-loop cyle and it still fight to maintain a/f but you will get some lean or rich conditions, CEL codes or bad gas mpg it will just be drivable but not as much or nice

[EniGmA1987]

I also agree the car has a heavy tip in on the throttle like a big hump (voltage curve) at 0-2000 rpm you have to get on it to take off like a surge then lay off to cruise into the 2500-3000rpm throttle hole of the DBW. Or you can baby it from 0-2000rpm but it doesnt seem to accelerate at all like 0-30mph would take 1 min if I just gave part throttle
So I agree with you here as well.

That sounds so strange to me. I have never experienced anything like that

[jjcuff1]

I guess simplest way to describe it is a part throttle hiccup or surge loss of gas around 2500 rpm when cruising, random and not all Time and has sort of been absent for a while I think it is:

1: bad gas an Evap leak or gas cap combo

2: in certain situations app and tps relearn get lost due to
Poor start up sequence