TOPIC: 1998 Maxima Grooved, not getting mpg gains, Help.

Hi,
I had my 1998 Nissan Maxima grooved (sent my TB to a certified gadgetman)and also plugged the air intake on engine (also tried without) and I did not notice any mpg gains.

I also replaced my two front sensors and still no mpg gain.

I use 100% v-power shell gas and my car is in great shape.
Air, fuel filters replaced, TB cleaned, spark plugs changed, IACV cleaned...

I also had the mechanic check for vaccum leaks...nothing found.

My car has 270,000 kms and gets about 23 - 24 mpg.

What else can I check or missing? Any help is appreciated.

Thank you!

Hi Julius,

Did you reset the disconnect the battery to reset the ECU?

Hi Julius

There are things that have to happen to get the mpg gains, You said you had your IACV cleaned... did you do anything to reduce the air flow through the IAC?

Two things will directly effect the mpg gains

1) the PCV connection to the intake manifold needs to be re-routed to the air intake side
2) The IACV depending on its configuration needs to be mod'd to reduce the air flow. This would either be in the way of a modified gasket or blocking the existing path and re-routing it on the Throttlebody.

If you can pull the TB and take some photo's of it and the IAC and pathway we can make a better recommendation.

Karl Fortner
Tacoma, Washington

Thanks for replying.

Yes I did reset the ECU. On the 4th gen maxima, you just have to turn the screw on the ECU twice and it resets.

I don't have the new TB pics that went in the car, but I do have the before pictures.
I hope this helps. I also did cap the intake valve, but I don't have a pic of it, but I do have a picture of what I did. (my camera is out for the moment).















In this pic circled in green, it's a rubber cap, but I'm not sure if that should be capped or not.



If you need more detail pics, let me know and I'll borrow a camera.

Hey Julius.

Where are you located? This may allow us to find a G-man nearby to take a look.

Also, while your method of resetting the ECU may be valid, I don't trust it. That is why we recommend using a jumper wire. Remove neg cable, connect to positive and turn the ignition switch into the "RUN" position. This will result in complete draining of the adaptive memory circuit in more than 95% of apps.

I would like to see the work done personally and to know who did your mod. This could help in the diagnostics.

Ron

"Remove neg cable, connect to positive and turn the ignition switch into the "RUN" position."

Ummm..come again?
I disconnect the negative cable...ok
then connect what to positive?

Thanks.

(I'm in Montreal and Aaron from Ontario did my groove)

The full quote is "That is why we recommend using a jumper wire. Remove neg cable, connect to positive and turn the ignition switch into the "RUN" position."

I thought it would be obvious that we were talking about the battery cables. Is there another positive of which I am unaware?

Go to the Documents section (above, under Gadgetman land) and read, read, READ. There is a lot there to digest, but is all helpful when attempting service on your own vehicle.

Now, two questions remain unanswered.
1) Where are you located.
2) Who performed the modification for you?

Care to share?

Thanks for your efforts on this. You'll be glad you did.

Ron

Hi Ron,
Thanks for the response.
Talk to me about frame-rates,codec compression and bit-rates, but talk to me about mechanics and you get a "uh?"

Yes I know it's battery cables, but I never thought you can remove the negative and put it on the positive.I just wanted to make sure I understood you correctly before I lose the remaining sides of my hair

Yes, I did answer your two questions..did you READ? (all in good fun eh?)
(Montreal, and Aaron)

Thanks for your help..hopefully we can solve this.

OOPS!

Hi Julius, this is TracyG . In doing research about another Nissan product I think I figured something out. It may or may not apply to your MPG situation. In your 6th pic, the last close up of your TB. Left of the cap circled in green.
Look at the throttle linkage. There's a spring loaded fast idle cam touching the stud on the throttle cable cam. Other end of fast idle cam is against a thermal dashpot. The dashpot is mounted in a coolant passage, it has a wax pellet in it that expands as the engine heats up. As it expands it presses against the fast idle cam which starts to rotate against the spring--lowering base curb idle speed. Looking at your dashpot, I see it has been leaking coolant (green residue).
What is your engine idle speed like? IS it higher when cold, decreasing as it warms up? Has there been a change in the cold/hot idle speed, i.e., does the idle speed remain higher than it used to? If it is that is hurting MPG.
Evidently this idle dashpot (Nissan may call it something else) is used on different Nissan's--I'm researching a 2002 Frontier. And evidently the "dashpot" will develop a coolant leak. I think it is a replaceable part, but I'm not certain yet.
I see no IAC on this TB, it may be elsewhere on the intake manifold. They may do it like Ford does, w/ another air inlet passage to intake manifold, just not on TB. Ive noticed that Nissan often likes to do things the complex way!!
Bottom line: need to find out if there is an IAC valve on your Maxima, and if there is, its airflow to the intake manifold needs reduced. IF your idle speed stays high after engine warm up I'd suspect this "dashpot". I'd suspect this critter anyhow, 'cause it's leaking coolant!

I hope this is useful for you!
TracyG Gadgetman Reno

Hi Tracy,

Thank you for taking the time to respond to this thread.

You are right on! Wow.
What is your engine idle speed like?
The car starts up fine, and it revs at about 1200-1300 rpms

IS it higher when cold, decreasing as it warms up?
Yes, after driving for maybe 10-20 minutes, I do notice that the revs are returned to normal, which has always been around 800rpms

Has there been a change in the cold/hot idle speed, i.e., does the idle speed remain higher than it used to?
Yes! Not sure when it started, but I did notice when driving the car, that as I came to a stop, I let go the gas and the car would keep going and the speed stayed constant and it was harder to stop. When I was stopped at a light/stop, it was always at 1200-1300.

Your right about the coolant leak....it's soo small that you don't see it until you pointed it out.

On a Maxima, it's called "Thermo Element Kit".
Part number: Element Ki part #16391-31U00

Quick research says it should fit most nissans...probably a generic part. It costs $100.

The IACV is not attached to the TB but further down the intake.

Here's some pics

General view of the air intake.


Closeup #1 of the IACV



Closeup #2 of the IACV



Closeup #3 of the IACV. Photo taken from under


Photo of the IACV on where it's located.


A pic of Thermo Element Kit or some called it wax kit. This was the original TB without the groove.



Does that answer your IACV question about "its airflow to the intake manifold needs reduced"

Also, what if you just cap off that coolant hose that connects to the TB?

Thanks Tracy, that was a tremendous help. 5 stars for you!

I'll probably have to order this piece

One Karma for going to such effort to find a solution, Julius. So many start, fail, and quit that I am personally ashamed. You are setting an example, and a GOOD ONE that others would do well to follow.

Have a great day and thanks for reminding me there are others like me out there!

Ron