Hello all,

Well yesterday I went to go visit Kevin (KRRZ350) to get my maxima finally tuned after completeing the 00VI swap a year and a half ago. I have been waiting to get the money and time to do this and finally yesterday matched up with both of those. I mainly did the tune because I was the the dragstrip last week and my numbers were worse than when I was running just a full Cattman exhaust (headers back). So before my numbers with just exhaust were 15.7 and then when I went with the 00VI it was 16.05. So it was obvious something was up, so I called Kevin and got myself a tune yesterday.

While getting the tune two weird things occurred.
1. Between 4500-4750 rpm the air/fuel ratio could not be corrected properly no matter what Kev did.

2. My hp number is at 173 which is a lot less than expected by Kev and myself with full exhaust and 00VI swap. I asked Kev what numbers he usually sees with these kinds of set-ups and he said usually between 195-205 hp.

The set-up I am using is full 00VI upper lower fuel rail tb iacv and I am even running the 5th gen sotck air filter box instead of aftermarket. Other factors that maybe needed to know is I have a full cattman exhaust headers back, I am auto with DR mod and tranny cooler (which really wont make a difference), and my tuning device is an Apexi VAFC-II.

Any help would be greatly appreciated, Kev and I believe that it could possibly be the air intake holding back the power. So please let me know asap.

Thanks in advance
Stephen

 

do you have the dyno sheet? What's your VI activation point? Was the VIAS working or did the power just go down after 5000rpm or so?

 

Yeah I have the dyno sheet, I'll be posting it up in a lil while. Kev found the best activation point for the vias for my specific car was 5200rpm, and the vias is working like as you said the power does not die down after 5000rpm.

 

The track time difference was maybe due to hotter weather? As for the dyno, I would guess you're maybe 5-10hp short. A stock 4th gen auto puts down what 150hp? 25whp from headers, vi, and tuning isn't that off.
I gotta ask, how is your gas mileage with the 5th gen fuel rail and injectors, has it gotten better after the VAFC tune?

 

Try removing the power rod. See where that gets you. If you feel (or see, if youre on the dyno and/or tuning it at the time) a difference, then its possible your VIAS either isnt opening properly, or not all the way, or the cup is damaged. The 00VI manifold itself is a better performing manifold, and even with the power rod not/partially opening, you wont see as much of a drop as you do past 5000rpms.

What kind of A/F were you getting in that 4500-4750 range?

 

It was a lot cooler last night than it was when I ran with just the cattman exhaust. I hope your wrong about the dyno to be honest I was expecting more than that.

I only just got the dyno yesterday so I have yet to experience the gas mileage with it properly tuned but even when I was not tuned I was getting really good gas mileage when I was driving reasonably meaning my lowest was 20mpg and my highest was 26mpg.

What kind of a difference would I feel if I removed the power rod? Also how would I remove the power rod without damaging the intake manifold? And would that mean I would have to remove the intake manifold to take out the power rod?

As for the A/F I was getting a ratio of 12.

 

Interesting. I actually had the same tuning issue with mine. I made corrections but it didnt seem to do anything from the time my VI opened.

 

Remove the vias solenoid part first. remove spring. Then go to the otherside and undo the block off. Then pull the rod though.

IIRC i think you need to take off the manifold in order to get the rod past the timing chain cover.

But if you havent replaced the screws with some bolts i would take it off reguardless

 

Nevermind thanks for the refresher I now remember where it is located and how to remove it. And yes I did replace them with bolts thanks again. But what type of difference should I be looking to feel from removing the power rod?

Thanks for the help/advice
Stephen

 

Im assuming your auto since your a auto.

Im sure you will feel less power down low.

But you will gain more top end.

But i wouldnt recomend it unless you have your limiter raised.
But for a testing purpose it will work.

 

And what kind of numbers were/are you making with this issue present?

 

O ok so pretty much what will be happening is the valves will be open so the longer runners in the manifold will be used like when the vias is kicked in when the manifold is working properly correct?

My dad has also been doing some searching cuz he is puzzled with this lack of power and he pointed out that maybe it is because my catalitic converter could be clogged. Could this be a reason as to why I have lost this amount of power?

 

both the short and long runners are used when the vias opens. It doesn't close the short ones when it opens up it just adds the long ones into the loop.
I just took my cat off and I could barely see out the other end. Put on another car and there is pretty much no difference. I guess on a dyno it might show 2-3hp but the butt dyno can't detect taht...

 

You do NOT need to remove or unbolt the manifold to get the rod out. On the right side, there is a metal cap with two screws. I just unscrewed the cap, and slid the power rod out carefully, I did have to move the electrical harness rod that runs there and get it around it. Dont even need to remove the VIAS.

 

My knock sensor was bad so the numbers sucked.

 

O alright makes sense on the runners thanks for the explanation.

Hmm well I think I may have a backpressure guage around somewhere so I'll see if im getting a regular reading if not then maybe I'll think about replacing that cat. Not just for the perfomance reason but also because its better for the environment with a properly working cat.
Alright sweet I will try this asap and will let you know the difference in the feel of low and high end difference.
O ok well thanks anyway just trying to see if maybe that had something to do with the low power numbers but that really wouldnt make that much sense.

 

Here is the dyno graph:

 

Actually I just rescaled my dyno sheet the same way yours is and my numbers are very close to yours. Have you checked your codes?

 

^^ my thoughts exactly! you need to check your knock sensor.. thats what my bets are on this problem

 

Hmm ok so what you are saying is that once you fixed your problem with the knock sensor that it fixed your low power numbers? So what kind of numbers are you making now with this corrected?
I will check my codes again, see thing is I always have my check engine light on because I have the DR mod so I do a check on my codes everyonce in a while to be safe so yeah.


One thing my dad reminded me when we first installed the VAFC-II when we had the unit installed fully and correctly we would get a check engine light for the knock sensor so we tested the knock sensor and it was fine. So we ended up just disconnecting the knock sensor to the VAFC-II. Could this have anything to do with it?

 

You're not supposed to use the VAFC knock sensor wire to splice into the knock sensor. It gave people problems from what I read. Maybe you cut the KS wire or it somehow broke somewhere along the way?

 

I havent redynoed yet but on my bad knock sensor I ran a 16.8 and with the new one I ran low 15's in hot weather. Also I'm almost positive you dont need your knock sensor hooked up to your vafc-II. I know mine isnt.

 

You do not need your KS hooked up to the VAFC.

If you want to bypass the KS to see if its the sensor, you simply need to wire the resistors in. I have a premade bypass resistor I am not using anymore, if you want it let me know and its yours if I can find it.

 

If his Knock sensor is hooked up to the VAFC-II, it is most deff. the problem. It has been reported in the past that it causes power loss and itchy idles.

 

+1

I had my KS hooked up to my EU and it threw a code as well so its not just the vafc

 

Alright that makes sense however my knock sensor is not connected upto the knock sensor wire on the VAFC-II. I checked for codes yesterday and nothing other than the transmission code because of the DR mod.

I was curious yesterday whether my catalytic converter really was clogged so the way I tested for it was using a pressure gauge on a vacuum port on the intake manifold. This would also tell me if I had an intake manifold leak. The test results at idle perfect at higher revs perfect.

MOHFpro90 what exactly is a bypass resistor I am slightly confused how you would make one? I am fairly handy with electronics so rather than steal yours that may need at a later stage with your max or another car i'd make my own...

Also one more thing I have grounded out on the y-pipe in the past a couple times. Could an exhaust leak in the y-pipe cause such a power decrease? We spotted a leak in the y-pipe once but we sealed it back up with exhaust leak sealant stuff ( i forget the exact name of the stuff).

Thanks for the help and advice its greatly appreciated, this is really bugging me and I just want to get this situation worked out.

 

470k resistor from radio shack and stick it in the KS subharness

 

As far as I know, and when I went, they didnt have a 470K. I had to put two in series, Im not sure what the values were, I could go check later if you want. But basically just make a 470K resistor value.

 

So all I do is solder or in some way connect a 470k resistor(s) onto the knock sensor wire? I connect the resistor(s) to the knock sensor wire inside the car down near the ecu correct? Now what exactly will this do? What is this testing? If this does what you believe might happen what exactly does that mean and do I then have to replace the knock sensor?

Thanks

 

no no here

Very simple


Credit: Jime

and here is the product # from radio shack
271-1133

When i went to my local radio shack they didnt have them but they looked in their computers they said there was one down the free way that had a few.

 

Dang mine didnt even have any 470K resistors in their store, let alone the part # for them...

I just put 2 in parallel that added up to 470K just like Jime did above.

 

O ok gotcha but still confused on what I'm supposed to be experiencing differently doing this?

 

it simulates a working knock sensor. If you notice gains, you'll know your problem is because of a faulty knock sensor.

 

Isn't there only 1 wire coming out of the connector in he picture above?

 

o alright sweet I'll get a 470k resistor asap tomorow when radioshack opens there now closed here where I am. Thanks for your help I'll let you guys know how this goes.

One more question though how do you make sure the resistor stays connected to the plug while you are trying it out to see if there are noticeable power gains from doing this?

 

It generally stays in there pretty well. So id just eletrical tape it up

 

Alright well I told my dad about this idea now and he said he is kinda worried about doing this idea and after he fully explained to me the full reasoning of what a knock sensor does and the great importance of it I kind of feel the same way. So when you did this were you not worried about the chance of knocking in the engine and i don't have the money to fix/replace my engine? Any reinforcement on this issue is greatly appreciated because I want to fix this power loss asap!!!

 

if you haven't heard knock til now and ran 91+ octane gas this whole time, why would it start knocking all of a sudden?

 

^this. knock sensor is just an Alerting mechanism for the ECU to take it easy... What YOU'RE going to do is trick the ECU into thinking your Knock sensor is working properly with the resistor method to see if your performance changes due to a "safe mode" being triggered by a faulty knock sensor. If it does, buy a new Knock sensor. If not, plug your old knock sensor back in.

either way, its just method to test if your ECU is being told to go into safe mode. 2/10 on the dangerous scale.

 

knock sensor is like $30 on ebay. If your car is up there in mileage anyway, just replace it.