I dynod my car today and these are the numbers i got.


hp/trq


trq/AF

i am happy with the numbers in general it was a cooler day compared to last itme i dynoed and i had the 5 spd swap done. yellow is what i did in 3rd when i was auto.

green was what i did today. i am really worried about my A/F ratio. its at 15.3. that is really high. i noticed my fp was between the 80-90psi range. i had the 6:1 fuel disk in there and we swapped it out for an 8:1. fuel pressure did not change i thought 8:1 should bring fuel pressure over 100psi. the person dynoing as well as a honda-etrs friend (nissan field mech) was telling me im either maxing out the injectors, or the fuel pump is bad. i really have no idea of where to begin. i have a set of 370cc injectors waiting for me at work but i do not have the money to get all 3 of them now. why is my car running so lean up top????? can anyone help me out???

this is what i currently have.
99 5spd
s/c 3.125 seeing about 10 lbs of boost. ( have to e-mail the dyno guy i forgot to get my boost print out.)
what is suppose to be 8:1 fuel disk.
walbaro 255 high flow fp
sard fpr
stock injectors

help please!?!?!?!?!?!?!?!

thanks
frank

 

Maybe you need an injector cleaning service done to your injectors. 300zx injectors are not hard to install. Take upper manifold off and thats it they are right there. Just take the fuel rail off because injectors are a ***** to take off. Make sure you get all the little o-rings for the injectors. I think there is 2 for each injector.

 

Get new O rings...it (the injector/injectors) will probably leak otherwise. As to why it's running lean...man, there could be any number of reasons (most of which you already stated). Just do some simple troubleshooting and eliminate the problem. If you're sure an 8:1 disk was used, then troubleshoot backwards. That will eliminate the fuel pump side of things. Then work on the injectors.

 

just like my case - running super rich in the beginning and running super lean a few months later.
FYI : http://home.earthlink.net/~doctorkiw...o-14vs10-1.jpg

assuming that you have boosted fuel pressure:

I would say check the MAF first and make sure it is working properly. You injector cycle is controlled by MAF reading.

Another thing you can do is to monitor the fuel injector duty cycle with a little gauge like the one that Stephen Max has. or pay a nissan dealer to have someone going to a test drive with you with a Consult II. I got quoted for $110 for an hour and I can do anything I want with the consult II.

here is my thread on this similar problem...icey2k1 helped me a lot.
http://forums.maxima.org/showthread.php?t=255734

 

thanks maxi-overdose...

question did you ever find out what the problem was???

these were my last dynos when i was automatic. in march last year.
http://fastforward.lchu.net/church%20data/FSC-FWT2.JPG

http://fastforward.lchu.net/church%20data/FSC-FWT.JPG

the difference between the two dynos is i am now 5spd, w 99 5spd ecu.

i read the intire thread maxi-od but with the 8:1 fmu i did not see 100psi.
i know that. i was looking at the fp gauge after we poped in the 8:1 disk for the thirs dyno.

 

Was there any sign of detonation? I can't believe you would be making 10 psi with an afr of 15.3 without serious detonation, and I also don't believe you would be making 300 hp if your engine was detonating. I suspect a problem with the afr measurement, like a leaky exhaust system that allows air into the pipe in front of the O2 sensor. Next time you dyno, see if they will put the O2 sensor in the y-pipe where the front bank O2 sensor normally goes.

 

thx~

no, I never found out the cause. I stopped it before I could monitor my fuel injector duty cycles. My MAF was reading fine and there's lot of fuel pressure, but somehow it just wont go into the engine. so I gave up, return her back to NA and this is something interesting - the EGT is still pretty high at NA, just like when I used to run lean. I can get up to 780C under 2nd - 3rd - 4th acceleration to about 100mph. so I guess it is just my car.

do you have a dyno graph with AFR curve? it will be a lot easier to see if you have one just like mine. see I started to run lean at all rpm range? seems like nothing flows into the engine.

you should get >100psi with 8:1. that's something to look into, but first verify your fuel pressure reading with another guage. then check the MAF and fuel injectors. You can also check the plugs right after boosting, you will see if it happened to all cylinders or just 1 or 2.

 

ok i i will try as much as i can later maxi-od.

stephen: there was a guy standing there that said he did hear it detonating. church the guy that was doing the dyno said he heard it begin to detonate but he was looking at the a/f and he just shut it down when it went past 15:1. so your saying i have an leak somewhere????? i know that i have a broken cat bolt which we had to fix. other than that a busted y pipe may be throwing the a/f ratio off?????

the only thing that has changed is the 5spd swap. what i did notice was right after the swap was done. i took it easy breaking in the clutch. but the first time i decided to open it up i heard at around +/- 5200rpm i would get an crackling/rattling sound almost sounds like i had a stragight pipe. buddy of mine from work said right away "its detonating" it does in first most of the time. second all the time. but i can't hear it in 3rd or 4th.

 

Okay, sounds like you are detonating, and the afr really is high, although I still find it hard to believe you got as high as 15.3 - but you better take it easy until you get this sorted out. If you are detonating in first and second, you probably are in third and fourth, too.

But what you are describing sounds like my experience after installing a 3" pulley. I never dyno'd it with the 3.25" pulley, so I don't know what the afr was at that time, but I never heard any detonation until I went to the 3 incher. I was running an 8:1 disk. My fuel pressure never got above about 85-90 psi. I had the Walbro 255lph and no inline aux pump. I eventually solved that problem by using an SAFC to add about +12% at the higher rpm.

 

hmmmm maybe its time i install the super afc sitting in my closet.

stephen: on the 8:1 fuel disk is the slit that is cut into it suppose to be smaller than the 6:1??? arrrgghhh.

 

oh and am i reading the a/f right. since boost does not kick in till around 35k is it basically the same as an n/a car with the 14.x:1 a/f ratios.

when i hit boost i start out at 12.7 range the a/f ratio goes up as i build boost??

 

That's how it looks to me, too.

It looks like you start out getting enough fuel, but as boost rises with rpm the fuel supply can't keep up. I wonder if one or two dirty injectors would cause symptoms like that. Or maybe the pump isn't reaching the pressure it needs to be at.

You might try testing your pump by starting your car and letting it idle, then pressurizing your fmu with a Mityvac and seeing if you can get fuel pressure up to 100 psi. You'll be idling really rich during the test, but not long enough to do any harm.

 

let me add that to the list of things to try.

ok i have base fp set at 39psi cause im scared right now. with the 8:1 fuel disk. if i pump the fmu 1psi the fuel pressure sould start to rise am i correct??? assuming my fuel pump is not malfunctioning. i sould en up to around 100psi fp????? if i pump the fmu with 10 psi of pressure??

 

You got it. This would be a static fuel pressure test for the pump. This won't test the pump for pressure vs. flowrate, but if you can't get 100 psi under static conditions, then you won't when it is flowing.

 

so if i do not get the 100psi mark i know that the fuel pump is not supplying the right amount of fuel???

thank you for the help stephen

 

it can be your FMU too.....did the needle of the FP gauge flickering near 80psi? if so, probably the fuel pump can deliver that much fuel

 

ok i was able to do one thing. i took a leak down tester set it at 10psi. hooked up the other end of the leak down tester to one of those hand blowers then connected it to the fmu vacumm line while the car was at idle and it hit 100+psi. little past the 100 mark on the gauge. when i would press the andle on the blower thingy the fp justed to 100+ psi. so can i assume that i am getting the fp and my fuel pump is working right???

now can it be dirty cloged injectors then.???

 

ok i got my 370 injectors yesterday. they are sitting on my desk at home. (heheheh payroll deduct each check for one injector)

now i was talking to the head tech at the dealer ship today. (Nisnan MAster tech) He told me that the ECU is aways looking for the best operating temperature for the cat to work right. N/A being 14.xx:1.

i read in a thread when you go into WOT the ecu stops taking the o2 reading but uses the maf. now when its in WOT (can't remember if it's called open loop or closed loop) would the ecu be running a predetermined program to keep a/f at the 14.xx:1 range while using the maf to as its only sensor? or does the ECU supply the right amount of fuel according to the air readings from the maf?

so if i put the 370 injectors in would the ecu not do the same???

im curious and like to learn. i have a nissam master tech telling me somehting. but he does not work on supercharged maxima.

thanks
Frank

 

what should a normal A/F Ratio read?

 

i guess 14ish : 1

 

13.5

1234567890

 

stephen: can the fact that the o2 sensor probe the dyno was using was measuring the exuast after the cat have an effect on the a/f reading????

seems kind of funny that you can get an accurate reading that far back.