So I went to get my car dynoed today and this was really a scary experience.


first run....
car's pinging really bad at 5000rpm so it was cut off. I added another fan to get better air flow.

second run....
sucessful run but it is freaking lean! a 14:1 AFR on a SC'ed maxima.

result : 261whp @ 14:1...compared to the best run from last time: 273whp @ 10:1 AFR. The only power mod that I added was the Greddy Cat-back since the last dyno. (well, the bleeder valve on FMU doesnt count because it is off all the time)

I switched to 1-step colder NKG copper....dunno if it matters. I have no CEL too...

so WTH happened to my car???

My AFR this time is like that from an NA maxima!!!! I am getting the fuel pressure but it was just lean as hell! could it be the ECU trying to adjust my richess?
how am I going to diagnostic and id the cause of this?


how am I going to correct the problem? S-AFC? addtional injectors?

I dunno~

please help and here is a copy of my dyno. red line is from this March and blue line is from today.


thx

 

Maybe your fuel pump is experiencing issues? Or something is up with your FMU. Vortech FMU?

I've never heard of the ECU being able to compensate like that. Plus you were at WOT which I thought meant the ECU went into open loop and was running at a preset level and would not adjust for A/F. I thought the ECU only adjusted for A/F during partial throttle and it read the O2 sensors then, but not at WOT.

As for diagnosis, I'm not even sure how you diagnose something like that. What fuel pump are you using? I'd first check the plugs to see their condition.

 

thx for the reply. I am using vortech FMU, 8:1 with the inline pump from stillen. I am getting fuel pressure at WOT (>100psi) according to my fuel p. guage.

so the ECU only adjust partial throttle but letting the fuel pressure taking over at WOT? I have been running lean from low rpm @ 3500 and my high only richen a little. Does this have to do with ECU?

should I put my stock heat range plugs back and see if it is better?

here is a picture of the plug from cylinder no. 2. looks dark because I didnt turn on the flash.


another pic with flash on


thx for your help

 

hmmmm...does it have anything to do with short/long term fuel trim? I dunno...my lean AFR run looks really flat and isnt 14.xx what an NA max supposed to get?

on the other hand....my rich AFR run is taken right after the fuel pump is fixed. (my fuel pump wire was cut before the dyno). Since then...I only reset the ECU once when I installed my fuel p. gauge.


possible?

 

Inline pumps aren't necessarily the best overall solution...

 

14:1 is what an N/A car should make. And your 14:1 is really flat for a boosted car only running the FMU and fuel pump. Most boosted cars running rising rate FMU's get really rich in the high RPM's. It's hard to get a flat A/F running a rising rate FMU without additional fuel control.

At 100+psi, maybe you're maxing out the fuel pump? Fuel pump flow is inversely related to fuel pressure. What size pulley are you running? 100+psi is really high for the Max and I don't think it would need to be that high for the SC setup.

 

hmmm...but it still pushing fuel into my engine....

 

so something is hold up the injectors? I am still seeing fuel goes in there. unless...unless, my fuel p. guage is screwed up.


If I maxxed out the fuel pump...wont I see the fuel pressure dropped? or maybe the pressure is high but the flow passage is restricted....

I am using 2.87 and I see 10psi on my boost gauge. hmmmm...maybe I should look into a new fuel pump.

 

Question to ECU experts...

can stock ECU do something like this? I know fuel trim is able to adjust richness/leaness by reading thru O2 sensor. But is it able to lean out the car that much?

14.1 seems fine to stock ECU because it doesnt know that I boost the car. I think that's why its not throwing any lean code.

 

Holy crap That's scary, but it could be worse... I freaked out when I was in the 13's.

It's not the ECU though - it can't be. If it were compensating like you say, you'd see blown vqs literally getting blown left right and center


I think several members have had issues with the crusty vortech pump failing - personally my stock pump has been making lots of noise lately (I think I overheated it one day when I screwed up and "forgot" about the gas gauge being too low <cough> jerry can <cough>).

I'd say try ironing out the possibilities by swapping aux pumps first - is there anyone local to you that you could switch with? If that fails, what kind of pump are you using from the tank? OEM or walbro (sorry, I forgot and it's 4:36am, I'm sleepy). If you're OEM look at it this way, you can upgrade to something better

As soon as you get fuel pressure back you will know your AFR is healthy again - lucky you have a fuel pressure gauge that tells you this!

If the fuel pumps are fine, I guess it comes down to the injectors, which should be able to handle themselves fine with 10psi/8:1...

If the dyno accurately portrayed 10:1 ratio earlier and you're at 14:1 now, no need to afc or other tuning devices.. something's just wrong somewhere and needs to be replaced.

 

Hi Jer...thx for the reply. no need to sleep?

I still have good fuel pressure so that's even more scary. I see 100 psi of fuel entering the engine. if I only see 50psi then I know the fuel pump is not working. pop in another one and problem solved.

now the fuel pump is still buzzing and I am getting pressure reading. I know it might not be the pump unless the fuel pressure gauge is not working too..

my dyno is lean all the way from 3500 to redline. sounds like the symptom when the fuel pump is not working. But I still cant explain why do I see fuel pressure.

 

alright....you are right, Jer. unplugged the battery over night and it still lean as usual.


just few things that I can think of about my lean AFR:
1.in-line fuel pump is falling apart
2.fuel injectors
3.bad coil
4.need to use plantium plugs with stock heat range.
5.bad tank of fuel?

 

That's one lean curve, but pretty damn smooth.

Although, you're registering 100+psi fuel pressure, I'm not buying it. Something is wrong. Either your gauge is wrong or your injectors aren't flowing properly.

Can you rig up a manual FP gauge like Bags did an drive around ghetto style for awhile and take some FP vs. RPM measurements? If the gauge is correct, your injectors are suspect IMO. Pull them and throw in some different stock ones. A guy is selling some 2K injectors w/rail and manifold in the FS forum. They look like they've seen better days though.

 

1.in-line fuel pump is falling apart
---Not if FP gauge is correct.
2.fuel injectors
---Maybe
3.bad coil
--- Don't see that.
4.need to use plantium plugs with stock heat range.
---
5.bad tank of fuel?
---Doubt it would affect A/F ratio.

 

yup...seems like my car is tuned at 14:1 AFR.

I will double check on the fuel pressure. I will try to route the gauge and tape it onto my windshild. gotta spend more money now.

question : if an injector is failing...should I get fuel leak during startup or idle? I shouldnt get something like this, right? This is way too smooth and does a dyno run with bad injector look like this?


bottom line : if that gauge is working properly, it is the injectors then.

 

so the injectors can get locked up half way or something?
all 6 plugs look the same though. And it seems strange when all 6 failed at the same time. Both banks seem lean. How can I verify this without taking off the injectors?


doesnt bad coil cause pinging.

just want to make sure....the car put down 273whp with stock plugs.



how about:
-bad heated O2 sensor

-dirty injecotrs


thx for your response, Alex.

 

If you were NA that'd be perfect.

I don't know what an injector does when it's failing, but I'm sure others here or on the net will. Never had nor seen one.

If the gauge is working and you're getting that fuel pressure to the injectors, my *GUESS* is they are either bad or go STATIC from too much fuel pressure/duty cycle? I don't know what else it could be.

Maybe you could invest in one of those pulse width monitors like Stephen Max got? Or I think you can ghetto rig up your own with a scope or dwell meter if you don't think it's worth the investment.

 

The higher the fuel pressure the longer it takes the injector to open/close. Once you reach the max pulse width possible at XXX fuel pressure, they pretty much "stick" open, I think. IF they stick, you can force a little more fuel through them with more pressure, but not much. At this point, I think you burn them up.

I'm not exactly sure how a bad coil causes pinging, but I'd guess due to the ignition timing being off, so peak cylinder pressure is reached at the wrong time.

Lean condition PLUS hotter plugs?

You're at WOT on the dyno, which is in open-loop control, ie no feedback from the 02-sensors. The MAF is used though. Hmmmnnnnn.

Maybe....you couldn't hurt dumping in a batch of Chevron injector cleaner(not fuel system cleaner) w/Techron and running Chevron only gas. Otherwise, maybe one of those "petro cleanings"?

You've GOT to figure this out NOW rather then later. My GUT is telling me that you're getting the 100+psi fuel pressure, but your stock injectors can't flow enough fuel for the amount of air your SC is pushing. You've got your fuel pressure sky high, but your not getting enough fuel. I think it's time for bigger injectors, an aux injector/controller, or maybe sending in your injectors to be flow tested by RC Engineering to see what they are capable of.

 

Where are all the dyno gurus when you need them? Tell me what you see here?

1)What is the hp/tq drop before 5252rpm from?
2)The BLUE A/F ratio doesn't DIVE right away, why?
3)The BLUE A/F ratio is dropping from 4.4K-5.8K, so it appears the FMU is somewhat increasing fuel, right?
4)The BLUE A/F ratio starts rising from 5.8K-Redline, so injectors aren't flowing enough fuel right?

 

oops sorry maxi, I thought I read your fuel press. was lower

Where did you tap into your fuel pressure?

An o2 sensor shouldn't affect it - I know that because I've gone through both front and rear, and no ill-effects...

I'd say forget/separate the pinging from your AFR problems, you're lean and that's your primary concern anyways... pinging can only be confirmation

Bad coils can't contribute to AFR, ditto for fuel.. even if you somehow filled on 87 octane or something this wouldn't make your afr fly...

The only one thing I could speculate that sounds extremely funny is that your exhaust leaned out your mixture

Try icey's idea and see what happens.. there's just no other way

Try to find a 2000-2001 maxima that you can rent for a day otherwise...

 

I tried something on the way back from work tonight. I re-install the bleeder valve and bleed off some pressure to the FMU. So usually downshifting from 4th - 3rd, I get 80psi of fuel at 5000rpm. now I am only getting 60psi. Then the car start to ping and I quickly let go of the pedal. It is worst than pushing 80psi of fuel. just want to see if my fuel pressure is read correctly.

this is the suggestion I got from an engine forum:



check for intake leak?

maybe something stronger? like the 3m ones that goes to the fuel inline instead.


I will check each injector to see if they are working (listen to the buzzing sound or check the resistance.

I am going to do an oil report to see if something's damaged.

and verify if my fuel gauge is working right....too many things...to little time.

 

right after the inline pump. btw, are u still using the inline pump or u upgraded to walbro?

gotcha! thx for confirm, Jer & Alex

what do you mean?

<sigh>....maybe clean the injector first....

btw, how did you get the 13:1 AFR?? was the curve similar to my 14:1??



are u suggesting an injector swap from a rental?

 

I'm still using the supplied vortech, and stock pumps. The exhaust thing was a joke btw

I'm thinking at WOT you're not concerned with intake leaks... there is no such thing as a "leak" at that point - your intake/sc will be pushing as much air as they can and the engine will be using whatever fuel it can get from your fuel system - ignoring all readings (again, including O2). An intake leak aka MAF sensor acting crappy on you would not happen at full throttle (believe me, I've sampled this when I was making my CAI... lots of stall-outs, surging and other issues).

I guess everything up until your FP gauge is checking out OK though - even with clogged injectors, I don't think you should be seeing such a shot in A/F....

Is it possible that perhaps the dyno's wideband o2 was fubarred? Did anyone else run that day? The pinging incident could have just been fluke - I had a run at the track once where the car began to ping rather wildly.. it was just the gas.

Adunno.. If I were you I'd think about the injectors now, or maybe dynoing elsewhere if nobody else sampled their sensor...

Let's not forget my last experience 2-3 months ago at the dyno shoppe where readings were going from 13 to 10:1 WITHOUT adjustments on the afc (or going "the wrong way" after decreasing airflow). It could have been the hookup, it could even have been the sensor.

And yes the AF curve was similar for me when I was hitting my 13's... I'll post the dyno graphs tomorrow (once again, it's 4am and I'm at work..see anything wrong with this trend )... then I'll promptly have to forward the datafiles to Ice for the dyno thread

 

do you have the stock intank pump? If so that maybe your problem, I burnt two oem pumps up in one day. I don't think it can supply the quantity to the aux pump. I then bypasssed the aux pump and installed a holley 255lph pump , not high psi though, it still runs at stock psi at idle, and then the psi goes upto around 70 psi when I'm seeing boost.

 

IC......
I wanted to check if there's an intake leak after the MAF. The blower may still draw air from the leak but the MAF will measure less intake air reading and thus leaning out the car as necessary....but again...at WOT, I am at open loop and anything shouldnt matter....just simple as pushing fuel, air and get power and have fun.

I am wondering how much fuel does it take to lower the AFR from 14:1 to 10:1.....my mpg is around the same since the good dyno.
I am pretty sure that my car is running lean. I have high EGT problem since...I forgot when... that's one. Last time I unisntalled the ypipe to check the flex section and I noticed the O2 sensor from rear exhaust manifold is snow white....that's lean. Then on the Dyno day (bad one, 2 days ago) The car was pinging except for one run. I had 5 run total, I told the dyno guy to cut off the 2 runs because of pinging....one good run, and something went wrong with their brake on the roller and the car almost jumped off the machine. Then we called off the dyno and he gave me a discount.

so you had a 13:1 run and then wat happened? how did you bring it back down to the safe zone? with S-AFC? cant wait to see your dyno!

thx for your help, jer.....

 

thx for the info

yes, I still have the stock pump in tank.
hmmm...you know what, this was suggested by somebody else from an engine forum. he stated that the stock pump cant support high fuel pressure and just shut it off and then it was running only on the aux pump. but I am still getting fuel pressure reading at WOT...assuming my gauge is working properly


So what's it like when you just run on the aux pump? does the car idle normal? I unplugged the aux pump yesterday morning and the OEM pump still seems fine at idle.

 

MAF voltage IS used at WOT to add/subract fuel. So if you're getting unmetered air, you'll be leaner. I wasn't thinking about that though, just maybe your MAF is not working properly, but you'd probably get a CEL if not.

I wouldn't think the stock fuel pump is the culprit, since you're getting 100+psi, however that's at peak, right? What about earlier on?

 

peak pressure is 100psi...that's correct.


80psi @ 6psi of boost. it goes to 100psi (to be precise 110psi on my fuel pressure gauge) when I pit 10psi of boost at redline.

 

We NEED to figure out a way for you to test your injector duty cycle. I believe that will help. Do you have access to dwell meter or oscilloscope? Although, don't ask me how to use them.

IF the injector duty cycle is 90%+ and the fuel pressure is 80-100psi, then the injectors aren't able to flow enough fuel. Whether they're clogged or worn out from going static all the time, I don't know. They'll need to be replaced with either newer OEMs or hopefully RC Engineering/PE injectors along with an adjustable FPR.

 

what about my 14:1 at 3000rpm? compared to last time I am a lot leaner at low rpm already. seems like something's wrong from the beginning, when the fuel pressure is low.

I am going to check on the injectors tonight...well, at least the front injectors.


thx

 

more dyno graph for your viewing pleasure.

1.this is all the lean run I had on Monday. Two runs were cut off due to pinging.



2.2.this is the lean run vs rich run. I ask them to make the window bigger so we can see the AFR better. Seems like both AFR are parallel.

 

Woah....... what happened? What was changed on the car since the first dyno session? We'll work from there.

Sorry I couldn't make it on Monday. We had major email issues over the weekend and I was stuck fixing it on Monday.

 

Hi Kevin...how are ya? thx for helping me out.

since the last super rich dyno, I only swap the plug to 1step colder copper plug. that's the only fuel related mod. I even took off the bleeder valve when I see the 14:1 AFR and the dyno graph above is taken without the bleeder valve.

other than that...I add a fuel pressure gauge, an oil cooler, your greddy cat-back...

that's it.


thx again~

oh~ dont worry about the dyno. we will go again. I need to get her spinning 280whp to the wheel.

 

Hmmmn....could that sender unit be the reason? I mean if it's restricting flow or something.

 

good point. I'll try without the sender and see if the EGT decreases.

maybe I should relocate the sender to be tapped before the FMU. I will get better fuel pressure reading at boost.

 

Done yet?

The suspense is killing me!

 

not yet, boss....

I am at my gf's. I only have tools to remove plugs.



but thanks for your help, alex. you and keving, jer and others are helping me a lot. Hope I can get this resolved.

 

I did something this morning.

I followed Hayne's manual to check the pressure of my fuel system. I first disconnected the in-line pump because it raises my idle fuel pressure.

I first switch the key to On position and the manual stated that I should hear my in tank pump buzz. I didnt hear that. well, I think it is ok because I did see some response on the fuel pressure gauge. It was read at 40 but the manual stated that the fuel pressure when engine's off is supposed to be 43psi. So I turn on the car and the pressure was 34 - 35psi, within the spec range. Then I disconnect the FPR and it went back to 40psi. This is a little low but I think it might have something to do with the accuracy of my gauge. I use the in cabin eletronic gauge.

then I turn off the engine and put the key back to On switch, the pressure dropped to 30 and came back to 40ish. The manual stated that if the fuel pressure dropped rapidly, it could be the injector's leaking or the fuel pump check valve is not working. But since I see the fuel pressure came back, I doubt this sudden drop of pressure has anything to do with the acutal pressure reading in the system.


any comments?

 

Sounds normal.

 

thx Stephen.

btw, from your experience.....if my injectors are clogged...is it possible that I have a good idle and no drivability problem at all while getting a lean mixture and pinging at the mid-high range rpm?

btw, I didnt see my EGT dropped when I heard pinging...it just keep going to 810C at redline.

thx