Mysterious Pfc Missfire In An R32 Gtr

[jimBNR32]

hi folks, very interesting topic

holly thread revival!

anyway, im not sure if my car issues 100% replicate what you guys are experiencing, but similar in nature!

be grateful for some advice?

spec, forged r32 gtr, nismo afms, stock ignition, bkr7e (0.8mm), powerFC, nismo fuel pump (wired off battery), sard 700s, about the only important things werth mentioning.

symptoms;

missing at idle

after car is warm, if i sit at idle, i notice on my commander unit that the battery voltage drops slightly, starting at 13.7v, and drops gradually by like 0.3vs and i notice my afrs getting leaner and leaner. quick rev brings voltage up and in turn afrs. but back to idle again is very lean, 16 a/f s, 17s then off the chart.

when i put my headlights on, commander shows very low 12.9-13.0v and my afrs go mental lean and it stalls

before this i had been driving the car fine, boosting well, soon as i parked up, putting car in the garage, this happened.

any ideas??

only things ive checked is battery, which is 11.8v non running, but when car started shows 14.2v. (so alt ok? ) commander generally shows about 0.7v less than what the battery is seeing.

definatly feels to me like the fuel pump is loosing power (gradually got less loud, especially when i put my headlights on), this im guessing ment less power to fuel pump (tho ive yet to check voltage at pump), and in turn less fuel pressure? causing leaning out and stalling??

initally i was looking to find out why the car died when i put the headlights on, now i know its because im loosing 0.5v instantly at the commander and it must be dropping the fueling???

had no missing before and during the drive!

on cold start its fine, im guessing because revs are 1200-1400rpm at this point and giving the car plenty of voltage.

should the pfc be seeing more than 13.3-13.5ish volts at warm idle??

it seems odd to me to be reading a good 0.7v less than when measuring voltage at the battery with a multimeter?

where to start given the info above???

thanks

[shnaped_second]

After so many people reading this then it happening to there cars, im gona be pissed if it happens to mine lol

[SiR_RB]

mine does this somtimes when crusing in 5th gear at around 60-70km/h with very light throttle....does like a bleep like the ecu stops thinking for a split second lol

doesnt do it too often and doesnt bother me too much to stress over it

[Hadouken]

Mine did that. And it started to become a constant thing. Just before it warmed up, and every 10 min on the freeway.

[Don Dada]

Jimbnr32 what you are describing is sounds like a different issue. This thread is about an intermittent miss that occurs while driving along under low load where the car feels like it loses all power for a split second, and otherwise acts normal at idle, high loads etc.

Not sure what your issue is tho as the battery voltage you described above seems normal.....Does the battery have enough juice to start the car easily first start in the morning?

Edited January 29, 2013 by Don Dada

[jimBNR32]

i do believe i have experienced the cruise issue before tho, once or twice. it does freak you out thats for sure.

i just thought that maybe those may have experience something similar to myself also that could potentially be related?

it generally doesnt have a problem starting in the morning, but leaving it a week it struggles, sometimes catchs, other times needs a recharge.

obviously battery needs changing, but the issues ive experienced cant be down to battery as the alt brings the voltage up when running.

i just think it odd why the powerFC would see 0.7v of difference to the battery when running.

do these numbers ring a bell to anyone running a powerFC?

my issue has to be afm or ignition related im sure. to lean the car out seems odd.

[Rolls]

Sounds like battery, low battery means low volts to pump = lean doesn't it?

[jimBNR32]

Thanks for reply.

thought id update

I have a funny feeling the 'loosing 0.5v' when headlights on and the leaning at idle may not be linked together.

I didn't get a chance to start the car today, but I did jump in it, turned ignition to on, straight to sensor check on commander and noticed the no2 (top) afm was reading a little lower than no1, left it on for another 10secs and no2 dropped down into the 0.03v range and went black on commander! may explain why its fine for a moment, then after time the afrs went leaner and leaner???

Clearly an afm/wiring issue and would explain the missing and leaning out at idle after the drive?

I swapped afms around, and they appeared to be similar in voltage around 0.1v and no sensor error. Odd I thought, which would suggest nothing's wrong and it just needed a wiggle or clipping/unclipping to sort it out.

Back to there original layout and again no2 dropped voltage! Odd!

I swapped in a stock afm and it held its voltage fine on no2.

So not entirely sure if I should be looking at wiring to the no2 plug or the actual afm?

The 4 wires to afm, what does each one do so I can follow it along the harness?

I may pop open both afms anyway and resolder? Or asking for trouble with expensive Nismo afms?

I checked my tps voltage too on commander, and showed 0.39v and I think 3.98v at wot, engine off. Ok readings?

Not sure how accurate the readings are given the weak battery, which I had to charge up again.

But interesting none the less.

[Don Dada]

Make sure the pins on the afm and the socket is clean and free from corrosion...used some electrical contact cleaner.

I say to swap the no2 afm to the no1 position and monitor it for a few days or so to see it you still get the problem, and it you do check the sensor check screen to see which afm is playing up so you will know if its definitely the afm or the harness. And it is possible to have a dud nismo afm.....they are electronic like any other afm and can go caput! Might be lucky if its just a matter or re soldering it to fix if indeed it is the problem

Tps voltages are good.....and get a new batt

[jimBNR32]

thanks for the reply.

i opened up the nismo afms, they look perfectly fine to me (the 4 contacts), i may resolder them anyway while its open, we'll see.

yeh i was going to swap them around and see how they performed (as i read ecu takes an average of the readings anyway so should work which ever way round you put them).

im going to resistance test my afm wiring (assuming i can trace the wires) just to be sure.

got me a copy of the ecu pinouts so this should help also.

ill take one step at a time.

[Don Dada]

You cannot always see a cold solder joint....might as well do it while its open, and seal it back well to avoid moisture getting in

[jimBNR32]

Ok update from today, new battery in.

The car seems to have no issues above 1.5k rpm. Boost, cruise, everything's fine.

Cold idle perfectly fine, 13s afr. No missing. (probably because of high idle).

Warm idling, late 14afs for 10secs its ok. But a blip and you will feel a slight miss. Soon as its sitting for more than this time, afrs start to get leaner and leaner up to 16.5 (maybe even higher but id rather it not. When i give it a blip afrs rise, but i can feel it missing up until 2k rpm ish.

I opened up afms, resoldered and cleaned them, made no difference.

Not sure if related, but i noticed on commander that afm1 reads lower if on the move with no throttle (coasting), it reads 0.2-0.5v whereas afm2 read 1.2v roughly. No ill effects. Soon as I touch the throttle, the voltages level out to each other. If anything, afm1 voltage rises quicker once coming on boost and overtakes the afm2 voltage readings slightly.

I swapped around afms and got the same voltage results on afm1 and afm2 on commander.

So perhaps its not the afms that are dieing?

Warm idle tho afm voltages both at afm1 0.6, afm2 0.8v. So similar.

I can't be sure if the low voltage on afm1 is down to mapping when coasting (no throttle)? Any reason why tuner would do this if it is mapping?

Any ideas here folks?

I didn't have this issue on stock afms and 440s.

Is there any way I can test out and boost on stock afms without a remap? can i simply select a different afm in the commander? Is this ok to do? If so, what option am I picking?

Hope someones got some ideas?

[paulr33]

dont select any other afm, that will alter the tune

you cant "map" the voltage off the airflow meters, what ever voltage they read, they read, the ECU then interprets the voltage and works it out based on the ecu tune

so you can't make the afm show 0.5v instead of 0.2v if that makes sense?

it is probably showing different voltage because there's different resistance across the hotwire / ie ; different airflow

[jimBNR32]

Is this voltage difference ok tho?? Be interested to know what other Nismo afm equiped cars see?

I realise now the car is mapped for how these particular afms behave. Good or bad. But i think on hot idle, something isn't right.

Now I need to work out where it is a part issue, or map issue.

I do have a stock ecu/injectors/afms to pop back on.

Perhaps I need to swap back just to rule out whether it's the nismo afms I guess! Annoying.

I may check my fuel pressure first and swap in a new fuel filter, see if that helps.

I heard sometimes oem fpr does t like an uprated pump, this true?

[scotty nm35]

The stock FPR should be fine, it will be something else you have recently modified.

Did you hardwire the fuel pump to battery voltage? Which type did you install?

[jimBNR32]

Yep I have hard wired the pump. Nismo pump intank

30a relay, switched via the oem live pump wire.

I have a feeling could either be afms or injectors.

Before mapping I ran on pfc, that was rev limited for running in period, pump was hard wired.

So really all I swapped in was afms and injectors at dyno.

I've been reading oem fpr only good for oem levels. I'll check pressure anyway and swap filter while that fuel line is off.

[jimBNR32]

Thanks for all the reply by the way.

[Don Dada]

The difference between your two afms does seem kind of far a part and 0.2-0.5v is definitely too low for crusing voltage.....should be around 1v.

To tell you the truth I had the same problem with my pfc as well, where it would get lean if left sitting while hot. Thing is water temp never rose, only air temp by a few degrees, and as normal with any ecu, fuel is added with an increase in temp but the pfc showed exactly the opposite!.......I also had the O2 feedback off so that also ruled out a bad O2 sensor......so I just gave up after a while and let it do its own thing ,as i never had reason to have it parked stationary for so long where the afrs would have become dangerously lean anyway.

Also I had no misfires or anything out of the ordinary otherwise....well except for that common dead spot that I described before and which nearly everyone else has experienced..... This was on stock inj and afms too btw.

[jimBNR32]

Another update.

I measured fuel pressure at idle and with vac line disconnected (I assume you just block the vac line with a bolt and leave the fpr open to atmosphere? Least that's what I assume it ment).

Anyway, had cold idle 3.6bar, 3.8bar with line disconnected

Decide to fit a new fuel filter, supposedly oem filter, but did look a little different. Anyway swapped that in, and got

3.4bar cold idle, 3.6bar with line disconnected.

I didn't measure fuel pressure at warm idle, ran out of time/daylight.

Do seem like high numbers? But perhaps my fuel pressure gauge is off slightly? (mechanical one).

I thought was sorted after a 15minite drive, it idled fine, late 14afrs, dip to 15s but did go back to 14s, happy days I thought.

I drove the car for a further 30-45minites. And let it idle again and it did its usual thing, afrs started to dip into the 16s again and could here is missing slightly, dam!

Car still cruises, boosts great, is purely an idle issue.

I noticed my tps voltages on commander.

Still 0.39v with foot off throttle, around 3.9 at wot, that did drop on boost into the 3.6/3.7s high in the revs.

Fuel pump voltages, cold idle, 13.6vs.

Warm idle 13.4v, with headlights on 13.3v

Voltages at battery, cold idle, 14.3v, headlights on 14.2v

No idea what this really tells anyone, but it great to get some feedback again.

Thanks

[nobby]

Going through the looms in car and removing the wires from plugs 1 at a time and soldering each pins crimp has made a huge difference to my gtr.

even unwrapping the ign coils loom and soldering all the crimps in the common circuits has paid off as well.

think from memory 6 earths in this loom share 1 ground wire.

It's a slow process and the problem is still there but no where as bad.

might blip once a day now, not every 12 min's like it used to.

And when I did the air con connectors it made a big difference to the way it work.

Not claiming a fix as I haven't finished all connections, but feeling confident.