Strange missing at idle! Gets leaner and leaner :-/

[jimBNR32]

little help if possible
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, 16s, 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

[Skym]

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??

Correct. Can get AA or similar in UK to test battery, alternator (free if a AA member).

Could be alternator is on the way out or battery if over 3 years old and hasn't been changed. Also remove trunk light bulb, as it's known to drain battery when car sits for a while (common problem with R32).

[jimBNR32]

Thanks for reply.

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 run the car today, but I jumped in the car, 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!
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.

[hp44incgtr]

i would start by changing the battery cause if the car is not running an good battery should sitting at 12.6 not less not more..

[jimBNR32]

Any thoughts on everything else? Ie my afm and tps results.

I realise a battery change is in order already :-)

[jimBNR32]

Ok update from today

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?

[maxmumboom]

I had an issue just like that on my old power fc. It got so bad the car wouldnt start It was progressive. It ended up being the ECU itself and It was **** canned for a new one. No issues since. It drove me insane.

[Skym]

From what I understand, GTR ECU finds the middle ground between the readings from MAF's. I think it's normal for the MAF's to be at slightly different voltages.

I would think the blipping throttle = lean, engine stalling gives it away. Someone on here had a similar leaning out problem (same A/F ratio's), fluctuating idle problem as well and found TPS at fault when he swapped it out for a known good TPS.

I found TPS to cause random stalling which you are experiencing, but didn't link it back to the fluctuating idle problem my car had (replaced TPS, o2 sensor at same time, but thought o2 sensor was the cause). But thinking about it, made sense, as TPS does affect transient fueling and like you said "leaning out" makes it hit the go rich trigger on ECU for o2 sensor and then goes rich (revs drop) and then hits the go lean trigger that when combined with faulty TPS makes it go really lean (revs rise) and repeats (ECU adjust's ignition timing to suit). The fluctuating idle usually happens when there's intake manifold flange airleak causing engine to go lean.

[Bossman]

Get a battery charger, charge your battery up and see if you can bring the voltage above 12 volt, if not then your battery is at the end of it's life. Don't forget to check the fluid level on the battery, low fluid will give you low voltage; battery fluid is distill water. Your other problem is you alternator voltage with load, with the headlights on, blower and rear deforested, and radio on your voltage should be around 14.5. Two other things to check are the belt tension on the alternator and make sure your battery terminals and posts are clean. You need to check these basics first because it you are not getting enough voltage to begin with then everything that is electrical will give you all these 'low voltage' issues.

[jimBNR32]

Sorry I should have said, I popped a new battery on.
Still the same issues.

As said in first post, it is reading 14+v when the car is on, so well within spec and should confirm the alt is fine?

Skym, my idle isn't fluctuating. It holds solid. Only when it starts to go very lean does the idle drop a little and it starts to miss.
I haven't had any random stalling issues. I took car out for a good 1.5+hrs today on a run, no stalling. So I'd like to think that does rule out the tps how you've described it??

Still doesn't like it when I switch the headlights on tho.

Am thinking maybe the idle learn on the powerFC wasn't done properly perhaps, hence it throws a fit when alot of load like headlights is turned on. Running everything else, a/c, amp, gauges are all fine. Just the main beams it doesn't like. Odd. This issue is secondary tho, I'd obviously like to fix the missing issue first if I can!

I'll get round to testing voltage at fuel pump, and change my fuel filter.

I do still have oem injectors/afms and ecu, I may pop these on worse case just to rule out if issue is related to Nismo afms and powerFC. My 700ccs were flow tested and cleaned before mapping, so I don't suspect those.

Any further ideas would be helpful, frustrating as car goes so well behond 2k rpm. And to not be able to use the car at night is annoying as well, lol.

[Skym]

Only way is to try another TPS (known good TPS or new one) and see if problem disappears. A faulty TPS can cause random stalling (out of the blue). But usually voltage drops when TPS has failed and triggers TPS error code on ECU (should do the same on PowerFC, where I think it puts a X next to sensor on screen). But TPS can be faulty and produce good voltages. The correct TPS voltages should be around 4V at WOT, 0.44V at idle on idle contact. The fact that it has dropped a little bit to 3.98V makes me suspect that it could be the cause or misadjusted, especially at idle with 0.39V.

Also the fact that it happens under 2000rpm. That's where the TPS is often used / looked at by ECU for fuel enrichment.

Sometimes stuttering (similar to missing coilpacks) can be traced back to intake airleak after MAF's (loose intake hose clamp, cracks in rubber intake piping inbetween ribs or under intake hose clamp).

[Bossman]

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

As said in first post, it is reading 14+v when the car is on, so well within spec and should confirm the alt is fine?

No. If you have the lights and everything on at idle your voltage should jump up to 14.7 for a good alternator after your car is warm, if not then it's either the alternator or a worn belt. This is how you load test your alternator with out taking it to a shop for testing.

[jimBNR32]

Thanks for reply.
I'll try and borrow a tps of I can. Werth a shot and I assume pretty easy to swap out.

Bossman, sorry I should have double checked my batt voltages after the new batt install.
Bu what I ment by the 13.5+ voltages in your quotes is that is what is seen on the powerFC. The voltage at the actually battery is a good 0.7v more than this when the car is on. So in the 14s.
From what I've read online, low 14s is perfectly acceptable. I didn't read anywhere of folk getting high 14s.

[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 se feedback.

Thanks

[Skym]

Should be around 35.5psi at idle with vacuum hose connected and 7.1psi higher without vacuum hose connected to FPR when factory. But with hardwired aftermarket fuel pump it might be in low 40's with vacuum hose connected to FPR.

One way to drop voltage by alot is turning on aircon. From testing I have done, light's only drop it by small amount (which you found out).